20 Most Recent 1991 GMC C1500 Questions & Answers


this is probably a bad u-joint(s) crawl under the truck engine off and in park and on a flat spot, twist the drive shaft if it clunks at all or has some up down or left right slop the joints are shot and will need replacing. And yes the u-joints will cause a drive line vibration that seems like a transmission issue it goes away with speed as the shaft will spin fast enough the vibration will become only a hum.

1991 GMC C1500 | Answered on Jan 24, 2018


Yes the trans can wipe out the crank bearings or the spacer behind the crank(forget what its called) it can let the flexplate move and the bolts can hit.That may be what your hearing. Does it still have good oil pressure?

1991 GMC C1500 | Answered on Oct 17, 2017


Possible faulty park/neutral switch. Hold key in start, while moving gearshift up and down. Be sure to have a foot on the brakes! If it starts, or tries to, the switch is bad or out of adjustment. Possible bad ground too. Follow the negative cable from the battery to where it connects to the frame or engine, undo the bolt and clean it well with a wire brush.

1991 GMC C1500 | Answered on Dec 26, 2016


That means both bank one and bank two oxygen sensors are reporting the same signal IN FRONT OF and BEHIND the catalytic converter. This could be from the catalytic converter failing or it could be from a manifold leak, wiring problem etc.

1991 GMC C1500 | Answered on Apr 05, 2016


With truck off, you can turn the crankshaft nut from bottom of engine. To bring to top dead center. Remove #1 plug and insert a straw or similar into plug hole on top of piston. When the piston just starts to go back down from all the way up, that's top dead center, The number one cylinder in the 4.3 V-6 is the front wire on the driver-side of the engine. God-Bless!

1991 GMC C1500 | Answered on Mar 03, 2015


look for exhaust restriction like converter
hope it help

1991 GMC C1500 | Answered on Feb 03, 2015


Why don't you just cut 2 wires where you know they're good, add 2 new wires, and run them to the back, and by-pass whatever the problem area is, and your done?

1991 GMC C1500 | Answered on Mar 20, 2014


just rebuilt700r4 transmission and it is sliping in reverse what can cause this.

1991 GMC C1500 | Answered on Mar 14, 2014


Rebuild your trans & do the upgrades

Need a better & larger external cooler

1991 GMC C1500 | Answered on Mar 07, 2014


check auto electrician to to determine if your fuse fuses have not been blown or the same have been grounded correctly

1991 GMC C1500 | Answered on Nov 12, 2013


the firing order is
1-6-5-4-3-2

1991 GMC C1500 | Answered on Aug 23, 2013


I suggest visit this link: consumerreports.org/cro/tires

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

1991 GMC C1500 | Answered on Feb 24, 2012

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