Running rough on the highway - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 10-08-2003, 02:35 PM
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Running rough on the highway

Recently I replaced my fuel pump because my 1996 GMC Z71 was hard to start in the morning. Now after my truck gets up to around 1700 rpms it starts bogging. On the freeway I have very little accelerating power, [img]images/graemlins/cussing.gif[/img] it hits overdrive and at 1700 rpms it bogs and my speed very slowly climbs to about 70 mph before leveling off. When I come to a stop the truck will die. If I put it in neutral with the engine running I can rev it to redline. I replaced the fuel filter, coil, plugs and wires. Maybe the EGR valve is dirty or the dual cats are clogged. Does anyone have a picture of the EGR valve for 1996 GMC 5.7L engine. Any help is appreciated. Thanks
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post #2 of (permalink) Old 10-11-2003, 05:19 PM
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Re: Running rough on the highway

What is the fuel pressure? If you have anew fuel pump and low pressure, then I'd suspect a defective fuel pressure regulator.
post #3 of (permalink) Old 10-11-2003, 07:03 PM
 
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Re: Running rough on the highway

This may sound stupid, but I have had 3 different trucks, all the 1996 year do the same as you are saying. The guy would get in, start it fine, and drop it into gear and the truck would die. Or if he kept it running and got out on the road it had no power. After searching all over the truck I found that it was the + battery cable that runs to the under hood fuse box was completely corroded inside the rubber boot where the wire goes in. You couldn't see the corrosion without cutting open the rubber boot.

Anyway, just a thought as to what may be wrong, I've only seen it on the 96 model year and it's always been on 454's.

It was always like if you could get some rpm's up while in N or P the alt would send enough voltage out to keep things going, but the added current draw when dropped into gear would kill the truck or the added current of the ignition system when trying to accelerate would kill the truck.

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post #4 of (permalink) Old 10-11-2003, 08:39 PM
 
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Re: Running rough on the highway

Heres a pic of the EGR valve, not the greatest but it will get the point across.

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File Type: jpg 1201150-96EGR.jpg (78.9 KB, 4 views)
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post #5 of (permalink) Old 10-13-2003, 07:46 PM
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Re: Running rough on the highway

SierraPilot, How do I measure and adjust the fuel pressure? I think the regulator is under the intake manifold. Is there a way of adjusting the pressure from the engine bay? And approximately what psi should it be putting out? Thanks for the help.
post #6 of (permalink) Old 10-14-2003, 11:28 PM
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Re: Running rough on the highway

Well, I broke down and drove to the Chevrolet Dealership to get a diagnostic run. The estimate was $200. I get a call 3 hours later saying I have low fuel pressure and it's going to cost $600 [img]images/graemlins/cussing.gif[/img] to replace the fuel pump and filter. I tell them just button it up and I'll pick it up. The diagnostic cost $190, so I ask to see the readout saying that I am running lean. The [img]images/graemlins/AR15firing.gif[/img]service manager explains, it doesn't work that way. That it flashed two codes 171 and 174. So can someone explain to me how it takes 2 and half hours to read an OBD II computer [img]images/graemlins/lame.jpg[/img] I changed the fuel pump myself and saved $400 on professional insallation.
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