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Tractor Talk Discussion Board

Re: Gmc 7000 no one can fix


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Posted by jimg.allentown on January 15, 2015 at 05:19:00 from (98.115.105.174):

In Reply to: Gmc 7000 no one can fix posted by Zach Scherf on January 14, 2015 at 17:59:44:

One guy says it is the throttle body (that you just paid to fix). Another says it is the distributor. Yet another says it is the EGR.
HOLD ON!!!!!

Pulling codes might tell you something. However, the older OBD1 systems were a lot less complicated than the newer systems, and a lot less sensitive. Getting a bit of understanding about the system will help considerably. As you can see, the "shotgun approach" is expensive and ineffective. You already spent a small fortune, and it is still not working right.

The system is basically a feedback system. The main important components are the OXYGEN SENSOR, the MAP SENSOR, and the INJECTOR BODY.

The injector body (throttle body) contains the injectors, throttle position sensor, and fuel pressure regulator. If it has been rebuilt and verified, it is likely NOT the problem. That can be verified by checking the fuel pressure and observing the injectors. The fuel feed can be observed from above. It should look like a fine mist coming from each injector in a fan shaped pattern. No droplets or drips.

A bad OXYGEN SENSOR can cause the engine to run rough and rich. The system is a "feedback" system. The primary mixture control is feedback from the O2 sensor to the CPU. MAP sensor (that has been replaced) is secondary, and is more important in open loop than in closed loop operation.

A worn distributor shaft will usually result in rough running to a no start condition depending on the amount of wear. This is a condition that would come on progressively over a period of time.

All things considered, I would discount the "short answers" given by some because there is NO SHORT ANSWER. If it was the same problem each time, there would be no need for repair shops or mechanics.

Sadly, I have a few tools that might help you out. I have several older OBD1 scan tools that allow you to read sensors "live" on GM products. If you are still stuck, maybe I can send one to you. I no longer use or need them.


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