TA/30th 1002

99 Silverado 5.3 Z71 ...

Has anybody else experienced this symptiom?

As near as I can pinpoint my problem: At aprox. 0.8%-1.6% throttle position the PCM will bump ignition timeing some 15* or so. If the throttle is held in such a position it will occilate between 0.8%-1.6% causing the ignition timeing rate of change to occilate too. This seems to be causing a surging with my engine.

I can duplicate this surge at hot low idle by manualy opening the throttle; by driveing the truck in low range/light load. In low range the surge can become so violent it'll cause the trans to hunt between gears.

>I have fooled with the throttle stop adj. ... no differance.
>I have disconected the throttle position sensor ... problem went away.
>I have compared throttle position sensor incriments to my 99TA ... same calibration.

***My prognosis is the timeing calibration**

Does anybody have any thoughts on this?

Thanks ... Ron

BigTex

iTrader: (16)

I have something similar. Under load with very low rpms and throttle, timing will go up and down quite a bit. If I give it more gas, the converter will unlock and rpms will go up and it will stop. But if I continue to make it happen, it will eventually show KR and have negative timing. Really weird. I took out some timing and moved up the converter lockup speed. That has helped me some.

TA/30th 1002

Ahh BigTex:

Thanks for the reply. From your reply I take it you have LS1-Edit! I have edit for my F-body, but not my truck. I woundering if the timeing can be altered at low throttle positions [below 1.6%] to smooth the low throttle responce transition!

ie) give it about 6% more timeing at hot idle < 0.4%-0.8% TP ...

ie) give it about 6% less timeing at > 1.6% - 2.0% TP ...

How much timeing did you pull and at what % TP?

Ron

oxidizr

iTrader: (4)

You may want to do a TSB search ... from what I recall in 99' there is a TSB for PCM reflash for just that. The TSB description uses similar verbage refering to the trans hunting for the appropriate gear at low throtle position. There are quite a few TSB's out there for tranny related operation faults.

Richard