To the Forum. I am at my wits end and asking for help.
I have a 1971 Cutlass Convertible with a 1995 LT1 swap I did about 4 years ago.
At the end of last summer something broke and has been causing a light throttle hesitation and when the car warms up you can feel a miss at a stop light some of the time.
The car runs fine at 75% to full throttle. This is a partial throttle issue and it happens all the time. It is not an intermittent issue.
There are not computer codes and I have replaced about everything I can find on the forums that have similar issues. I have even spent some money with a local expert who works on corvettes and had a mechanic in the shop that specializes in the LT1's.
Here is what I have changed with no change in issue. Most parts have been OEM except for the Wires, Mass Air, Intake air temp and Coolant temp sensors.
Wires, Optispark(2 of them, One AC Delco the other not), Spark Plugs, Coolant Sensor, Intake Air Sensor, MAP sensor, Throttle Position Sensor, O2 sensors, Mass Air Flow sensor, fuel filter, O rings on injectors and timing chain(it was pretty stretched out), trans fluid change but only what I could get out of the pan changing the filter.
Fuel Pressure is at spec at idle and when driving (taped fuel gauge to window while driving)
Took the fuel rail out and developed an injector cleaning system with some vacuum line and a can of injector cleaner. Pulsed each injector with a battery to verify spray pattern and leakage. Spray patterns looked good.
Changed the Intake Gasket
Changed every vacuum hose.
Cleaned throttle body and put new gaskets on.
Changed PCV
Have sprayed numerous times with carb cleaner looking for a vacuum leak with no luck. The corvette mechanic couldn't find any vacuum leaks either.
Took all grounds off and cleaned.
The wiring harness is aftermarket purpose built for resto mods and the 4L60 trans is part of the harness and used in the car. I have started to pin out the computer connectors to the sensors. I have pinned each injector, the Opti, Map, Mass Air Flow and O2's so far. No weird resistance from corrosion.
The car has no pollution control items such as EGR or Air injection, the car also has no Cats. Not required until 1972.
Exhaust is dual 2.5" with Dynomax mufflers, these are new as well in case the others were clogged.
The only issue I can see in the computer is the BLM is high. Runs in the 140's which from what I can read indicates the computer thinks the car is running lean. However, until this issue I never paid attention if this was part of the tune.
Any help or advice is greatly appreciated. I have a few free trials left on datamaster so if someone knows how to read these things I can take a run with it recording. I'm also willing to pay someone for time to help diagnose this issue so if anyone knows of an LT1 expert in the central New Jersey area please let me know. If not in New Jersey Skype works for me as well.
Warmest Regards,
1971 Olds.
I have a 1971 Cutlass Convertible with a 1995 LT1 swap I did about 4 years ago.
At the end of last summer something broke and has been causing a light throttle hesitation and when the car warms up you can feel a miss at a stop light some of the time.
The car runs fine at 75% to full throttle. This is a partial throttle issue and it happens all the time. It is not an intermittent issue.
There are not computer codes and I have replaced about everything I can find on the forums that have similar issues. I have even spent some money with a local expert who works on corvettes and had a mechanic in the shop that specializes in the LT1's.
Here is what I have changed with no change in issue. Most parts have been OEM except for the Wires, Mass Air, Intake air temp and Coolant temp sensors.
Wires, Optispark(2 of them, One AC Delco the other not), Spark Plugs, Coolant Sensor, Intake Air Sensor, MAP sensor, Throttle Position Sensor, O2 sensors, Mass Air Flow sensor, fuel filter, O rings on injectors and timing chain(it was pretty stretched out), trans fluid change but only what I could get out of the pan changing the filter.
Fuel Pressure is at spec at idle and when driving (taped fuel gauge to window while driving)
Took the fuel rail out and developed an injector cleaning system with some vacuum line and a can of injector cleaner. Pulsed each injector with a battery to verify spray pattern and leakage. Spray patterns looked good.
Changed the Intake Gasket
Changed every vacuum hose.
Cleaned throttle body and put new gaskets on.
Changed PCV
Have sprayed numerous times with carb cleaner looking for a vacuum leak with no luck. The corvette mechanic couldn't find any vacuum leaks either.
Took all grounds off and cleaned.
The wiring harness is aftermarket purpose built for resto mods and the 4L60 trans is part of the harness and used in the car. I have started to pin out the computer connectors to the sensors. I have pinned each injector, the Opti, Map, Mass Air Flow and O2's so far. No weird resistance from corrosion.
The car has no pollution control items such as EGR or Air injection, the car also has no Cats. Not required until 1972.
Exhaust is dual 2.5" with Dynomax mufflers, these are new as well in case the others were clogged.
The only issue I can see in the computer is the BLM is high. Runs in the 140's which from what I can read indicates the computer thinks the car is running lean. However, until this issue I never paid attention if this was part of the tune.
Any help or advice is greatly appreciated. I have a few free trials left on datamaster so if someone knows how to read these things I can take a run with it recording. I'm also willing to pay someone for time to help diagnose this issue so if anyone knows of an LT1 expert in the central New Jersey area please let me know. If not in New Jersey Skype works for me as well.
Warmest Regards,
1971 Olds.