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Old 09-22-2018, 03:43 PM   #1
DJ31499
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Join Date: Jun 2018
Location: Brewster, New York
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Stalling under high throttle

My 1990 K5 has been having issues with backfiring for the past couple of months. Originally, I had a trouble code for the EGR valve/solenoid and got the solenoid replaced, helped keep the backfiring down for a little while but it was back in a few weeks. It happens at highway speeds of 65-70 MPH, between 2000-2500 RPM's, under heavy throttle (going up a hill, trying to speed up to pass someone). The engine almost 'pops', cuts out for a split second and keeps going. This week, it started doing it several times after driving up and down several hills on the Merritt Parkway. Next time i took it out, the engine fully cut out/stalled going up these small grades/hills at only 25 MPH. I was pretty low on gas at the time, which makes me think that it has something to do with the fuel pump, could be not sending enough fuel to the engine and it's starving under high throttle. But it could be anyway, the truck sat for an extended period of time before I bought it, so plugs, wires, cap and rotor, etc. I'm looking for some help on what to look for that may be the problem. Thanks!
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Old 09-24-2018, 03:51 PM   #2
OutlawDrifter
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Join Date: Aug 2012
Location: Northeast KS
Posts: 1,277
Re: Stalling under high throttle

Quote:
Originally Posted by DJ31499 View Post
My 1990 K5 has been having issues with backfiring for the past couple of months. Originally, I had a trouble code for the EGR valve/solenoid and got the solenoid replaced, helped keep the backfiring down for a little while but it was back in a few weeks. It happens at highway speeds of 65-70 MPH, between 2000-2500 RPM's, under heavy throttle (going up a hill, trying to speed up to pass someone). The engine almost 'pops', cuts out for a split second and keeps going. This week, it started doing it several times after driving up and down several hills on the Merritt Parkway. Next time i took it out, the engine fully cut out/stalled going up these small grades/hills at only 25 MPH. I was pretty low on gas at the time, which makes me think that it has something to do with the fuel pump, could be not sending enough fuel to the engine and it's starving under high throttle. But it could be anyway, the truck sat for an extended period of time before I bought it, so plugs, wires, cap and rotor, etc. I'm looking for some help on what to look for that may be the problem. Thanks!
TBI engines are very sensitive to EGR valves, universal replacements often do not work.

What kind of parts did you use for the tuneup? You say plugs/wires/etc...does that mean you have done a tuneup, or maybe you should?

When was the last time the fuel filter was changed?
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1991 Z/28, 6.0L/T56
1949 GMC 250, S10 Frame, 6.0L/4L80E
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Old 09-24-2018, 06:15 PM   #3
Koz1
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Location: USA
Posts: 20
Re: Stalling under high throttle

Ignition control module,or could be on the fuel side,pump,fuel filter.
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Old 09-24-2018, 09:31 PM   #4
Kudzupatch
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Re: Stalling under high throttle

It's going to take some diagnostics to find but just to toss something out, it could be a clogged injector and the engine is running lean. I ran into that. I hooked up my laptop and driving around I could the O2 sensor reading and under load it was lean, no backfiring but really sluggish and fall on it's face.
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