Hi all
Still having grief with my 75 v12
Every video i have watched or book read shows bosch Lucas temp sensor starting out receiving 5v from ecu
Two different 3cu computers are sending closer to battery voltage. 10volts to be precise.
My engine dies after perfect start within three to four minutes and the sensor is using 3.5 volts at death Engine will not restart til cold.
Does the djetronic system send battery voltage to sensor by design or is something else going on?
I had previously tested resistance and all is well with both water and air at sensor and ecu
You should not check Voltage, you should check Resistance.
Short the contacts at the sensor plug (engine infinitely warm) and see if it makes a difference.
Thanks
My resistance values have been within spec. I will try the short test and see if engine starts. I will recheck ohms as well.
My thinking was if sensor input voltage was either too high or too low the computer would correspondingly be creating an incorrect injector opening time (regardless of the resistance to the incorrect voltage). Garbage in garbage out.(?) This condition would be true(I think) with a more modern engine management system but perhaps not to djetronic.
If the car refuses to start in an “infinitely warm” state
what would that indicate to you?
Aristides,
My resistance readings with the sensor disconnected at 8C is 4.15k ohms. This reading is the same at the ecu pins disconnected from the ecu. Wiring is good.
Engine started instantly, Idled perfectly. After 20 seconds I shut off engine and shorted the sensor. No start. Reconnected sensor and after 5-10 seconds of clearing out excess fuel it restarted. It idled well (700rpm)until temp gauge began to climb. Just before gauge hit the C mark with engine beginning to stumble and heater hose warm bur radiator hoses still cold I disconnected sensor and checked the sensor resistance. It was 500ohms. I then shorted the sensor again and another no start was experienced.
It seems to me that as the engine warms it is going to a way rich state.
Vacuum leak you say?
I have disconnected and plugged every hose that could suck air. I have checked for leaks with a smoke detector. I cannot find one.
The car has recently, between similar failures, gone 100mph and burned off tire rubber from a dead stop. This leads me back to fuel management as opposed to ignition, compression or ?
If map sensor is bad would it start?
I could have a vacuum leak. I could have lots of things.
But why does it start and idle perfectly for 2-3 minutes and then die?
I am beginning to lose hope that I can fix this without chasing the very expensive and wildly hopeful part replacement model.
Does the 75 have the GM Ignition Amplifier?
Maybe the CTS has a dead zone?
Fuel pump getting tired?
ECU cold joints?
Fuel filter/screens/sump tank getting clogged with debris after a while?
Fuel pump new
It’s a coupe so no sump tank
Just saw video pointing out inaccuracies in fuel pressure gauges these days so might try to make sure I have true 30 psi in rail with another gauge.
Currently bypassing fuel return line with tube from cooler so no back pressure and pump runs till engine dies.
Regarding ignition
It’s stock first generation. Not ib14.Still Reed switch in dizzy.
I haven’t gone down this route because failure is so consistent timewise. Plus it starts every time like clockwork.
Having said that if after confirming fuel pressure and possibly temporarily replacing coolant temp sensor with a newer Bosch close cousin(to see if any difference obtained) I guess ignition could be the issue.
Did the short test tell you anything?
Regarding the tps. Moving it does not change failure duration. Engine still running out of or receiving too much fuel as it warms up.
Unless ignition amp is failing really fast. Still have spark after it dies.
Thanks
If you still have good spark but engine does not catch it’s fuel related.
Do the injectors click while you are trying to start?