QuestionTo Roland Finston
I have a 90 Dodge Caravan It has
3.3 v6 engine AT,PS,PB, not ABs
Fuel Injected 180,000 miles
When I tryed to start the car It would crank over OK but wouldent start When I turned the key to on I couldent hear the fuel pump running.
I sprayed gas in the intake and the engine would start and run for a short time and then stop even while I sprayed gas to try and keep it running.
I think it is fuel pump trouble but
The fuel pump was replaced 2yrs ago around 170,000 miles
I searched your Q& A and located the ASD relay and replaced it but that dident help.
I shorted the contacts on the ASD relay plug, that puts battery to the pump (the ones that are closed then the relay operates) and the car would start and run ok
Next I put at test light on gnd (-bat post) to find the ASD relay plug termenal that had batt+ on it when the key was inthe ON position
With the light between gnd and the term that should have batt on it when I turned the key to ON the light would blink once and go off it would stay on while the engine cranked in start position It seemed like I could hear a faint click when I turned the key to ON
After turning the key to ON and off many times The test light stayed on with the key in the ON sw position IS THIS A CLUE? When I worked for the Phone Co this would be a came clear while testing. Condition
Ok Now I put the test light across the ASD relay plug terminals the Batt one and what I think should be gnd, the only one left not tested And turned the Key to the ON position several times And the test lamp would NOT light No Gnd.
I tryed to trace out the wiring from that terminal to find where the gnd should come from
But after much moving the wires around searching for the wire I never found I turned the key to ON and the light still across the terminals CAME ON
I put the ASD relay back in the plug and Guess what the car started and ran ok
I hope that you can give me a clue to where the problem was
Im afraid to drive the car to far from home. I tryed to give you all the things that I did so you might have a thought to what the cause was or is
Do you have any suggestions ?
Bob / mertym@aol.com
AnswerHi Bob,
Thanks for the very detailed and informative history.
The ASD system works this way:
The switch section has one wire that is hot all the time (red/white). That same wire is attached to the fuel pump relay's switch.
One side of the actuation coil of both relays gets 12V from the ignition switch in both the run and start positions (dark blue wire).
The far end of both relays' actuation coils are actively controlled (float until purposely grounded*) by the dark blue/yellow wire which is actuated (grounded) by the engine controller at pin 51.
When the ASD relay switch closes, the voltage from the bat is applied to the dark green/orange wire which feeds the injectors and the spark coil.
When the fuel pump relay switch closes the voltage from the bat is applied to the fuel pump (dark green/black).
For the pin 51 actuation to occur, the power to the engine controller must come "on" but it will only stay grounded for one second unless the engine is turning over (running or being cranked). Thus the power to the fuel pump and the spark and the injectors will only be connected continuously for the purpose of to start and to run the engine. Otherwise those are shut off for fire safety purposes.
I am not sure in re-reading your history exactly what was wrong in the scenario. *The only uncertainty that I have about my above circuit analysis is whether the pin 51 relay control wire floats at all times when it is not being activated by the controller or maybe it has 12V on it when it is "at rest" but either way it will only actuate the relays when the ignition switch is in the run or crank position (12V on one end of the coil) and then it is grounded (on the other end of the coil) actively by the controller. That issue might explain the anomalous results that you got. That still doesn't explain why you had the 'no start' situation, I am sorry to say. Maybe you will have to wait until it occurs again (hopefully it won't).
Let me know if something is unclear.
Roland
