Salguod
06-27-2005, 02:34 AM
I own 1991 #553 Turquise/Blk. It's been a great car. My dream machine. My home club is Circle City Corvette Club here in Indianapolis
Recently I was troubleshooting what is appearing to be a shorting secondary injector. If my logic was correct (since the computer fires primary and secondary pairs in parallel and the secondary injectors only have +12 volts supplied when secondaries are opened) the faulty secondary injector was almost to a short circuit and this prevented the same cylinder primary injector from operating (the driver transistor in the ECM probably current limits to protect itself). Hence, when engine was hot and the faulty injector shorted, I would feel a miss if on the secondaries. If not on the secondaries the primary injector was operated OK and the engine was smooth.
This miss seemed to happen at low RPM's and throttle so to check what was happening I set up LED's with series resistors and connected them across the secondary injector relay drive signal (from ECM computer - pulled to ground to activate) and the secondary vacuum valve soleniod signal (also from ECM and pulled to groud). I positioned these to watch while driving.
These signals both were working (sec. ports opened 1/2 sec before sec. injectors to compensate for mechanical delay) but to my surprise the secondaries come on at the slightest touch of throttle at as low as 800 RPM. The secondaries come in on any acceleration attempt other then dead slow. They don't come in at all if the key is off or the engine is very cold as I would expect. I know my secondaries work because with the key on it pulls much harder and all the way to 7200.
So my question to anyone that has some experience here is why might this be? It is contrary to all I've heard and read in many places. I think my car is stock but could it have been re-prommed to do this? Has anybody heard of this being done.
Oh - and when the injectors are all injecting as they should the car runs great - smooth, fast - no drivability issues at all. Low power mode runs perfect as well - just not as much pull as RPM's climb.
Any thoughts out there? Thanks in advance for any responses.
Added note - with the engine hot (after I got the miss) I checked all the injector resistances through the wiring from the ECM connectors and the secondary injector relays. Injectors are supposed to be about 13.4 ohms. I have 3 primaries and 1 secondary at around 9.5 to 11 ohms and one secondary at 1 ohm. That would mean about 12 amps to pull that one. I'll bet they read better when cold. Next stop - gaskets and a source for injectors.
Save the wave,
Doug Gifford
Recently I was troubleshooting what is appearing to be a shorting secondary injector. If my logic was correct (since the computer fires primary and secondary pairs in parallel and the secondary injectors only have +12 volts supplied when secondaries are opened) the faulty secondary injector was almost to a short circuit and this prevented the same cylinder primary injector from operating (the driver transistor in the ECM probably current limits to protect itself). Hence, when engine was hot and the faulty injector shorted, I would feel a miss if on the secondaries. If not on the secondaries the primary injector was operated OK and the engine was smooth.
This miss seemed to happen at low RPM's and throttle so to check what was happening I set up LED's with series resistors and connected them across the secondary injector relay drive signal (from ECM computer - pulled to ground to activate) and the secondary vacuum valve soleniod signal (also from ECM and pulled to groud). I positioned these to watch while driving.
These signals both were working (sec. ports opened 1/2 sec before sec. injectors to compensate for mechanical delay) but to my surprise the secondaries come on at the slightest touch of throttle at as low as 800 RPM. The secondaries come in on any acceleration attempt other then dead slow. They don't come in at all if the key is off or the engine is very cold as I would expect. I know my secondaries work because with the key on it pulls much harder and all the way to 7200.
So my question to anyone that has some experience here is why might this be? It is contrary to all I've heard and read in many places. I think my car is stock but could it have been re-prommed to do this? Has anybody heard of this being done.
Oh - and when the injectors are all injecting as they should the car runs great - smooth, fast - no drivability issues at all. Low power mode runs perfect as well - just not as much pull as RPM's climb.
Any thoughts out there? Thanks in advance for any responses.
Added note - with the engine hot (after I got the miss) I checked all the injector resistances through the wiring from the ECM connectors and the secondary injector relays. Injectors are supposed to be about 13.4 ohms. I have 3 primaries and 1 secondary at around 9.5 to 11 ohms and one secondary at 1 ohm. That would mean about 12 amps to pull that one. I'll bet they read better when cold. Next stop - gaskets and a source for injectors.
Save the wave,
Doug Gifford