Number 7 Cylinder misfire

[2001ZR2]

I have been fighting an intermittent misfire on Cylinder 7.

The new coil and ICM reduced the misfire from most cylinders to 7 and 2.

The new cap and rotor cut it back to mostly 7 and sometimes 2.

Messed up the MAF pins and running on a rebuilt unit from Advance Auto.

Previously changed plugs and wires. The plugs were from a 2-3 years ago but the wires from 2004 and 180k miles.

Changed the fuel filter in March.

So I was trying to isolate the source of the misfire and I put back on one of the old plugs and now 2 doesn't misfire any more than the other cylinders.

Then yesterday I tested the fuel pressure and the 7 year old pump put up 61 psig and held pressure for 10 minutes slowly falling back to 59 psig. So may pump and poppet style spider seem to be working at least to hold pressure.

Decided to swap plugs between 1 and 7 but test compression while I had the plugs out. The cylinders were within 5 psig of each other at 165 psig and 170 psig for cylinder 1 and 7 respectively.

fired it back up and drove it the misfire was still on 7 but now have a P1351 code whien I had a pending P0300 and P0307 codes previously.

Found the body to frame ground against the exhaust manifold and it it about shot just few stands. Will replace it but don't expect it fix the issue.

Is there anything I should look at?

Besides adding fuel system cleaner and saving for a new spider and lower intake gasket. I will pull the valve covers then and look for damage but this a late June or early July plan.

 

[stutaeng]

Do you have lower intake manifold leak? Check vacuum with gauge with engine running. I believe leaky gasket would cause a misfire.

I would do an injector balance test if you can. After long digging on my 5.7 with a lean code on bank 2, I discovered a sticking #6 injector via injector balance test. Strangely, never got a missfire code on mine, just computer seemingly dumping more fuel due to lean readings from O2 sensors, I think...The guy from TY channel "Ratchets and Wrenches" has a video doing one with a little gadget that sells for around $30 on amazon. There's also an OTC model that sells for about $120. Or, some more advanced scanners will do it also.

Isn't the P1351 code related to ICM high voltage? I would try to resolve that first. Not sure if that would be related to missfire?

 

[Schurkey]

https://www.gmt400.com/threads/rough-idle-p0300-help.49025/

If this guy had paid attention to Post 6, he wouldn't have spent a week of frustration.

I would verify spark... ...with a spark-tester calibrated for HEI. If you've got enough spark to RELIABLY fire a genuine spark tester, you've got enough spark to run the engine.
​

Test at the spark-plug end of your "problem child" #7.

Clear your code, see if it comes back.

 

[2001ZR2]

Upon further research I think the P1351 code is a result of cranking the engine with the coil wire and fuel relay pulled but I do have a failing ground so it should be addressed.

I had about 20 inches for vacuum at idle so I am not thinking I have a vacuum issue from the LIM. But it is weeping oil and I will replace it along with the fuel spider but don't expect those to fix the issue.

I will get a spark tester but I am thinking the nozzle to the cylinder is partially plugged or I have a cam issue (much less likely).

I have cleared the throttle body and EGR valve when I was getting ready to tow my son's truck 250 miles home. Also when I changed the fuel filter, spark plugs and wires.

I haven't seen a cam/crank position issue so I am not thinking it's the distributor gear/timing chain. But when the distributor is out it will be looked closely for wear. I had to replace the distributor when I broke an ear off of it. When is good shape 5 plus years ago.

The timing chain is down the list of things to be done/repair after the LIM/Spider, steering box & pitman arm, and AC restore/repair.

Current compressor is leaking at the center o ring and won't a charge overnight.

I think the big things I will identify or eliminate are coming when I do the LIM/Spider which I hope will correct my abysmal MPG which is 10-12 mpg with more Highway than stop and go.