1999 C3500 Misfire

[ken_man_1]

Here we go again...

I've got a 1999 Chevy C3500 truck Auto trans, 7.4L engine.

Had a ton of codes, and the truck ran like absolute garbage. Did a tune up on it cap rotor wires plugs...very little help.

Checked FP, reading about 42 and leak down almost immediately. Changed pump, along with fuel lines from pump to engine including new filter (Wisconsin salt truck... fuel lines were getting pretty thin), along with new FP regulator. Truck perked up pretty well, but still having trouble with misfire. Also changed the cam and crank sensor, but no help. Changed them because the test voltage was irradic, so replacing them was my choice.

With all of that said, FP is real decent, about 52 at idle, and perks up to about 56-58 wot. Deadhead pressure is about 95.

At one point I got codes 171 and 174, but the PCV valve line had a crack in it, replaced and they went away.

I'm now stumped as to what to look for. Only code is P1351, and it has a severe studder in the acceleration, even pops in the intake. Idles pretty nice, unlike before, but you can tell there is still the hesitation. PLEASE HELP ! ! !

Thanks for looking and any thoughts would be greatly appreciated!!

[jdmccright]

I'd check the ignition coil and the wires.

[ken_man_1]

Originally Posted by jdmccright

I'd check the ignition coil and the wires.

Brand new:

cam sensor, rotor, cap, wires, plugs.

Considering new coil and module, but tired of throwing money at the problem

[777stickman]

For the P1351 code. Besides numerous checks for open or shorted wiring and connector checks, only 2 replacements are called for. Ign Control Module & VCM.

You mentioned changing the CKP (crank). If that was done the Crank Variation Relearn needs to be done also. Requires a high end scan tool in the hands of a capable technician.

[ken_man_1]

Originally Posted by 777stickman

For the P1351 code. Besides numerous checks for open or shorted wiring and connector checks, only 2 replacements are called for. Ign Control Module & VCM.

You mentioned changing the CKP (crank). If that was done the Crank Variation Relearn needs to be done also. Requires a high end scan tool in the hands of a capable technician.

Thanks for the heads up on the relearn process.

I changed all of that stuff out because there were probably 8 different codes, and I was able to nail them all down except this one.

Going to try swapping a good known coil / ign module today...

[ken_man_1]

Well, no luck with the coil and module. I had a truck with a good known coil / module. Relearn process tomorrow...hopefully.

[j cAT]

Originally Posted by ken_man_1

Well, no luck with the coil and module. I had a truck with a good known coil / module. Relearn process tomorrow...hopefully.

make sure the body grounds are all cleaned and secure. inspect the distibutor for bearing wear/wobble..check the pcm connectors/wiring..

remove distributor and check for cam gear worn.

[ken_man_1]

A shop nearby has a Snap-on Solus, and he was able to do the "injector balance test", and found some injectors were having a pressure drop as little as -5psi, and some as much as -22psi. I think we might have narrowed down the problem. I was so sure it was a fuel pressure issue, guess I was kinda right..