QuestionQUESTION: I have a 1998 Chrysler Town & Country LX with 3.8L engine with 110,000 miles that we purchase new. It is having stalling and rough idling problems. The problem started about a month ago. When I would start the car with a cold engine it would take about 3 times starting it before the stalling would end and it would idle fine. With the key in the run position the fuel pump would buzz for a second or two and buzz for short bursts every few seconds with the CEL and the cruise control light on the instrument panel blinking. As time went on it would run rough and stall at any time. The tachometer and speedometer would act erratically or would drop all the way down. I would put it in neutral and it would start right back up by turning the key back on. The rough idling and stalling was mostly when I would take my foot off the gas pedal or make a turn on to another street. The CEL would come on but there were no fault codes found with a scan tool.
I have the Chilton repair manual for 1996 thru 2002 Chrysler T&C van. I also have the power distribution and engine controls diagrams for this van.
The fuel filter, PCV valve, and the ignition switch were replaced by my mechanic.
I did voltage drop test with a digital multimeter by back probing with t-pins on pin# 10 and pin# 50 of the PCM connector with each showing .01 volts. Pin# 46 (fused B+) showed 0 volts. Pin# 44 (8 volt supply) showed -12.68 volts and pin# 61 (5 volt supply) showed -7.2 volts. The 8 volt and 5 volt supply readings look suspect. I removed the connector for the camshaft position sensor and checked 8 volt supply (org) to ground (blk/ltblu) and got 8.9 volts. The crankshaft position sensor 8 volt supply (org) to ground (blk/ltblu) was 8.9 volts. Are these too high? Also the voltage drop test for the fuel pump power (dkgrn/wht) was .49 volts and ground (blk) was .17 volts.
Also I should mention the battery was replaced June of this year. Some of the electrolyte from the old battery leaked onto the cable bundle from the PCM that runs under the battery tray. I looked at the cable bundle and could not determine if the acid damaged the wires. With the engine running I wiggled the cable bundle and could not get the engine to stall with any certainty. I still have a concern about these wires.
Yesterday I took the van to a Chrysler dealer to have the problem diagnosed. They said the vehicle has intermittent loss of PCM on bus, several faults for sensor voltage, and relays and fan click on and off. They recommend to replace PCM first then diagnose. I can buy a remanufactured PCM on eBay programed to match the VIN and calibrated with the newest software from the manufacturer. This is a lot less than what the dealer wants for a PCM. If I install the new PCM will I do it harm if I have wiring or sensor issues? Can you advise my how to find and fix these issues? It is hard to do any more voltage drop tests at the PCM connectors because of the close proximity to the strut housing. I did some other voltage and resistance checks on other sensors if that information would be helpful to you. Any assistance in this problem solving would be greatly appreciated.
Thanks,
Don
ANSWER: Hi Don,
I wonder whether the dealer did a fault code readout?
You can do that yourself: Turn the key: "on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the odometer window in the cluster to see the mileage reading be replaced by a 4-digit number preceded by a P. Let me know and we'll go from there.
I do have a suggestion in the meantime: check the exhaust gas recirculation valve (egry to see if its valve stem may be sticky and preventing the valve from closing tightly. That produces a lean mixture which causes just the type of problems you describe.
It is located along a narrow diameter pipe which branches off the rear-side exhaust manifold and routes toward and under the throttle body. The body of the valve is in that pipe, mounted sideways, and it has a round vacuum hose-operated top piece and a flange in between that and the body of the valve. Inside the flange area you will see the valve stem which has a circumferential slot into which the tip of a screwdriver can be inserted to move the stem from side to side. Spray some WD-40 on the stem where it enters the valve body and then move the stem back and forth, against spring-action in one direction that tries to close the valve. Make sure it closes to a dead stop. Then try to start and run the engine.
I would not buy and type of PCM before doing the above.
Please read the PS below and respond to it.
Thanks,
Roland
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QUESTION: Hi Roland,
The service department rep at the dealership told me there were numerous fault codes for the sensor's voltages being too high. He also mentioned about the intermittent loss of PCM power on the bus. He did not give me any specific fault codes.
I did the fault code readout with the key: on-off-on-off-on and leave on. The mileage reading never changed to any fault codes. I read recently that this feature was not available on the 1998 Town & Country.
I also cleaned the EGR valve stem as you suggested. It closes to a dead stop. The stalling and rough idle are still there after starting the engine.
Thanks,
Don
ANSWER: Hi Don,
Sorry about self-readout suggestion, I overlooked the '98/'99 not having that possibility.
I would prefer having the fault codes so if we can't sort this out it would be helpful to have them read again at the dealership for free (because they apparently didn't write them down on your paperwork which should have been done).
The lack of 12v on pin 46 of the pcm suggests that fuse 16 in the pdc is either blown or flakey, or the wire connection from it to the pcm is 'open'. So fix that first, its the third in line from the rear of the box (20 amp). The rest of the voltage readings should be re-done after that is corrected, because that is a main supply for the pcm and the fuel pump relay output voltage when activated. The negative voltages may then be positive and the sensor voltages closer to 8v. Also check positive temp coefficient fuse-like device in the fuse box under the dash, specifically PTC #1 at the left hand end of the row on the bottom of the box. The fuel pump reading would only show 12v when the fuel pump is activated and that only happens for about a second when you turn the key to 'run' and then returns when you start cranking it over.
Let me know what the reading are after you get fuse 16 going again. Fuse 17 is also key to the engine because it is the output source for the automatic shutdown relay. When checking the fuses look closely for the presence of a subtle crack in the wire.
Thanks for the rating and nomination, which you are welcome to do again if you would care to.
Roland
---------- FOLLOW-UP ----------
QUESTION: Hi Roland,
I'll contact the dealer Monday about getting the fault codes.
My reading of 0 volts on pin#46 fused B+ (red/wht) of the PCM was a voltage drop test.
Fuse #16 (fuel pump relay) checked OK. I got 12.59 volts on both sides of the fuse. It also checked OK with an ohm meter.
With fuse #16 removed I got 0.2 ohms between fuse terminal to wire #46 (red/wht) of PCM connecter.
Fuse #17 for auto shut down relay checked OK.
At PCM pin #67 auto shut down relay (dkblu/yel) I got 12.57 volts.
Voltage drop test (PCM)
Pin #43 sensor ground (red/wht) .68 volts
Pin #10 ground (blk/tan) .01 volts
Pin #50 ground (blk/tan) .01 volts
* Pin #46 fused B+ (red/wht) .01-.03 volts
* Pin #44 8 volt supply (org) 11.74-12.12 volts
* Pin #61 5 volt supply (vio/wht) 6.7-702 volts
* Denotes voltage fluctuating with fuel pump and fuel pump relay turning on and off every second or two.
I would like to emphasize how the fuel pump buzzes and the fuel pump relay clicks on and off constantly with the key on and engine off.
With the camshaft position sensor connector removed and checked 8 volt supply (org) to ground (blk/ltblu) I got 8.9 volts.
With the crankshaft position sensor connector removed and checked 8 volt supply (org) to ground (blk/ltblu) I got 8.96 volts.
Your reference to the positive temp coefficient PTC #1 on the junction block under the dash is labeled 10 amp instrument panel illumination fuse in the owner's manual and at the junction block under the dash. It looks just like the other fuses and it is not hot in the run position. When I turn on the lights and the panel illumination switch I get 11.3 volts at this fuse. I can't seem to locate PTC #1. I wonder if they are located inside the junction block?
Thanks,
Don
AnswerOn the PTC's, I meant to say those 5 are located in the 10 socket row just below the 4 many-wire plugs of the junction box (not at the bottom of the box).
I guess you need to explain to me what is a 'voltage drop test'. It is a term I haven't heard before. I usually think of the voltage as measurement compared to chassis ground.
On the * readings, do you mean that when you turn the key to run position that the fuel pump relay and fuel pump spontaneously start clicking on and off? That suggests either a failure of the pcm, because the click on-off should occur only once when you turn the key to run. It should not click again until you try to crank it over; or I suppose if there were a flakey ignition switch contact in the run position then every time switch 'opens' on its own the fuel relay would do another on-off, etc. etc. Might you have a bad ignition switch?
Any how, let me know what you find about the fault code numbers.
Thanks for the recent rating. By the way you can do up to 5 'nominations' during the month, once for each answer, and they will be 'counted'.
Thanks,
Roland
PS On the fuel pump relay/fuel pump oscillating as you described, another possibility is that the fuel pump/relay circuit is pulling down the battery voltage do to a short circuit, which is then 'seen' by the PCM as if you had actually turned the ignition switch off; as the result then when the relay opens the battery voltage goes back up and the pcm "sees" that and thinks the ignition switch just was turned on again, and then it cycles through the same behavior ad infinitum. So watch the battery voltage when you turn the key to 'run' to be sure that the voltage on the system is not being dragged down (maybe that is what you mean by a 'voltage drop' test).
If that relay/pump were operating like that when the engine is running I can imagine that would produce the rough running you are trying to correct.
Thanks for the rating and nomination.
