Engine/Transmission (1998.5 - 2002) Cam sensor misery

[Vaughn MacKenzie]

About 20k miles after I bought my '98.5 the tach started acting crazy sporadically so I replaced the cam sensor, and crank while I was at it. Both looked fine, had about 174k on it at the time, immediately cleared up the problem. Less than 7k miles later it's acting up sporadically again. For a few days it runs perfect, then all of a sudden first thing in the morning it's bucking and missing and the tach is jumping all over the place or twitching a lot. Other times the tach doesn't bounce around but twitches nervously and the engine is jumpy. The Check Engine light comes on, then after driving it 3-4 times it runs perfect and the light goes out for a day or several days til it acts up again. Might run perfect for a week then act terrible. It's getting worse though.

I thought it was a wiring connection even though I did dielectric paste the last time I replaced the sensor. I wiggled the wires with it running but it didn't seem to have any effect. Wiring and contacts look good. I'm going to replace the sensor again I guess but it's a bugger getting to it, last time I had the injection pump out for something else and it was easy. I fought it for an hour with no luck, can't tell what size screw head it is or even physically get anything on it. Suggestions? What size is it? I should remove the intake horn and fuel lines to the pump since they're right smack in the way for sighting it and access. It's disconcerting two have apparently failed in such a short period of time, I put a Cummins sensor in it so it should have lasted far longer than that.

 

[JR]

What codes are you getting? As far as I know if you are having issues like you are describing it is going to be your crank position sensor not cam sensor. On the early 24 valves the tone wheel is at the crank sensor and that is where the ecm gets the signal for the tach. I'm not aware of any actual driveability issues that could be caused by the cam sensor

 

[DavidC]

If your 98.5 is the same as my 99 (probably is) the cam sensor is for diagnostics only and the crank sensor is doing all the work. I would remove the crank sensor and see if it was beat up. If it is you may have tone wheel problems. If it appears to be ok maybe try another sensor. It appears to be rare but I have heard of the tone wheel bolts loosening.

 

[BarryG]

While yours is a 98 and mine is an 01 which does not have the crank sensor just the cam sensor I had a period of time that I was having a very similar problem that lasted for weeks. Engine would miss, generally run like crap, tack might bounce, it might not, it might drop to zero. Would be fine one day and not the next. The symptoms got progressively worse in frequency and severity. Changed the sensor to no avail. I checked all I could think of. I posted my situation and member Jlandry provided some testing procedures. I followed the tests to the best of my ability and tools would allow. I still had no resolution. Exasperated I took it into a trusted diesel shop. He had it for several days and checked many things and could find nothing wrong yet it still did it. He finally came back and told me unless you are willing to change the entire wiring harness which was upwards of $1000 from Dodge he was out of things to test and check. Fortunately he only charged me a nominal fee for his work. Told me since he couldn't figure it out he didn't feel right charging for the hours he spent on it. In any case after I picked it up and mulled over the $1000 harness I was doing an oil change and just giving everything under the hood a good once over. I spent a few minutes messing with the alternator wires as something in Jlandrys testing procedures I think wanted me to use an oscilloscope for part of the testing which I did not have or have access to and something about AC voltage. So I was just messing with the alt wires looking at them, separated them a bit. I didn't even really know what I was looking for, honestly all I did was that. Ever since then it has never done it again and that was 5 or 6 years ago and approx 100k. So while I have no idea what caused it or fixed it messing with alt wires seems to have fixed it. I actually have no idea what fixed it since I didn't really do anything except move some wires around but that was the only thing I did out of the ordinary, I also did an oil, filter, fuel filter change that day, topped off washer fluid, checked coolant level and PS fluid. So whether that really had anything to do with it who knows but might be worth looking at.
below is the thread with Jlandry's testing procedures in it
https://www.turbodieselregister.com/threads/204391-CAM-Position-Sensor-Help

 

[SnoKing]

While yours is a 98 and mine is an 01 which does not have the crank sensor just the cam sensor I had a period of time that I was having a very similar problem that lasted for weeks. Engine would miss, generally run like crap, tack might bounce, it might not, it might drop to zero. Would be fine one day and not the next. The symptoms got progressively worse in frequency and severity. Changed the sensor to no avail. I checked all I could think of. I posted my situation and member Jlandry provided some testing procedures. I followed the tests to the best of my ability and tools would allow. I still had no resolution. Exasperated I took it into a trusted diesel shop. He had it for several days and checked many things and could find nothing wrong yet it still did it. He finally came back and told me unless you are willing to change the entire wiring harness which was upwards of $1000 from Dodge he was out of things to test and check. Fortunately he only charged me a nominal fee for his work. Told me since he couldn't figure it out he didn't feel right charging for the hours he spent on it. In any case after I picked it up and mulled over the $1000 harness I was doing an oil change and just giving everything under the hood a good once over. I spent a few minutes messing with the alternator wires as something in Jlandrys testing procedures I think wanted me to use an oscilloscope for part of the testing which I did not have or have access to and something about AC voltage. So I was just messing with the alt wires looking at them, separated them a bit. I didn't even really know what I was looking for, honestly all I did was that. Ever since then it has never done it again and that was 5 or 6 years ago and approx 100k. So while I have no idea what caused it or fixed it messing with alt wires seems to have fixed it. I actually have no idea what fixed it since I didn't really do anything except move some wires around but that was the only thing I did out of the ordinary, I also did an oil, filter, fuel filter change that day, topped off washer fluid, checked coolant level and PS fluid. So whether that really had anything to do with it who knows but might be worth looking at.
below is the thread with Jlandry's testing procedures in it
https://www.turbodieselregister.com/threads/204391-CAM-Position-Sensor-Help

When John speaks we should all listen! He is really on top of things! SNOKING

 

[Vaughn MacKenzie]

Interesting I guess I was backwards about the sensors. The crank sensor I replaced not long ago and it was physically fine.

As soon as my check engine light comes on the engine smooths out and runs OK (but weaker) even though the tach still bounces around, so I guess it switches over to the cam sensor for position reference.

BarryG interesting story, thanks for sharing, maybe I'll start with the alternator/wiring first! I have an automatic, which shifts good without any flaky torque converter lockup operation, but you never know I guess...

 

[JR]

If the crank sensor were to totally crap out the ecm would pick up the timing off the injection pump and run but I believe once you were to shut the truck off you would get a no start.

 

[DavidC]

From the 99 service manual

Dave

 

[Vaughn MacKenzie]

Now this is becoming a mystery, yesterday I pulled the starter and discovered the wire harness plug was loose to the crank sensor and not snapped in all the way. Wallah, found the problem!! That was easy! So I thought. Plugged it in, ran beautiful yesterday, but crap again today! Bouncy erratic tach. I futzed with it again tonight, connector is still plugged in tight, I loosened the retaining bolt a bit and slightly repositioned it and then when I started it the tach just sat at 0, just sat there no matter where I revved the engine. Repositioned it slightly again and then it starts and runs perfectly. I don't think much of the chintzy oddball metal retaining piece, doesn't seem to consistently hold it in place.

Darn thing is driving me nuts, now I'm kicking myself for not going ahead and putting the new one in anyway... guess I get to R&R the starter and try again

 

[DavidC]

At least you have it narrowed down

Dave

 

[JR]

Was that a Cummins sensor as well?

Any contact marks on the sensor from the tone ring?

 

[DavidC]

May not be the sensor as it maybe the plug. I would try this whether you change the sensor or not. Get some plastic safe contact cleaner and some dielectric grease. Clean both sides as best you can with wire brush, emery cloth etc. Spray the contact cleaner on both sides liberally, let them dry. Then coat the pins with dielectric grease and reassemble. This has solved a few problems for me as the pins sometimes develop a coating that interferes with low voltage signals.

Dave

 

[DavidC]

May not be the sensor as it maybe the plug. I would try this whether you change the sensor or not. Get some plastic safe contact cleaner and some dielectric grease. Clean both sides as best you can with wire brush, emery cloth etc. Spray the contact cleaner on both sides liberally, let them dry. Then coat the pins with dielectric grease and reassemble. This has solved a few problems for me as the pins sometimes develop a coating that interferes with low voltage signals.

Dave

 

[Vaughn MacKenzie]

JR, as I recall it's a Cummins sensor. No contact marks at all.

DavidVT thanks for that suggestion, I did do that originally last year but wouldn't hurt to try it again. Visually it looks great, in this region with mild climate there's very little issue with corrossion and contacts getting messed up. And before here the truck lived in Southern Cal.

 

[DavidC]

True climate plays a factor. I once had the ABS light coming on at 40 mph. Tracked it down to the plug on the back side of the trailer plug at the hitch. Cleaned and greased, been fine since then. This is in Arizona so you never know.

Dave

 

[Vaughn MacKenzie]

Still having issues with tach and erratic drivability from time to time. Truck will run perfect for a couple days to a week but then suddenly tach goes crazy and engine runs erratically. Then it'll be fine again for days.

When it does happen it's within the first 2-3 minutes of driving after starting, never beyond that...I can drive hundreds of miles with no hiccups
When it does act up it'll settle down within a couple miles. Or if I stop the engine and restart it.
Occasionally when it does it the engine will die, but it always restarts no problem.

I don't think the crank sensor is bad. I'm wondering if it's the PCM or ECM? One time when it was acting crazy I pulled over and shut it off and restarted it, but then the tach worked but the speedometer was dead. Stopped again and restarted and then all was good. That has me thinking PCM.

I may throw another new sensor in but next thing I'll try is unplug the PCM and ECM and add dielectric paste and reconnect them.

 

[JR]

I had a VP44 PSG act similar for a few years. Anything below 140* coolant temp and it would get a funky dead pedal, once you got above that 140* mark it was like flipping a light switch and ran perfectly;. I had 3 VP44 failure related codes but it ran like that for a couple of years. I was putting my wife through an expensive 4 years of college so I just learned to live with it.

 

[DavidC]

Grounds ?

Dave

 

[Vaughn MacKenzie]

As an update, the truck ran great for almost a week then started running badly one day, engine conked out cold once and almost died a few other times. So I pulled the starter and replaced the crank sensor. That was two weeks ago, no more issues or CELs so far...fingers are crossed it was just a bad sensor after all! It seems to run a bit better, it smokes a little more under heavy throttle but MPG is back up. Last tank was 20.6 with about 2/3 of it highway.