Electrical Gremlins

[aball4620]

I've been having massive issues with my '88 2.9 since replacing a head gasket. Super rough idle, doesn't like to rev above 2k, moderately low fuel pressure at ~29psi that won't hold with engine off, and basically not driveable. I've run through the fuel pumps, injectors, FPR, TPS, and pretty much everything on the truck besides the computer. I finally decided to get the wire piercing probe out and check the computer. I first wanted to confirm continuity between the TPS and pin 47. TPS is between 0.86-4.55 with no jumps, and pin 47 is 0.82-4.52 with no jumps. Seems good (code 63 is the only code this ever throws and it is only in the continuous memory). Pin 8 from the fuel pump relay shows KOEO 0.0 and KOER 14.3v. Pin 22, however, also to the fuel pump relay is showing KOEO 12.02 and KOER 1.14v..... my understanding is that pin 22 is at 12v (or 14 with the alternator?) with the key on. Full stop.

Could this be showing a bad computer? Every time I bring it up it seems I'm told that these things rarely go bad and that it must be something else. Are there any other tests on the computer I should be running?

 

[Dirtman]

There is nothing computer related that will cause the fuel pump to loose pressure after the engine is off. It should hold for weeks. So as much as you want to blame the gremlins I think you need to look back at the mechanical end. If the fuel pressure drops instantly with the key off its leaking somewhere, and if it's running like crap my guess is it's leaking into the cylinders. Remember, just because you replaced parts doesn't mean they work. New doesn't mean good anymore.

 

[aball4620]

There is nothing computer related that will cause the fuel pump to loose pressure after the engine is off. It should hold for weeks. So as much as you want to blame the gremlins I think you need to look back at the mechanical end. If the fuel pressure drops instantly with the key off its leaking somewhere, and if it's running like crap my guess is it's leaking into the cylinders. Remember, just because you replaced parts doesn't mean they work. New doesn't mean good anymore.

Yes I understand that, my question however is about the readings I’m getting in the computer.

 

[Dirtman]

Oh ok sorry.

 

[aball4620]

Oh ok sorry.

I don't mean to be short. I likely have a bad FPR. I blew up two looking for the source of my crazy high pressure on the rail before I discovered that the tank selector (dual tank) return valve had seized between the two tanks and was not allowing return to either tank. It is a needle valve. Blew out two diaphrams in the process because I have a new and fully functional high pressure pump that was hitting almost 60 psi. And while there is likely something going on with the regulator, there also appears to be something going on with the electrical system. I've driven this truck with a blown out regulator. I've driven other vehicles with a ruptured regulator. They typically run, albeit not well. This truck barely runs, misses, and wouldn't have the power to get out of the driveway. It barely has the power to move between the parking paddock and the shop without stalling, which is about 40 flat feet.

 

[Nelson and Hudson]

Maybe a silly question, how is the compression in each cylinder? You replaced the head gasket?

 

[aball4620]

Maybe a silly question, how is the compression in each cylinder? You replaced the head gasket?

Good question actually, I don't have the numbers close at hand but I did check and they were within about 5-6 psi of each other. Somewhere all around 180, except there was one that was a little squirrelly at about 169. I do have rings that are relatively worn and probably needing a full bottom end rebuild but didn't want to invest the time and money. These are also not the original heads - through 88 they tended to crack.

 

[Dirtman]

I would definitely get a new or rebuilt ECM. Don't gamble with a junkyard unit, buy new. Junkyard units get wet, hit, abused, not worth the risk. Spend the money on one that's been tested.

 

[aball4620]

I would definitely get a new or rebuilt ECM. Don't gamble with a junkyard unit, buy new. Junkyard units get wet, hit, abused, not worth the risk. Spend the money on one that's been tested.

Any recommendations on where to source that? Seems like they're all from Cardone, but nobody locally seems to be able to get one. Haven't gone the RockAuto route yet.

 

[Dirtman]

Cardone sucks. Find a company that specializes is ECMs. I dont know any specific companies cause I've never bought an old obd1 Ford ECM.

 

[aball4620]

Cardone sucks. Find a company that specializes is ECMs. I dont know any specific companies cause I've never bought an old obd1 Ford ECM.

I'll do some research. Thanks!

I think I do have a fpr issue as well, but diagnosing one piece at a time when there seems to be a computer problem makes things difficult. On the bright side, I've installed and removed every component in my fuel system and know it inside and out now! I'm still feeling a little suspect with the tank selector as it was not OEM. I may still pull one off an F150 to see if it behaves the same.

 

[Dirtman]

Yea diagnostics suck.... luckily a new ECM fixes everything.

 

[rusty ol ranger]

If youre losing fuel pressure that fast with no obvious leaks outside the vehicle then you got one (or more) injectors stuck open.

Cycle the key 10 times or so and pull the plugs, see if they are soaked in fuel.

The ECM fires the injectors by grounding them. So in theory it could be an ECM, but its doubtful.

 

[aball4620]

If youre losing fuel pressure that fast with no obvious leaks outside the vehicle then you got one (or more) injectors stuck open.

Cycle the key 10 times or so and pull the plugs, see if they are soaked in fuel.

The ECM fires the injectors by grounding them. So in theory it could be an ECM, but its doubtful.

What do you make of the eec showing a huge decrease in voltage st pin 22 between KOEO and KOER?

I’ve done what you said many times, with two sets of injectors (one remaned and one cleaned and checked for function and spray pattern), hoping for a different result each time. Nothing. Exact same symptoms. I suspect that my fpr has failed internally as even priming many times won’t get my pressure up to 42 psi. That is supposed to be the preset spring tension in the fpr, yes?

There are two things I haven’t done yet. One is to throw on an old regulator with the return line capped to see if it will then hold after priming. That isolates the rail and high pressure check valve. The other is to hard line the fuel pumps with 12v to see if the changes it’s behavior. But again it seems I have two issues here. Unless the readings I’m getting from the computer check out?

 

[RonD]

Pull out the Computer and open it up, its out of warranty, lol

Look at the 3 blue or black capacitors, blue ones seen here: http://www.auto-diagnostics.info/ford_eec_iv

These go bad and leak after 20-30 years, not hard to replace, 1994 and earlier computer this is 99% of why they start to "act funny"

Just did this on my 1994, cost $5, back to normal
Mine had 1 that was obviously bad, broken wire, but 2 were actually bad/broken, of course, replace all 3