The 89 gmc continued
Printed From: Unofficial Allis
Category: Other Topics
Forum Name: Shops, Barns, Varmints, and Trucks
Forum Description: anything you want to talk about except politics
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=152113
Printed Date: 29 Aug 2025 at 3:50am
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Topic: The 89 gmc continued
Posted By: bobkyllo
Subject: The 89 gmc continued
Date Posted: 15 Jul 2018 at 5:26pm
So guys you know I've been screwing with this 89 gmc 2 wheel peeler pickup with the 5.7
Any way what I've done. I ohmed the coolant sensor found that in spec. Ohmed the idle air control and that was in spec but also moved freely. Made a jumper harness for the throttle sensor and checked the voltage sweep. Also ohmed injectors. That turned out good. New cap, rotor, ignition module. I had a hopefully good map sensor. I'm not sure why I'd keep it if it was junk but hey stranger things have happened.
I did try a new fuel regulator. That did seem to help it start a little better. As I had it running it sounded like a horrible vacuum leak with brake cleaner I found the intake to throttle body gasket to be bad. Changed it but not much help. Vacuum leak did go away.
I'm honestly at a loss for now. I can't think of anything else that can be screwing me. One thought that come to mind is possible egr not closing. Tomorrow I'll make a block off plate just to verify my thought. As it's running there seems to be little exhaust coming out of the pipe. It will rev up good though.
It still wants to start hard and it's idle is very poor. Still hunting for a happy spot.
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Replies:
Posted By: truckerfarmer
Date Posted: 15 Jul 2018 at 8:36pm
Have you bothered to check the timing?
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Looking at the past to see the future.
'53 WD, '53 WD45, WD snap coupler field cultivator, #53 plow,'53 HD5B dozer
Duct tape.... Can't fix stupidity. But will muffle the sound of it!
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Posted By: bobkyllo
Date Posted: 15 Jul 2018 at 11:56pm
No I have not because if you can manage to get it above idle it will run pretty decent not great but decent.
The customer says that this is an all of a sudden problem.
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Posted By: bobkyllo
Date Posted: 15 Jul 2018 at 11:56pm
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Plus it does not want to back fire like it's out of time.
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Posted By: truckerfarmer
Date Posted: 16 Jul 2018 at 6:38am
Start with the basics. Air, fuel ignition.
Just because it doesn't backfire, doesn't mean it is timed right. Backfiring usually means timing is advanced. With retarded timing it will have a tolerable idle, but won't hardly pull itself when you put it in gear. Check to see that the vacuum advance is functioning properly. Being that old, the vacuum line to the distributor might be hard and not sealing. If you had one vacuum leak, there is a good possibility you have another.
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Looking at the past to see the future.
'53 WD, '53 WD45, WD snap coupler field cultivator, #53 plow,'53 HD5B dozer
Duct tape.... Can't fix stupidity. But will muffle the sound of it!
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Posted By: Stan IL&TN
Date Posted: 16 Jul 2018 at 9:03am
If I had very little exhaust coming out I would suspect that the catalytic converter may be clogged and would want to disconnect the sucker to verify. I believe you can remove the O2 sensor and insert a pressure gauge in it's place to see if you have too much pressure before the converter.
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1957 WD45 dad's first AC
1968 one-seventy
1956 F40 Ferguson
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Posted By: HudCo
Date Posted: 16 Jul 2018 at 9:23am
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yes i would check the cat plus if i am correct that dist . dosnot have vacumm advance but is electronic advanced no timing marks on the dampner but has marks in side the distributor cap that have to line up at tdc also the dist. may be going bad
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