93Rubie
Well-known member
Ok, here we go. I got a 94 Corvette LT1 auto I am working on.
No Codes, runs perfect above 140 degrees coolant temperature.
Runs perfect cold too, the problem is under moderate accleration when coolant temps are between 100 and 140 the car backfires through the intake manifold. The car is still in open loop at this point.
When the car goes into closed loop it runs prefect. I verified this with a scan tool today having someone else drive. Again runs perfect cold as well. Under 100 degree water temp.
Under cruise and very light acceleration it does not backfire between 100 and 140 only upon more throttle will it do so.
I saw nothing in all the data I was seeing that would indicate any obvious problems. Except for the TPS it reads .72V closed and 4.10V open. That is off some and I am going to investigate this. Also, as an experiment I unplugged the MAF and ran the car in continuous open loop. It ran fine at all times and temperatures.
Now that being said, this occurs in open loop between 100 and 140 with everything hooked up. What could possibly be operating in open loop at that time but yet when I set a code will not operate because of the code?
I do not suspect any base engine, basic fuel, basic ignition, or other basic systems as a fault because the car runs perfect most of the time and especially in closed loop.
One thought I had is that what if the Secondary Air Pump is running when it should not be, yet with a code it may not operate at all? IDK? Still researching that one. How would I take out the Secondary Air without throwing a code?
Your thoughts, this is an odd one and not something you find everyday. I personally like this kind of stuff and hate it at the same time. This stuff is what separates the men from the boys. Never hurts to get different ideas from others, however, no one can think of everything, hence the post.
Thanks, and bring your brain.
No Codes, runs perfect above 140 degrees coolant temperature.
Runs perfect cold too, the problem is under moderate accleration when coolant temps are between 100 and 140 the car backfires through the intake manifold. The car is still in open loop at this point.
When the car goes into closed loop it runs prefect. I verified this with a scan tool today having someone else drive. Again runs perfect cold as well. Under 100 degree water temp.
Under cruise and very light acceleration it does not backfire between 100 and 140 only upon more throttle will it do so.
I saw nothing in all the data I was seeing that would indicate any obvious problems. Except for the TPS it reads .72V closed and 4.10V open. That is off some and I am going to investigate this. Also, as an experiment I unplugged the MAF and ran the car in continuous open loop. It ran fine at all times and temperatures.
Now that being said, this occurs in open loop between 100 and 140 with everything hooked up. What could possibly be operating in open loop at that time but yet when I set a code will not operate because of the code?
I do not suspect any base engine, basic fuel, basic ignition, or other basic systems as a fault because the car runs perfect most of the time and especially in closed loop.
One thought I had is that what if the Secondary Air Pump is running when it should not be, yet with a code it may not operate at all? IDK? Still researching that one. How would I take out the Secondary Air without throwing a code?
Your thoughts, this is an odd one and not something you find everyday. I personally like this kind of stuff and hate it at the same time. This stuff is what separates the men from the boys. Never hurts to get different ideas from others, however, no one can think of everything, hence the post.
Thanks, and bring your brain.