[ozcob]

Does anyone have an idea of the maximum charging voltage that the EEC will safely handle?

I was stranded today after the EEC fuse blew (and a replacement fuse). When I looked at the data log the charging voltage at times during the drive hit 15.0v!

I've only done a bit of diagnosis this afternoon but it seems the EEC may be fried because each time I turn the ignition on it will blow the EEC fuse but if I remove the 60 pin plug and turn on the ignition the fuse remains intact - so to me its pointing to the EEC?

[decipha]

could be a short on one of the outputs

unplug the maf and and fuel pump relay to make sure one of those aint doing it

15v aint nothing, Ive already shot 20v to an eec before when the alternator regulator failed

[ozcob]

Thanks for that suggestion decipha, here is what I found.

I unplugged the MAF, fuel pump relay & canister purge solenoid with the same result (blows fuse when ignition turned on).

Without the EEC plugged in (and the above still unplugged) if I measure between ground and a VPWR wire in the loom I have an open circuit, as soon as I plug in the EEC I get a dead short to ground.

I have another EEC (L1C - different strategy but very similar pin use) so I plugged that in and it measured 830 ohms between ground and a VPWR wire in the loom.

To me it is still pointing to a blown EEC - but is there anything obvious that you think I may be missing?

[decipha]

nope sounds like its shorted

ctank open the case and make sure theres no spare parts in there

[ozcob]

Thanks for the confirmation - even though it's not what I wanted to hear!

I opened the case and there were no obvious signs of failure but that's about the extent of my diagnosis capabilities.

Now to source another T4M0 to Australia from the US - any leads on where to get one apart from the obvious EBAY listings?

........and what would be a fair price to pay?

Thanks in advance.

[jsa]

Another visual check, have a look at the backside of the PCB for longish component legs, and corresponding contact point on the EEC case.

IF the T4M0 is anything like the EEC-IV's I've seen the insides of, there are a number of diodes that protect reverse polarity and overvoltage.

The diodes of interest are Zener diodes to be precise.

They are installed directionally in the EEC. When reverse EEC/car polarity is applied, the Zener's is effectively short to ground and blows the fuse. When correct EEC/car polarity is applied at a voltage higher than the Zener reverse bias voltage rating then current flows through the zener to limit the voltage and usually blows the fuse.

One or more Zener's could have failed to be short circuit both ways.

As is typical of EEC-IV's Vpwr got to pins 37 & 57 and ground goes to pins 40 & 60, on mine.

On mine, Pin 37 has the largest Zener marked Z1 on the PCB, the other side of the Zener is common to pins 40 & 60. Pin 57 has one of the smaller Zener's marked Z11 on the PCB, the other side of the Zener is common to pins 40 & 60 also.

With a multimeter on ohms, EEC removed from car, you can test from the Vpwr pins to grounds pins, respect the EEC polarity with your multimeter lead polarity. See if you get a low ohm reading, something like an ohm or less. If you find a low ohm reading then you have found the narrowed down the offending circuit. If you find the readings are high in the order of k-ohms (1000's) then that is not the offending circuit. If all Vpwr pins are high reading you are looking for a fault elsewhere.

If you identify a low ohm reading Vpwr pin the test from that pin to both ends of the zener diodes in the EEC. You are looking for/a zener/s that gives the low reading on both ends indicating it may be shorted.

Take note which way the suspect Zener/s is/are installed.

Desolder the apparently shorted zener/s and remove.

Retest from Vpwr to the PCB holes where the zener was, one side should be low reading, the other side high reading indicating the bad component has been removed. Connect the multimeter probes across the removed zener, using both probe polarity options. A low reading for both polarities indicates the Zener is faulty. Check that no other Vpwr pin is low reading to ground pins and if OK connect to car, key on engine off, see if fuse blows. If fuse OK get a replacement Zener and solder in the correct way.

If you don't have a multimeter and are confident the EEC is the issue, take note of all zener positions. You can desolder the Zener's one at a time, power the EEC checking the fuse until it does not blow. Start with the one marked Z1 on the PCB. If not marked on the PCB, best practice would be to have the Vprw zener's close to the 60 pin connector, start with the largest. Once the fuse is ok reinstall the zeners one at a time in the order of removal except for the last removed, retesting against the fuse for each in turn. Again get replacements for the duds.

Another more dodgey method is to power the EEC with a fresh fuse and feel for a warmer component.

Could also be a capacitor or other component, but they should be obvious to the naked eye if they are blowing fuses.

http://en.wikipedia.org/wiki/Zener_diode

[ozcob]

I think you may have put me onto something!

Z1 zener has a resistance of 0 ohms in each direction so it may be the culprit (or one of them).

The designation on the component appears to be 'W9410' which doesn't yield any results with a quick internet search, but maybe I will need to remove the diode and see if there any extra numbers underneath to allow me to buy a replacement (or equivalent).

Unless you would happen to know a likely suitable replacement component number?

Thanks for your help.

[jsa]

Yeah, pull it out and see if there are any other numbers.

The spare EEC I have here has a Motorola 2101DE part for Z1, also hens teeth.

If you have an EEC you can pinch one from, that would be the best bet.

In the absence of authoritative information I think 16-18v rating of the highest watts available that fits. That looks like 5W from what I can find quickly.

This is my suggestion,

http://au.element14.com/on-semiconducto ... dp/9558110

[ozcob]

Thanks for that info. :)

Out of interest I rechecked the data log I was taking when the ECU fuse expired and the VBAT peaked at 15.94v on a few occasions (2 seconds each) during the log and then for a longer period (about 8 seconds) just before it cut out.

Given that the you have recommended a rating of 16-18v for the replacement would that high charging voltage be the possible cause of the diode failure?

I know decipha mentioned he had seen up to 20v when a regulator failed without damage to an ECU - but it does seem a coincidence that my voltage peaked just before the engine cut out.

I'll have to get my alternator looked at to see why it was charging at that voltage.

[decipha]

I seen 20v on the actual cluster gauge, the ecu only logged up to 16.xx volts in the datalog

[jsa]

Thanks for that info. :)

Out of interest I rechecked the data log I was taking when the ECU fuse expired and the VBAT peaked at 15.94v on a few occasions (2 seconds each) during the log and then for a longer period (about 8 seconds) just before it cut out.

Given that the you have recommended a rating of 16-18v for the replacement would that high charging voltage be the possible cause of the diode failure?

The strategy docs available from this site have a little detail about voltage measurements. it is stated that Vbat is clipped to 15.94v. Elsewhere it gives detail of 0.0625/4x1023counts which give 15.98 volts.

Overvoltage is the probable cause of the failure.

I know decipha mentioned he had seen up to 20v when a regulator failed without damage to an ECU - but it does seem a coincidence that my voltage peaked just before the engine cut out.

As decipha mentions in his reply, 20v was seen on a gauge not the log. Voltage at the gauge and ecu could be different depending on what was running at the time and the wiring in the car. That particular eec version could have different component specs. In any case the logged value is clipped at 15.94v, maybe you got more than 20v but it is not measured. Maybe he's just lucky.

[jsa]

I'll have to get my alternator looked at to see why it was charging at that voltage.

Absolutely Only key on engine off for testing your EEC until that is sorted.

There is the possibility to minimise EEC failure due to over voltage by adding a Zener external to the EEC.


It must be fused, you don't want to set fire to the wiring loom. That fuse must also feed the EEC circuit so the EEC is disconnected from the supply. There is the option of that fuse also feeding the rest of the 12V devices that run back to the EEC. The EEC and devices would have their existing fuses as a Sub-fuses. An alternate is to add more than one external zener, each fused, each then off to the sub-fuse for the EEC / devices respectively. Depends on how the car is wired and how much trouble you want to go to. Think about how the KAM feed (EEC-IV pin 1) is integrated into the vehicle circuitry.


It needs to be as close to the power source as possible, that's the battery or alternator. The choice will depend on how your car is wired and how much trouble you want to go to. The idea is to grade the response of the external and internal Zener's. We want the big external Zener to do the dirty work, and the internal to have as little to do as possible. Voltage drop from the alternator to battery and eventually the EEC will work in our favour if we position the external close to the power source.


The cable from the power source to the fuse and then external zener needs to be as short as possible to minimise voltage drop in the external protection circuit. The cable needs to be of large cross section and suitable to the fuse size. Keep in mind that cable will be handling short circuit current until the fuse blows and you don't want it melting or catching fire. It will also be acting as a partial heat sink for the zener, so high temp silicone insulated is an excellent choice.


16V maximum seems to be a common theme with various max values in the EEC, like Vbat, MAF Max and probably more. So 16V smells like the right choice for voltage protection, without knowing what ford put in the EEC or what tolerance parts they used.

So looking for available options for a 16V external zener with tightest tolerance and high wattage finds;
http://au.element14.com/solid-state/1n3 ... dp/1862952
A 16V nominal 50W 5%, so 15.2-16.8V in practice. Nicely above normal alternator output.
Anode stud mount, that can be screwed to some chassis metal work for the ground side and provide some heat sinking.

If you knew for sure that there was at least 1.6v drop in the wiring from the external Zener location to the internal Zener in the EEC, then the internal could stay at 16v nominal. We want to grade the response and are working against tolerance stacking, we don't want the external working at 16.8V and the internal at 15.2v. We might be lucky and both selected zener's are at the same tolerance drift.

Gut instinct says go for 17v nominal replacements for your internal and rely on some voltage drop, hence the reasoning behind putting the external close to the power source. So looking for available options for a 16V external zener with tightest tolerance and high wattage finds;
http://au.element14.com/on-semiconducto ... dp/9558128
17V nominal 5W 5%, 16.15-17.85v in practice.

If not relying on voltage drop to assist grading then 18v nominal;
http://au.element14.com/on-semiconducto ... dp/2317466
18V nominal 5W 5%, 17.1-18.9v in practice.


If the EEC etc. is fed direct from the ignition switch then an additional relay/s would be required to do this. Choose a relay with back EMF protection resistor or diode.


Choose a quality protection fuse not one of the cylindrical things that bayonet together with a glass fuse. They are a liability for this application. Choose a jumbo blade fuse and carrier, something that does not have tails already terminated - see above about wiring. These jumbo blades have 3/8 or so size tags. Might have to choose normal blade if lower rated fuse suits your car's wiring.

[ozcob]

Thanks for all the comprehensive information.

Clipping of the displayed VBAT holds true because 15.94v seems to be the maximum logged (at various times) during the drive. As you say, the voltage more than likely peaked well over that when the diode in the ECU broke down.

I have a boot mounted battery, with the alternator output commoned at the starter solenoid. I did all the wiring for the car over 10 years ago so I'll need to sit down and think about your suggestions and see how it can be applied to my particular power layout.

(I sent a PM about your attached sketch)

[jsa]

Doh, thanks for the heads up, edited to attach correct file

Battery in the boot, just gives a 3rd option of the starter tag to pick up from. Volts drop from starter to battery with starter size cable is negligible for the EEC related loads.

The battery is not going to go over volts by itself (but could get hooked up backwards), it's the alternator that causes the problem.

Where do you take your feeds for your EEC and other loads from ?

[ozcob]

I'll have to do a sketch of my power feed layout.

When I wired the car originally I always intended consolidating the pages and pages of hand drawn diagrams into a single AutoCAD drawing - 10 or so years later I'm still talking about it!

[jsa]

I here you

[ozcob]

OK - finally sourced a 16v /5w zener diode (the one jsa suggested in an earlier post) and replaced the shorted component in the ECU. The original zener diode was a Motorola 2101DE for which I could find no direct replacement or even a data sheet.

Alternator regulator also replaced to fix the overcharging condition.

At this stage all looks good, with the car starting and the QH seeming to function normally, so maybe no other components or QH was damaged.

I am wondering though whether the zener going permanent short circuit may have been caused because I have too large a ECU fuse (10A). Ideally wouldn't the protection be designed for the diode to reach it's threshold voltage (approx 16v), short to ground and blow the fuse before damaging the zener diode itself.

This was a 'kit' car, so when I wired it I probably looked at available info for other EFI cars here in Australia and chose what seemed an appropriate fuse size.

Can anyone suggest what size fuse I should be using for the ECU?

[jsa]

That's great news.

Yeah, in a perfect world zener should take out the fuse before itself.

Ford put a 16A fuse on my thing for the main eec feed & 3A for KAM feed.

[ozcob]

Perhaps the 10A fuse wasn't the reason the diode permanently shorted then.

I did source another T4M0 which is still making its way to Australia, so at least I'll have a spare ECU.

Thanks for all your help.