Hello all,

In my continuing attempts to solve an intermittent miss or stumble at idle I was playing around with my MAP sensor and a hand vacuum pump and voltmeter, and found 5.4V at the sensor on the sensor input voltage pin. I believe it should be 5.0 +/- 0.1. Is 5.4V too high?

I was thinking of looking at the pcm contacts and cleaning them. What is the best method to do this? Should I use a scotch brite pad, or a spray can of contact cleaner?

I have cleaned the battery posts, and wire connections, and all major contacts around block and alternator.Any other electrical contacts I should clean?

Any areas in the fuse block, or power distribution center I look at? I did clean up the pins on my relays in the PDC.

My truck is a 2001 Ram 2500 4x4, 5.9L gas, 46re Auto Trans, 8600 gvw (or 8500 can't remember exactly), about 170,000 km (not miles).

I don't really think my truck is old enough to have corrosion issues, especially being a Vancouver truck (no snow, or salt).

I was looking at the SCT tuner to get rid of the death flash (which I believe I have being a 2001). Any chance the SCT would help smooth out my hiccup at idle?

Thanks,
Chris

 

Manual says "Approximately 5 volts." So..... you are probably ok there.

SCT tuner would be a very good plan, will it fix your issue though? Probably not.

How do your plugs/wires/cap/rotor look?

 

My plugs/wires/cap/rotor all look good. I replaced all when I got the truck about a year ago. I also replaced the coil, timing chain (with a double roller), and most recently replaced all lifters (had one that wasn't pumping oil). As well as the usual maintenance fluids and filters.

I cheaped out on the wires though, and have been regretting it ever since. I tested them all before I installed (for resistance), and they all tested okay.

I have been wondering if they could be the casue of my miss at idle. I have read on here that some guys have had problems with cheap wires. I figured I would give them another year before replacing them with a better set. I was thinking MSD, is there a better brand to get?

Is it easy to screw up a pcm by "scrubbing" the contacts with a scotch brite pad?

Will the spray on contact cleaner do a good job in exposing new contact material?

 

5.4V is not 5.0V +/- 0.1. Since your are try to solve a very minor "problem" I would try a replacement and see if that fixes it. Make sure you can return it though.

For plug wires look in the stickies or do a search. There are some very good write ups about plug wires. From what I remember MSD is not a very good plug wire brand for computer controlled vehicles. I have Taylor Cables on my truck and have used them on a few others with no problems and they are considerably less expensive than the MSD wires.

By the way why do you have (LD) next to the 2500 in your vehicle data? Light Duty dodge 2500's are 7400# GVWR and were only made from 94-97.

 

Thanks for the info Gerehead. You suggest to replace a part, but I believe the source votage comes directly from the PCM. Are you suggesting I should replace the PCM?

It is my understanding that replacing the MAP sensor would have no effect on the source voltage to the MAP sensor. Is this corerct?

I had a look at the Taylor wires, they look pretty good. Maybe I will pop my current wires off and test them again. I never tested them "warmed up", or twisted a little bit.

The LD beside my vehicle data is from when I first setup my account. I had read that Dodge made LD 2500's and I saw that I had a NP 241DLD and assumed my truck was LD. I later learned that you only get a NP 241DHD with a V10 or a diesel. I will remove the (LD). Thanks good catch.

Has anyone had experience with corroded PCM contacts, or other corroded contacts causing high source voltage at sensors?

Any other casues for different source voltages at sensors?

Thanks,
Chris

 

Corroded contacts and such would cause a low voltage condition..... not high. Changing sensors will also have zero effect on supply voltage.

I would suggest checking what the sensor return voltage is, and make sure THAT is within spec. After all, that is all the computer really cares about.

Most of the sensors get their power from the same source, if one is high, then, all of them should be high..... If that isn't the case..... then something is most certainly awry there...... not sure how that could happen though. What kind of meter are you using? Wonder if you are just not seeing some inaccuracy due to the meter......

Simply ohm testing the wires isn't going to tell you how well they fare under load conditions, or, how well they protect against induction firing of the wrong cylinder. There is a tech service bulletin about plug wire routing in the faq section, might wanna have a look at that.... Or, get some good quality plug wires, and see if that doesn't resolve the issue. (I would try this fix first....)

 

Thanks HeyYou... it could be my $30 mulit-meter. I will try to confirm by measuring sources at other sensors.

I have used the wire routing TSB. Is there no way to test the wires I have now at home on the bench?

Maybe I will try new wires, it has been on my mind for a while. I am thinking of switching to Champion copper core plugs too.

Thanks,
Chris

 

You're right on this, the 5V or 5.4V this DOESN'T MATTER at all and they are coming from the PCM .You can test the output(center pin) of this sensor at idle (high vacuum) will be less than 1V. This voltage will increase (max value of 5V) with the throttle advance and vacuum decrease. By the way, don't you have any diagnostic trouble code?

 

No codes at all. I find that frustrating. With my little hiccup at idle I would expect misfire at one cylinder, or random misfire.

I have a code scanner, and I have done the "key dance". Nothing.

 

Is this problem when is cold or when is at op temp? I'm asking because I had this problem in my first '94 RAM and it was the O2 sensor but the problem was always after reached the op temp and no codes as you.