Hi All

Been fighting this problem for some time now so here is a little history.

95 LT 4x4, 4.3L vortec engine type W. 150,000 mile. Bought at auction 2 months ago. SES light was on when I bought it. (I didn't see the light on at the time or I never would have bought it. ) Code at that time was P1345 and P0141. Replaced the crankshaft position sensor and distributor with junk yard parts. The SES light went off and it ran great for about 2 days.

Third day the light came on again. It start out flashing and then went to on steady. Code was P0305. Replaced fuel filter, spark plugs (plugs looked good) and wires with new AC Delco. No improvement. Fuel pressure test showed a slow leak. Replaced the FPR and the nut kit. SES light went out and it ran great for a day. Light came on again. Fuel pressure holds at 62psi

This time the codes were P0305, P0141, and P0122. Replaced the coil and ICM with junkyard parts and it ran great again. SES light came back on the next day and it dawned on me that after every time I disconnect the battery it runs great - not just OK or good. It actually runs great, nice and smooth. After driving around a bit it starts to run rougher and rougher until the SES light comes on and I can feel the misfire. I confirmed this by disconnecting the neg battery cable for about an hour and performance improved - for a while.

Today I replace the PCM with a junkyard part. Drove around for 20 minutes - ran great. Sat at idle for 20 minutes and the misfire slowly returned and the SES light came on. Code P0305 again.

Other things I have done so far - inspect the EGR valve, inspect the pcv valve, replace the MAP sensor, 2 bottles of fuel injector cleaner.

So where do I go from here?

Mike

 

Lets start off with the diagnostic sheets:
P0122 - Throttle Position Sensor Circuit Low Voltage
P0141 (GMT360/370) - HO2S Heater Circuit Bank 1 Sensor 2
P030x - Random/Multiple Cylinder Misfire Detected

The GMT360/370 manual was all that I could find the P0141 code in from the manuals I have on hand, but the diagnosis should be the same.

Looking at this, it may be a ground that is causing your grief. Check the grounds on the back of the head.

Another thing to look at is the gear on the bottom of the distributor.

 

Thanks for the quick reply.

I looked over the diagnostic sheets for those codes when they first set, but since I don't have a scan tool I wasn't sure how to test them. Can they be tested with a multimeter? Or is my best bet to replace the O2 and throttle sensor? Also they only came up once. Disconnecting the battery cleared them and they haven't set the last 2 times I had the code read at Auto Zone. Could they still be a problem or was that a one time thing?

The distributor gear could be the problem. The one I installed looked Ok but it was a used distributor.

I'll check out the grounds.

What has me confused is it runs fine and no SES light for a bit after the battery has been disconnected. I assume this resets the PCM to default settings. Is this correct?

 

the battery resets the codes...until the root of the problem is found they will return unfortunately