2000 7.4 mysterious misfire/ dead cylinder 4/ p0174

[TheTruckOfTheseus]

I made a post regarding this truck a while ago and was not able to update it nor delete it so I’m making this one. It’s a 2000 K2500 with the 7.4, as the title states. I was having running issues and more recently, starting issues but most of it has been figured out. The previous owner didn’t reset the distributor after replacing it, so it was 14° off, causing rough idle and intermittent rough/ no start as well as a P1345 code. I took it to my mechanic and he was able to figure that out, but he is stumped with its misfire.

Cylinder 4 will not fire, although he said it’s getting good spark, the plug looks good, it’s getting good compression (155 PSI), good fuel injection, and that the valves were going up and down just fine. He used a bore scope and thinks he saw some marring on the head of the piston, but nothing definite. It was also throwing a P0174 code in case that’s helpful to y’all

He’s going to do more testing Monday (maybe a leakdown test) but as of now we’re both stumped. Wondering if y’all might have any ideas or maybe similar experiences?

 

[movietvet]

P0174 is indicating a lean condition on that cylinder. Like in a vacuum leak. Need to inspect for that and maybe do a smoke test. Has the MAF been cleaned?

 

[TheTruckOfTheseus]

Right. I’ll ask tomorrow about other tests they could do, including a smoke test. I have not cleaned the MAF or any other sensors. I don’t feel like a simple vacuum leak would cause a completely dead cylinder, but I could be totally wrong.

 

[TheTruckOfTheseus]

Sorry for the long wait, but we got it figured out. Fuel pressure regulator and it was 14° out of time. The FPR was leaking right into cylinder 4 pretty much flooding it. Anyway, it was luckily a cheap fix and we’ll be on the road again soon (after a front end rebuild.

 

[Road Trip]

Sorry for the long wait, but we got it figured out. Fuel pressure regulator and it was 14° out of time. The FPR was leaking right into cylinder 4 pretty much flooding it. Anyway, it was luckily a cheap fix and we’ll be on the road again soon (after a front end rebuild.

Thanks for coming back and closing the loop on this. If everyone would follow your lead we would
have a higher percentage of threads with hard-won solutions to help others troubleshoot similar issues.

By the way, did you happen to get a picture of the #4 spark plug? I'd assume that it would not
match how all the others looked? If it isn't already cleaned up & put back in service (or thrown away)
that would be an instructional photo.

Congrats. And safe travels --

 

[TheTruckOfTheseus]

By the way, did you happen to get a picture of the #4 spark plug?

I did not, however I do plan on changing the spark plugs soon and will post pictures of each individual plug or at least 4 compared to the rest of the rest are similar. I was told the plug looked to be in good shape but will post either way

 

[Road Trip]

I did not, however I do plan on changing the spark plugs soon and will post pictures of each individual plug or at least 4 compared to the rest of the rest are similar. I was told the plug looked to be in good shape but will post either way

If you were to take a 'family photo' of all the plugs arranged in the exact way
that they were installed we might be able to figure out if there are any familiar
patterns going on? (Here's an example of what I'm trying to describe, taken
from my own '99 C2500 454: Spark plug family photo)

Again, your photo contributions will be most appreciated by all the students
of keeping the big block GMT400s on the road & earning their keep.

Good stuff!

 

[TheTruckOfTheseus]

Sorry to all who may be waiting and watching this thread in real time. I am in the middle of moving and have been so busy between that and maintaining my ‘98 I haven’t had the chance to begin working on the 454. Thank you all to those who’ve helped and I hope to be more active soon