Well that was short lived

I now have a cylinder 6 misfire...FML

Does anyone know how to test a PCM to see if it is bad or if you even can? I would hate to replace it and that not be the cause as I already threw a new motor in her and thats another costly repair....

 

Well I cleared the code on it and reseated the spark plug wire and so far no code for a misfire. Although honestly if you ask me it still has one just isnt throwing a code for it

While doing this I also managed to clear my P1289 code for the CHT by taking the connectors off two wires that didnt connect to nothing and soldering the wires together....they were the same color so figured why not lol

One more code to go and hopefully the truck will be good as new again and thats P1500 (VSS) that only pops up every now and then. I have done some research on this one and it can affect the fuel system among other things and often is misdiagnosed as a bad coil pack and other things that cause a misfire so Im gonna change it out and hope this might solve the mystery misfire.

Will update later...

 

Well I must have spoke too soon as I had to go to Norfolk today and on the way home I got P0306 and P1500 Gonna try and get the VSS changed out this week and will let y'all know. Getting tired of this that's for sure. It almost feels like I'm not getting fuel every other half second if that makes sense. Unfortunately I can't afford the deposit AutoZone wants to borrow their fuel pressure tester too see if its my register or pump maybe.

 

The VSS is just throwing a fault code. Replace it with a OEM unit. They are about $60 it located on top of the diff. Also sounds like you may have bad front oxygen sensors. A bad oxygen sensor will cause the issues you are having. You can take it to the dealer and have them run a PCM diagnostics. I was having a similar situation a few months back. Mine would randomly miss fire any cylinder at one time, then it would be fine. I found my issue to be worse when the a/c was on. In the 97-98 the a/c drain is right over B2S1 oxygen sensor. It will cause it to short out an spike the return side of the PCM. I would have that checked.

 

If it was an O2 sensor wouldn't I get a code for that? That does make me wonder though since my cats are gutted...

So I went to AutoZone and the part they gave me for the VSS doesn't fit! If you ask me its just a tad to big but it won't go in the whole and when comparing it to the one that I took out of the truck they said that's Fords recommended part number....not sure what to do now. Should you have to hammer it in?

 

If the oxygen sensor is shorting it self out you wont get a code. I wasnt. I didnt get the code because it took out a ground circuit in the pcm when it did.. My issue involved a bad pcm along with bad front oxygen sensors. get a VSS from ford. I went through 4 from autozone until i got tired of changing them and picked up a vss from ford.

 

Thanks for your help. Is there a way to diagnose the pcm yourself as I have thought about this also being the culprit.

 

Man that sucks i hope you can get it working!!!!

 

Want to recap just in case I might be missing something that usually causes a misfire not to mention refresh my memory lol

1997 Ford F150 4.6 Romeo
Straight Piped, Spectra Air Intake System, and Superchipped (set to performance)

Symptom:

Cylinder 4 misfire

Treatment:

Changed MAF
Changed coil packs
Changed spark plugs
Changed spark plug wires
Changed fuel injector
Changed fuel filter
Gutted cats
Replaced engine (was told I had a burnt valve #4)
Checked compression and it was good in ALL cylinders
Changed drive belt (after it shredded lol)
Checked wiring harness for damage or other defects
Checked for vacuum leaks
Removed, cleaned, and regapped spark plugs

Symptom moved to Cylinder 6 misfire

Treatment:

New spark plugs
Fixed CHT code
Swapped fuel injector 6 with 5
Cleaned and oiled air filter
Cleaned MAF
Checked and cleaned spark plug wires

I can go 3 days of city and highway driving without it throwing a code but you can still feel the misfire then the code will continuely reappear for a couple days and then repeat the cycle. No other codes are present at this time.

Anymore ideas from anyone else?

 

Air/idle control valve or tps, sounds like an intake issue