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Odd Stumble After Intake Gasket Change

shorgasm

By shorgasm
in Ask A GM Technician

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shorgasm Enthusiast

shorgasm

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1999 Denali 5.7.120k on her.

Friday night she blew the intake gasket out pretty good and heated up to about 230ish but made it home.Never got past the 3/4 mark and only briefly flashed the check gauges light.It had a slight leak for over a year but it was so small it never even required coolant till you used the heat.You would never see the coolant just smell it.I knewit was coming though.

 

Anyways, got the intake on and all seems well as we have no leaks and no heating up past 190 or so.That part went well.

 

We did have a great deal of trouble getting the dist. right.Got her running pretty good last night but just a touch rough idle.Nothing new though.Occasional idle stumble but got gradually better.We had run the battery down with the lights on.The bad part was at partial throttle acceleration it would stumble.Full throttle and it ran out fine.Still needed plugs and wires.I put a new cap rotor on last night.SES light was on from the second we started her up.Went to AZ and they pulled a MASS code and P1345 misfire.I knew we had the dist wrong or at least close.Got on here and read about the 8 mark and we re-did it.Fired right up and great idle.No idle stumble at any time.SES light still on.I dumped the water in the rad and put fresh coolant, as I went back to check the temp the SES had gone out.Never came on again.Changed the oil/filter and put new plat plugs and wires on.No issues what so ever.Now everything is new..cap/rotor/plugs/wires.All routed correctly and put back in there respective holders.

 

Cranked right up and smooth idle with no issue at anytime.Smoothest it has idled since I have owned it.Took it for a drive and I'll be damned, the stumble is still there.BUT, it more intermittent now and less noticeble.Only light throttle acceleration will produce it and about half the time it won't even do that.It feels like it cuts out ever so lighlty.No backfire or popping at all.Drove it for about 20 minutes and the stumble got less and less but at times it was still there.Even when it would stumble,I could push the pedal down farther and it would go like normal.WFO never a issue.Idle never an issue.No SES at anytime.

 

I'm stumped guys..any ideas?

shorgasm Enthusiast

shorgasm

Posted
  • Author
Posted
You may need to do a crankshaft position relearn after having the distributer out.

 

 

The P1345 code made that cross my mind.

 

How does one go about the re-learn?

 

Someone also mentioned the timing might be off a bit still and needs some sort of zero-out scanner to reset the computer.

Heck I dunno.

shorgasm Enthusiast

shorgasm

Posted
  • Author
Posted
You may need to do a crankshaft position relearn after having the distributer out.

 

 

The P1345 code made that cross my mind.

 

How does one go about the re-learn?

 

Someone also mentioned the timing might be off a bit still and needs some sort of zero-out scanner to reset the computer.

Heck I dunno.

 

 

 

I should mention that we did start the truck without the mass air and the other air box sensor plugged in.Just for a couple seconds..she rev'd up pretty high(2500rpms) pretty quickly and I shut it off.

shorgasm Enthusiast

shorgasm

Posted
  • Author
Posted

Any other ideas guys?

 

Maybe EGR got dirty when cleaning the manifold?

I've never had any issue out of this truck other than a fuel pump.*knockonwood*

 

The intake runners on the manifold where nasty looking and caked up with black but the injectors where spotless shiny at or around the tips.

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