Engine/Transmission (1998.5 - 2002) Tach Dies And Engine Won't Start

[SmithM]

I don't own a 24V myself and this isn't my truck to diagnose... I'm just a 4BT owner posting this for a buddy. Thought this one would be an easy one for someone familiar with Dodges:



"The problem that I am having is that at random (normally inconvenient) times the tac just drops out while driving. There is no noticable difference in proformance when this happens. After a random amount of time the tac will just start to work again. If you shut the truck off while the tac is off it does not want to restart. It will restart if you crank on it for a while and then let it sit and try again later. More recently it has started doing the not wanting to start thing when shut off with the tac working. Again, it will start back up with the crank then wait technique. Its a 1999 Dodge. "



Off the cuff my take was that the engines used a crank position sensor that went bad, and that there was an interlock that prevented the engine from starting if there was no good tach signal. I searched the forum but didn't find anything definitive for a 99... only that there is a CPS on these trucks. Other people's trucks seemed to run erratically when this happened... apparently his isn't, so its not obvious that it would be the same crank sensor problem...



Thanks for any help!



Matt

 

[Babyfat]

mine did the same thing replaced cps and everything is fine, it could also be the wires are corroded where it plugs in

 

[SmithM]

Anybody have a part number, and how involved is it to replace? I read 37$ on another thread, but a pain to access...

 

[Babyfat]

local dealer had it in stock, around 40-45 bucks i think, pia to change remove starter un plug wiring fight like shell to get it out of the block took about hour to hour 1/2

 

[SmithM]

Is it necessarily the sensor or could the tone wheel be bad? Another thread said the tone wheel came off on somebody! I think the tone wheel was on the crank... so that must mean this thing sticks into the block perpendicular to the crank, behind the starter?

 

[DavidC]

Most likely the sensor. The tone wheel coming off is very rare and I have only heard of one so far.



Dave

 

[KWentling]

Coming clear off is rare (and usually disasterous), but loose isn't. If the ring comes loose it damages the end of the sensor. When you replace it you need to look at the end of it and see if it's been rubbed on. This happened to the father in law's truck. Had to drop the oil pan and put 2 screws back in it (cleaned them all and Loctited). I know it's happened to at least 3 or 4 members here.



Kim

 

[KWentling]

By the way, only the '98. 5 and '99's and maybe a few '00 have the tone ring inside. Not one of Cummin's better ideas.



Kim

 

[SmithM]

Thanks everyone. Thats enough to tell my buddy what his potential problems are.

 

[wtfd6]

Is it necessarily the sensor or could the tone wheel be bad? Another thread said the tone wheel came off on somebody! I think the tone wheel was on the crank... so that must mean this thing sticks into the block perpendicular to the crank, behind the starter?

yes, mine was one of them. i think what actually happened was the ring came loose. it caught ahold of something and then it broke off. mine was the same way. intermittent ckp sensor. if the tach didnt read it wouldnt start. the engine didnt even know it was cranking over. hopefully the sensor is the only problem. that was the first thing i did. but it still didnt start right away. then i jiggled the wiring and it started. so i thought i had a wiring problem. but the next day is when the ring broke. hope this helps. oh and yes it is directly between the starter and the block.

mark