So yesterday I took my truck to a mechanic friend of mine to get the clutch/slave cylinder replaced. Well, we couldn't get the truck in the shop right away, so we decided to scan the computer to see if I had any trouble codes (CEL light didn't work).

Well after hooking the scan tool up, we discovered that we could not communicate with the PCM at all. It wouldn't even power up the scan tool (Snap-On Scanner).

We believe the PCM to be bad. We talked with several different people who also said that they believe the PCM to be bad. Anyone ever had this experience before?

Second question. After trying and unsuccessfully communicating with the PCM, the truck will not start right.

As soon as you try to start it, the engine is instantly flooded. The only way to get it started is to unplug the fuel pump relay, start the truck and then plug the relay back in. Then the truck will idle at ~2500-3000 rpms, then idle down somewhat.

Could this flooding problem be caused by a bad PCM? Obviously we are getting fuel and spark as well, but the truck will not start right. Before it always fired right up.

Also, what is the difference in PCM's that have California or Federal emmissions, other than the Cali PCM's are ~$100 more

Thanks guys, this truck has us all stumped.

 

Update


I spoke w/ my mechanic today and he was able to scan the computer. However, he got a bunch of codes.

114 Air Charge Temp
116 Engine Coolant Temp
121 TPS
341 something to do with octane
335 EGR
522 Vehicle out of park
539 AC/defrost on during KOEO
542 Fuel pump
543 fuel pump

Something is seriously wrong here. Whenever you try to start the truck, something is telling it that the engine is at WOT.

Code 539 is a bit odd too. My mechanic told me that neither was on during the test.

The truck was taken for a drive where it ran perfect and horribly on the same test drive (10 mile drive for the PCM to relearn). Still unsure if the PCM is bad or not.

This truck has everyone scratching their heads.

 

If it were mine, I'd focus on the fuel pump codes and the TPS code.

Has a fuel pressure test been done?

You can do some testing of the TPS, see: http://fordfuelinjection.com/index.php?p=30

 

Had a simular problem couple of years back. Codes that didnt exist or not appropraite to the vehicle. The shop recommended that I replace the computer so went ahead and did so was about $125 exchange at either checkers or autozone, anyhow did it and have not had any computer related problems since. Did have fuel pump relay problems but I think those are built in sometimes (LOL).

 

I'd suspect a grounding or power problem first.


Steve

 

Rockledge,

I tested the TPS earlier this week and found the current one to have a dead spot. I bought a new one and installed the day we first tried to read the PCM.

What do the fuel pump codes mean? The pump is working well enough to flood the engine instantly upon startup.

My mechanic could not get the computer to get rid of all the codes. It wouldn't clear codes when prompted to do so.

This truck really has us stumped. We're not even sure which codes are legitement. The truck has always started right up, but when we hooked up the scanner the first time we trigered something.

Something is telling this truck that it is at WOT during startup. I can't even describe how much fuel is being throw into the engine.

We're gonna tear into tomorrow and hopefully get this sorted out. This could still be a bad PCM.

 

Maybe there is some kind of corrosion on the PCM connector? Maby try unplugging, and plugging the PCM back in.

The fuel pressure regulator may be going, causing to high of a fuel pressure. If it is a manifold vacuum operated one, it could also be dumping fuel right into the intake

 

PCMs certainly do go bad, and if you can get one for $125, it seems reasonable.

However, I agree that you might want to look at the simple stuff. It's no fun to have a high $ part not fix things. Even worse if you damage the new part.

My F150 had a PCM power relay that had bad connections. The way Ford works, Rangers probably do as well. Take a look and see if the connections are cruddy. Low or noisy volts to a compute can make it act oddly.

I also though that the pressure regulator thought was a good one. I think that if the diaphragm fails, you can suck fuel right into the manifold.

Maybe even a quick read on the voltage and grounds from the battery. Same reasoning as checking the PCM relay.

Good Luck.

ford2go

 

Well, last friday when my mechanic was working on the clutch, he may have found the problem. He was able to easily pull the main ground wire out of it's lug. He also said that the lug itself wasn't bolted up very tight.

Hopefully this is the source of all these problems. We'll know later this week after the truck is back together.

 

Check with a wiring schematic for power and grounds to the PCM first. If all is good with that, then yes possibly pcm. But check the fuse that runs the Diagnostic Data Link. I see many times scan tools won't power up or comunicate with the pcm because the fuse that gives power to the DDL has blown.