I have a tpi 350 in a 91 z28. I have replaced the distributor and the coil and I'm still getting a code 42. I'm at a loss as to why.

Anyways the motor runs fine but when i accelerate is seems to have a lack of power at first and then all the power surges back and it's fine. Only when starting off does it do this and it's not that bad but it is noticeable any ideas on both issues?

I'd try diagnosing it using the trouble tree. Replacing parts usually just costs money. http://chevythunder.com/est_code_42.htm

Grab a meter and start measuring. Maybe this will help. Might have an ecm issue or some poor ground to the ecm.

Interesting I'm having the same issue on my scanner it shows all this (code 42 est grounded/ info flag-open est detected / one esc sensor open and both esc sensors open) also has code 43 ..,,I've replace ecm, prom chip, complete new distributor ,coil and spark plugs plugs and knock sensor, im interested to see what u find?. let us know ..thanks

Any updates

The car runs fine except it only gets 13.5 mpg on the interstate. Still have the code 42. I will be testing for grounding issues with the ecm tomorrow.

alright keep us updated, i hooked up a scanner to my car the other night and found No more codes, but its running lean soon ill be checking for a vacuum leaks and replacing the original 02 sensor if no vacuum leaks are found ill be doing a compression test as well , all my fuel components are new fuel pump, sending unit, filter, injectors and regulator also flushed out the tank, prior to replacing all the parts mentioned before car sat for 8+ years ..

Updates?