1998 yukon Mystery p0300 and rough idle still

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east302

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The upper intake can stay on and should since the MPFI injector instructions say not to unclip them once installed. Seems like a dumb design for those things.

Random questions that have come to mind…

Are we sure that there isn’t a vacuum leak? Your heater hose water valve solenoid’s vacuum line is intact all the way to the PCV fitting? Plug it at the PCV fitting if it is. The little breather hose coming from the passenger valve cover to the air intake is connected?

If you put it in gear, brake and bring the revs up, does any particular cylinder misfire count spike? Some of those cylinder counts could well be reactions to the adjacent cylinder in the firing order misbehaving.

Is it your gaskets? An external leak would help, but if they’re 11+ years old then it’s reasonable. I doubt that they are original and if they are then that’s a problem. Two styles of gaskets are available so there’s no telling what was used when they were last replaced: the non-reinforced GM style and a more-recent reinforced version that should last longer.
 
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OilBurner2003

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The upper intake can stay on and should since the MPFI injector instructions say not to unclip them once installed. Seems like a dumb design for those things.

Random questions that have come to mind…

Are we sure that there isn’t a vacuum leak? Your heater hose water valve solenoid’s vacuum line is intact all the way to the PCV fitting? Plug it at the PCV fitting if it is.

If you put it in gear, brake and bring the revs up, does any particular cylinder misfire count spike? Some of those cylinder counts could well be reactions to the adjacent cylinder in the firing order misbehaving.

Is it your gaskets? An external leak would help, but if they’re 11+ years old then it’s reasonable. I doubt that they are original and if they are then that’s a problem. Two styles of gaskets are available so there’s no telling what was used when they were last replaced: the non-reinforced GM style and a more-recent reinforced version that should last longer.
The only evidence that I have of no vacuum leak is that it passed the smoke test. I will double check the valve you’re talking about, I know Smoke Tests aren’t a guarantee. I will go try that rev thing and see what happens
 

east302

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Another thought since you now have the means, can you graph the two upstream (b1s1 and b2s1) oxygen sensor voltages? They should both oscillate, see if they are fixed.

Also see if it will read your fuel trims - long and short term for both banks.
 
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OilBurner2003

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I will check that tomorrow, I’ll have to find out if it has it in the package.
Another thought since you now have the means, can you graph the two upstream (b1s1 and b2s1) oxygen sensor voltages? They should both oscillate, see if they are fixed.

Also see if it will read your fuel trims - long and short term for both banks.
 

exp500

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As it appears you have removes distributor already, I'm not going to ask for fuel trims again, until you have re-assembled.
Not knowing your next steps planned I will give my recommendations to help reduce further unneccessary work.
1)Lower intake gaskets- gently pull back injectors leave in hole some since they are new. About 41/2 hours if organized.
2)Replace distributor, cap & rotor, maybe plugs NGK are cheaper and no fakes.
3)Replace plug wires- Packard / Delco/ Delphi.
4)Set CMP angle, re-check fuel pressure- key on eng off, leakdown time to10#loss, running, leakdown time, Scan all sensors- misfire codes, at multiple steady state speeds- 35,45,55,65.
5)Adjust valves-It's a real PITA (A/C compressor), but long term best. do it eng running one bank at a time.
This will give you a long term run, 30-50000 miles trouble free. Change dist cap if any misses in this time, Change fuel filter yearly. Depending on your location, use 15-40 diesel engine oil. RTV dist gasket to dist body(easiest). You had corrosion issues with new dist cap(Dist vent,replace Dist.)
 
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OilBurner2003

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As it appears you have removes distributor already, I'm not going to ask for fuel trims again, until you have re-assembled.
Not knowing your next steps planned I will give my recommendations to help reduce further unneccessary work.
1)Lower intake gaskets- gently pull back injectors leave in hole some since they are new. About 41/2 hours if organized.
2)Replace distributor, cap & rotor, maybe plugs NGK are cheaper and no fakes.
3)Replace plug wires- Packard / Delco/ Delphi.
4)Set CMP angle, re-check fuel pressure- key on eng off, leakdown time to10#loss, running, leakdown time, Scan all sensors- misfire codes, at multiple steady state speeds- 35,45,55,65.
5)Adjust valves-It's a real PITA (A/C compressor), but long term best. do it eng running one bank at a time.
This will give you a long term run, 30-50000 miles trouble free. Change dist cap if any misses in this time, Change fuel filter yearly. Depending on your location, use 15-40 diesel engine oil. RTV dist gasket to dist body(easiest). You had corrosion issues with new dist cap(Dist vent,replace Dist.)
I’m gonna be honest with you, I have no clue how to adjust valves and I don’t know if they even need adjusting. I’m sure there’s a diagnostics for that somewhere. Wires and plugs are a week old, truck hasn’t been driven other than my test drives, which are 5 mins long. I’m putting everything on hold until the distributor gets here. Cap Is AC delco and doesn’t have a long run time on it, I’ll probably stick to what the guys say and replace it if the misfires are still the same.
 
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OilBurner2003

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Another thought since you now have the means, can you graph the two upstream (b1s1 and b2s1) oxygen sensor voltages? They should both oscillate, see if they are fixed.

Also see if it will read your fuel trims - long and short term for both banks.
New distributor here! Installing now.
 
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OilBurner2003

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Good Luck! You have been chasing this 6 months starting with an oil leak.
Well uh...I had something that's most likely very bad happen. Got the distributor in, got it on the oil pump shaft, (I spent a great deal of time making sure it was correctly seated) put all the parts back together and tried to crank it. Popped off for a second and then stopped. Figured maybe I left my fuel pump relay out and when I go to check, there's smoke coming out of my Intake and my air box...Shit gentleman. Anyone care to tell me what I did wrong? I followed multiple videos to get this distributor in correctly, and I'm really unsure on what happened. I feel as if it's my fault tho.

Edit: according to sources, this might be a backfire? I hope I did the distributor wrong rather than have engine damage…
 
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