ZR-1 Net Registry Forums - View Single Post - 1991 Zr-1 Stumbling off idle

Enginerd101 · 02-08-2014

Hi - I'm not new to Corvettes (89 coupe, 1994 coupe, 1999 FRC, 2001 Z06), but have recently had the opportunity to purchase a 1991 Zr-1. It is a car that I have always been intrigued by and wanted.

I bought a 1991 Zr-1 with just under 60k miles (#407). It is arctic white. I bought it sight unseen from a dealer who surprisingly enough said that it runs great with no issues. HAHAHA... It will start and run, but seems to have a major stumble off idle. It almost seems like it is choking out when you give abrupt throttle from idle up to a little over 1,200 rpm. It idles reasonably smooth (probably not as smooth as the LT5 should though) and runs very rough in this range. Above 2k it seems like it runs ok. It had original multec injectors, which I wanted to blame for the issue, so went to work changing those out. Thanks to all of the tips and "how to's" here from all of the great forum members, I was able to do this job reasonably easy.

Finished it up this afternoon and fired it up. Much to my dismay, it is still exhibiting the same symptoms. I checked fuel pressure before and after i did the job, and is seemed to be adequate, ranging 40-50 psi.

I have no service history on the car and it does have a remanufactured ecu installed. Also has a Vortex air intake and B&B exhaust. I haven't really been able to road test, as I'm in the middle of a deep freeze in the Colorado front range.

Any thoughts or suggestions? I'm a bit stumped at this point.

Thank you!

02-08-2014	#1
Enginerd101 Join Date: Dec 2013 Location: Colorado Posts: 21	1991 Zr-1 Stumbling off idle Hi - I'm not new to Corvettes (89 coupe, 1994 coupe, 1999 FRC, 2001 Z06), but have recently had the opportunity to purchase a 1991 Zr-1. It is a car that I have always been intrigued by and wanted. I bought a 1991 Zr-1 with just under 60k miles (#407). It is arctic white. I bought it sight unseen from a dealer who surprisingly enough said that it runs great with no issues. HAHAHA... It will start and run, but seems to have a major stumble off idle. It almost seems like it is choking out when you give abrupt throttle from idle up to a little over 1,200 rpm. It idles reasonably smooth (probably not as smooth as the LT5 should though) and runs very rough in this range. Above 2k it seems like it runs ok. It had original multec injectors, which I wanted to blame for the issue, so went to work changing those out. Thanks to all of the tips and "how to's" here from all of the great forum members, I was able to do this job reasonably easy. Finished it up this afternoon and fired it up. Much to my dismay, it is still exhibiting the same symptoms. I checked fuel pressure before and after i did the job, and is seemed to be adequate, ranging 40-50 psi. I have no service history on the car and it does have a remanufactured ecu installed. Also has a Vortex air intake and B&B exhaust. I haven't really been able to road test, as I'm in the middle of a deep freeze in the Colorado front range. Any thoughts or suggestions? I'm a bit stumped at this point. Thank you!