Doctorbatman
Member
Hi All,
1986 Base Corvette, start it, let it idle or drive it, around 20-30 minutes it shuts down. Attempted restart and at time idles another 5-10 minutes then shuts itself down or won't restart. When attempt restart will only start if slightly open throttle, won't idle but can force a high idle around 1200 RPM. Won't rev higher, just bogs and dies unless let up of throttle slightly. Backfires through the intake like it's lean.
Let it sit a few hours, will repeat same action. Acted this way since I got the car 1.5 years ago. So far I've only driven it 20 minutes at a time. When I test drove the car before purchase I did not drive it 20 minutes so was not aware of the issue when I did buy it.
Replaced fuel pump, fuel filter, checked supply and return fuel lines are clear, replaced fuel pressure regulator with adjustable cover and set pressure to 42 psi at idle, removed and cleaned fuel rail, replaced all injectors, tested all injectors are flashing with test light before and after car dies after 20 minutes.
Replaced Mas Airflow sensor twice, replaced MAS Power and Burn off relays, replaced bad rear cooling fan motor, replaced fan relay, replaced, Idle Air Control Valve, all engine temp sensors, throttle position sensor (set. to .52 volts at idle), replaced entire distributor assembly, replaced ECM. Replaced with quality spark plug wires and AC Delco spark plugs.
Tested voltage drop for all ground wires from ECM - all in spec. Removed, cleaned and re-secured all body ground straps with dielectric grease.
Engine timing set to 6 degrees BTDC when disconnected to computer, when computer is reconnected, timing averages 24 degrees BTDC and goes to about 32 degrees BTDC when revving engine. Tested and dielectric greased all fuses in panel.
Tried powering distributor and fuel pump directly from battery bypassing wire harness and engine still dies at 20 minutes.
I can only suspect a problem somewhere in the car's wiring harness since I've replaced all 4 temperature sensors, TPS, Mass Airflow Sensor and O2 sensor as well as new ECM and I borrowed another ECM with PROM from another 1986 Corvette and tried running it. (As well as all the other stuff I've mentioned.)
I connected a second battery in case of too much battery drain when the cooling fan kicks on but no help.
Since the ECM takes in sensory data, makes the decision on how much fuel to use and when to spark, and I've replaced every sensor and connecting pigtail, I can't imaging where the confusion is coming from except from the wiring harness somewhere in the car.
Any other thoughts?
At this point I've had 7 mechanics (only lousy ones since a good mechanic might take all this fun out of it - just kidding of course) evaluate the car with the only remaining suggestion to remove fuel injection system and distributor and replace with carb and standard HEI vacuum advance distributor. In the absence of any new diagnostic info, that's what I'll be doing next week.
So far I've not found any solutions from searching on-line.
Any last ditch recommendations would be greatly appreciated,
Thank you all,
Doc
1986 Base Corvette, start it, let it idle or drive it, around 20-30 minutes it shuts down. Attempted restart and at time idles another 5-10 minutes then shuts itself down or won't restart. When attempt restart will only start if slightly open throttle, won't idle but can force a high idle around 1200 RPM. Won't rev higher, just bogs and dies unless let up of throttle slightly. Backfires through the intake like it's lean.
Let it sit a few hours, will repeat same action. Acted this way since I got the car 1.5 years ago. So far I've only driven it 20 minutes at a time. When I test drove the car before purchase I did not drive it 20 minutes so was not aware of the issue when I did buy it.
Replaced fuel pump, fuel filter, checked supply and return fuel lines are clear, replaced fuel pressure regulator with adjustable cover and set pressure to 42 psi at idle, removed and cleaned fuel rail, replaced all injectors, tested all injectors are flashing with test light before and after car dies after 20 minutes.
Replaced Mas Airflow sensor twice, replaced MAS Power and Burn off relays, replaced bad rear cooling fan motor, replaced fan relay, replaced, Idle Air Control Valve, all engine temp sensors, throttle position sensor (set. to .52 volts at idle), replaced entire distributor assembly, replaced ECM. Replaced with quality spark plug wires and AC Delco spark plugs.
Tested voltage drop for all ground wires from ECM - all in spec. Removed, cleaned and re-secured all body ground straps with dielectric grease.
Engine timing set to 6 degrees BTDC when disconnected to computer, when computer is reconnected, timing averages 24 degrees BTDC and goes to about 32 degrees BTDC when revving engine. Tested and dielectric greased all fuses in panel.
Tried powering distributor and fuel pump directly from battery bypassing wire harness and engine still dies at 20 minutes.
I can only suspect a problem somewhere in the car's wiring harness since I've replaced all 4 temperature sensors, TPS, Mass Airflow Sensor and O2 sensor as well as new ECM and I borrowed another ECM with PROM from another 1986 Corvette and tried running it. (As well as all the other stuff I've mentioned.)
I connected a second battery in case of too much battery drain when the cooling fan kicks on but no help.
Since the ECM takes in sensory data, makes the decision on how much fuel to use and when to spark, and I've replaced every sensor and connecting pigtail, I can't imaging where the confusion is coming from except from the wiring harness somewhere in the car.
Any other thoughts?
At this point I've had 7 mechanics (only lousy ones since a good mechanic might take all this fun out of it - just kidding of course) evaluate the car with the only remaining suggestion to remove fuel injection system and distributor and replace with carb and standard HEI vacuum advance distributor. In the absence of any new diagnostic info, that's what I'll be doing next week.
So far I've not found any solutions from searching on-line.
Any last ditch recommendations would be greatly appreciated,
Thank you all,
Doc