Hello.... Been working on car for a while , Have changed pretty much everything i can throw at it. Car is 03 monte carlo ss 3800 V6.(250k) mileage
new parts include ......Coil packs, plugs, wires, LIM&UIM gaskets, Fuel filter & fuel pressure regulator , ICM tested good , swapped injectors around to see if trouble code would follow. Ran seafoam and 93 octane fuel .Still have cylinder #3misfire. Any ideas or help ??? What should normal compression be and fuel pressure ? Thanks !!!

 

Key on pressure should be around 45 psi and running with vacuum removed around 55 psi . As for compression you should be under 120 psi or the cylinder is probably dead and I have seen posting's between 130 psi and 150 psi but you can easily compare to cylinders 1 and 5 since there right there. Should check when power to ignition is disconnected and throttle plate wide open. These numbers might not be exact but should be close enough for testing 1/4 million mile engine.

 

Don't ever rule out the MAF sensor.

 

Id just like to make sure nobody overlooks this.....

 

Update :: Did compression test 180psi across all cylinders. Swapped injectors around again and GOT random misfire instead of #3 misfire. So got all NEW injectors. Now it is back to Cylinder 3 misfire!! Im baffled...Any help???? Thanks

 

Would MAF sensor throw a #3 misfire ?? Is that the one in the air intake tube?

 

I mean, it's possible for random crap to happen if the MAF is bad. But have you checked all of the wiring to the injectors?

 

Bad MAF can cause a lot of crazy stuff. Injector pulse should be checked. Also, if your ICM tests good, it could still be bad. I've seen it firsthand.

 

Injector pulse was tested with noid light, allready done that one a while back...will double check them. ICM was load tested at Autozone or Advance dnt remember. Been throwing money at this girl getting old. Could it be a computer issue? ECU/ECM. It runs good doesnt seem be missing any power ...but can hear a lil miss and still have cylinder 3 misfire on the scanner. Grrrrrr

 

its rare but it may be a bad input on the ICM from the ECM


check this out around 14 minutes