Jeff1968

I have a 96 C1500 with the 5.7L VORTEC engine. My issue is that it stumbles on accelleration when cold, sometimes, not all the time. If I keep it steady at around 1700-1900 RPM it really does it bad, almost like a misfire. Once I have driven it awhile and stopped and restarted the truck it stops doing it. I can't figure out why it's doing this. I have tuned it up thinking this may clear the issue up, but does not. My code scanner gives me a code P0300 (misfire detected), but doesn't tell me where the misfire is, like which plug is misfiring. Can somebody point me in the right direction? Also, the truck has 277,156 mi on the odom if that helps. Thanks

sickvortech1

Howdy, Jeff1968. When you did the tune up did you replace the cap and rotor? The two otherreasons for the coad are, The Cam Sensor located in the distributer under the cap and the Crank Sensor located below the timingchain cover. most likly the Cam Sensor is the culprit.
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Jeff1968

I did a complete tune-up about 2 years ago. I drive a big truck for a living, so I didn't even think it would need another one. Should I just replace the sensors and see if that helps? They are relatively inexpensive, $46 for the Cam sensor and around $52 for Crank sensor. Othere than the stumbling it runs like it's new, real strong and still lots of power for the mileage it has on it. Thanks for your help, that will help move me in the right direction.

John86

u'll have to do a crankshaft sensor variation learn when u replace that sensor.

sickvortech1

Howdy, Guys. For the stumbling on accel when cold , The (IAT) sensor might be the problem, Haynes manual pg 6-8.

John89? The crankshaft sensor variation learn, I have not heard of and amnot clear about the proscess.

John86

i was checking but i don't think it applies to this vehicle but some cars u hav to do a crankshaft variation learn. As the crankshaft rotates, the reluctor wheel teeth interrupt a magnetic field produced by a magnet located in the sensor. The sensors internal circuitry detects this field and produces a frequency which the control module monitors on the signal circuit. The control module uses this signal in order to accurately measure crankshaft velocity, which is important to ignition control spark timing, fuel injector timing, and for misfire detection.