Hi,
Would a bad PCM cause the truck not to start? Basically a month ago I washed my engine down. After that she wouldn't start. I put the scanner on it and said PCM mal****ion. So I figured I burned it out or something. So I ended up by a used one off of Ebay for $80.00 it was for the same year, make, model , and engine but different part number. Shouldn't the engine atleast crank? Would I be able to "REFLASH" the used PCM I bought to work with my truck worst case scenerio? Thanks!!!
John

 

Yikes.

As in turn the key and no nothing, not even starter solenoid clickin'?

There's no pcm involvement in the raw cranking process, So I'd check all your fuses - you may have blown some as a result of the soaking ( speaking of which, don't do that).

Used PCM - you can get it flashed by the dealer.


Good luck

 

Hey thanks for the Quick response. I did check all the fuses but nothing. No, it doesn't even crank. With the old PCM it did at times and at times it didn't. Does anyone have a clue or am I goign crazy here. I figured mabye wrong PCM wouldn't make it crank at the least?

 

Do you hear the starter solenoid clicking, or not? Bad contact there, or possibly a gounding problem, exacerbated by the wash? Fusible links (I don't have a schematic for your truck; you should get your hands on one, though. What year?).

I'm telln' ya - the cranking circuit is little more than a switch, a relay/soleniod, the battery and the starter motor. Your problem is in that circuit; either primary high-current wiring, or the control side (e.g. ignition switch).

I'm not aware of any other interlocks/permissives from the PCM that would prevent simple raw cranking. PATS ( if so equipped - again, what MY?) would prevent an engine start, but not a crank. I think. Speaking of which, if ya do have PATS, then I think you'll need the dealer to program that too, IIRC.

 

Now you know why your truck comes equipped with a hood.

It ain't just for soccer moms, ya know?

 

There is no code that says "PCM malfunction." What code did you get specifically? What are we working on? Year/engine?

 

Hey,
First its a 2004 F150 FX4 5.4L 4x4. There is no clicking, absoutly nothing. I took a look at the fsuible link which look good didnt look burnt. The code was soemthing to do with PCM don't remember exactly what. But when it was cranking last week it wouldn't start. But the cranking would go in and out. Sometimes it would crank and sometimes it wouldn't. Go figure? Yes, I even tried cranking it in neutral and still nothing. All fuses look good, As of right now there are no trouble codes on the scanner, it would be nice if I can get it started or cranking. Then mabye I would get something.

 

The PCM in that truck has to be programmed to it with a Ford scan tool. Just swapping another PCM in isn't going to work.

I still need to know what code you originally had to try to figure out what's going on.

 

The logic chip in your key won't match the different PCM, so you will get no cranking. Go back to the original PCM and start looking for a starting problem that is related to your ignition switch or the under hood connectors that got wet. Good luck.

 

You sure about that? Can anyone cofirm?

I'm lookin' at a schematic for a older PATS F150, and I can't see anywhere that inhibits cranking. Starting, yes - but not cranking.

Hmmm.. maybe I need a better schematic, or new glasses LOL!

OP - put a voltmeter on the starter solenoid - any power reaching it @ crank? Just curious....

In any case, Q will crack this one - no worries ;-))


Good luck

 

Swapping pcm's would cause the the vehicle to not crank. The reason is the new pcm doesnt recognize the existing keys. The only way to make that pcm work is to have a dealer retrieve the info from the old pcm, and add it to the new one. They may be able to manually enter the as-built data, but you would save them a headache by bringing them the old pcm. When you put the key in to start it, the theft light is prolly flashing quickly, which will confirm what I'm thinking.

As far as why the vehicle wasnt starting in the first place, I have no info that would help.. But knowing what code # you pulle dout would be a good start

 

Thanks. Did not know this, and as I said, it's not immediately evident to me where the interlock is.

Do you know, specifically, how cranking is inhibited?

Thanks again - bubba learnin' sumthin' new every day !

bubba

 

The key has a chip in it that the PATS receiver reads as a programmed key. When it recognizes said key, it disables the starter interrupt allowing it to crank. If i'm not mistaken, the system is defaulted to interrupt so it wont crank without a good key.

***edit***
Dunno if thats how specifically you meant. More than that I'd have to ask a tech.. I would assume
the pats receiver sends signal to the pcm that the key is a good key, allowing the starter selenoid to operate..

 

OK, got that so far - but what exactly does the starter interrupt consist of?

Are you saying the PCM actually drives the starter solenoid? Or controls a relay interposed between the ignition switch and the primary side of the starter solenoid?

Thanks!

 

You beat me to my edit.. lol

And tech told me what I thought. PATS receiver tells the pcm its a go, and pcm would signal the selenoid. Passed that we arent sure without some real homework