1999 yukon 5.7 vortec misfire

[yukon_1990]

99 yukon 5.7 vortec 215k new plugs, wire, cap, rotor, fuel filter. Drives fine when taking off, but after it shifts into 2nd gear it's just gets weaker as it shifts. The fuel pressure was checked today under throttle it's about 63-65 psi about 55 idling. The your driving and you hold it above 2500 rpm for any sustained amount of time it will go to misfiring and bucking then after the torque converter locks up of its still misfiring the torque converter will unlock. The fuel pressure is above 60 psi while doing these symptoms, the only code it's thrown was cylinder 5 misfire I replace that injector, same problem it is the orginal poppets. The intake gaskets was done about 8 months ago with the fel pro gaskets. I was having the problem before the intake gaskets was done but the more i drive it the worse it does it, the first time it done it it was 6 months before it done it again. It's getting to the point it does it every time I drive it. I'm at wits end with it any help will be appreciated.

[yukon_1990]

If it stays above 2500 rpm for more than 5 seconds or so it will begin to misfire...

[operator556]

I'm having a very similar problem in my 99 Yukon. And it just threw a code for a leak in the egr so that was my problem. Try unplugging your egr solenoid before you start it and see if it goes away. If so boom there's your answer

[yukon_1990]

Yea I already did that same thing while driving with it unplugged....I'm thinking I've got a problem with the spider. I don't wanna put 350 into the upgraded mfi of that isn't the problem.

[yukon_1990]

It is the orginal spider, but I've also replaced the throttle position sensor. Someone told me I need to get a misfire history but don't know how to get it or were to go.

[yukon_1990]

When I replaced the #5 injector the misfire seemed to smooth out slightly. That's why I believe I have a spider issue.

[operator556]

Why don't you try taking the spider off and giving it a real good cleaning? There are plenty of videos on it and people have had very good results with it. Did you also try running it with the maf unplugged?

[yukon_1990]

Already cleaned it with same results and yes it ran like s***.

[T0PDOG]

Check you cam retarded trimming , you can do that only by using a scan tool .

 

 

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[dsmmace]

You may need a new distributor gear, they get sloppy with age and cause symptoms like you are experiencing.

[yukon_1990]

When I replaced the intake gasket the gear barely had any wear to it...

When I replaced intake gasket I had the timing set by a mechanic

[ifixedit]

Doesn't sound like a fuel delivery problem. How about a bad ignition coil? Fire it up in the dark, pop the hood and see if any visible sparks jumping around by the coil. You can go a step further and spray a mist of water at the coil with a spray bottle while it is idling, that might reveal the issue.

 

I know it's not the same vehicle and a slightly different coil arrangement, but I had a 98 Grand Prix, it would run fine until you stepped on it, then it bucked and missed like crazy, turns out a couple of the coil packs were bad, you could see sparks jumping off them in the dark. I replaced them and viola, ran like new.