Diagnostic Correctness: Open Loop at Idle?

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Hellwinger
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Diagnostic Correctness: Open Loop at Idle?

Post by Hellwinger » Thu Nov 29, 2018 4:46 pm

I am trying to determine if I am thinking correctly about my engine (see signature). I want to know what the EEC IV factory algorithm is responding to and doing. Is it supposed to be in closed loop or open loop at idle?

My plan is to work up to DIY live monitoring of engine parameters and perhaps a bit of performance tweaking, but first, I need to pass smog!

The engine runs great in closed loop with small short-term fuel trim corrections at non-idle engine speeds. Fails smog at idle. Passed smog 2 years ago. No significant changes, just new spark plugs, oil change since then. No vacuum leaks. No diagnostic codes have been set. Passes KOEO and KOER tests. Vacuum systems, tubing, sensors, and wiring all check out. Reading the live data stream yields nominal-looking (?) numbers. The problem is a rich misfire at idle that is not discernible to the ear (the 460 is a rumbling beast of an engine).

4-gas analyzer results | now | 2 years ago:
%CO2 | 7.5 (low) | 10.9
%O2 | 8.9 (high) | 6.3
HCppm | 250 (high) | 105
%CO | 2.5 (high) | 0.28

Bosch OBD1300 reading OBD1 data stream:

CANST PURGE ON
ECT (V) 0.7
ECT (degF) 189
ENGINE SPD 804
EVP (V) 0.3
EVP (%) 0
FUEL PW1 (ms) 5.0
IAC (%) 33
IAT (V) 0.9
IAT (degF) 165
LOOP STATUS OPEN
MAP ("HG) 10.1
O2 SEN1 (V) 0.02
SPARK (deg) 24
ST FTRIM1 (%) 11
TOT (V) 0.9
TOT (degF) 168
TPS (V) 0.8
VPWR (V) 14.2
VREF (V) 5.0
VSS (MPH) 0

(FYI, similar profile available for unloaded engine speed of about 2500 RPM)

I have no idea what nominal values actually are supposed to be, but most look reasonable to me. For some reason the EEC is trimming the fuel pulse width to be 11% richer than the base idling engine state - which seems like a lot. Maybe it isn't. Am I barking up the right diagnostic path here?

A colder engine requires a bit richer mixture. Is the open-loop EEC strategy responding to, maybe, an ECT reading that is a bit low? The measured engine temp looks OK, but I don't know what the factory spec is. The highest thermostatic temperature available is 195F. Not that different.

The open-loop idle ST FTRIM can be much higher when the engine is warming up - I have seen 25% at cold start and then 15% warm start. Gradually settles to, but never goes lower than 11% as engine warms up. Does not bounce around like it does in closed loop (of course).

Maybe the thermostat is stuck open? I have yet to check. The ECT RTD sensor is out of cal? I thought those things failed stuck at one resistance. Or am I deluding myself, chasing the wrong trail?

For my own edification and entertainment while driving, to monitor the loop status I have a dash-mounted 10-LED (3914 IC) bargraph display of the analog oxygen sensor voltage. I can watch it switch from rich to lean in real time. Great for monitoring overall performance, and indeed a real drunkard's walk that on average, passes through stoichiometric exhaust oxygen concentrations. BTW, as the exhaust flies, I would estimate a sensor-to-exhaust valve distance of about 3-4 feet for the furthest cylinder. It is a new heated sensor, replacing it was the first thing I did out of desperation.

When the engine speed is increased, it goes into closed loop, and all is fine. Close throttle and for a few seconds, it stays in closed loop just fine but with slower rich/lean wandering and then wham - open loop and steady high ST FTRIM numbers. It looks very similar to what is described in the thread titled "Going open loop at idle?" That thread also has some other tantalizing details that could be tweaked - but I want to get it all working in stock mode first and advance from there.

So, perhaps I should also ask if the data stream values are what is expected for a hot idling engine.

And also wondering if the canister purge valve is really supposed to be open at idle. Again, do not know what the control strategy criteria are. Maybe related?
- Hellwinger

Engine: 1994 Ford 460 (7.5L) EEC IV OBD1 MFI
VIN 1FTJW36G2REA00204
Aftermarket headers, various bodged exhaust heat shields - all else stock.
Mounted in an F-350 4x4 quad cab with extended bed chassis with E40D transmission.
Bed removed, extra frame rails and tag axle added - so now 4x6.
RV coach added w/bed area over cab. I am second owner, tinker with it constantly.
Search: "phoenix one road trip america" for some vehicle background. It's an adventure!

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Paulie
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Re: Diagnostic Correctness: Open Loop at Idle?

Post by Paulie » Fri Nov 30, 2018 11:40 am

It is normal for the heavy duty trucks to run in open loop at idle. The oxygen sensor is mounted so far away from the engine, it will not stay warm enough at idle to function correctly. Canister purge at idle is probably normal. Your read out shows the map reading 10" of vacuum. This seems really low. Have you checked vacuum with a gauge?
1990 Mustang 5.0, HCI, Vortech S-trim, FRPP 42# inj., PMAS MH95, A9L, Moates Quarterhorse, BE/EA, Innovate LC-1.

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Re: Diagnostic Correctness: Open Loop at Idle?

Post by mpaton » Fri Nov 30, 2018 6:22 pm

I've answered some of your questions on th eford460 forum, so I won't type them in here again, except to say that if you can tell us the calibration code from your PCM label, I may be able to answer more questions. And also if this is a California spec truck.

The figure you have labelled as short Term Fuel trim may well be labelled as that by Bosch, but it is really more like the long term fuel trim for the particular RPM/MAP cell in use.

I think you'll get better answers in this forum. Just watch out for people who want you to get an old Mustang PCM :-(

Michael

Hellwinger
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Re: Diagnostic Correctness: Open Loop at Idle?

Post by Hellwinger » Fri Nov 30, 2018 10:32 pm

Thank you very much, Michael. I will read your other posts and reply to this forum. As you can see, I was shotgunning it.

Yes, I was also thinking that the MAP reading needs to be checked against a gauge. Basically verify the calibration curve of key sensors, as read by the EEC. Thing is, the Bosh 3100 is at the local Oreilly Auto Parts. The guy behind the counter is nice enough to indulge me. We go out to the parking lot together, I run the engine through its paces while taking a video of the readout with my mobile phone. In other words, not convenient. I am obliged to go to the store with a plan, so as not to waste time dinking about.

On Amazon, there are inexpensive OBD-2 datastream converters and phone apps. Is there anything out there that can handle Ford's '94 version of OBD-1? I work at JPL, i.e. I know folks that can help with the more advanced electronics. Have done a wee bit of py on a pi. Just need a toehold to get started.

Stay Tuned - I will be working on it this weekend. And thanks, Man.

- Mark
- Hellwinger

Engine: 1994 Ford 460 (7.5L) EEC IV OBD1 MFI
VIN 1FTJW36G2REA00204
Aftermarket headers, various bodged exhaust heat shields - all else stock.
Mounted in an F-350 4x4 quad cab with extended bed chassis with E40D transmission.
Bed removed, extra frame rails and tag axle added - so now 4x6.
RV coach added w/bed area over cab. I am second owner, tinker with it constantly.
Search: "phoenix one road trip america" for some vehicle background. It's an adventure!

Hellwinger
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Posts: 11
Joined: Thu Nov 29, 2018 1:58 pm

Re: Diagnostic Correctness: Open Loop at Idle?

Post by Hellwinger » Sat Dec 01, 2018 7:22 pm

Michael,

I think the letters/numbers you need are TAG0. See attached photo of sticker.

So apparently even a heated O2 sensor can cool off too much? The zirconia membrane needs to be at 600F - maybe the heater just speeds up heating, but has not enough power to keep the sensor working?

And it makes sense. The fuel trim is lookup values for open loop conditions, and dynamic values in response to the O2 signal for closed loop. Not sure if this system has a learned long-term fuel trim it applies to closed loop.

I am going out to test the MAP now. Stay Tuned.
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- Hellwinger

Engine: 1994 Ford 460 (7.5L) EEC IV OBD1 MFI
VIN 1FTJW36G2REA00204
Aftermarket headers, various bodged exhaust heat shields - all else stock.
Mounted in an F-350 4x4 quad cab with extended bed chassis with E40D transmission.
Bed removed, extra frame rails and tag axle added - so now 4x6.
RV coach added w/bed area over cab. I am second owner, tinker with it constantly.
Search: "phoenix one road trip america" for some vehicle background. It's an adventure!

jsa
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Re: Diagnostic Correctness: Open Loop at Idle?

Post by jsa » Sat Dec 01, 2018 9:36 pm

Hellwinger wrote:
Fri Nov 30, 2018 10:32 pm

On Amazon, there are inexpensive OBD-2 datastream converters and phone apps. Is there anything out there that can handle Ford's '94 version of OBD-1?
- Mark
Mark I use ForDiag from Tomas, email;
fordiag (at) fordiag.cz

http://forum.fordiag.cz
Cheers

John

95 Escort RS Cosworth - GHAJ0 / ANTI on a COSY box code
Moates QH & BE
ForDiag

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Re: Diagnostic Correctness: Open Loop at Idle?

Post by mpaton » Sat Dec 01, 2018 11:34 pm

Hellwinger wrote:
Sat Dec 01, 2018 7:22 pm
Michael,

I think the letters/numbers you need are TAG0. See attached photo of sticker.
TAG0 is it indeed. This is the same "Strategy" as my own TOE0, and the "Calibration" is at least 95% the same.
I'm going to just respond to this thread on this forum, the 460ford one might prefer you had a carburettor.

On the other forum, you had asked about ethanol fuel, and sensors. The answer is that back in 94, ethanol fuel wasn't considered for these trucks, but it was for some others. There are PCMs that can take a fuel composition sensor, but it seems they were expensive and unreliable. As far as I know, only O2 sensors are used in flex fuel vehicles these days. And it is your O2 sensor that trims the fuel so that your engine can compensate for 10% ethanol. This only works because you run part of the time in closed loop fuel control. My class A RV is calibrated by Ford to almost never run in Closed Loop fuel control, so it cannot compensate for 10% ethanol.

The value you have labelled as ST FTRIM in your post is actually not Short Term Fuel Trim, it would more accurately be Long Term Fuel Trim, ie the stored trim value applied to the fuel value sent to the injectors. This is what your TAG0 PCM sends to its data stream. Bosch has mislabelled this. (I believe I found out at one time that these are not made by Bosch, but are someone else's unit, rebranded for Bosch. Short Term Fuel Trim would be the Trim value applied to the fuel signal, or injector pulse width in order to make the O2 sensor switch between rich and lean.
Hellwinger wrote:
Sat Dec 01, 2018 7:22 pm
So apparently even a heated O2 sensor can cool off too much? The zirconia membrane needs to be at 600F - maybe the heater just speeds up heating, but has not enough power to keep the sensor working?

And it makes sense. The fuel trim is lookup values for open loop conditions, and dynamic values in response to the O2 signal for closed loop. Not sure if this system has a learned long-term fuel trim it applies to closed loop.
The heated sensor speeds up the heating process, but the sensor needs to be in a hot exhaust stream to say hot enough to work well.

Again, the value you are getting from your datastream labelled as ST FTRIM, is actually LT FTRIM, which IS the learned trim value from the O2 sensor data gathered by running in close loop mode. This trim as intended primarily to compensate for wear and lack of maintenance, and is applied to all fuel values, open and closed loop.
Hellwinger wrote:
Sat Dec 01, 2018 7:22 pm
I am going out to test the MAP now. Stay Tuned.
Good. I hope you have a frequency meter, because that's what the MAP sensor outputs. In fact the PCM outputs frequency in its datastream, not inHg. It is Bosch or whoever, that makes that conversion, and of course they may have got it wrong. But you can still measure the frequency, and also measure the actual MAP and I should have some data somewhere that says what pressure corresponds to what frequency. I should also have some data that says what MAP my own engine idles at.

Because your PCM is setup to idle in open loop, there is no learned correction fuel trim for idling. So it should be leaner than Ford intended when the calibration was written due to the 10% ethanol which has a stoichiometric AFR of 14.06:1. But your exhaust gas test shows you are idling too rich. What could do that.

One thing could be the Fuel pressure regulator. The PCM just assumes this is working, and maintaining 39psi gauge pressure across the injector, no matter what the MAP is. So the regulator has a hose connecting to the intake manifold so it can correct fuel pressure for variations in MAP. If this hose has a leak, then the regulator will sense a greater pressure, and increase fuel pressure. And because you don't idle in closed loop, the fuel trim table won't be updated to compensate. I'm not saying that's it, but it should be easy to check that little hose; it may be 25 tears old.

Hellwinger
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Re: Diagnostic Correctness: Open Loop at Idle?

Post by Hellwinger » Wed Dec 05, 2018 9:42 pm

Ha Ha! They'd prefer a carburetor!

I envy those gear heads in the near future that will have the simplicity of electrics to deal with. Lots of market pressure to develop a better battery. Will be a real game changer when electrical storage approaches the practical energy density of a tank 'o gas.

Anyhow, thank you so much Michael, for your reasoning and assistance.

Yeah, no doubt the data stream variables are mis-labeled by the scanner - for example, the MAP readout appears to be not in "Hg as labeled, but in absolute PSI - but even then the conversion is not quite right, I think. More on that later - I am covering your good points in order.

OK, so the TAG0 strategy is similar to the TOE0. Question is, are the scanner-displayed values I get reasonable? From a diagnostic perspective, can it be said that the EEC IV system is doing what it is supposed to for the set of sensor inputs (good or bad) it is working with?

The scanner is apparently deploying the % fuel trim to injector time being applied at the time. In closed loop, this is a dynamic number, based on O2 sensor input. For my engine, which goes into closed loop right off-idle, displayed fuel trim bounces around somewhere between -3 and 6 % at other than idle speeds. When the throttle is shut and engine speed decreases to 800RPM, closed-loop control continues (I can see this on the loop status and my dashboard bargraph O2 voltage display), with a bit more wandering about in trim values. And then, after a few seconds, scanner-displayed fuel trim goes to 11%, loop status goes open, and O2 sensor voltage goes low.

So the 11% fuel trim at idle is the result of a long-term mean of closed-loop fuel trims, NOT a factory value built into the lookup tables? If +11% is a long term mean, that is indicative of a chronic lean condition during closed loop operation? Hmm.

Ah. Glad to know about the heated O2 sensor.

Yep, I have a Fluke multimeter with a frequency meter, oscilloscope and other goodies. I tested the MAP sensor. Even bought a new one and tested that. They both match, and match published frequency/pressure tables and expected output waveform and amplitude. Old hose tested good, put a new hose on it just for grins. They also both produce the same scanner-displayed data stream MAP values. Returned the new one.

About those scanner values: About 15 for KOEO and 10 for idle. Correlates to 0 inches Hg on the (tee'd in) vacuum gauge, and about 20 inches at idle. Sea Level barometric pressure is 14.7 PSI, I live at about 800 feet MSL, but it was a hot dry day in So.Cal, so 15 is reasonable. 1 PSI = 2.04"Hg
so 10 PSI absolute manifold pressure correlates to about 20 inches mercury vacuum? But wait, 0 PSI absolute = 30"Hg vacuum. 5 PSI absolute = 20"Hg vacuum. 10 PSI absolute = 10" vacuum. 15 PSI absolute = 0"Hg vacuum. So either both new and old vacuum sensors and the EEC IV are wrong, or someone at the outfit that made the Bosch scanner does not know their conversion Algebra (sign issue).

Oh wait - the 11% idle fuel trim is not learned? That's what is in the lookup table for the sensor values being read in?

Yep. Idling rich. What could do that?

Well, I have measured/checked:

Fuel rail pressure (within spec - 29 PSI @ idle to 40 PSI WOT- new hose too).

Fuel rail leak-down rate (static, i.e. no drippy injectors).

TPS new (old one was 1V at closed throttle, new one is 0.8 volts throttle closed).

Compression (good, even at 165 to 155 PSI).

Spark plugs new, good color after a short trip. New dist. cap. Wires a little older but still plenty good. No chronic misfires evident.

New canister purge solenoid (old one was always open). Have not actually verified proper operation tho. Will do.

PCV valve is clean and rattles around like it should.

New air filter and new filter on PCV hose.

Idle Air Control removed and inspected. It's clean. Idle goes up like it should when I put it in gear/ turn on AC.

Oil & filter new.

Passes KOEO and KOER tests. No codes set.

The throttle stop is at the factory setting.

Have not inspected the throttle plates.

Vacuum gauge reads as expected (no gross vac leak).

I have checked the ECT sensor resistance (good).

Have not checked air charge temp sensor (but the scanner readout looks reasonable, just as it does for the ECT).

I was thinking that the idle lookup table was calling for a richer fuel trim because the sensed temps were low.

CO is not made in cats - only comes from partial combustion at pressure in a cylinder. So high CO reading in 4-gas means rich.

High O2, High HC, low CO2 means misfire.

So it's either getting too much fuel or not enough air.

Hmm. I am running out of ideas, man.
- Hellwinger

Engine: 1994 Ford 460 (7.5L) EEC IV OBD1 MFI
VIN 1FTJW36G2REA00204
Aftermarket headers, various bodged exhaust heat shields - all else stock.
Mounted in an F-350 4x4 quad cab with extended bed chassis with E40D transmission.
Bed removed, extra frame rails and tag axle added - so now 4x6.
RV coach added w/bed area over cab. I am second owner, tinker with it constantly.
Search: "phoenix one road trip america" for some vehicle background. It's an adventure!

Hellwinger
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Posts: 11
Joined: Thu Nov 29, 2018 1:58 pm

Re: Diagnostic Correctness: Open Loop at Idle?

Post by Hellwinger » Thu Dec 06, 2018 11:16 am

More thoughts about what could be going on . . .

I am weighing likely scenarios to guide my next dive under the hood. Hence the diagnostic sanity title.

Proper EGR operation has been verified. It was taken off the manifold and brake cleaner does not leak through it. Tight valve seal. No EGR gasses at idle.

Compression is good.

Ignition is apparently good.

I have not checked timing, but that has not been changed and on-the-road drivability is as good as always. However, that does not cover the sender in the distributor, the ignition module, or the coil. I presume the cap and wires and plugs are good because they are new. There are no overt and obvious signs of a consistent ignition misfire. My question is: Can above fail in a way to produce observed symptoms? Will check it all out, eventually. Has not been considered a likely cause (so far).

Too much fuel?

The fuel rail pressures at idle and under load are good, the snap response rate is good, the leak-down rate is zero.

What other source of fuel is possible? The vapor canister system. Seems to me that liquid fuel would need to be making it past the canister purge solenoid valve into the PCV tube to make that much of a difference. I would assert that when operating properly for a while, the canister vent is a metered source of manifold air without much fuel vapor in it. It will be checked for proper flow on the tank venting side as well as the purge air venting side. The caps on the fuel tanks have been pressure tested and are good (part of a smog inspection in these parts).

Not enough air? Inputs with improper metering into the intake manifold (like the canister purge)?

The throttle plate is in the factory closed position as judged by the undisturbed orange paint blob on the screw threads and body housing.

Do the throttle plates have metered holes in them that can clog? Does the Idle Air Control valve have enough control authority to overcome that? Would too much IAC opening % show up in the data stream as a result? What is a typical IAC % open value for a healthy idling engine?

The IAC valve is not restricted, have removed and inspected it. The engine RPM jumps when it should during transmission shifting and AC operation. Has passed the KOER test. However, I have not checked any restriction in the IAC connection to the intake tube leading from the air cleaner box to the throttle valves. Also, I do not know if there is any restriction after the valve, in the throttle body. Have been thinking that’s not as likely (so far).

The PCV system sources air through a little separate filter in the intake box into one head cover, and then draws it out of the other head cover through a seated-weight valve, then pipes that right into the intake manifold. The weight valve rattles around as it should when shaken. Apparently it allows a metered bit of crankcase vapors to enter the intake manifold when the pressure differential across the gravity valve is great enough. Rough but reliable pressure regulator, that. I have not checked the other elements of the PCV system for proper flow. Again, not as likely (so far).

There is also a very small metered vacuum leak coming from the dashboard pneumatics. Not significant. All other vacuum systems are closed systems (and have new silicone hoses).

The catalyst air-pump system is independent.

Are there other possible air sources that are clogged, potentially producing rich-at-idle conditions?

Which leads to the engine control system and its retinue of sensors…

For my situation, is the fuel trim and other commanded EEC IV outputs such as timing and injector pulse width nominal for the existing sensor inputs? That’s why I thought a tuner forum might be able to help. I imagine part of tuning is modifying the base multi-dimensional lookup table and other factors to optimize performance. So, who would know better what the typical data stream from a well-idling engine ought to look like? If, for example, 11% fuel trim at idle is too high, what does that say, diagnostically?

I have been assuming that the EEC IV system is working exactly as it is supposed to. All sensors providing a properly calibrated input. If an output is non-optimal for a clean idle, what set of conditions that the EEC is blind to are producing what we see?

Speaking of properly calibrated inputs, the engine coolant temperature sensor is apparently working, about 190F at idle as read out by the Bosh (oh crud - what if the Bosch converts the EEC output wrong like it does the MAP output). Well, I have measured warm and cold resistances in the engine. The Bosch displayed readings at least make sense but I have not measured an actual resistance by temp curve. Sigh. I can take the coolant temp sensor (and air charge temperature sensor) out and do the ice water and boiling water test, or just put new ones in there.

The thinking behind above is that 11% fuel trim may indeed be proper for a cold engine. The suspicion is that the ECT is out of calibration, telling the EEC that the engine is cold when it is not. Thereby producing observed conditions.

OR, the thermostat is opening too soon or not closing. Perhaps 185 - 190F (or whatever the sensed temp is) at that physical point in the coolant path is less than the fully-warmed up engine criteria buried in the look-up tables. Have been reluctant to crack all that open, but it is right there in front and relatively easy to get at.

So I have some paths to follow and narrow down. I just hope I am not too embarrassed by what finally turns out to be the cause of my problem.
- Hellwinger

Engine: 1994 Ford 460 (7.5L) EEC IV OBD1 MFI
VIN 1FTJW36G2REA00204
Aftermarket headers, various bodged exhaust heat shields - all else stock.
Mounted in an F-350 4x4 quad cab with extended bed chassis with E40D transmission.
Bed removed, extra frame rails and tag axle added - so now 4x6.
RV coach added w/bed area over cab. I am second owner, tinker with it constantly.
Search: "phoenix one road trip america" for some vehicle background. It's an adventure!

mpaton
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Re: Diagnostic Correctness: Open Loop at Idle?

Post by mpaton » Fri Dec 07, 2018 12:24 am

Here's a couple of things you might look at.

1 your value of IAC value of 33% seems low compared to mine at 48% for idling in Neutral/Park. I see you've checked it, but I'm wondering if it could be sticking (as 33% is what's being commanded, it's just assumed that it works. If it sticks an integrator does its thing and commands more (which also changes the fuel correction at idle, so there is a link up here). Also has anyone been fiddling wit the throttle stops on the throttle body? That might explain the low IAC value

2 This next one doesn't explain the high KAMRF(fuel correction) value; however it may affect idle mixture. The distributor cap is marked with the position of the #1 plug lead. Check and see if the wire at that position is actually going to the #1 plug. What happens is that people take the distributor out and put it back a tooth off. It won't start. They eventually work out what they've done, and are too lazy to pull the distributor again, and put it back correctly. So they just move plug wires around the distributor cap. Now it runs, so they are happy. However this system actually knows when cylinder #1 is supposed to fire, and now a different cylinder is firing when #1 is supposed to. The ignition is working fine, but the fuel injection is not. This engine has a batch fire system. It fires 4 injectors at one time, and those batches of 4 injectors are picked so that fuel will be injected on to the back of a closed intake valve. Yes, this can only happen correctly at lower engine rpm, and lower injector pulse widths. However in my distributor out a tooth or 2 scenario, there can be an injector firing onto an open intake valve which is going to affect the mixture distribution at idle.

You could also try warming up the engine, and while in park and foot off the throttle, vary the load on the engine (turn on the AC, or turn electrical loads on and off) and see how the rpm, IAC and ignition advance varies, and note some values. This should give us more data on whether the IAC is sticking.

Also, I know you said you had no KOEO or KOER codes, but what about CM (Continuous memory) codes. These can be present with no check engine light.

Michael

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Re: Diagnostic Correctness: Open Loop at Idle?

Post by Hellwinger » Fri Dec 07, 2018 4:33 pm

Ah. Good ideas about things to check. Stay Tuned. Thanks again.
- Hellwinger

Engine: 1994 Ford 460 (7.5L) EEC IV OBD1 MFI
VIN 1FTJW36G2REA00204
Aftermarket headers, various bodged exhaust heat shields - all else stock.
Mounted in an F-350 4x4 quad cab with extended bed chassis with E40D transmission.
Bed removed, extra frame rails and tag axle added - so now 4x6.
RV coach added w/bed area over cab. I am second owner, tinker with it constantly.
Search: "phoenix one road trip america" for some vehicle background. It's an adventure!

mpaton
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Posts: 376
Joined: Mon Jun 23, 2008 1:39 pm

Re: Diagnostic Correctness: Open Loop at Idle?

Post by mpaton » Sat Dec 08, 2018 2:25 pm

As I look again at the code, I see that both MAP in inches of Mercury and Map frequency in Hz are part of the datastream available. I don't know which one Bosch has chosen to display, and it may be that the MAP value you got was accurate. 10:Hg at idle seems a reasonable value.

Hellwinger
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Re: Diagnostic Correctness: Open Loop at Idle?

Post by Hellwinger » Sat Dec 08, 2018 10:19 pm

Thank you Micheal.

I'm wondering, do DIY tuners have access to the EEC lookup table values and know the decision tree well enough to predict what EEC outputs ought to be based on inputs?

If you have questions about how I am verifying proper operation of the various systems, and how I know what I know, feel free to ask.

Indeed 10"Hg absolute is a good idle vacuum. I measured the frequency vs. pressure curve for a new sensor and my old sensor and they are the same, so my rich idle problem is not the MAP sensor. It passes the KOER test as well.

Online, I found a good fit to my symptoms (read rabbit hole):

https://www.yourmechanic.com/article/sy ... heck-valve

So today I verified proper check valve operation (my engine has three) along with he smog pump and computer-controlled valve. Yup, it all works as it should for a cold start. One last test for that: Will verify it stops injecting air upstream of the O2 sensor once it warms up.

One more thing my problem is unlikely to be caused by.

More checking to do. Stay Tuned.
- Hellwinger

Engine: 1994 Ford 460 (7.5L) EEC IV OBD1 MFI
VIN 1FTJW36G2REA00204
Aftermarket headers, various bodged exhaust heat shields - all else stock.
Mounted in an F-350 4x4 quad cab with extended bed chassis with E40D transmission.
Bed removed, extra frame rails and tag axle added - so now 4x6.
RV coach added w/bed area over cab. I am second owner, tinker with it constantly.
Search: "phoenix one road trip america" for some vehicle background. It's an adventure!

mpaton
BIN Hacker
Posts: 376
Joined: Mon Jun 23, 2008 1:39 pm

Re: Diagnostic Correctness: Open Loop at Idle?

Post by mpaton » Sat Dec 08, 2018 11:55 pm

Hellwinger wrote:
Sat Dec 08, 2018 10:19 pm
Thank you Micheal.

I'm wondering, do DIY tuners have access to the EEC lookup table values and know the decision tree well enough to predict what EEC outputs ought to be based on inputs?
By tuners, I'm guessing you mean the devices you can attach to your EEC-IV to allow you to inspect ROM and RAM values. You can get devices that allow that, but it's not especially cheap if all you want to do is pass your state inspection. You would need to spend at least $250 for a hardware device, have a Windows laptop, and then you'd also need a combination of a software program to display all these values, and also what's called a def file which essentially tells the software program the addresses in ROAM and RAM of the various tables of interest. These def files are the result of up to many tens of hours of work by somebody, and also cost. Cheaper is available, but possibly of lower quality.
Hellwinger wrote:
Sat Dec 08, 2018 10:19 pm
If you have questions about how I am verifying proper operation of the various systems, and how I know what I know, feel free to ask.
I'll send you a PM
Hellwinger wrote:
Sat Dec 08, 2018 10:19 pm
Indeed 10"Hg absolute is a good idle vacuum. I measured the frequency vs. pressure curve for a new sensor and my old sensor and they are the same, so my rich idle problem is not the MAP sensor. It passes the KOER test as well.

Online, I found a good fit to my symptoms (read rabbit hole):

https://www.yourmechanic.com/article/sy ... heck-valve

So today I verified proper check valve operation (my engine has three) along with he smog pump and computer-controlled valve. Yup, it all works as it should for a cold start. One last test for that: Will verify it stops injecting air upstream of the O2 sensor once it warms up.
I was expecting your thermactor air system to have only one valve. Can you post a photo of your VECI label if it's still there. It's a 1.5" by 4" black on white decal on the outside rear vertical surface of the driver's side valve cover. The VECI label that matches your TAG0 PCM only has one. It has a Calibration of 4-98A-R00 which should also appear on a 1.5" by 1" white on black decal on a door jamb or door post.

Michael

Hellwinger
Gear Head
Posts: 11
Joined: Thu Nov 29, 2018 1:58 pm

Re: Diagnostic Correctness: Open Loop at Idle?

Post by Hellwinger » Sun Dec 09, 2018 11:19 am

Will look for requested decals shortly. In the meantime, here's what I have of the driver's door, in case it is relevant.
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IMG_4182.jpg (111.4 KiB) Viewed 167 times
- Hellwinger

Engine: 1994 Ford 460 (7.5L) EEC IV OBD1 MFI
VIN 1FTJW36G2REA00204
Aftermarket headers, various bodged exhaust heat shields - all else stock.
Mounted in an F-350 4x4 quad cab with extended bed chassis with E40D transmission.
Bed removed, extra frame rails and tag axle added - so now 4x6.
RV coach added w/bed area over cab. I am second owner, tinker with it constantly.
Search: "phoenix one road trip america" for some vehicle background. It's an adventure!

Hellwinger
Gear Head
Posts: 11
Joined: Thu Nov 29, 2018 1:58 pm

Re: Diagnostic Correctness: Open Loop at Idle?

Post by Hellwinger » Sun Dec 09, 2018 1:06 pm

The VECI label is also on the bottom of the hood.
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IMG_4277.jpg (62.08 KiB) Viewed 163 times
IMG_4177.jpg
IMG_4177.jpg (92.87 KiB) Viewed 163 times
- Hellwinger

Engine: 1994 Ford 460 (7.5L) EEC IV OBD1 MFI
VIN 1FTJW36G2REA00204
Aftermarket headers, various bodged exhaust heat shields - all else stock.
Mounted in an F-350 4x4 quad cab with extended bed chassis with E40D transmission.
Bed removed, extra frame rails and tag axle added - so now 4x6.
RV coach added w/bed area over cab. I am second owner, tinker with it constantly.
Search: "phoenix one road trip america" for some vehicle background. It's an adventure!

Hellwinger
Gear Head
Posts: 11
Joined: Thu Nov 29, 2018 1:58 pm

Re: Diagnostic Correctness: Open Loop at Idle?

Post by Hellwinger » Sun Dec 09, 2018 1:12 pm

A blowup:
Attachments
IMG_4177 (1).jpg
IMG_4177 (1).jpg (21.93 KiB) Viewed 162 times
- Hellwinger

Engine: 1994 Ford 460 (7.5L) EEC IV OBD1 MFI
VIN 1FTJW36G2REA00204
Aftermarket headers, various bodged exhaust heat shields - all else stock.
Mounted in an F-350 4x4 quad cab with extended bed chassis with E40D transmission.
Bed removed, extra frame rails and tag axle added - so now 4x6.
RV coach added w/bed area over cab. I am second owner, tinker with it constantly.
Search: "phoenix one road trip america" for some vehicle background. It's an adventure!

mpaton
BIN Hacker
Posts: 376
Joined: Mon Jun 23, 2008 1:39 pm

Re: Diagnostic Correctness: Open Loop at Idle?

Post by mpaton » Sun Dec 09, 2018 6:54 pm

So that calibration matches your TAG0 PCM, and the diagram shows a single thermactor air valve.

And yet you said you checked 3 check valves. What did I misunderstand?

Michael

Hellwinger
Gear Head
Posts: 11
Joined: Thu Nov 29, 2018 1:58 pm

Re: Diagnostic Correctness: Open Loop at Idle?

Post by Hellwinger » Tue Dec 11, 2018 5:47 pm

I doubt the bodgers who built the coach of the RV messed with the engine *that* much. They did add aftermarket headers, tho, with all of the EGR and air injection fittings. But it is strange the factory documentation does not catch this.

The smog pump on my engine has two 1" inlets coming from some sort of can (filter?), and two outlets. One outlet pumped-air path goes through a check valve (over passenger valve cover) and then heads to an exhaust injection point right upstream of the cat (just 6" or so downstream of the O2 sensor). The other pumped-air path goes to the computer-actuated valve (also over passenger valve cover) that either dumps the air or passes it to a tee, which feeds two separate check valves, which inject air into one of the rear header cylinder pipes on either side of the engine. So it appears the cat gets supplemental air at all times (but not injected between the reduction and oxidation biscuits), and sometimes gets more via the headers. The air injected into the headers is for reducing emissions during cold starts. It encounters hot rich gasses and starts burning excess HC upstream of the cat - so eventually, during a warmup cycle, the vacuum signal from the solenoids mounted over by the EGR valve should diminish, and the diverter valve returns to its default state of dumping air through a little muffler thingie mounted on top of the aforementioned filter can.

It all seems to be working as expected.

I have bench-tested the IAC valve. It is shot. So, the first definitely bad thing I have found. I have ordered a new one and will bench test it as well and then report results and details once it all passes smog. I hope that is not as presumptuous as that sounds!

Stay Tuned
- Hellwinger

Engine: 1994 Ford 460 (7.5L) EEC IV OBD1 MFI
VIN 1FTJW36G2REA00204
Aftermarket headers, various bodged exhaust heat shields - all else stock.
Mounted in an F-350 4x4 quad cab with extended bed chassis with E40D transmission.
Bed removed, extra frame rails and tag axle added - so now 4x6.
RV coach added w/bed area over cab. I am second owner, tinker with it constantly.
Search: "phoenix one road trip america" for some vehicle background. It's an adventure!

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