1999 Tahoe Miss/knock/shake

[mmoss10]

I have posted about this before, but I'm still having the same issue, so I thought I'd start another thread. My Tahoe is a 1999 four door with 100k miles. For the past 6 months, when I merge into traffic, or when I'm going up a hill on the interstate and I reach 70mph under throttle, the truck loses power and starts to miss and shake. It usually kicks out of overdrive. When I get off the gas completely, it will settle down and then I can run it however I want (80-90mph) with no problem. Lately, when this happens, I sometimes get a strong odor in the cab like burning coal. I suppose that's the carbon? The truck knocks and pings terrible on anything but premium. It has never set a check engine light and my actron scanner returns no trouble codes. These are the things I have replaced in the past few months to try to fix this problem. All are GM/AC parts unless otherwise noted: Plugs, plug wires, distributor cap, rotor, Borg Warner EGR valve, fuel pump (entire module) fuel filter, Monroe Sensatrac shocks, rear U-joints, transmission flush, pressurized fuel system cleaner. I need some suggestions for where to go from here. If you have this same problem, please respond to this thread. If you have had success in fixing it, please let me know what did it!

[WHATDIDYOUBREAKNOW]

fuel starved?

[mmoss10]

Originally Posted by WHATDIDYOUBREAKNOW

fuel starved?

I thought that might be the problem, that's why I changed the fuel pump and filter. The pump didn't fail. But it still hasn't fixed it. Pressure was about 60psi before I changed the pump. I need to check the pressure again since I changed the pump. I'm starting to think it may be the spider?

[WHATDIDYOUBREAKNOW]

tps?

[Treblig70]

I also have a 99 tahoe 2WD 5.7 eng. I was having problems with valve clattering under load and loss of power at freeway speeds. When I accelerated going up-hill on the highway the eng would stall and clatter and stumble. When I drove constant without accelerating it acted fine.
Turned out to the the injector spider was leaking inside the intake. I'm not sure how to check for this problem without removing the upper plenum. As soon as you remove the upper plenum you'll see a fuel soaked intake. It should be bone dry in the intake. The dealer will tell you that this is a common problem with the older injector spiders. The new spiders are much better and made my Tahoe run like new under all conditions. I would have never figured it out if I hadn't blown a water seal (gasket) under the intake which forced me to remove everything on top of the eng. In your case you would only have to remove the upper plenum (3 hr job).
Maybe someone on this web site can tell you an easy way to check for leaking injector tubes. You can't tell with the leak down test. Mine checked out fine on pressure test and it also passed the leak down test. So you can't tell that way. I had replaced the fuel pump, distributor, timing chain, plugs, wires, fuel filter and many other items before I figured it out (injectors). If you could get someone to stick a borescope into one of the intake vacuum ports you could easily see the wet intake (on the inside). Good Luck........Gil in Tex

[rhandwor]

Try cleaning the egr valve if this helps put a new on the vehicle.

[WHATDIDYOUBREAKNOW]

Check You Intake Boots For Lose Or Leaks...when You Accel It May Be Moving The Engine Enough To Move The Boot To Leak..then The Sensor Misreads