20 Most Recent 1991 GMC C1500 - Page 2 Questions & Answers


Definitely check the tune-up items. I have also had O2 sensors go bad on these trucks.

1991 GMC C1500 | Answered on Aug 28, 2011


raise the vehicle and check each wheel to see if the brakes get tight. If one is not check the rubber brake hose for it maybe collasped causing this problem
Also to remove all air from the brake lines you start at the furthest wheel from the master cylinder and work your way up to the closest wheel last. If you did not do it in this proceedure air will still be in the lines

1991 GMC C1500 | Answered on Aug 17, 2011


For your idel problem run mid grade gas

1991 GMC C1500 | Answered on Aug 05, 2011


may be a control module

1991 GMC C1500 | Answered on Aug 03, 2011


  • There are a couple things here that could be the issue. One would be your Catalytic Converter. The other would be your 02 sensors. It is possible you are running just a little bit rich. There is a sensor on the exhaust not far off the manifold (this is called the upstream sensor). There is another 02 sensor down the exhaust a bit by the Converter (this is called the downstream sensor.

  • Most of the time you will know when the 02 sensor is bad because your fuel mileage will go way down. Often times a check engine light will come on as well (but not always). A failure 02 sensor will run a vehicle rich and that left over fuel from combustion can cause pollution and a failure of an emissions test. However, if you are not loosing any fuel mileage, and you don't have a check engine light on I would be inclined to think that the converter has passed it's point of functionality and needs to be replaced.


Regards, Tony

1991 GMC C1500 | Answered on Apr 29, 2011


Hello and welcome to FixYa!
If it's not turning over then the problem will be on the firing. If there's no current to the plugs, the engine won't fire up. Few things to look at to resolve the issue... First, the ignition coil can be faulty. Second, The ignition switch can be faulty. Third will be the starter. If it's faulty, it won't kick the flywheel. One good reason why it won't turn over.
Hope this helps and thank you for using FixYa! Have a good one!

1991 GMC C1500 | Answered on Apr 28, 2011


Take it to a shop where they can change the transmission fluid and filter and also have them do a good flush of the transmission with a special solvent they use. If this doesn't help it may be time for a rebuilt transmission.

1991 GMC C1500 | Answered on Apr 03, 2011


It should be either in the thermastat housing or in the center intake manifold near it, if not in either of those 2 then check behind the exhaust manifold probably on the right side in the engine block look for a wire going down there to find it.

1991 GMC C1500 | Answered on Mar 17, 2011


Usually this means that the timing needs to be set again, until it is 100% right.


  1. Remove the timing cover. This will allow access to the timing chain.
  2. Crank the engine until the timing marks on both sprockets are nearest each other and in line between the shaft centers.
archaeology_31.jpg

Here's a diagram -- often these are as good as pictures --

archaeology_32.jpg

The "A" points to the 2 timing marks visible in the photo above.

1991 GMC C1500 | Answered on Mar 15, 2011


IAC idle air control valve is not working right. Second a vacume leak.

1991 GMC C1500 | Answered on Mar 01, 2011


change out radiator cap it may be loosing pressure

1991 GMC C1500 | Answered on Feb 28, 2011


the throttle position sensor

1991 GMC C1500 | Answered on Feb 28, 2011


I would check the MAP sensor first, and then the Idle air Control valve. If those check out it might be a vacuum issue. The EGR Valve has a line on it that is very good at leaking and can cause a rough idle.

1991 GMC C1500 | Answered on Feb 27, 2011


How do you know it's running lean or flooding? Best way to know is to check the condition of your spark plugs. They will be dry black (carbon) if running rich, oily if you're burning oil, they will be white if burning correct mixture, and the ceramic that surrounds the electrode will be unevenly worn or have little pin-sized deposits on it if you're running lean. You can look up "spark plug diagnoses" to see some visual references.

1991 GMC C1500 | Answered on Jan 23, 2011


Sounds like your linkage is out of whack. You need to readjust the linkage so it goes through the whole range. Sounds like you are not in drive when the gear selector says you are. Undo the linkage, put the transmission in park manually then reattatch linkage to make sure that what it states on the selector is concurrent with the transmission. Good luck.

1991 GMC C1500 | Answered on Jan 03, 2011


pull the rear drums and see if there is axle grease on the shoes from leaking axle seals, if they look dry sand the shoes with 80 grit sandpaper and wash them off with water and bevel the edges, of course replace them if the are less than 30% of new shoes thickness.

1991 GMC C1500 | Answered on Sep 26, 2010


try un hooking a battery cable and it will usually reset them if u dont have any problem it should go off, but usually if it comes back on there will be a problem somewhere might just be a sensor, sensor are one of the main reasons y the engine light turns on. just take it to auto zone or something and they can tell u y the light keeps coming off if, that other solution doesnt work

1991 GMC C1500 | Answered on Sep 22, 2010


the timing chain might be off or a bolt my just be lose somewhere.

1991 GMC C1500 | Answered on Sep 22, 2010


well since u just got it rebuilt they might of did something wrong rebuilding it. but do u not have reverse at all? i used to have a 700r tranny and went threw 5 within a year if u was going to put a new tranny in it or a rebuilt one i would go with the turbo 350 or just the 400 they wont have the overdrive in it so u might not get as good gas mileage but all the money u will end up putting in the tranny it would just be better to put a different one in it. thats wat i did about 6 months ago i put a turbo 350 in my 1989 chevy 1500 with a 350 in it and its works fine. but when you put it in reverse does it just rev. up or does it move a little bc i had a problem just like that but it would move still just not very much

1991 GMC C1500 | Answered on Sep 22, 2010

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