1996 GMC Z71 Ext. Cab


Old 03-07-03, 06:43 AM
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Angry 1996 GMC Z71 Ext. Cab

Truck Had engine long block replaced with 1999 Long Block out of a wrecked truck and when you start it it would run but would build up and blow black smoke out the exhaust then would clear out and run fine after about 15 min. But only gets about 240 miles out of a full tank (10 miles a gallon) well yesterday I changed the fuel pressure regulator and the spider injector assembly and put new gasket on upper intake, and little oval oring gasket around the electrical part of the spider Inj. I cant find any intake air leaks, I have replaced the Maf sensor, spark plugs, egr valve, but now it has a miss in the engine and doesn't have the power that it used to have. also the Check engine light just blinks off and on, before it used to just stay lit. I also replaced the computer with a 1996 vortec 350 computer from a wrecking yard. and has been reprogrammed. even though I had to let it idle for 15 min when I first started it before until it cleared out, it ran better than it does now. and I am stumped Can Anyone help please?

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Old 03-07-03, 07:40 AM
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How's the fuel pressure? Check it with a hand-held gauge. It must be DEAD ON spec on a Vortec.
Old 03-07-03, 12:20 PM
Join Date: Feb 2003
Location: New Jersey
Posts: 229
Sounds like you've done a lot of work around air/fuel, but don't rule out ignition. I had an ignition module go bad that made the engine behave just like that. It was running REALLY rich (black smoke) and had a miss that I couldn't pin down. Trouble was that it was intermittent. Gas mileage was really poor. I replaced EVERYTHING: MAF, cam position sensor, fuel injectors, EGR, TPS, FPR, ECM (tried multiple chips, too), plugs, wires, etc. Thinking maybe I had a "minor" headgasket leak I did a leak-down test and a compression test. It was acting exactly like a vacuum leak, so I replaced ALL of the vacuum lines and checked for intake leaks. Turned out it was the ignition module ($70 problem) - it was firing weakly and intermittently.

Good luck,
Old 03-08-03, 03:08 PM
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1996 GMC Z71 Ext. Cab

A Mechanic Friend of mine told me the fuel pressure is supposed to read between 56-62 and mine is 58 so I think I am Ok there what is your Opinion?

I will try the Ignition Module next..... I appreciate everyones help on this, I am really burnt out on this truck mentally and financially. might as well have payments on a new one if I am going to spend money on it every week
Old 03-09-03, 07:18 AM
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Putting the wrong year engine in there was the first error . Always stay with the correct, recommended combination with an OBDII vehicle---the computer system is very sensitive.

Double check that both the 99 and 96 vehicle engines have the same fuel pressure, and that they use the same fuel pump!

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