99 tahoe stalling/clattering under load

[Treblig70]

I've had my Tahoe for 2 years and I love it. 4.7 auto. But lately I've noticed the valves clattering or pinging when I accelerate under load or going uphill. No codes except gas recirculation system. I replaced gas cap, timing chain, distributor, cap/rotor and fuel filter (filter was clogged big time). I've also tried premium gas with no difference. I also noticed that the engine misses or stalls slightly when I accelerate going up hill. I've sprayed a whole can of electroclean around intake and associated areas with no change in engine idle. I've also noticed that the idle will change from its normal 800 prm down to 300 or 400 for a few seconds then jump back up to normal. After spending over $350 on items listed I wonder if its better to get it analyzed by the dealer before I spend any more money. My only concern is that the dealer will identify one or two items (which I will replace) only to have the problem continue. I do plan to check fuel pressure next Tuesday, PCV and MAF are also on my list of suspects...Any help is greatly appreciated. Gil in Tex

[Treblig70]

Fuel pressure reads 50 PSI during start-up and during normal engine operation. Max PSI was 52. I can't believe no one else has had a similar problem...these tahoes have been around for over 10 years.

[2000CAYukon]

I am pretty sure that fuel pressure specs for the Vortec is 60 - 65 PSI.

The regulators are also known to leak on these trucks. What does the pressure do when you turn the key off? Watch it for 5 minutes. It will drop but should hold pressure.

//2000CAYukon

[GMMerlin]

Fuel pressure is low.

[Treblig70]

Fuel presuure held nicely at 50 PSI for about 5-8 minutes but slowly decreased after about 15-20 minutes. IT never got above 52 even when I acclerated and held the brake in drive. I bought a new fuel pump ($209)
and I hope it's not the regulator. I hate spending $60 on the regulator only to find the pressure still low because of the pump. I read that many Tahoes won't even start or run with 50 PSI. Mine starts and runs but I can't accelerate at all without hearing pinging and clattering as the engine misses and jumps. I should know something by the end of today (Thurs). I will post my finding, including new fuel pressure readings....THANKSGil in Tex

[99TahoeST]

I have a very similiar problem, under strain like going up hills, if I need to put my foot in it, engine runs rough and shakes. If I let off accelerator, it smoothes out (but I am now going a lot slower). If I keep my foot in it, with rpms up, it will continue to run rough ans shake until the "check engine" light comes on.

I had a couple of people look at it, including a dealership. Their opinion was the gas had so much crap in it (additives or whatever required in the metro area I live in) that you get build up in the valves. The recommended I try a top end fuel additive to clean the build up. It will also clean injectors, so you have to be careful what you use. The locals here use Lucas brand so it won't hurt injectors with regular use.

I did this for a while and had good results. If I lay off of it for a few months, it comes back, so I treat it regularly. Been doing it for a couple of years now. I do have problems still, even when I use it, but it does help.

Now I am having some transmission issues, which could also be in play with the shaking and all, but I don't think the check engine light would come on if that were the case. If anyone has thoughts on that, I'd appreciate some insight.

[Treblig70]

I installed my new pump today. Tahoe ran much better and I couldn't detect any pinging/clattering. I'll know for sure tomorrow when I drive uphill, it always bucks a little if I accelerate going uphill. Anyway the new pressure was only 54 PSI. I was very disappointed. If the minimum pressure is supposed to be 60 PSI how am I supposed to get it after installing a new pump?

PS - the sock on the old pump was black or covered with black sediment. I could see small chucks of black particles (appox. .40-.05 of an inch in diameter) on the sock. The new sock was white. Was the original sock white also??? If it was originally white my old pump might still be OK if the clogged sock was restricting flow.

How do I get my pressure up to 60 PSI??? Gil in Tex

[Treblig70]

I heard there was a sb which warned against using anything except GM injector cleaner. Something about damaging the plastic fuel tubes under the intake of the Vortex engine...GM MERLIN should be able to tell us? Gil in Tex