End of my rope. 99 GMC 5.7 Suburban 4x4


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Dec 18, 2018
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Fresno, Cal
18 months, two shops and no one can figure this out.

Suburban is used to towing my boat. Build date of 4/98. 230,000 miles, 4x4. 5.7 tow package

at 229k we put new heads, new injection,new MAF, new 02's, new Magnaflow cats, and so on, TPS, MAP, etc

There is nothing left to replace.

Engine ran fine for 1500 miles, then on a moderate hill pulling the Airstream it began to buck, misfire, both out the exhaust and intake. You floor it, you hardly move. It coughs and pops.

Take your foot out of it, it will take off, but you feel a misfire when it upshifts.
Pulling the trailer as we come on the freeway, as it goes thru the gearbox, when it hits OD, it begins to buck, pop, you feather the throttle, it will smooth out,

I have about 50lbs at the fuel injection rail, we went thru 3 pumps, all were the same. I have no idea what the pump is putting out but at the TB connection, there is about 50+-.

EVERYTHING that we could replace we have tried. Two shops. Still nothing. Other than going to the dealer, handing over my GMC, and my checkbook, I am stumped.

Today, with a SnapOn scanner we found the base timing at 6 deg. we rotated the dizzy back so it was idling at 0.

BTW the chain was tight and two dizzys installed off KNOWN good Yukons.

All that is left is seveal things

ECU, Harness, or a 1 ton fuel pump that cranks out 80-100lbs of fuel pressure. Is the fuel regulator gone? I don't know, we did put a new one on when we did heads.

To this point, I am baffled and stalled. It is driveable but I can't tow with it.
idles smooth. Step into it, sometimes it will run out other times it stumbles across the intersection then takes off.