I am at the end of my rope with this truck. basics.... 1997 gmc yukon, 4x4, 5.7 (r code), 4dr. I got the truck about 10 months ago with about 150k miles on it. I now have 160k miles on it. About two weeks ago it blew a lower intake manifold gasket (common). So I replaced it and everything was fine. about a week ago I took a trip to AL and when we were almost there and we got off the highways I noticed it would shutter when the tranny dropped out of lockup. Checked tranny fluid and it was fine. Even though I thought the tranny was going a tranny shop told me it was a miss in the motor. Crank/cam corr. code was thrown. So they said simple fix dist is just one tooth off.... so I thought

Symptom: massive misfires with no codes. Started out under light load, now is there at idle with no load as well. lessens at the high rpm.

Attempted fixes

1. Motor to TDC on #1 make sure Dist. is in correct (checked 3 times) this got rid of the crank/cam code as it was off a tooth, but misfire continues.

2. swap rotor and cap (no change)

3. swap wires (no change)

4. swap plugs (no change and they looked absolutely fine)

5. swap TPS (no change)

6. test ICM (tested good)

7. swapped injection "spider" After smelling lots of fuel, pulled the butterfly and saw a bunch of raw fuel in the upper intake manifold. (no change )

8. Swapped the ECM/PCM (bought a pre flashed unit, no change)

I only ran it in park but to say the least I am frustrated. Every step I have taken has made sense to us (plugs, wires, rotor, and cap were all warranty swaps) But still I have over $400 in it with nothing resolved.... someone PLEASE help me out here... Only other thing that makes any send at all to me would be the distributor.... but I hate to just throw another part at it!

 

I know this will sound basic. But are all the wires in the correct order? I had the same thing happen to a friend of mine that was upgrading his wires. The diagram he had didn't match his firing order and a couple of the wires were reversed for companion cylinders. Idled fine, but as soon as you hit the throttle it would bark and burp..

 

Did you set the distributer to 0v on the obdII? Sounds like the timeing is off

 

Not to rain on your parade, but I'd do a compression test on it, I've seen those "R" motors (vortec 350) wipe out a cam or have a lifter start bleeding down after a failed intake gasket. they don't like coolant in the oil very much. Also check timing with a scan tool, you can get one stabbed correctly but still have the timing off by several degrees and they won't run right. Good luck, keep us updated.

 

Wondering if a head gasket didn't contribute to the intake gasket going? Maybe do a die test too?

 

Cbtumedic- the intake manifold blew external, not internal, so hopefully all is well. There was no water in oil.
Redleg- no obvious signs of HG but I guess the possibility is still out there

If I didn't say it earlier, it ran great for about 5 days before the issue started. I will put a scan tool on to check the timing and go from there... I'm quite sick of this problem.

 

Does the engine pop when flooring the accelerator? I have seen worn cams and collapsed lifters on both the 5.0 and 5.7. Usually with a worn cam lobe you will get a constant popping at high revs. I have also seen distributors go bad, especially with the mileage on it. I have seen timing chains jump teeth from wear. I know you have triple checked a lot of things, however do you think you may have cracked a plug when putting the new ones in? Did you notice any play in the dist shaft when you had the dist out of it?

 

what was 1 tooth off? the distributer, or the crank pos sensor tone wheel?

 

hvytrkmech, i have been reading a lot about both the dist and timing chain lately. It really seems to smooth out at high revs, no pops at any rpm.

biododge1- the dist was off one tooth, advanced. I have not gotten a chance to check the timing on a computer yet...

 

Have you checked fuel pressure? And not just at idle, under load.

 

idle and revved, not really under load