I have a 98 GMC Sierra 5.7 Auto. 74,500 miles

Here is the prob..

After a starting vehicle cold (like leaving work) vehicle starts ans idles fine.
Pull off lot driving normal. Pull up to first stop sign, make right hand turn, and hammer down 3/4 to wide open throttle.

Truck accelerates normal for about a second, then begins to ping, rattle, and stumble until shifting into second.

The weird part is that after the temp guage hits around 180-195 its is like you flip a switch and the problem is gone. You can hit WOT all you want from a stop or rolling start, and it runs great.

I know you shouldn't drive a cold enging hard, but I noticed this one day, and I know it cannot be right.

Here is what I have found and done so far. The surge/ping shows a bad misfire on #8, also a few on #6 with a scanner. I have cleaned the injectors, changed the plugs, cap, and rotor, swapped the #8 plug wire and checked fuel pressure (around 50psi) and checked timing. Everyting checks out.
This problem is consistant, happens everytime I drive it hard when the eng is cold.:fb:

Thanks

what about the coil packs check that yet? how about grab some nylon pliers and pull the number eight spark plug wire off while its running see if it makes a difference see if you here the wire arcing meaning the coil to that cylinder has fire, next step check the compression on that cylinder, also another thing those are notorious for is the intake gaskets due to poor designing with less intake bolts not saying that has anything to do with it but see if any coolant is dissapearing or you can smell it even if thats not a problem might wanna check that out hope i've been somewhat helpful

Forgot to mention, the intake was leaking, and has been resealed using new Gm gaskets. Notice the miss after doing intake, but not sure I ever really stomped it cold before that.

well you may still be sucking air around the intake, take a can of carb cleaner and spray around the intake while its idling and see if it changes the way it idles. you'll have to do it everywhere around the intake to make sure if it started after you changed the intake gaskets thats where i'd start looking first.

Aren't you supposed to have about 65psi fuel pressure? I had a very similar problem with my 98, except it never really went away. I was showing random misfires on 3 cyls and never tripped a engine light. Worn cam gear, changed and now it is better. Fuel injectors were my first thought too, but the worn cam gear was allowing the timing to move a little too much. And no, the computer will not make up for it if it is far enough off.

I forget the exact psi I had, but I made a note that is was about 3psi below min spec at idle, but if that was he prob, wouldn't it show all the time? Not just until the tstat opens? How many miles did you have with the worn cam gear?

I am the second owner and it has less than 75,000 miles.

ever checked to see what the temp guage is showin ive had a truck drive it would say colder than normal or sometimes say its to hott and turn out to be the temp guage

I had about 220,000 miles when I changed the cam gear. 75000 shouldn't be enough to wear slack in a cam gear, but stranger things have happened. As a side note, your problem sounds fuel or timing related and the only way to set the timing properly is with a scanner. If your intake gasket was changed, that could be your problem.
To set timing right- or check:
Hook up scanner and check the cam retard, it should be between -2 and +2, you must bring rpm above 1000 and let it return to idle to get proper reading. If you move distributor, you must again raise above 1000 rpm. A little turn of dist shaft goes a long way. The computer will only compensate for so much, you could be just outside that range.

Well, yesterday I had a SES light come on. Found a code for intermittent crank sensor signal. Found small peice of spring left over from failed front crank seal on tip of sensor (possible cause of light). Went ahead and replaced sensor.

Also install used distributor due to the fact that while messing with the timming, I cracked the distributor where the cap screw goes.

Test drove this afternoon with Tech 2 installe and shop foreman riding with me. No ping, rattle, shudder, timming retard or misfire. I guess the distributor or the cam sensor on the distributor was the prob.

Just glad it is gone. I have a used PCM comming in that I am sending out for custom programming for more power and better shift points and pressure.
Gonna keep my stock PCM just in case.

Thanks for the advice, and I will let you know how the custom tune works out.