i have an '88 5.7l with the AIR garbage. The catalytic converter had been replaced with straight pipe when I bought it. the car has had a 51 trouble code since i bought it. Could remving the cat and putting a aftermarket mufffler on it have anything to do with the engine trouble. i have heared that removing the cat can cause probles but i dont see how since there is no 02 sensor downstream. Anyone else had problems afte the cat was removed?

 

Code 51 is a PROM code. It is defective, not properly installed, incorrect PROM, or defective ECM. I would pull the PROM and clean the leads up good then plug it back in. If that doesn't solve the problem, buy a new PROM (could probably buy a used one as long as you know for sure it's good) and if that doesn't do it then you know it's the ECM. Good luck with it.

 

I've got an 88 305 tpi iroc with cat removed, installed a straight
pipe. no problems so far (2 months). the engine seems to
'spool' up faster and really wants to run.

there is no O2 sensor downstream so no codes should be set.
i like my straight pipe performance except for the louder exhaust.