Random Misfire

Any MT or AT 05-06 will work, PATS can be handled via tune temporarily, VIN is not relevant.

I would sincerely go for an used replacement instead of a repaired unit, if it was not the issue you can sell it back again.

Saleen304 said:

Never mind. I am blind. I found out it is the 5R3A-ACC.

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How did you decipher the correct number from the other ones? Just curious in case I run into this same issue.

46addict said:

How did you decipher the correct number from the other ones? Just curious in case I run into this same issue.

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I just wasn't looking hard enough. There is a label on the side of the PCM with the part number.

lito said:

Any MT or AT 05-06 will work, PATS can be handled via tune temporarily, VIN is not relevant.

I would sincerely go for an used replacement instead of a repaired unit, if it was not the issue you can sell it back again.

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Thanks Lito. Got your email as well. I decided to send it in to SIA electronics and have them test and repair, if necessary. If it's not bad, I'll be out a little shipping and diagnostic fee.

I am also looking for a pcm for my 05.
I have a feeling I have weak coil drivers.

Will ford actually flash an 06 ecu to a 05 calibration.

Just got off the phone with SIA electronics. They have fixed the PCM. They said there were several cold solder joints that they needed to fix and would effect injector and coil pulsing. Seems to be root cause. Hope it's fixed!

Saleen304 said:

Just got off the phone with SIA electronics. They have fixed the PCM. They said there were several cold solder joints that they needed to fix and would effect injector and coil pulsing. Seems to be root cause. Hope it's fixed!

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Good news.

Received the repaired PCM and installed it as soon as I got home today. Seemed to run a bit better, but it was probably a placebo effect since my misfire is still present. Cylinder 5... damnit.

may be time to source a salvaged unit since Ford doesn't make them any longer as I understand? STill don't know how they get away with that. I thought automakers as well as other product mfgr's are required to support product 10 years on parts after the last model which would equate to end of service falling in 2019 as the 2009 still used that PCM unless there was a switch I am not aware of. Another member on here had a similar issue and sent his in some place to be repaired and it lasted a short time. He found a used one in a salvage yard and has been running well since.

Could it be the primary O2 sensors? It only misfires in closed loop. Wot and open loop it runs fine.

WOW! Good question and I cannot answer that one.

Staying on the cylinder 5 issue, have you again tried swapping COP's to see if the cylinder 5 misfire changes or stays the same? It may be a weak COP as well as those cold solder joints. also is it just five? have you checked the wire back through to the cap transformer on the red wire feeding the COP? after all the PCM simply supplies the ground (so to speak) allowing the coil to fire. The potential from S104 where 5-8 are all tied to is always present on the COP with key on as I understand the schematic and the basics of the theory on this circuit in the tech manual.

redfirepearlgt said:

WOW! Good question and I cannot answer that one.

Staying on the cylinder 5 issue, have you again tried swapping COP's to see if the cylinder 5 misfire changes or stays the same? It may be a weak COP as well as those cold solder joints. also is it just five? have you checked the wire back through to the cap transformer on the red wire feeding the COP? after all the PCM simply supplies the ground (so to speak) allowing the coil to fire. The potential from S104 where 5-8 are all tied to is always present on the COP with key on as I understand the schematic and the basics of the theory on this circuit in the tech manual.

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It's not always cyl 5, but it is most of the time. COPs are brand new. I guess there could always be a bad one. If the wire was bad, wouldn't it be more likely to misfire at wot?

redfirepearlgt said:

may be time to source a salvaged unit since Ford doesn't make them any longer as I understand? STill don't know how they get away with that. I thought automakers as well as other product mfgr's are required to support product 10 years on parts after the last model which would equate to end of service falling in 2019 as the 2009 still used that PCM unless there was a switch I am not aware of. Another member on here had a similar issue and sent his in some place to be repaired and it lasted a short time. He found a used one in a salvage yard and has been running well since.

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I noticed Lito specifically mentioned using a 05-06 pcm for OP's 05 car. There may have been differences between the 05-06 and 07-09 PCMs.

Oooooooooooooooooooh! I must have misread the original post. I was still thinking it was specific to jug 5. That then does possibly bring the O2 into play if the misfires are all on one bank. That also brings into play the Capacitor Transformer that feeds bank two COPs as well. Again assuming that all of your misfires are in fact on bank 2 (drivers side).

So keeping with the COP I would next start looking at the voltage on any COP red wire on bank one (which I assume is running fine) with a voltmeter. I would then compare that voltage with the voltage on any red wire on any COP on bank two. May be best to do this with key on engine off so that the PCM is not pulsing the voltage which can make it difficult to get an accurate voltage reading. Also then check with engine on. Compare the two obviously. If you find a lower voltage on bank two this may be your problem as all COP's get their potential from Cap Transformer 2 (there is a sep for bank one) and they are all tied together at a splice location on for bank 2 at S104. You will need to find the location of that splice and the Cap transformer as I have no means since I have a 14 now and never had a problem there.

If that all checks out then I would begin looking into the O2 sensor and as mentioned in other threads the best way to test this is to PHYSICALLY swap the O2 sensors as well as the electrical connections. You should only have to sway sensor one however as the second o2 simply monitors efficiency of the cat for no better description.

Aren't the cap transformers just used to remove noise from stereo components. Looking at schematic they are not in series with the coils.

Yes, but they could fail and drop voltage to ground. I mentioned them because I was looking to see where they were located and came across an issue on Ford Focus' having had issues with them that have led to COP misfires. So just something to rule out. In troubleshooting it is as important to eliminate distractors as it is to isolate the fault. And never assume something is good simply because "those things never go bad". Especially after all of the typical likelihoods are not panning out. If I had a nickel for every time I heard some old "sea lawyer" here at work tell me that only for it to turn out to be that very component I'd have a good 10-20 bucks in my pockets worth of nickels.

Ok. Just making sure. I now know where they are located then. The one on the driver side is bolted to the alternator and the pass side one is next to the Cam position sensor. I did replace the driver side one in the last year or so due to me breaking the wire.

You could just lift the wire on the ground side (unbolt cap if I recall correctly) to see if the misfire goes away. No reason to check for capacitance.

If it's true that the misfires are limited to one bank and are random on that bank, indeed the +12 to the coils AND injectors are are good culprit. I would also not rule out the O2 sensor nearest the engine on that bank and also the VVT and associated components.

In my 30 years experience, weak ignition shows up at high cylinder pressures under high load. Bugged up fuel injectors usually result in bad idle and misfires at high RPMs.

What do the fuel trims look like on that bank? An exhaust leak before the first 02 sensor and cat will richen the mixture causing large fuel +fuel trims (since the 02 sensor is reading too much oxygen, the computer adds fuel). If it gets over 20% extra or so a code will be set.

And another thought, the dreaded alternator difficulty with these cars can cause all kinds of problems. Usually i see cam position problems, but who knows what else it can effect.

Sorry for your problems, but this is a good thread. Please keep us posted.

redfirepearlgt said:

You could just lift the wire on the ground side (unbolt cap if I recall correctly) to see if the misfire goes away. No reason to check for capacitance.

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I unplugged the drivers side cap transformer and no change. Still showed misfire on cylinder 5. I also checked the voltage at each COP and they were the same. 12.1V with engine off.