2001 GMC Jimmy

Our Jimmy went into the shop last Tuesday to get a tune up. It had been acting a bit sluggish, and the SES light would turn on occasionally (only when going up hills).
After the tune up, the Jimmy started to run even worse. It has such a hard time accelerating, and it takes it a long time to do so. You can tell that it is working very hard to accelerate but the power is just not there. We cannot go past 70 km/hr. When we reach 50 km/hr, it starts to buck. If we go much faster the 50 km/hr, it starts to make a tapping noise. The problems only worsen if we are going up a hill. The SES light is still coming on occassionally, and sometimes it is flashing.
It has been in the shop for 4 days. They have ran so many tests, they have changed the fuel pump, and they also gave the engine a TerraClean. Still no improvement, and if anything it has gotten worse. Any ideas? Thanks :)

We need to know what was done in the "tune up". Distributor cap and rotor, spark plug wires, spark plugs, fuel filter? What brand of spark plugs? What DTC's, (Diagnostic Trouble Codes) are are in memory? Advance auto parts and Autozone will read them for free. Post the info here and we can help.

Well all I know at the moment is what happened in the tune-up. I can find out tomorrow what the codes are that are coming up and what brand the spark plugs are.

For the tune-up, they replaced the oil filter, distributor cap, roter button, spark plugs, air filter, PCV, and spark plug wires.

I know that they have run a number of tests for codes and tomorrow I will ask them what the actual codes are.

Thanks! :)

Have them give you the codes in the order they were retrieved, then post them here. The 4.3L is very fussy on spark plugs.... Use AC Delco ONLY.

So I spoke to the mechanic this morning. He did not remember the numbers on all of the codes, because he did the test last week. Here is what he told me about the codes and the order:

P0300- random multiple misfire
?????- mass airflow sensor
?????- lean at bank one (02 sensor)

The spark plugs are AC Delco.

Thanks!

Have they perfomed a pressure test on the exhaust? If not it wouldn't hurt to do so. I had similar problems with my blazer and it was the catalytic converter that needed to be replaced because it was plugged. It started acting sluggish then one day it gave out, I couldn't go faster than about 50 mph.

It is interesting that you mention that because I just got a phone call and they now think that it is the catalytic converter. We hope that this is the problem and that it will be fixed soon. Thanks! :)

It is interesting that you mention that because I just got a phone call and they now think that it is the catalytic converter. We hope that this is the problem and that it will be fixed soon. Thanks! :)

Thinking and hoping does not fix the problem.:iceslolan :lol2:

Tell them to do some proper testing before throwing cats at it.
A back pressure test or a engine vacuum gauge reading at adle and at 2K rpm will tell the story about the cat.
Good Luck

It did end up being the catalytic converter. They replaced it, and it is running great now! :)