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Jon
Jon, ASE Certified Technician
Category: Chrysler
Satisfied Customers: 310
Experience:  Master Chrysler Jeep Dodge technician
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I have a 2000 Town and Country LXi with 3.8L that died going

Customer Question

I have a 2000 Town and Country LXi with 3.8L that died going down the highway at 65mph. Engine just shut off. No codes stored or pending. Now the van will only start if throttle is about half open and dies immediately if the throttle returns to idle.
Fuel pressure at the rail is 49psi
TPS sensor is 16.5% at idle position and 75.6% at WOT (scan tool)
Coil pack tested a little weak so I replaced it with a used one I had on hand.
IAC was not engaging so I replaced and now seems to function normally.
With the throttle body removed the engine starts fine but idles runs rough. I cleaned the throttle body while it was removed and I was replacing the IAC.
MAP sensor showed a constant 4.6v without any fluctuation so I replaced it. with the throttle body installed and the MAP sensor removed the engine starts but runs rough. if I plug the MAP sensor hole it dies. Replacement MAP sensor also reads constant 4.6v on the signal wire. Supply wire reads constant 5.1 volts and ground wire is good. Just out of curiosity I disconnected the the MAP sensor and checked the voltages. 4.6v on the signal wire. I cut the signal wire at the PCM and checked again still 4.6v coming from the PCM on the signal wire. with the signal wire cut from the PCM and connected to the MAP sensor I get a variable voltage in accordance with the vacuum applied. I have been unable to locate any shorts of that signal wire so I am left with the PCM emitting a constant 4.6v on the MAP sensor signal wire.
At the suggestion of a local Chrysler tech I replaced the PCM with a remanufactured unit. Still getting 4.6v on the MAP signal wire from the replacement PCM but now I also get seemingly random DTC codes: P0108(Signal wire is still cut), P0340, P0118, P0351, and a couple more I don't recall now. I have checked the wiring harness but it looks to be intact and I have not been able to find any shorts. The codes come and go without me resetting them so I am wondering if they might just be the new PCM learning the existing sensors without the vehicle actually running, but the PCM should not be sending a 4.6v signal on the MAP signal wire and yet both PCMs are doing just that... PLEASE HELP!
Submitted: 1 year ago.
Category: Chrysler
Expert:  Jon replied 1 year ago.

Hi, when you unplug the MAP, it should go to 5 volts on your scanner. Then short the signal wire to ground and it should go to 0 volts. Can you try that and let me know what happens?

Customer: replied 1 year ago.
My scan tool does not show volts for the MAP sensor - all scanner readings for MAP are PSI all volt readings are from DMMSignal wire is cut close to the PCM connector so there is no connection to the MAP sensor unless I jump that cut.I also disconnected the Wire harness from the MAP sensor just in case the other connections might skew the results.Key on my scan tools says 15.2psi for the MAP sensor. Voltage reads 4.6v. I did notice that the scan tool reading does drop to 13.2 psi as I test the voltage with the DMM.Shorting the signal wire from the PCM to the Sensor ground from the MAP Connector causes the scan tool to drop to 3.2 psi (Yep distinctly different from the 13.2psi reading while the DMM is attached, I even graphed it to be sure).
Expert:  Jon replied 1 year ago.

Try unplugging the cam sensor, A/C pressure transducer and crank sensor and see if that voltage comes up to 5.00. 4.6 seems low.

Customer: replied 1 year ago.
Those three unplugged, still 4.6v
Battery is 13.4v both at the terminals and PDC to body ground.
Expert:  Jon replied 1 year ago.

Can you ohm the 5 volt supply to ground with everythingdisconnected from it including the pcm?

Customer: replied 1 year ago.
Just to be sure I'm getting what you want:
Disconnect the Terminals from the PCM and check ohms pin 61 to ground?
Expert:  Jon replied 1 year ago.

I'm not in front of a computer right to give you pin #'s now but basically isolate the 5 volt circuit from all the sensors and pcm and ohm it to ground. It doesn't matter which end, the pcm pin or any of the sensors. It should have no continuity to ground. If it does, that would explain the 4.6 volts and not 5. I'm basically going after is the circuit shorted to ground.

Customer: replied 1 year ago.
OK. MAP, TPS, and A/C transducer disconnected.Infinite ohms from PCM pin 61 to negative battery terminal and body ground. Also checked MAP 5v supply to both grounds, same result.
Customer: replied 1 year ago.
MAP 5v supply to MAP ground, same result.
Expert:  Jon replied 1 year ago.

Is there and other program you can get for your scanner that will give you the voltage of all you 5 volt sensors? That will make it a lot easier for me to help you through this.

Customer: replied 1 year ago.
No, it's an inexpensive one I picked up so I could read and clear codes. I don't usually get this deep into automotive electronics...
Expert:  Jon replied 1 year ago.

Ok, I'm going to opt out then. Maybe another expert can help you further.

Customer: replied 1 year ago.
OK, Thanks for the help!
Expert:  Jon replied 1 year ago.

I see nobody jumped on your question. I'll try looking at a wiring diagram tomorrow, if you could possibly borrow a scanner to read the 5v sensors in voltage, it will make it a lot easier. With the unit readings your scanner gives, it's going to be a lot of conversion calculations to make. Voltage readings would simplify that dramatically.

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