1991 GMC C1500 - Answered Questions & Fixed issues

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?

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.

check timing ?

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?

check volts in baterry

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.

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.

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!

look for exhaust restriction like converter hope it help

its a 350 small block,im not sure what you are asking

Rebuild your trans & do the upgrades Need a better & larger external cooler

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

first have a look to gauge fuse

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

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

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

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

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

may be a control module

• 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