99 tahoe misfiring

[hart]

Any help will do!
My 99 tahoe has been misfiring on cyl.5 for some time now, I have changed cap and rotor, wires, plugs, and a cylinder pressure test. Then it would not start. Took it to the dealer and they changed the injector. It starts fine now and still has a misfire and the mechanics were puzzled, and did a injector balance test and turned out fine.
I am moving across the country in a month and would love to solve this issue.

P.S. Anyone in Cali with a misfire there is a warranty recall pushed by the state of Cali, since they are a big emisison state. I can give more details if anyone needs it.

 

[tim@sp]

Take out the plug after running it... Is the plug wet or dry? If it is wet then you are not getting any spark, if its dry then you are not getting any fuel.

Check the harness on the top of the upper intake plenum. Put some contact cleaner and dialectric grease on the pins... that took care of my #7 misfire.

 

[hart]

I put my timing light on #5 and I have spark the plug is wet, I will check the connection thanks

 

[tim@sp]

Sounds like its in the Distributor. I remember hearing about the distriutor gear getting to wore and causing a misfire...

You know now its not fuel... its spark, so concentrate your efforts there.

I will do some more digging and see what I can find...

 

[hart]

I was starting to think that today as well. I am going to dig some more this weekend, I like to hear someone also came up with the same idea.

 

[rsashea]

Tite Valve Guides

I chased a missfire for about a year that would occur under a load, most of the time on accel onto a parkway. Turned out to be tight valve guides causing the exhaust valves on certain cylinders to hang open momentarrilly and then return to normal. The check for this was to remove the valve cover, rocker arm and valve spring on the suspect cylinder.(Do this with the piston at the top of the stroke to keep from loosing valve into cylinder) Pull up on valve stem to seat valve and rotate. If valve seems to be sticking this is a good indication this is the problem. There are two options to correct. GM says to open up guide clearance an additional .002 however I opted to just replace the heads with a good set of new aftermarkt units. Just some food for thought, hope it helps. Ron

 

[treepete]

Hi Ron, welcome to the forum.

What type of heads did you use as the replacements.. just curious.

 

[Blue96Tahoe]

it could be a tight valve also. I adjusted one of mine too tight on mine and it caused a miss. If it has done it for a long time you could have burnt the valve

 

[rsashea]

Thanks for the welcome.

I got the heads from a friend who owns a machine shop. They were just some generic aftermarket assembly's. Ron