Do I need a new PCM?

[tstripe76]

So battery is fully charged, sits at 12.4 volts. Disconnected the alt signal cable, but still no start situation. Tested both primary and secondary resistance on the coil packs, all are good. Disconnected the 3 harnesses that connect to the PCM, checked pins, reseated. Cleaned MAF Sensor with MAF sensor cleaner, and have followed the entire harness from PCM to all the different end destinations, if there are any breaks or issues, they are hidden, as its all still in the protective sleeve, no signs of melting or other compromise, nothing pinched, etc;. I also scanned again hoping to get another code to help, but instead the P1636 and the P2107 are now gone (i did not clear them). Still have P0103 and the 4 O2 sensor codes, but that should not cause no start situation. Going to check the throttle body, not sure what else to check. Is it possible that even though the crankshaft position sensor is reading and sending rpms, its still faulty and that might be the issue? Thoughts?

 

[Logan97]

I just bought a pcm from flagship one for my 07 expy. I'll let you know how it goes when I get it in case you still want to go that route.

 

[Brandonian]

Did you take the alternator for testing? - p1636, from the few moments I was able to look it up, can be specific to a low voltage - so disconnecting your alternator may have done that one! Could be another sign of an alternator issue - If you have not tested the alternator, I'd remove that and take it in, as I said the test is not a tell-tale sign as it could read good and still be bad (if you have a keen nose - you can sometimes more often than not smell if an alternator burned up by sniffing it up close, sounds really silly but I have previously fully been able to on the alternators that have burned up on me. Glad to hear the battery is reading 12.4volts, always worth checking the easier stuff before moving straight into more complicated lol.

I think this is electric related now...but since the codes changed I am hard pressed to believe the PCM is bad now - can never know from far away though .

 

[Brandonian]

Also follow your ground wires down below - not from the PCM up top - but check the frame area grounds. If there's a fault there it'll stand out.

 

[Brandonian]

sorry not sure why I looked up p1636 again, obviously I can't read...If the MAF sensor went bad - that's a fairly cheap and easy replacement - did you check your filter? Take that filter out and shake it really good and see where that gets you - I wasn't joking :0 .Lol

 

[tstripe76]

I did not have the alt tested, just disconnected the signal wire. The air filter is new, but I also disconnected the whole air intake on top amd still nothing. Usually with all that off it will run, it will be a little off without the maf readings but still start and run. I'll check the grounds umderneath.

 

[tstripe76]

So checked grounds, seem good, not broken, not corroded, not loose. As for the alt, if it was bad, wpuld disconnecting it resole issue (at least temp)? I know it wouldnt run long, but it should run right? Only ask because like was mentioned, it may still test good on the bench, so only way to know is to replace (or I like the idea of the sniff test). They are not cheap and hate just throwing parts at a problem.

 

[Brandonian]

Sorry - for some reason I don't get e-mails of new replies to a thread I've chimed in on lol.
I cannot give a "definitive" answer to that...with so many checks and electronics, I am inclined to believe if the alternator was not connected it would not start - because of all the electronics checks and balances contained therein of our lovely "modern" day computer controlled engine systems - the battery does not provide enough juice to run through all that.

I would still test it and see. Worth a quick look. But the code did change when you unplugged it and plugged it back in - so that's actually a hope that may be it. The grounds aren't typically something to look for that's why I became fixated on the alternator, and how it died while mid drive like it did.

Definitely don't throw parts lol - I would remove the alternator, sniff it good - and take it to get tested (however if you sniff it good and you can smell any burnt at all, you found your issue) - I would test it 2 places if the first one tests good (two different store front types like one at oreillys and one at autozone or something) just to be sure. Once that's ruled out we can move on with something different, I'll try to give this some extra thought.

 

[Steve Hartman]

I had this problem with my '07 Expedition! It would start for a second and then stop! Every time the same thing. What was it? It was an air leak in the intake from when the tune-up was done. The big rubber hose that goes from the intake line to the thingie that looks like a carburator (but ain't!) was smashed, came loose, and was letting a ton of air in! And even little ol' me was able to figure out that if the engine is suckin' air, it ain't suckin' gas! LOL! I'd look there, first! And let us know, would you please? Good Luck!

 

[Honocor]

I keep getting stuck on the O2 sensors. I had a mountaineer that did the same thing. After almost checking EVERY SINGLE fuse the 47th one iirc was blown. I never figured out what that fuse was for exactly but it prevented starting. Turned out one of my O2 sensors had a broken wire that was only held together by the plastic and when the wire shorted it blew the fuse and caused a no start. Took me about 3 fuses to finally figure it out.