Immediate help needed (long thread)!

[pj8847]

OK, to start, I'll explain what has led up to my current problem...

Went away for the 4th of july to PA. It's a 120 mile drive from where I live. Truck made it there fine, and almost made it back ok.I was about 2 miles from home when I made a right turn and the truck just cut off, couldn't get it restarted. next day I went out and started the tedious task of diagnosing what was wrong, turns out the fuel pump died, had almost no pressure. So I changed that.

Here is where it gets out of hand. After replacing the fuel pump and filter, I went to start the truck, still wouldn't turn over, the motor cranked, but wouldn't run, so I went on to the next step and did the whole gamut of tests on everything. I had spark, I was getting fuel pressure. So i reset the computer, it then started up, but ran like total crap. I took that oportunity to pull codes from the computer, of which, with KOER I got the codes for "primary" and "secondary fuel circuit failure". I then checked the relays and all were fine. So I rest the computer again, and all came up clear. Truck started and idled fine, then died again after 10 minutes! I again pulled the codes for both KOEO and KOER...KOER indicated lean condition on both O2 sensors and KOEO indicated MAF sensor signal low AND TPS signal low. SO I proceeded to check the plugs and wiring BEFORE picking up new sensors, plugs/wiring all fine, MAF upon testing showed it to be bad, and TPS was fine, but i replaced it anyways. To remedy the LEAN code, I checked all hoses and vacum points for leaks, of which I found none, SO i pulled off the upper intake, checked the lower,retorqued the bolts and put in fresh upper gaskets and seals to be sure I wasn't experiencing any leaks with the intake.

After all this work was done, I started the truck up and it idled like it was brand new (motor is brand new, 70k on it, so it should run that way) and I though all my problems were over, I ran it for 1/2 hour to make sure and it idled like a champ. Checked the computer for any codes and I got an ALL CLEAR...no codes thrown, all was good. I then proceeded to take the truck for a ride after cleaning up and getting all the tools put away. The truck took off like It always has, had a bit more power as it spun the 31's I have on it, I was happy...until...I get about a block away, the truck starts to bog down, the more gas I give it, the more power it loses, and then dies again!

I get it started back up and bring it home, check computer for codes, NOTHING! truck idles fine yet again, and I can gas it all I want to as long as I'm not driving it. I take it out again, figuring maybe it was just a fluke, and again, after a block of driving, engine starts to bog down, like its not getting enough gas, and dies. Started the truck back up and got it back home, again, checked for codes, again nothing, but this time I noticed that all THREE of the big relays in the power distribution block are burning hot, they never were before, and upon starting the truck now, it idles up to 2500 rpm on startup and comes back down to where it suposed to be within 7 to 10 seconds, the engine temp is hot, the exhaust is boiling hot and the relays are all boiling hot, after replacing them all of course. So i decided to call it a night and work on it yet again the followin day. I come out and start it, and the idle is up to 3000 cold, but comes down within the 7 to 10 seconds as before. I know the idle is to high on startup, and I know those relays shouldn't be that damn hot, as well as the exhaust being extreamly hot, which idicates a super lean condition...

SO here is the question... WTF could be causing this? I know I have absolutely no vaccum leaks, I know the MAF and TPS are good, the IAC is new, egr pressure sensor is new, all wiring checks out fine (after HOURS of tracing and testing EACH one to the PCM) fuel pump and filter is new, all relays and fuses NEW, only sensors that were NOT replaced as of yet are the O2 sensors, because they test fine and are in spec, and the coolant temp sensor, because again, tests fine and in spec. I talked to a friend and fellow mechanic who works for ford (nice perk... ) and he said after going through it with him, it sounds like the PCM may have decided to go. I happen to agree with him as there is no explaination as to why this is happening and after a week out of work due to no transportation and countless hours of testing and replacing parts, i'm still without the truck and I need it ASAP or I will be out of a JOB SOON!

P.S. as I was thinking about how to write this post, I took a break and went and pulled codes again, KOER= 511 and 512 "unable to control RPM during high rpm test" and "unable to control RPM during low rpm test". Sounds like PCM more and more, but maybe someone else has a better Idea, because i'm about to torch this thing and bring my camaro out of storage!

 

[Brian_B]

Any chance a cat is pluugged? Just a wild guess from the bogging down and the hot exhaust. Other than that dunno.

 

[boominXplorer]

an irratic problem like that sounds like the PCM

 

[Derbytown]

What a partially stopped up fuel filter. I'd at least check the fuel filter before I bought a new PCM. It'd be a lot cheaper if that's the problem. LOL. Good Luck.
Derbytown

 

[pj8847]

I thought about the cats too, was going to check but exhaust is flowing good, no blockage, PCM *seems* to be the culprit.

Although tonight, while letting the truck idle and rechecking for any vaccum leaks, I leaned on the IAC and that little motor was RED HOT! The manifold being plastic was cool, and the temp of the engine wasn't hot at the time, I found this odd, So I took it off to check it and sure enough the sucker was NOT moving, it tested fine electrically, but mechanically it wasn't working, so I sprayed it with some "blaster" and got it moving, reinstalled it and the idle upon startup was perfect, and I was able to drive it around for about half an hour, power was ok, but it was hesitating quite a bit, but again, it was running, and stayed running. Brand new IAC, bad.

SO it would appear I *may* have solved part of, if not the whole problem, I'll be picking up ANOTHER IAC and returning this one, still not sure as to why the relays are burning hot, but a bad IAC would explain the lean condition and boiling exhaust if it isn't closing upon acceleration. I haven't ruled out a bad PCM as of yet, it is still possible it may be shot as well. although the IAC being locked up and the PCM supplying the voltage for it could explain the unusual behavior of the PCM itself, maybe even the cause of the power relays running so hot as well.

 

[pj8847]

Well, it would appear I solved whatever the problem was. after replacing the IAC again, everything seems to be back to normal, if not better than before.

The relays are staying cool since I replaced the IAC and the truck is running better than it ever has. Plenty of power, quick acceleration and an idle that is so smooth you can't tell the truck is running unless you pop the hood.

PCM still comes up with a 511 and 512, but seems to have no effect on how the truck runs. No CEL. I ran half a can of seafoam through it and it only improved, i'll be changing the plugs tomorrow just so I know I have a fresh set of motorcraft double plat. in there and that should be it. PCM will get replaced down the road if I encounter erroneous codes in the future, I think it is damaged in some way I personally can't test for, and for $104, it isn't that painful to replace.

Thanks to all that have read, I know this was a strange one to figure out, but it would appear that a bad IAC can cause erratic problems with the PCM as well as how the engine runs.

 

[Derbytown]

Glad ya got it fixed. That was a very interesting problem.
Derbytown