EEC-4 Codes Not Listed From ECA, MIL and Fuel Pump Stays On With KOEO

You said it yourself... the STO and MIL share the cicuit, didnt you?

And you said STO is 10k or more with bulb out.. thus it isnt shorted to ground. Which you verify by saying it's 12 volts... if the STO/MIL was shorted to ground, the light wouldnt come on.

Put the leads of the meter on the bulb.. yep, 35 ohms

And I dont think the current allowed by a 29k resistance is enough to energize that FP relay.. but I could be wrong. You need to read the VOLTAGE at the relay feed test point to determine the proper operation

So either you are reading the scales wrong or you have a real weird thing going on there.

Bottom line: Unless you have a weird grounding problem in the harness at the PCM connector, the PCM is probably fried.

The bulb in this case was 6 ohms across it so that left 29 ohms unaccounted for between the common feed on the other side of the MIL bulb toward the ignition switch. which didn't go away BTW when I disconnected the ignition switch which feeds the whole thing, hence the question with the book being right or not concerning theQA pinpoint test. This is my main concern, written accuracy in the 16 year old Motor manual.

The 29K resistance at the FP relay at the negative inducting coil wire going to the processors' timer is causing the FP relay to energize. At first I thought it was because of a leaking diode but it's coming straight from the FP timer circuit in the processor because there is no diode to bleed current that I know of..

Those processors are pricey. I'd hate to plug one in to watch it blow because of a bad wire.

Fried processor, yes I feel you're right because of the FP if nothing else. I'm wondering if a strange wiring short caused the old one to blow, specificly that 29 ohms I can't account for, or if 300,000 miles, and 16 years of wear and tear on the old processor in Houstons' 100 degree summer heat finally took it's toll on the old part.

Like you say the processor is most likely shot. This one has me really thinking though. I've never seen a problem like this where the fuel pump runs and the STO wont put out. It just smells of a short somewhere and I'm worried I may blow a new processor.

Fords are great and last forever until they break down. :-)

Ed

here's a dumb question... have you tried it without the MIL bulb installed?

Without the bulb the short goes away yes because between the "QA5 STO Short To Ground" "(1) Key off." "(2) Breakout box installed processor disconnected. DVOM on 200,000 ohm scale." "(3) Measure resistance between STO at self test connector and engine block ground." "(4) Is resistance less than 10,000 ohms?"

The resistance is less at 35 ohms. The location of the resistance is between the MIL bulb feed and the engine ground. It's going to the STO through the instrument cluster as the MIL feed feeds everything else including the guages on the cluster.

The answers for the test are:

"(A) Yes resistance is less than 10,000 ohms: Remove breakout box. Reconnect processor. Service STO or MIL/SIL circuit for short to ground. Rerun quick test."

"(B) No: Go to QA6"

Did the person writing that part of the book just consider the MIL/STO circuit starting at the MIL bulb and just write it wrong or is there a 35 ohm short in my instrument cluster between the MIL feed and ground that blew the old processor?

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The 29K at the FP relay is there with or without the bulb so that tells me the processor is bad.

I just dont want to blow a new one. Those suckers take days to get. :-)

Ed

Don't read too much into the resistance value on these sorts of tests. I'm not particularly familiar with the PPTs you are performing but asking if resistance is above 10,000 ohms on a circuit is Fords way of asking if there is continuity. Similarly, when they are asking if resistance is 5 ohms or less, they are also checking continuity. Additionally, these manuals can and do contain misprints.... they also can contain inappropriate procedures for the test we are performing.

It becomes important for us to study the test step and determine just what it is the engineers wanted us to test... in the case of QA5, they want to see no continuity between the STO connection and engine ground.....

OK... I got off my fat duff and scanned briefly through the PC/ED for 92 (sorry, the oldest manual I have on hand but should be pertinent). Couldn't check the EVTM since my laptop is at home with a weak battery and my power cord is at work...... In a case like yours, it is excrutiatingly important to work through the quick tests in the correct order... neglecting steps or performing inappropriate tests WILL have us replace a module, perhaps needlessly.

Looking at QT3, we see towards the end, that it makes a difference if we pull a pass code or if we pull no codes at all during the KOEO self test. Remeber that, during KOEO, On Demand codes are displayed first (this is where we should see our first PASS (11 or 111) code.... this is followed by a separator code which is followed by a Conitnuous Memory code. If you ARE seeing 11-10- or 111-10-, you would need to verify that the is not part of your concern. If you retrieve 11-10-11 or 111-10-111, you would go to symptom charts and would be directed to ML1. If you retrieve no codes at all... this includes PASS codes, you would go to QA.

It is important that we do NOT perform any tests that we aren't specifically directed to. If the PC/ED directed you to go to ML1, you should ne be in QA unless a test step has you go there... vice-versa

HTH

Jim and Backyard Mechanic first off I want to thank you both.

The two of you seem to be saying the 35 ohm resistance at the MIL bulb is no big deal because it's over 5 ohms (not shorted to ground) and when I unplug the bulb the short goes away.

Because the timer in the processor is shorted causing the fuel pump to run all the time with the key on and because no codes are outputed and the light is staying on all the time including during cranking which would mean the processor is running in hardware mode only ignoring software altogether, i think I'll take a leap of faith and install a new processor.

Now all I have to do is find one. I may buy the Cardone 78-4351. Takes a few days but has a lifetime warranty.

Hopefully when I plug it in it will hold. All the other voltages and resistances at the breakout box are showing to be fine.

Looks like I'll just bite the bullet and hope for the best.

I'll let everyone know what happens.

Ed

specifically

I had an 85 T-Bird ,3.8 with EEC-V The fuel pump power relay went bad resulting in the pump turning itself on every 15 or 20 seconds even with the key off and out of the ignition until the battery ran down over night.

Oh I know what that's like. I had a few of those myself.

I also had an old 70 something Ford truck I left in gear with the break off and one morning I went to open up the shop to find it in front of the support beam holding up the garage with a burnt up starter, a busted headlight, and a dead battery. Seems the starter solenoid kicked in all by itself. Ever since then I disconnect the battery before working under the hood on a Ford especially.

Ed

"Glen Cooper" wrote in news:dfcf0o$9fh$ snipped-for-privacy@domitilla.aioe.org:

Come on... quit over-informing!

Does the car have the bad driveability symptoms with the bulb removed, yes or no??????!

Look, Glen.... for one thing you are placing far too much emphasis on resistance reading and it's confusing. I know electronics and I used to design logic and driver circuits.

In relay and lamp drivers, 29K is usually inconsequential...unless the relay is of the 'current-sense' type which it isnt. Those are used as sensors not switchers.

What you need to do FIRST is actually determine FOR SURE that the opposite side of that MIL lamp circuit is supposed to be attached to the cluster ground. The NORMAL design is to ground circuits to activate them. I dont have the diagrams available to verify which way Ford does it on the CEL/MIL.

Second... if it's true that the non-switched (cluster) side is grounded, and the light is on at normal intensity, there is NO short in that lead to the lamp! Forget the lead resistance.

The problem THEN would be that the driver itself, inside the PCM, is always turned on... or shorted Meaning the PCM is dead.

There is no external input I can think of that would cause the PCM to simply toast itself, other than a 12v supply over-voltage surge such as MIGHT occur if your Alt. Voltage Regulator went temporarilly{sicx?} belly up and your battery couldnt absorb the current (thus keeping voltage down) for some reason

I'm sorry.. I dont usually advocate this but now is the time to throw a used part at the problem.

Agreed.

I'm getting an ECA on Tuesday with a lifetime warranty for 109.00. I took the old one apart and a can type capacitor had melted down and actually burned spilling it's guts everywhere.

Sorry for over informing :-)

No it didn't change. See the other reply, bad ECA. Thanks again.

Virtually all the EEC4 PCM outputs of that vintage are 'low-side' drivers. The MIL is connected to +12V (through the ignition switch) on the constant supply side. The PCM provides the ground to turn it on. If the MIL lamp is out, a test light may be connected to STO instead, with its other lead returned to +12V (not ground). Older manuals talk about connecting an analog voltmeter in the same fashion. Those pull a bit of current (a fraction of 1 mA, typically). If you want to use a digital multimeter and the MIL lamp is removed, provide a load to +12V (something like a 10K resistor will do). Not sure, but I believe that with the ignition off, STO is still driven to ground, because of the constant (unswitched) power available to the PCM. So measuring resistance in that state will not provide any useful information -- it will appear to be shorted to ground. Essentially, the way to tell is to put the PCM in a diagnostic mode (invoke the KOEO test by grounding STI). STO should then embark on its sequence of flashes. If it remains constantly driven to ground, there is something obviously wrong with the PCM.