Truck started acting up a few days ago. Tachometer goes off for a second and engine runs rough, then tach comes back and engine smooths out. This triggers the Check Engine light. After a few OFF-RUN cycles on the key light goes out but comes back when tach falls off again.

I spent an hour or so on Saturday cleaning connections and grounds and test drove without problem but today while running errands it happened again but this time worse; tach stayed off for about a minute or so. While tach is off engine surges and sputters.

I've read a previous thread here on this but there isn't any conclusion on it so I figured I'd ask this again.

Please help!

Thanks

 

I would say LP, IP, Apps, or ECM. The only reason why I said all of those is because I had the same kind of problem and those are all of the things that I have replaced in the last 4 months. I would look at your cam shaft position sensor also.

Are you getting any codes?

 

Just got back from AutoZone where they pulled the codes for me: P0336 Crankshaft Position Sensor; P1680 IPM crank sensor does not agree with ECM crank signal.

If it's the position sensor I don't understand why the issue is intermittent?

 

on my 1998.5 it came and went like yours. Pulled the starter and changed the crank sensor and no more problems. Do a starter contact replacment while you have the starter pulled. I didn't and about 30 days later had to pull the starter and do the rebuild anyway.

TallTom

 

I'm off to NAPA to get the sensor. I'll change it in the morning and let you know how it turns out.

Thanks!

 

Its the crank position sensor, just had same problems. Changed it runs great

 

Changed out crankshaft position sensor this morning and seems to have fixed it.

Found BIG difference in price on the part: AutoZone - $62; Checker - $55, Dealer - $112, and NAPA $45. I'm glad I shopped around by phone before I bought.

 

I've had the same problem with my Tach, but ONLY when it's raining and the roads are wet. When the roads are DRY, I never have a problem.

Where should I check for loose connections? or Where should I spray some silicone to water proof my connections?

Thanks
-Tim

 

Believe it or not-I had same problem with 99 QC 2500 frequently an wound up being fuel cap. Apparently was not venting ,creating vacuum and starving engine of fuel.When tach bottomed out I had to open cap an truck would be fine. Such a vacuum- it would cave in fuel tank until relieved.

 

check your connection on the back of your transfer case that should be on the tailhousing. That is where i would start.