truck bucking

[Bryan22]

Hey guys, haven't been on in a while but this has really got me stumped. My truck (94 2.3l 5sp) started bucking last week. It's almost predictable when it will do it, dosen't do it above about 4000 rpm and dosen't do it if i hold the throttle at one or two different positions. from idle to 3900 rpm and in most of the throttle range it bucks pretty bad.
Last time it did this it turned out to be a bad coil pack. So that was the first thing i checked. everything checked out fine. I checked the ICM,coil packs, plug wires, vaccum hoses, TPS and fuel pressure so far. Everything seems like it's doing what it should but the motor is still running horrible.

If any of you guys can spot something I'm missing, your help would be greatly appreciated! thanks.

 

[BlackDogSociety]

Check your EGR valve and its sensor. I've read that a malfunctioning EGR valve causes can cause bucking.

 

[Bryan22]

forgot about that, i dissabled the EGR system with no change. anlso just checked the timeing. it's good also.

 

[Bryan22]

ok finally found the problem. It was the cam position sensor. unplugged it and the truck runs great.

 

[expotrek]

where is the cam position sensor on the 2.3 i have an 89 that doing something similar and i've done about all the same things you listed... and by the way the truck still runs without it?

 

[Bryan22]

your truck dosent have one. only 93 and 94 california models with a manual tranny had one like mine. and ya my truck runs without it. I'll just have to get it fixed before i need to get a smog check again b/c the CEL is on. What's yours doing and what exactly have you checked?

 

[Macgiobuin]

I had the same problem with my '00 Merc mountaineer. Camshaft position sensor fault code (P0340 in the OBDII computer) kept coming up, even after replacing the cam sensor. Tried alot of things, finally, I thought that the problem may be the alternator. I just put a new one in about a month before the problems all started. How to diagnose: Charge up the battery. Clear out the codes. Run it until the CEL shows, see if it is the camshaft position sensor again. Bring it back home. Clear out the codes. Disconnect the alternator. Yes disconnect the alternator. Isolate the battery terminal at the alternator from any short circuits by wrapping it in elec tape. Take the car on the same trip. If the code does not set on, you found the problem. The voltage regulator is transmitting stray AC voltage that is being picked up by the cam sensor or the PCM and throwing the whole system off. Do the test in daylight with no loads on--no radio, no headlights, no blower. I didn't believe it was possible, but now I am a believer. Write back with your results. -Mac