QuestionQUESTION: Roland,
My 1992 LeBaron (2.5L non-turbo, 4-door sedan) turns over but refuses to start. Bear with me... This will be a long description. I've done a lot of diagnostic work.
History:
In a two-week period this happened about four times in varying weather conditions: I'd be driving, usually at low speed or even idle, and the car simply shut off. As far as I could tell, everything still had power (engine would turn over but no start), but I'd have to let the car sit for 5 minutes before it would start again; it would then run fine for several days. The last time this happened, I had just started the car, put it in reverse, and begun to leave a parking spot when the car shut off again. This time, the car did and still does refuse to start. So I put on my amateur mechanic hat and went to work.
Condition of car:
Battery is a few months old and seems to work fine with little parasitic current draw. Distributor cap, rotor, spark plugs and wires were replaced a year ago as part of a tune-up. Connections between coil, distributor and plugs are well-protected. Car attempts to start (chugga chugga chugga) but never catches. All cabin electronics (lights, radio, etc.) work fine.
Diagnostics already done:
Codes set are 12 (battery disconnect) and 21 (O2 sensor error). The 21 has been a recurring code for the past several years. These don't seem relevant. However, a screwdriver test revealed no spark and the fuel pump cannot be heard coming on when the key is turned to the ON position. I disconnected the fuel pump connector from the pump and it does NOT get 12V for any length of time when the key is turned to the ON position; the same goes for the ignition coil. I tested each relay near the driver-side strut tower (powered them up with 12V and tested continuity across other 2 pins) and all work well. Fusible links near that strut tower appear to be fine with a tug-test. I believe I was able to run the fuel pump when I simulated an "ON" condition on one of the relays by shorting two of the connector's pins, but like I said before, the relay itself operated fine. Another interesting thing I noticed was that with the car powered off, both pins on the power connector to the ignition coil measure 0V relative to car ground; then, when I simulated an ASD relay "ON" condition using a jumper wire, BOTH those pins float up to +12V relative to car ground. This seems like some kind of grounding issue.
The important things:
No spark, no fuel pump action.
No +12V to fuel pump or ignition coil when there's supposed to be.
Relays on strut tower all work OK.
I'm confounded at this point. Do you have any idea what I should do from here? Money is a serious constraint; I'm a poor college (electrical engineering, if you couldn't already tell) student.
Thanks for your help!
-Bill
ANSWER: Hi Bill,
The start and die scenario is often attributible to a failing engine rotation sensor, in this case the Hall effect unit in the distributor. But with no sound of the fuel pump and no 12v to the coil, expecting both for a couple of seconds when you first turn the key to 'run', suggests that either the ASD coil is not getting power from the ignition switch on a dark blue wire, or it is not being activated, or it lacks a current supply to it points. So begin by checking at fuse 6,7 or 8 which also are connected to that dark blue wire and see if you have 12v or not in the run position. The source of the asd output current, if its points close, comes to it on a red/white wire directly from the battery via a white fusible link. So check that wire on the ASD relay plug which is the front-most relay on the inner fender. Let me know if both of those are OK. The next possibility would be that the smec is not being powered so as to activate the relay coil.
Roland
PS Please 'rate' my answer. Where you see the question about 'volunteer of the month' I would appreciate your consideration of answering 'yes'.
---------- FOLLOW-UP ----------
QUESTION: Roland,
I appreciate the quick reply and apologize that I couldn't get back to you until now. According to my multimeter, fuses 6 through 8 are all +12V while the key is in "run". I noted that fuses 1, 3, 4, and 5 are 0V, which may be normal. Also, the red/white wire on the ASD relay plug has continuity to the positive battery terminal.
One weird thing happened during testing, however. The first two times I turned the key to the "run" position, but none of the times thereafter, the fuel pump could be heard coming on. I turned the key another 4 or 5 times, but couldn't hear the pump come on any of those times. The car would still not start even after hearing the fuel pump turn on.
Odd.
Anyway, what should be my next move?
Thanks again for your help.
-Bill
ANSWER: Hi Bill,
The 'cold' fuses are OK, so don't worry about that.
The intermittency of the fuel pump response is the first thing to straighten out, as without it there is no chance of starting. I would suggest that you check the various wires of the fuel pump relay when you turn the key to run:
the dark green/black wire should show 12V for a couple of seconds. If it does, but the fuel pump doesn't run then the wire to the pump or the pump itself is flaky. If it doesn't, then verify that the dark blue wire is getting 12v with the key in the run position (just like that same wire at the ASD relay) and also verify that the red/white wire at that relay has 12V always.
If that checks out, then watch the voltage on the dark blue/yellow wire: it should be grounded (0v) when you turn the key to run but it should show 12v after a couple of seconds (when the fuel pump cuts out) OR if it shows 12v all the time from the moment you turn the key to run and stays that way, then there is a problem with the PCM or the same color wire to pin 51 of the pcm is flaky in its connection. If it is showing the voltage change I expected, then the relay should click softly and 12v should appear reliably on the dark green/black wire. If it doesn't, even though the relay clicks, then the internal points of the relay are oxidized such as to not reliably forward current for tne red/white wire to the dark green/black wire of the relay.
While there are thus several reasons for why you aren't getting reliable fuel pump action, the above set of tests should sort it out.
For the no spark, the ASD relay itself has exactly the same set of wires (except the output wire is dark green/orange instead of dark green/black) and so it should behave exactly identically as described above for the fuel pump relay. The dark green/orange wire goes to the spark coil.
So go through these measurements and tell me the results and we'll go from there.
It may be, if both the fuel pump and spark coil voltage are similarly flaky, that you have defective PCM. It has to ground the dark blue/yellow for a couple of seconds when you turn the key to run, and again when you start cranking it over it has to ground that wire until you stop cranking it. Otherwise you will not get fuel pump or spark action.
Roland
PS Thanks for rating my answer and for the nomination.
---------- FOLLOW-UP ----------
QUESTION: Roland,
You certainly deserve the nomination. I did some probing according to your advice; however, I understand that you can't let one person take up all your time, so feel free to answer some others' questions before you get back to me. I'd just like to post the follow-up while the information is still fresh in my mind.
-I looked for 2 seconds of +12V on the Dark Green/Black (Fuel Pump Relay) and Dark Green/Orange (ASD Relay) after the key was turned to "on". These wires never deviated from 0V.
-The Dark Blue and Red/White wires on both the Fuel Pump and ASD Relays read +12V properly.
-The Dark Blue/Yellow wires on both relays did NOT drop to 0V for 2 seconds when the key was turned to "on". These stayed at a constant +12V.
-As an extra test, I grounded (via battery terminal) the Dark Green/Black wire on the Fuel Pump Relay. This caused the ASD relay to click on. Grounding the Dark Green/Orange wire on the ASD relay caused the Fuel Pump Relay to turn on and the fuel pump itself could be heard running in the tank.
Like I said, I don't expect an immediate response since there are likely others who need advice.
Thanks again! Let me know what my next move should be.
Bill
AnswerHi Bill,
I am a bit confused because the dark green/orange and dark green/black wires need +12V (not 'grounding') to fire up the spark coil and fuel pump respectively, and in any case doing anything to the ASD dark green/orange wire will not cause the fuel pump to run. Did you perhaps mean that you grounded the dark blue/yellow wires at both relays that caused the fuel pump to run?
If so, then for some reason the PCM is not grounding that wire for a couple of seconds, reliably, although you said that earlier you did hear the fuel pump run momentarily so it must be an intermittent non-function. Why, I am not sure.
That dark blue/yellow wire comes from pin 51 of the PCM plug, so I would try verifying the continuity of that wire. Also, pull the ASD relay and the fuel pump relay, and take a look at the voltage on the dark blue/yellow wire at the relay sockets when you turn the key to run and what happens after 2 seconds at the same points. The problem is basically that the PCM is not controlling those 2 relays as it should.
Check that pin 9 of the PCM shows 12V when you turn the key to run just to be sure that it is getting current to operate the PCM. That wire is the same one that supplies the two relays and is dark blue in color.
Roland
Thanks for the rating and nomination, and the kind remarks.
