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K1500 5.7 vortec 4x4, 1500rpm throttle sag and stalling


builditwright

Question

Posted

Hello and thanks for reading, I need some help here. I am just about at the end of my idea list.

So here goes

1997 GMC K1500 5.7liter v8 vortex z71 4x4 132,500 miles.

I was on about 9 hours into an 11 hour long drive when I stopped in in NJ to get fuel. About 30 miles later I was going 72mph around 1500rpms and had no throttle power. I could maintain about 65 but couldn't pass or accelerate quickly. Milked it to where I was going and parked it for about 3 weeks. Surfing that time I drove it a few miles here and there but saw no issues. I wrote it off to a long drive in an older truck, I just pushed her too hard. On the way home it did it again.

 

Several weeks go by and all the while the problem continues to grow stedily worse. It got to the point where I would have to really leave a lot of room if I was going to pull out in traffic due to almost no acceleration. At 1500rpms the truck would go dead. It stayed running but I push in the throttle and it just view quiet. No acceleration, a little studdering and I would have to reply feather the throttle to convince it to go. At its worst I couldn't attempt a big hill without pleanty of room to carry speed with me because I could not maintain speed on hills.

 

Here is what one done.

New:

Plugs

Wires

Distributer cap (i was very careful not to cross wires)

Air filter

Checked the air intake, vacume hoses and air filter housing for cracks and leaks, found a few mouse holes, taped them with a high end weather sealing tape.

Fuel filter

Throttle positioning sensor

Cleaned Mass Airflow Sencor (with proper cleaning solution)

Sence the problem started I have used hundreds of gallons of fuel, but the last three have had a bottle of Iso-heet, the second had Gumout, and the current tank has a bottle of Heet.

I am starting to lean towards clogged injectors, or a bad fuel pressure regulator.

I don't think its related, but the fuel sending unit is fouled up giving poor tank readings, could the pump be affected by this?

I also had to do lots of work to it to het a state inspection sticker, part of which meant removing all the tailpipe. So I only have the headers, cats, muffler and about 9" of tailpipe. Could I have to little back pressure? But the problem was there before the exhaust fix.

You can see my delema.

also, no check engineering lights or anything, but it does work.

 

Help me help me help me.

Thanks guys.

7 answers to this question

Recommended Posts

Posted

so I am going with the cheaper option first, I am changing out the Fuel Pressure Regulator. My Haynes manual says its part of the fuel management system and that its under the Intake Maninfold. Does that mean "Under" or "inside" I cant seem to find it.

Posted

Well, I found the FPR. It is inside the intake manifold. This seems to have fixed the problem, I think I was getting to much fuel.

For anyone doing this by yourself, a few pointers:

First dismantle the air intake vacum hoses

Second dismantle the throttle cables

Third dismantle the radiator hose, it may seem you don't need to remove it, but you do. Do not skip this step because you will get coolant inside the manifold if you do.

Fourth, get out your trusty 10mm socket with extension and undo the 8 or so bolts. Unplug the 6 or so plugs and remove the 8mm nuts that hold the two fuel lines on. I gently pried them up out of the way, others might remove them all together. Then rock back and forth to pry the manifold from the spider injectors. That will stay in the lower manifold. The FPR is mounted on that. Undo the clip, slide it out and rebuild in reverse order.

Thanks for your help!

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