QuestionQUESTION: Roland -
This is a continuation of the thread:
en.allexperts.com/q/Chrysler-Repair-807/2010/4/92-2-5L-4cyl-2.htm
I ran out of follow-up questions so I've started a new question thread. Here's the situation after your last answer on the old thread:
I made a mistake in saying that the DkGrn/Orange wire on the ASD relay plug turned the fuel pump on when connected to chassis ground. The fuel pump does seem to run when I manually "simulate" the fuel pump relay being ON using a jumper wire, which just means that the pump itself works.
I verified continuity of the dark blue/yellow wire from the PCM plug to the relays. No issues there. However, I've started to notice a pattern. If the car is left to sit for around 10 minutes, turning the key to the "ON" position causes that wire to go 0V for a second and the fuel pump can be heard. This seems like normal operation to me. However, the car still refuses to start, and if the key is turned to "ON" (or RUN, if you prefer) soon after, no response can be seen as far as changing voltage on any wire or sound from the fuel pump. No response when cranking, either. It's as if the first attempt at turning on and starting the car triggers a 10-minute timeout where nothing works.
I managed to snag another PCM from a wrecked car at a junk yard. I swapped it for mine, but the same exact behavior results. The only code present is a 12, which is irrelevant.
Pin 9 on the PCM plug DOES show +12V when the key is in RUN.
One more observation I made today is that the 12V power wires to the ignition coil never get any voltage across them, even when cranking and even when I simulate the ASD relay being closed (on) with a jumper wire from the red/white to the dark green/orange wires (well, their places in the relay plug). Is there a fusible link I should check between the ASD relay and the coil?
This problem is very confusing and I feel I'm at the point where all I can do is start replacing random parts like the Hall effect unit, MAP sensor, etc.
What are your thoughts?
ANSWER: Hi Bill,
At the "one more observation" paragraph you said "... that the 12V power wires to the ignition coil never get any voltage across them, even when cranking and even when I simulate the ASD relay being closed (on) with a jumper wire from the red/white to the dark green/orange wires (well, their places in the relay plug)." I am not certain what you mean by "12V power wires to the ignition coil" but if you are putting your voltmeter across the + and - terminals of the spark coil you won't ever see voltage unless the black/gray wire on the - post is grounded (which the pcm will do pulsingly if the engine were being cranked or were running normally, but your meter will not likely notice the pulsing to ground because it happens too quickly. The measurement of interest is the voltage between the dark green/orange at the + post of the coil and chassis ground (or battery - post, or pcm 'signal ground'). That is the 12V measurement that should be 'seen' when the ASD closes. So try that and see if when you crank it you get 0V, 12v for 1-2 seconds, or 12V for as long as you crank it. And then try the same thing a minute later. And then try it again 10 minutes later. I can't think of any obvious reason for the 10 minute fuel pump time out observation, so I would like you to verify whether that same behavior is mimic'd by the actual voltage output of the ASD or not. Let me know and we'll go on from there.
Roland
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QUESTION: Roland -
You were correct in guessing that used a multimeter to try and measure voltage across the "low-tension" (my own term) terminals of the coil. I'm not sure why I expected to see a DC voltage across these.
Anyway, I probed the dark green/orange wire relative to chassis ground. The voltage remained at 0 at all times, although the multimeter did respond with a ~ 50mV perturbation during cranking.
-Bill
ANSWER: Hi Bill,
The coil dark green/orange should show 12v for a second when you turn the key to run, just like the fuel pump humm, then show it again when cranking it. If you can't get either of those responses at all times then either the red/white power wire to the fuel pump and asd relays is flakey (check that, it comes from a fusible link directly connected to the battery), or if you just don't get 12v while you are cranking it, then I suspect that the hall effect sensor in the distributor has gone bad so the pcm thinks the engine isn't turning over and so it opens the ASD and fuel pump relays for reasons of safety against a fire. The dark blue/yellow you have found to be reliable at the relays so that has to be ok. You might also try switching the relays, just in case one of them is flakey.
Roland
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QUESTION: Roland -
I appreciate you sticking with me through this.
The red/white wire to the fuel pump and ASD relays is OK. Just double-checked and it has 12V whenever the car is in RUN.
Since I don't have an oscilloscope, all I could do for the Hall effect sensor in the distributor was to inspect it visually and measure the DC voltage relative to ground on all three of its wires. It looks clean and dandy. The orange wire showed +9V at all times, including when cranking, and the other two wires showed something negligible like 20 mV.
Should I try replacing the Hall effect sensor? I tried to start the car a few times and then checked the fault codes immediately. Still only getting a 12.
Thanks for your patience.
-Bill
AnswerHi Blll,
About what to expect from the hall effect sensor, in this case the black/light blue wire is a common sensor ground wire (a 'clean' ground without other electronic noise that would be present in the overall electrical system of the vehicle) and the gray/black is the sensor signal wire. So put your two leads across those two wires, turn the ignition switch to run position, but instead of cranking turn the engine over by hand with a ratchet on the crank shaft pulley bolt. That way you should see pulsing voltage that varies between 5V and 0.3V as you turn the crankshaft (I believe twice per revolution). If that is present and you do the measurement at pin 4 and 24 of the pcm (SBEC) by means of pins thru the wire insulation, then I would believe that the hall effect sensor is working.* If that pulsing is not present, then you would expect an 11 code, and as the result you would also expect to not see the 12V on the dark green/orange wire at the coil 'hold' when cranking it over. So let me know what you observe.
Roland
* You could just as well check for voltage pulsing at the harness wires right at the distributor, but then do verify that the wires are actually connected to pins 4 and 24 of the SBEC plug by measureing for 0 ohms between the pins at either end of the wire, just to be certain that the signal will get through to the SBEC.
