High MAF voltage at idle

Anything about Ford EEC tuning. TwEECer and Moates questions dominate, but there's some SCT and OBD-II knowledge too.

Moderators: cgrey8, EDS50, 2Shaker, Jon 94GT

Post Reply
LukasMC
Gear Head
Posts: 9
Joined: Fri Jun 08, 2018 1:46 pm

High MAF voltage at idle

Post by LukasMC » Tue Jun 18, 2019 6:46 pm

Hi everyone!
I've gotten my 94 f150 to be pretty drivable, but am having trouble smoothing out the idle. It seems to be surging quite a bit. The vaccum doesn't seem too low, but it does bounce between 20-25 in. I went through a procedure I found online to set base idle: disconnect IAC and throttle plate stop screw in/out until the engine idles just high enough not to die. The result of this process is a screw that seems pretty far in to me, much farther in than the procedure using a feeler gauge + 1.5 turns. My data logs show an MAFv of ~1.4v which seems really high to me since I see threads of other guys who idle well below a volt. What do you guys think? Is this reading abnormal, and what would you recommend researching/adjusting to get it acceptable?
Thanks!
1994 Ford F-150
302 with Trickflow stage 1 cam, skip white aluminum heads stock 19LB/hr injectors
Stock truck intake and MAF
CBAZ0 with quarterhorse and binary editor
4R70w transmission with reprogramming kit

User avatar
Paulie
Tuning Addict
Posts: 502
Joined: Thu Oct 23, 2008 9:05 pm
Location: Chicagoland

Re: High MAF voltage at idle

Post by Paulie » Wed Jun 19, 2019 11:12 am

What is the rpm when the maf is 1.4 volts?
1990 Mustang 5.0, HCI, Vortech S-trim, FRPP 42# inj., PMAS MH95, A9L, Moates Quarterhorse, BE/EA, Innovate LC-1.

User avatar
cgrey8
Administrator
Posts: 10714
Joined: Fri Jun 24, 2005 5:54 am
Location: Acworth, Ga (Metro Atlanta)
Contact:

Re: High MAF voltage at idle

Post by cgrey8 » Wed Jun 19, 2019 12:10 pm

Like Paulie asked, what RPM are you at when the engine is about to die? But yeah 1.4v even with the smallest of stock MAFs is high for idle...particularly for an idle that's been set just above where the engine wants to stall.

Initially I was thinking ~1.4v MAFv was erroneous. But then you described that you had to turn the idle screw way in to keep the engine idling (ISC disconnected). If the TB butterfly is having to be cracked open that much, it's quite possible the MAF is reporting ~1.4v legitimately. But that, in itself, is telling you there's a different problem. An engine just barely staying above, say 600ish RPMs while pulling down that much air suggests to me that maybe the timing is WAY retarded...like on the other side of 0 retarded. Get a timing light connected and if you see 10 on the balancer with the SPOUT pulled, make sure that's not 10 After TDC when it should be 10 Before TDC with the SPOUT pulled. With the SPOUT connected, you should see 15-20 degrees BTDC...something relatively near whatever you are datalogging it to be at that moment (assuming the tune doesn't have it bouncing all over trying to maintain RPM).

The thing that negates this theory is your vacuum numbers. Those numbers don't suggest a low RPM engine sucking down lots of air. Those numbers suggest an engine with a healthy vacuum...almost too healthy for a 302 with heads and aftermarket performance-oriented cam. Even the Stage 1 TrickFlow cam is more akin to the E303 than it is to a stock cam, so it should be much more labored to idle at low RPMs than a stock engine would be. I mention TF since that's what is in your signature. Although you don't indicate which TF cam. I would've thought teens for vacuum at RPMs below 700...but I'm not an expert.

But while on the subject, one thing you will noticed is the engine should take less air the more advance you give the engine at idle, up to about 25 BTDC. The problem with giving too much advance at idle & off-idle conditions is it makes the engine temperamental. The slightest little upset, and the engine will more-than-likely conk out where an advance value in the teens is likely to be more tolerant of sudden loading and more likely to recover without stalling out completely. This is particularly important for manual trans vehicles. It took me YEARS to learn this!

If timing checks out, then start looking at fuel. What is the HEGO doing? I'm assuming you only have 1 being this is an F150. At stabilized WARM idle, it should be switching 0.0-0.5v. If you have a WB, what is it reporting?
...Always Somethin'

89 Ranger Supercab, 331 w/GT40p heads, ported Explorer lower, Crane Powermax 2020 cam, 1.6RRs, FMS Explorer (GT40p) headers, Slot Style MAF, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, Innovate LC-1, GUFB, Moates QuarterHorse tuned using BE&EA

Member V8-Ranger.com

LukasMC
Gear Head
Posts: 9
Joined: Fri Jun 08, 2018 1:46 pm

Re: High MAF voltage at idle

Post by LukasMC » Wed Jun 19, 2019 2:14 pm

I played around with it a little more this morning and remembered I had the neutral idle rpm set pretty high at 800 rpm until I got the rest of the tune dialed in. The MAF was reading 1.4v at around 900-1000 rpm while the desired rpm was 896 and around there. Previously when I was setting the idle screw, it would die somewhere around 800 without lots of the screw if I'm remembering correctly. I went ahead and reduced the idle to 700 rpm and was able to back the screw out quite a bit without killing the engine. With this new setting it is idling around 680-790 still surging. At this idle the MAF is now reading a more reasonable 1.1xx volts.

I double checked the base timing, and without the spout it is set at 10* BTDC. You are right that it has a trick flow stage 1 cam, I forgot to add that to the signature, it's added now. At this new idle speed it is reading a lower 15 or so in-hg. Thanks for the tips on idle timing, I'll look some more into that.

You are right about the single HEGO, logs say it is bouncing around .1-.2 with short bursts up to .7 my wide band reports an A/F moving around in the 14.3-15.0 range. The idle is still surging quite badly, it seems to be going through a very fast cycle of overshoot-undershoot. Let me know if logs would be helpful.
Thanks for the help!
1994 Ford F-150
302 with Trickflow stage 1 cam, skip white aluminum heads stock 19LB/hr injectors
Stock truck intake and MAF
CBAZ0 with quarterhorse and binary editor
4R70w transmission with reprogramming kit

User avatar
cgrey8
Administrator
Posts: 10714
Joined: Fri Jun 24, 2005 5:54 am
Location: Acworth, Ga (Metro Atlanta)
Contact:

Re: High MAF voltage at idle

Post by cgrey8 » Wed Jun 19, 2019 6:34 pm

Ok. Hunting, surging, or general idle instability can be caused by either fuel or spark. It sounds like you've eliminated both. So that leaves...the tune.

I remember the A9L and X3Z both had some fairly aggressive spark multipliers for RPM error that were intent on controlling RPM changes. However for my setup, they were always too aggressive and caused more problems than they solved. To confirm, I neutered those functions down to very little adjustment ability. And sure enough, my idle calmed down.

Find your strategy's idle spark and idle ISC adjustment functions based on RPM error and see if you can "calm" them down just to see if maybe that's what your problem is too. What worked with bone stock engines often doesn't work well with aftermarket add-ons that make the engine's response much different than stock.
...Always Somethin'

89 Ranger Supercab, 331 w/GT40p heads, ported Explorer lower, Crane Powermax 2020 cam, 1.6RRs, FMS Explorer (GT40p) headers, Slot Style MAF, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, Innovate LC-1, GUFB, Moates QuarterHorse tuned using BE&EA

Member V8-Ranger.com

User avatar
EDS50
Administrator
Posts: 3735
Joined: Sun Apr 05, 2009 9:17 am
Location: Tampa Bay, FL
Contact:

Re: High MAF voltage at idle

Post by EDS50 » Thu Jun 20, 2019 9:36 am

I would be curious to know what your tps voltage is at idle.
1992 LX - 25.1c Chassis, Vortech Blown Dart 332, Lentech Trans, TRZ Backhalf, A9L, Moates QH/SL v1.9, BE, EA, TunerView

User avatar
cgrey8
Administrator
Posts: 10714
Joined: Fri Jun 24, 2005 5:54 am
Location: Acworth, Ga (Metro Atlanta)
Contact:

Re: High MAF voltage at idle

Post by cgrey8 » Thu Jun 20, 2019 10:42 am

EDS50 wrote:
Thu Jun 20, 2019 9:36 am
I would be curious to know what your tps voltage is at idle.
That'd be an excellent thing to check particularly given he had to run the screw in so far. Although as of his last post, it sounds like he got the screw out further and got a stable idle at lower RPMs. So his TPS hopefully is back under 1.25v. Although I doubt high TPS voltage would cause hunting.

Another thing that could cause this is stock values in the tune keeping the EEC in Open Loop fueling longer than necessary...and if his fuel isn't dialed in, excessive rich or excessive lean would definitely cause hunting, even at 800ish RPMs.

I modified my tune to go Closed Loop Fueling just after 30 seconds after crank. With my setup, I found my HEGOs were warm-enough to be used by Closed Loop in 10-15 seconds even in the coldest cranking conditions. However if his HEGO is really old, has a bad heater, or is too far down stream, he may not be able to get away with that. The good news is he's seeing HEGO voltage going up to .7v which means it's at least trying to work. If it wasn't going above .4v, that would definitely be a problem either causing an excessive rich or exposing a lean running condition...either of which could cause idle instability.
...Always Somethin'

89 Ranger Supercab, 331 w/GT40p heads, ported Explorer lower, Crane Powermax 2020 cam, 1.6RRs, FMS Explorer (GT40p) headers, Slot Style MAF, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, Innovate LC-1, GUFB, Moates QuarterHorse tuned using BE&EA

Member V8-Ranger.com

User avatar
EDS50
Administrator
Posts: 3735
Joined: Sun Apr 05, 2009 9:17 am
Location: Tampa Bay, FL
Contact:

Re: High MAF voltage at idle

Post by EDS50 » Thu Jun 20, 2019 11:06 am

Just for reference, my 92mm Pro-M idle voltage (mafv) at operating temperature is between .400-.500 mafv at 900rpm idle in park with a .95 tps. Once I put the car in gear, it idles 850 and the mafv will dip into the .300 mafv range which caused a maf error requiring me to update vmafr1 and vmamin to 0.2500 to not activate a maf error. I have an Accufab TB on a Massflo EFI intake (same as an Edelbrock SuperVictor EFI) with a custom aluminum elbow and if I even touch the idle set screw to try and lower the idle to 800 which in turn affects the tps setting the car flips out and immediately drops afr from 14.5 idle afr to 11 within 30 seconds. That's how temperamental mine is since it drops mafv into the .200 range if I try to fool with the idle. I mentioned his tps because I am quite sure it was well above 1.0.v with the tb set screw turned in as much as it was which puts the tune into part throttle mode evident by the high mafv and vacuum reading. The o/p should have no problem getting his combo to idle at 800 with a 14.xx afr, with a realistic 12-14 in. hg vacuum with a tfs stage 1 cam. When I had my 89 gt with the same cam it was happiest at 900 rpm.
1992 LX - 25.1c Chassis, Vortech Blown Dart 332, Lentech Trans, TRZ Backhalf, A9L, Moates QH/SL v1.9, BE, EA, TunerView

User avatar
cgrey8
Administrator
Posts: 10714
Joined: Fri Jun 24, 2005 5:54 am
Location: Acworth, Ga (Metro Atlanta)
Contact:

Re: High MAF voltage at idle

Post by cgrey8 » Thu Jun 20, 2019 12:36 pm

Agreed.
...Always Somethin'

89 Ranger Supercab, 331 w/GT40p heads, ported Explorer lower, Crane Powermax 2020 cam, 1.6RRs, FMS Explorer (GT40p) headers, Slot Style MAF, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, Innovate LC-1, GUFB, Moates QuarterHorse tuned using BE&EA

Member V8-Ranger.com

LukasMC
Gear Head
Posts: 9
Joined: Fri Jun 08, 2018 1:46 pm

Re: High MAF voltage at idle

Post by LukasMC » Fri Jun 21, 2019 4:18 pm

After some searching, I wasn't able to find an idle specific spark function in my strategy, but I was able to find a scalar called isc rpm deadband which is currently set to 100 rpm. Is this the adjustment you were referencing cgrey?

Right now, the engine is idling with a tps voltage of 1.04v which from what I understand is within the acceptable range for the ecu. The MAFv is also in the high 1.1x's. The ecu is in closed loop fueling while idling like this, since I can see KAMRF adjustments change. Nice to see someone else with the same cam, thanks for the info :biggrin: Where it's idling right now it holds about 15 in hg

Thanks for the responses!
1994 Ford F-150
302 with Trickflow stage 1 cam, skip white aluminum heads stock 19LB/hr injectors
Stock truck intake and MAF
CBAZ0 with quarterhorse and binary editor
4R70w transmission with reprogramming kit

User avatar
EDS50
Administrator
Posts: 3735
Joined: Sun Apr 05, 2009 9:17 am
Location: Tampa Bay, FL
Contact:

Re: High MAF voltage at idle

Post by EDS50 » Fri Jun 21, 2019 4:22 pm

Tps voltage needs to be under 1.0v. When you reduce it via tb set screw or adjusting tps your mafv will also be under 1.0v.
1992 LX - 25.1c Chassis, Vortech Blown Dart 332, Lentech Trans, TRZ Backhalf, A9L, Moates QH/SL v1.9, BE, EA, TunerView

LukasMC
Gear Head
Posts: 9
Joined: Fri Jun 08, 2018 1:46 pm

Re: High MAF voltage at idle

Post by LukasMC » Fri Jun 21, 2019 4:25 pm

I'll try backing the screw out some and see how it does.
1994 Ford F-150
302 with Trickflow stage 1 cam, skip white aluminum heads stock 19LB/hr injectors
Stock truck intake and MAF
CBAZ0 with quarterhorse and binary editor
4R70w transmission with reprogramming kit

LukasMC
Gear Head
Posts: 9
Joined: Fri Jun 08, 2018 1:46 pm

Re: High MAF voltage at idle

Post by LukasMC » Fri Jun 21, 2019 5:34 pm

Backed it out to about .98v. Now has MAFv of about 1.2xx while floating around 880rpm
1994 Ford F-150
302 with Trickflow stage 1 cam, skip white aluminum heads stock 19LB/hr injectors
Stock truck intake and MAF
CBAZ0 with quarterhorse and binary editor
4R70w transmission with reprogramming kit

User avatar
EDS50
Administrator
Posts: 3735
Joined: Sun Apr 05, 2009 9:17 am
Location: Tampa Bay, FL
Contact:

Re: High MAF voltage at idle

Post by EDS50 » Fri Jun 21, 2019 6:15 pm

I would try adjusting the tps on the tb so its lower like 0.90. What is your target idle speed at operating temp?
1992 LX - 25.1c Chassis, Vortech Blown Dart 332, Lentech Trans, TRZ Backhalf, A9L, Moates QH/SL v1.9, BE, EA, TunerView

LukasMC
Gear Head
Posts: 9
Joined: Fri Jun 08, 2018 1:46 pm

Re: High MAF voltage at idle

Post by LukasMC » Fri Jun 21, 2019 8:30 pm

I'll try to loosen the TPS and turn it some. Right now I've got target idle at 800rpm
1994 Ford F-150
302 with Trickflow stage 1 cam, skip white aluminum heads stock 19LB/hr injectors
Stock truck intake and MAF
CBAZ0 with quarterhorse and binary editor
4R70w transmission with reprogramming kit

User avatar
EDS50
Administrator
Posts: 3735
Joined: Sun Apr 05, 2009 9:17 am
Location: Tampa Bay, FL
Contact:

Re: High MAF voltage at idle

Post by EDS50 » Fri Jun 21, 2019 8:51 pm

Yes. Key on engine off. You can hit the datalogger and set it to the display. Depending on how much adjustability you have; you may need to drill the holes out a little larger to get the adjustment where you need it. You want to set your idle according to what your commanding in the tune at operating temperature.
1992 LX - 25.1c Chassis, Vortech Blown Dart 332, Lentech Trans, TRZ Backhalf, A9L, Moates QH/SL v1.9, BE, EA, TunerView

LukasMC
Gear Head
Posts: 9
Joined: Fri Jun 08, 2018 1:46 pm

Re: High MAF voltage at idle

Post by LukasMC » Sat Jun 22, 2019 12:59 am

Just to make sure I'm interpreting right, you mean to set the idle rpm with the screw (with iac disconnected) to the commanded idle speed when warm?
Thanks!
1994 Ford F-150
302 with Trickflow stage 1 cam, skip white aluminum heads stock 19LB/hr injectors
Stock truck intake and MAF
CBAZ0 with quarterhorse and binary editor
4R70w transmission with reprogramming kit

User avatar
EDS50
Administrator
Posts: 3735
Joined: Sun Apr 05, 2009 9:17 am
Location: Tampa Bay, FL
Contact:

Re: High MAF voltage at idle

Post by EDS50 » Sat Jun 22, 2019 7:45 am

Well, depends on how far you want to get into it to get things right. I would recommend to perform a base idle reset with the factory tune settings at normal engine ect operating temps....say 190f degrees with the correct base fuel pressure and timing.
1992 LX - 25.1c Chassis, Vortech Blown Dart 332, Lentech Trans, TRZ Backhalf, A9L, Moates QH/SL v1.9, BE, EA, TunerView

Post Reply

Who is online

Users browsing this forum: No registered users and 13 guests