QuestionQUESTION: I have a 1996 Dodge Caravan with the 3.0L V6 and currently the engine will turn over but it will not start. I left it alone for a week and a half and then yesterday, I managed to get the car to start by replacing the PCV valve as well as the fuel pump relay. After replacing the PCV valve and the fuel pump relay, it started without any hesitation and I drove it problem free for 20 minutes. While driving the car I noticed no missfiring or lack of power at anything from idle to highways speeds. Believing I had solved the problem, I parked it overnight. Today I went to run an errand and now it will turn over but not start, again.
I have run out of ideas. The car had no reliability problem prior to not starting the first time, and then once again it ran problem free for twenty minutes, so I’m assuming that since mechanically everything is working, this must be an electrical problem related to starting the vehicle.
I have pulled the error codes using the ignition on-off-on-off technique, and I got 12-24-55. Now I know that code "12" means that the battery has recently been disconnected, code "24" is the throttle position sensor is receiving over 4.96V, and that code "55" is the end of the codes. I disconnected my battery, disconnected and reconnected the TPS and battery, and still nothing. The car will turn over but it will not start. There is just the sound of the engine turning over. I am out of ideas as to why my van refuses to start.
Any assistance would be greatly appreciated.
Thank you,
Scott
ANSWER: Hi Scott,
An inaccurate reading of the throttle position sensor could well result in an incorrect mixture for starting. When the throttle is closed the signal voltage should be a fraction of a volt, and when fully open a bit less than 4.5 volts. The maximum is 5 volts which is the supply voltage to the 'voltage divider' which is the basic idea of the sensor. The possible causes are an 'open' in the sensor signal wire, the sensor is bad, or the ground wire is 'open'.
You could check the wires on the plug connections to the pins of powertrain controller plug for continuity (the orange/dark blue center signal wire goes to pin 22, the black/light blue ground goes to powertrain controller pin 4, and the 5 volt violet/white wire goes to pin 6 of the powertrain controller plug. Then you could measure the resistance between the center pin of the sensor itself and both side pins. As you move the throttle the resistance should vary smoothly across the entire range of motion. Check to both sides from the center pin, the resistance readings should be inverted in the two tests. Also, check that with the plugs removed at both ends that the 3 wires are not connected to each other (infinite resistance).
That should sort out whether you have a sensor or a wiring harness problem. I would visually check the harness wire as far as you can do so as it could be that heat from the exhaust system over time has melted the insulation. If the voltage is falsely high when starting, then you will have too rich a mixture to sustain an idle.
So give that a try and let me know what you learn.
Roland
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QUESTION: Roland,
I did a visual inspection of the wiring harness and there was no damage or breaks in the wiring insulation. I do not own a voltmeter, so I cannot test the wires.
When the car was running, there we're no hesitations or stumbles during acceleration. Also, when the car cranks over, the engine is not receiving fuel (it isn't running lean or rich on idle). I also tried disconnecting and reconnecting the MAP sensor.
What other sensor could be telling the computer to kill the spark and/or fuel to the engine? Because I believe that this is my problem.
Sorry for not being able to test the wiring.
Thank you,
Scott
ANSWER: Hi Scott,
Alright, so is there or isn't there a sound of the fuel pump humming for about a second when you first turn the key to the "run" position, before trying the starter (there is supposed to be such a short hum sound)? And there is no spark when you are cranking it?
Please verify both those or tell me otherwise. If you have no spark AND no fuel pump when you are cranking it, then that would be consistent with a faulty senosor(s) in the distributor but then you would also have a code 11 or code 54. Maybe check the codes again to verify what is current. However, it also could be that fuse #12 in the power distribution box under the hood is blown if you don't have the 1 second fuel pump hum, so check that one.
I will await to hear back from you.
Use the 'thank/rate' tab to get back to me as I will not be available again until tomorrow morning. If this is useful information, please consider a nomination for 'expert of the month'.
Roland
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QUESTION: Roland,
The fuel pump hums when the ignition is switched into the run position, and the fuse is still good. When I went to crank the engine to test for spark this time by disconnecting one of the spark plug wires, it started. It ran a little rough after startup for two or three seconds (probably because I was holding one of the spark plug wires). But after reconnecting the spark plug wire and starting it up again, it idles perfectly. I moved it off the street and into a friend's garage, and I will try and start it again in the morning.
Also, it is still reading codes 12-24-55. So it is still saying that my TPS sensor is at fault.
So is this simply a "gremlin" or does any of this help diagnose a problem?
Thank you,
Scott
AnswerHi Scott,
As you know if you disconnect the battery you will erase the 24 code, but the 12 code will remain. You could try that one more time and if it does come back, then you are going to have to check the wires and the sensor as described earlier. There is no reason to suspect any other sensor if you still have the 24. I believe I have gone over all the possibilities except the egr valve which might be sticking ajar, so check that out. Move the valve stem back and forth by means of a screwdriver inserted into the slot in the valve stem, and verify that the spring-action closes the valve to a dead stop. If not, try lubricating the stem where it enters the valve body with some WD-40.
Roland
PS Use the 'thank/rate' tab to get back to me if I am unavailable to take a question. Again, I would appreciate your giving me a nomination as 'expert of the month' if I have been helpful. Thanks
