The question I have been wondering about while attempting to trouble shoot my Cyl 8 Misfire is....

"Would any of the 8 injectors suffer more then the others if the fuel pressure was on the low end of being in spec?"

I had already swapped the coil for another cylinder but the misfire stayed on cyl 8. The weather is keeping me from troubleshooting in a timely manner which gives me too much time to think and not do. Plugs were new last year along with the wires. I will do an injector swap next when weather allows but I was curious about fuel pressure as my fuel pump is Original @ 230k. I have full power and smooth acceleration, just a little idle hiccup on #8.

Any thoughts would be greatly appreciated.

 

No - if fuel pressure was low enough to cause misfires, it wouldn’t present more on one cylinder as compared to the others - it would present as random misfires across all cylinders.

Use a stethoscope (long screwdriver or wood dowel works) to listen to the #8 injector with the engine running and compare it to the sound of the other injectors. If it sounds similar in speed and pitch/volume, it’s not likely to be at fault.

When is the misfire happening? Have you noticed any other issues such as coolant or oil consumption?

 

thanks for the response Gumby22

"When is the misfire happening? Have you noticed any other issues such as coolant or oil consumption?"


I do have a mechanics stethoscope and will maybe try tonight. As far as when it misfires.... started about 1 month ago only at idle, a slight stumble every 10-20 seconds, but now its more like every 5 secs and enough to trigger the misfire code. Oil and coolant looks fine... if it was not the #8 I would have pulled the plug by now but too much snow and Cold to deal with it right now and more on the way.

 

Is it still only at idle or will it persist during acceleration and at cruising speeds?

 

Stethoscope revealed no obvious difference between all eight injectors.

The stumble on Cyl#8 is only at idle or high idle... nothing more in upper rpm reveals the misfire stumble. Acceleration is smooth and full power. Cruising speeds are also smooth.

I may try to take out the plug before it snows today, if time allows.

 

Update on trouble shooting the #8 misfire....

* Coil swapped to another position - result in #8 misfire

* wire swapped to another position - result in #8 misfire

* Spark pug swapped to another position - so far no misfire and idle appears smoother. A very slight change in idle is noticeable now ... so basically an occasional "light hiccup" that probably only I can notice being the daily driver of the Suburban. If curious, I moved the Spark Plug from #8 to #4. I will drive it for a few days to see if I get a code again... if not then change out that plug for a new one.

Is there Cylinders that do not cause as much as a rough idle as others if there was something small malfunctioning.. like a spark plug??

 

cold 17 degree day this morning and pulled a code for misfire in Cyl 4.... so the spark plug appears to be the issue which is odd as it appears malfunctioning worse under 30 degree temps

 

When were plugs last changed? Sounds like time to do them again or at least the one.

 

my oem NGKs were changed at 140k only because the were old, then I changed those after 80K only cause I needed a project to do. Now these current NGKs are maybe 10k old and one out of 8 are faulty. Starting to think I was sold Knock-offs

 

actually my 140k OEM plugs were Ac Delco which I happen to find in my spare parts bin. I may take one and pop it in for a test tomorrow