I started getting intermittent coding for misfires on cyc 1. I had all the spark plugs (AC/Delco), spark plug wires (AC/Delco)replaced and I've also replaced the coil pack for cyc. 1 & 4. This didn't fix the problem - still coding misfire cyc 1. I paid to have the fuel injectors from cyc 1 and 4 swapped to cyc 3 and 6 to see if the misfire coding traveled to the other cyc. The coding is still on cyc. 1. The car runs great but can't get three of the sensors to set ready because of this coding. I replaced the computer about two years ago and the crank shaft position sensor about two and half years ago. Sun Auto says the crank shaft position sensor is functioning properly. Their diagnosis machines can't seen to find a problem with the electrical. I do get very quick hesitation loss of power and back to normal while going down the freeway 65mph - very intermittent though maybe one every couple of days. Any ideas where to troubleshoot next? Thanks! Jack
Intermittant Misfire Cyc. 1 on 1999 Buick Century
I can think of a few potentials...fuel pressure regulator, after sitting for 5-10 min pull the vacuum line off and see if fuel shoots out when the key is turned to the on position, might need a buddy to turn the key for you. If fuel shoots out you need a new one, but the fuel press erg usually causes a semi hard start or long crank too. Next would be an intake air leak, maybe a torn or warped intake gasket. This may be more of a fantasy than a theory, but what about the throttle body leaking coolant internally into the intake...eh probably not. Maybe check compression, were there any ash deposits on the old plug maybe indicating a valve or seat problem. Maybe the injector slightly plugged or sticks open.
I would check the intake system first, most misfire issues that are not causing other codes to surface are usually a base engine issue. Also the E.G.R system can cause misfire and rough idle issues.