Tahoe Misfires after Heavy Accleration

[McClane]

I have a 2000 OBS z71 that is doing something very odd. It runs fine during normal driving but if I need to give it 3/4 throttle or more it starts misfiring when I let up off the gas to cruise level in overdrive. If I let off the gas completely and then give it half throttle again the misfire goes away. Any ideas? All ignition parts are AC Delco plugs are a year old and the cap, rotor and wires are about 4 years old with around 15,000 miles on them.

 

[drakon543]

Does it pop a check engine light when it starts doing it? How many miles are on it? Possible problems off hand are a bad throttle position sensor, a weak injector, distributor needs replacing, vacuum leak thats only leaking during high vacuum.

 

[McClane]

It has 204,000 miles on the body. Engine was supposedly replaced a year before I got it and I have put an additional 20,000 on it. Fuel injection spider was replaced 4 years ago with the newer version that uses the more standard injector design. I think the check engine bulb has burned out. Need to replace it. I'm going to run by a parts store after work and run the codes to see what comes up.

 

[drakon543]

Ok post any codes that come up. You can also try replacing the tps as its fairly cheap and easy to replace. It is possible for the upper end of the tps to go bad so its not reading that part of the throttle position.

 

[McClane]

0141 and 0161 which are rear O2 heater circuits and 1345

 

[drakon543]

Replace the distributor under light to medium throttle its holding its timing. When you accelerate harder the timing is going beyond the +/- 2 of 0 throwing the timing off. If you can mark the distributor enough you should be able to just set in a new one in the same place and be good to go. If you have access to one a live data scanner capable of reading cam retard will help set the new distributor faster.

 

[DallasTahoe]

0141 and 0161 which are rear O2 heater circuits and 1345

Yea your timing is off, it can cause the other two codes too, get to a place where they can put a real scanner on it and set the advance to +\- 2 degrees. Keep an eye out and see if the distributor hold down is tight, and how far the dizzy needs to move to get it set. If it's a lot it may have never really been set if the hold down is tight. Since you need to get to it anyway I would mark it before loosening it and pull the dizzy to check the cam gear for excessive wear


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[McClane]

Took a look at the dizzy. One of the ears for holding down the cap is broke off. Time for a new one. I have a buddy that owns a performance shop that's going to set it for me with his scanner next week. Will report back once it's fixed.

 

[willxfs]

I bought the re-manufactured ac delco on rock auto for 135 after the core return. Worked great. I did have to knock out the split roll pin on the gear on the bottom and turn the gear 180 degrees to get the cam offset set correctly. Couldn't get the adjustment right otherwise. I was working with a different cam shaft on a newly built 383 motor. Good luck and keep us posted. Thanks

 

[drakon543]

I tossed in a cardone reman from advance and its been great for about 3k miles so far.