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Old 09-12-2011, 10:12 AM
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Default Engine kicking/missing at highway speeds and more!

Hey all! I have a 96 GMC Sierra K1500 5.7L 4x4 Z71, 165k on the clock. I was having a boatload of trouble a few months ago, replaced plugs, wires, cap, rotor to no avail. Took it to a mechanic who replaced the throttle position sensor, map sensor, a few bad grounds, and the left bank O2 sensor (which didn't need replacing as it didn't fix the problem-no 6 misfire).

It's been running fine (aside from the no 6 miss) but last week started to kick/miss at highway speeds when i put light-medium pressure on the pedal. Full throttle or near clears it up. Gas mileage appears to be about the same, 13mpg on last tank but I was hauling six or seven hundred lbs for half of the tank, in the throttle around town for the other half. I have four codes coming up, no 6 misfire (nothing new but perhaps related), transmission control system malfunction, P1192, which my scanner does not have but online found "Post-catalyst Fuel Trim System Bank 1". Also should note the mechanic said I had high vacuum pressure, like 10 or 15 lbs or something; possibly a cracked plenum, but it was running alright even with this condition. Thoughts?

My initial thought is the fuel pressure regulator. Checked the fuel pressure and it reads 52lbs at idle, ~60 in the higher rpms. I can't really find out if that's normal or not, but it seems okay.

Any thoughts? Any help would be much appreciated!
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Last edited by reddituser; 09-12-2011 at 10:20 AM.
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Old 09-12-2011, 11:01 AM
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Do you remember how the plugs looked?
When is the last time you replaced the fuel filter?
Are you losing any coolant - Vortecs are infamous for blown intake gaskets.
Coolant temp sensor
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Last edited by Mr_Shamrock; 09-12-2011 at 11:11 AM.
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Old 09-12-2011, 11:54 AM
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Still have the plugs I'll have to take another look at them. One of them was fouled for certain. The fuel filter looked new when I bought the truck about 4k miles ago so i didn't replace it. I think I am losing coolant, but very slowly.

Edit: four of the plugs were fouled. Don't remember where they came from specifically.

Last edited by reddituser; 09-12-2011 at 12:06 PM.
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Old 09-12-2011, 02:43 PM
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I think I would start with the coolant temp sensor first then - not the one for the gauge, but the one for the computer. It can cause a rich condition if it isn't reading properly (ECM thinks the truck is always cold). If you are losing coolant at all I would definitely check for an intake gasket leak. If the leak is external it should be evident. If you don't see any sign of a leak then it could be leaking internally which isn't good for bearings. Keep an eye on your dipstick for signs of water (milky looking) although a very slight leak won't be real obvious. That could also be your vacuum issue that the mechanic found.
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Old 09-12-2011, 02:43 PM
 
 
 
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1992, 4x4, 96, chevy, coolant, engine, highway, miss, misses, missing, para, pickup, sensor, silverado, speeds, temp

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