1994 performance problem
Thread Starter
Racer
Joined: Aug 2012
Posts: 289
Likes: 41
1994 performance problem
I am working on a 69000 mile 1994 corvette with a performance problem. It starts quickly and runs well until warm. Then it stumbles badly and backfires on acceleration. The following parts have been replaced:
Fuel pump
Fuel filter
opti spark distributor
new coil
Control module
The following test have been completed:
Fuel pressure test and it seems to be fine. 45 lbs on key turn. 40 running and holds on acceleration. 5 lbs increase to 45 when vacuum line pulled off fuel pressure control valve. When shut down hold pressure at 40 lbs. When the mass air flow line in disconnected the engine dies.
Code 64 did show up on dash when tested.
Since the car was sitting for awhile I am going drain some gas and put in new and add some sea foam to the tank.
Any additional suggestions as were to go next would be appreciated.
Thank you
Rich Harris
Fuel pump
Fuel filter
opti spark distributor
new coil
Control module
The following test have been completed:
Fuel pressure test and it seems to be fine. 45 lbs on key turn. 40 running and holds on acceleration. 5 lbs increase to 45 when vacuum line pulled off fuel pressure control valve. When shut down hold pressure at 40 lbs. When the mass air flow line in disconnected the engine dies.
Code 64 did show up on dash when tested.
Since the car was sitting for awhile I am going drain some gas and put in new and add some sea foam to the tank.
Any additional suggestions as were to go next would be appreciated.
Thank you
Rich Harris
Thread Starter
Racer
Joined: Aug 2012
Posts: 289
Likes: 41
This is what happened today. I decided to disconnect the throttle control sensor. I started the car and let it warm up. It ran great, no stumbling, no back fire. The service engine light did come on. I then reconnected the TCS. I took it for a ride and other than shifting at a high RPM it really had power. NO service light. When I got back I ran the codes C12, H22, H64. Took it for a second test drive. Shifted much better but did stumble a little, no where near the previous condition. I will be putting a new TCS tomorrow. I will be putting in a new OY2 sensor this weekend. What are your thoughts?
Le Mans Master
Joined: Aug 2015
Posts: 6,125
Likes: 2,001
From: St. Charles MO
Yes it would. And the giveaway is that it runs fine until it warms up. What's happening is that on cold startup, the engine is in "open loop" mode where it ignores most sensors (including O2) and only targets a set air:fuel ratio. Once it warms up (probably ~140F coolant temp), it goes into "closed loop" mode where it bases its control of the engine on all the various sensors. If one O2 sensor is bad, it will run badly. I would be money this is your problem. It's a good example of why strong diagnostics is really important before throwing parts at a problem. Unfortunately, I speak from experience on this one!
