I have an 03 Silverado SS with about 105K miles. I have been getting a cylinder7 misfire. It will drive rough and flash check engine light when on throttle. It has come and gone before but if you drive long enough (30 mins or more) it will start running rough with check light flashing. Took it to get scanned and no code pulled just cylinder 7 mis fire. Took it to Pep Boys to get diagnostics and they said it was a bad injector. I had just put a new injector in there. So I bought a second new injector swapped them same issue.

I have replaced all of plugs with Irridium platinum (cant think of the name of them but researched them here and think its tr55), new wires (10.4mm Accel), new injector on cyl 7 (tried 2 different new injectors), new coil pack.

I'm at a loss for what to do next. I have read thread after thread here and haven't found an answer.

 

how did the old plug look?

 

Old plugs didn't look bad at all. Not oiled up or fouled or anything like that.

They were actually new plugs (less than 1000 miles) that were some AC Delcos that my buddy at the parts store gave me. I just upgraded to the iridium cause I read they were the better plug in hopes to help elimnate this problem

 

Old plugs didn't look bad at all. Not oiled up or fouled or anything like that.

They were actually new plugs (I put less than 1000 mile on them) that were some AC Delcos that my buddy at the parts store gave me. I just upgraded to the iridium cause I read they were the better plug in hopes to help elimnate this problem

 

Time for a compression and leak down check... Could have a weak spring or lifter going south.... Also need to smoke the intake...

 

Friend had a similar issue. Ended up being the fuel pressure regulator was leaking into the vacuum reference hose. Pull that line and see if there's fuel in it.

 

Oddly enough I was just talking with a friend of mine at the station and he brought this to my attention as well.

So, I will be giving pep boys a call and see if they can run a compression and leak down check for me this week.

I had the system smoke tested and it showed a leak in the EVAP. Not sure if that would cause my issue or not.

I have a new one just wanted to get my new fuel pump so I can kill 2 birds one stone when I tilt the bed.

I never thought of this, where would I be able to find them to check?

 

Find the fuel pressure regulator at the fuel rail and look for the vacuum hose going to it. Pull vacuum hose and see if any fuel comes out of regulator where the hose connected.

 

Thanks, I will look at it this afternoon.

 

Ok, so I checked the fuel pressure regulator and the vacuum line attached to it and it was dry. No smell of gas or anything.

So I guess the next step is the compression test and leak down test. I will have to schedule it at Pep Boys