Car suddenly develope a multiple misfire. coils good< coil module good< SPARK PLUGS AND WIRE GOOD> replaced fuel filter and the old was not pluged. pump primes when key tuns on. Fuel pressure reads 40lbs and then drops to 38lbs. Could it be the fule pump geting weak

 

You get a check engine light with that?? The v6 in my s10 had misfire code and it was cam sensor inside distributor

 

I got a flashing check engine light and a p300 error code. I checked the cam saft sensor and it was okay.

 

DTC P0300 indicates multiple random misfires. This type of misfire is usually caused by a lean fuel mixture. What procedure did you use to check the fuel pressure? The numbers you got show fuel pressure below spec. Have you tested the pressure regulator?

 

I used a pressure gausge and attached it to the pressure port on the fule injector rail. The specs call for 48 - 55. I turned the key on but not start, heard the motor prime. I checked the gauge and it read 40 lbs and it dropped to 38 lbs in a couple of minutes. I did not check the regulator. If Imust how do I di it. The coils are not bad on this car. The ignition module tested fine. The cam Shaft sensor tested fine.

 

40 PSI is a bit too low and that will cause the fuel mixture to lean out to where the PCM can't correct. It may be time for a new pump or new pressure regulator.

 

Thanks pete, I think i will get the pressure gauge out and recheck it by priming 3 or foure times. If the pressure is still 40lbs or higher, i will start the engine and see if it decreses the appropriate amount. Am I on the right tract to check the regulator?