Recent drive city/residential trip, pulling away from light, stumble, no throttle, bang 1-2 shift, fluttering CEL... picked up, ran normal, light went off.

Couple miles later at 4-way stop, repeat, after 20-30 yards, again settled down ran normal.

Took it home ran the codes & got these:

552, KOEO, Air management 1 circuit failure (AM1/TAB)

113, CM ACT circuit has intermittently failed above the maximum of 4.6 volts.

118, CM ECT circuit has intermittently failed above the maximum of 4.6 volts.

123, CM TPS circuit has intermittently failed above maximum 4.5 volts.

334, CM DPFE or EVP circuit above the closed limit of 0.67 volts.

337, CM DPFE or EVP circuit above the maximum limit of 4.81 volts.

KOER, 412 Cannot control rpm during KOER high RPM check

Plus a 311 & 538 that aren't really relevant.

This is on my MAF conversion, but I'm not seeing a any real place where my alterations/wiring/splices would have suddenly caused these circuits to have excess voltage.

Is there a way I can set up my voltmeter to monitor the reference voltage... If that is what is spiking?

Is it a function of the ECU that sets the VREF that's breaking down? I do have a spare 94 MAF/E4OD computer to swap if needed.

Whats in it now is a Cadone reman (2 years "new") which looked great in & out & carried original labeling (HOG0)

Haven't driven it since cause the trust just ain't there although the triple A is paid up.

Suggestions welcomed. Thanx.

 

What is the reference voltage? Is it 5V or are you getting something else? Maybe the alternator is going out causing voltage spikes?

Just throwing out random thoughts of things to check.

 

I would plug the old PCM in and see what happens. You don't have to remove the current PCM. Just unplug it and plug the harness into the old one and rerun your codes. I think this would be the easiest thing to do at this point to eliminate the PCM.. Sandy

 

The codes & faults are intermittent. Once I had cleared them, I only drove the truck one short trip & no trouble & no codes.

But I'm certain they'll be back.

The alternator is new Motorcraft replacement, less than 6 months old.

I'm seeing at KOEO at the TB harness, 5.02 vlts @ brown/white (reference voltage output) to ground.

Gray/white (TPS input) to ground .98 vlts TB closed & 4.66 vlts @WOT

 

The alternator is new Motorcraft replacement, less than 6 months old., Curious , what other components were changed with in the last year ???

 

From my experience most components fail in the first 12-24 month. That would make the alternator highly suspect.

 

I upgraded to a 130 amp (used/reman) a few years back. Always had some bearing noise, so before last road trip, (Sept) I purchase new.

Since I have an e-fan, I've paid very close attention to the output. I have not seen any excess needle travel on the gauge.

Still would really like for the big brains school me on reference voltage production/modulation.

Nothing else changed lately.

 

Agreed, all symptoms point to voltage spikes, alternator, ignition (spark plug wires) ,electrical wiring , connections.

 

Interesting read: https://en.wikipedia.org/wiki/Load_dump

Maybe it helps.

 

The computer (PCM) generates VREF internally. The output is Pin 26. I would remove the PCM then give it an inspection to see if you have been "Cardone'ed". Might be worth the time to have the alternator tested. As previously noted voltage spikes, or a bad diode causing ripple, can cause the computer to trigger codes.

 

12.25 engine off, 14.41 idle at 750... BUT

The 31.4 vlts AC I have at the battery @ idle probly' means I have diode issues... Right?

And hence the excessive vref codes?

 

In my opinion yes, you most likely have an alternator problem. Diode(s) or voltage regulator.

 

Replacement in the pipeline. Still under warranty.

Will let y'all know how it shakes out.

 

Results so far:

Changed out alt with new identical unit & got 14.25 DC, 31.5 AC. Got same group of codes.

Changed out ECU, got same group of codes.

For giggles, put original 165K mile, noisy bearing, 95 amp unit, 14.15 DC & 32.1 AC...

Got same set of codes.

I have a 90% complete 94/MAF/E4OD stock harness that I'll be installing after a bit of clean up since all I can guess is there is a place where voltage is bleeding into 5 vlt reference circuit.

Still haven't found a repair/testing procedure that addresses finding cause of excessive reference voltage in case this is something not of my doing in the MAF conversion.

 

I cannot believe you are getting that much AC ripple with multiple alternators. Are you sure the meter is set to Volts AC and not Milli-volts range? Just a thought.

Make sure ground G101 by the battery is clean and tight. That is the main computer ground.

My old Fluke DVMs had a Min/Max function where you could set the meter to record the minimum and maximum values on a circuit. My thought would be to hookup the DVM to measure VREF, start the truck then set to meter to Min/Max mode. Drive for a few minutes then look at the recorded values to verify if VREF is spiking or not. The downfall is a DVM cannot usually capture higher frequency spikes reliably.