Posted by jimg.allentown on January 15, 2015 at 10:51:11 from (98.115.105.174):
In Reply to: Re: Gmc 7000 update posted by Zach Scherf on January 15, 2015 at 10:34:04:
Start with some basics. Check the timing with a timing light as per the instructions on the VECI decal that should be under the hood someplace. If you cannot find the decal, you will need to get the procedure from a manual. Next, I suggest that you check fuel pressure with a gauge. You can get an inexpensive universal gauge from Harbor Freight that will do the job for the little bit that you will need it. If the fuel pressure is too low, it will cause poor running.
Regarding the oxygen sensor: GM O2 sensors are notorious in that era for failing. The reading from that sensor is what puts the engine into closed loop operation. At that point, it operates as a full feedback system. Unplugging the sensor should only cause the system to go into open loop. It should not cause a no-start. Unplugging it does not prove or disprove the sensor. At this point, I would recommend replacing it just due to age and condition. They are not that expensive, and are a key component of the feedback system. Also, O2 sensors need to warm up to operating temperature to begin to function. As I recall from reading your repair invoice, the repair shop listed repairing the wire to the O2 sensor. That tells me that it ran before with the sensor unplugged.
Also, have you neglected some REALLY basic stuff, like how are the spark plugs? If the repair shop replaced them, did they put in ACs? Or Champions? I have seen SEVERAL cases where Champion plugs simply would not work right. They never work well in Ford or GM products, but are fine in Chrysler products. How about the plug wires, and firing order? A couple of switched wires can really cause problems.
Keep checking things, and don't dismiss anything until you are SURE that it is OK. Good luck!
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