I just bought a 98 dodge ram single cab short bed 2wd. It had a 3.9 v6 w/ a thrown rod. So i bought a 5.9 to put in it. I got a v8 wiring harness, computer, and flexplate. So i should be good to go, but, i got the motor in today and it starts and runs, but runs like dog crap. I hooked up the snap on modis and i have erratic rpm and within ten seconds i lose the sync. I have a brand new crank sensor because the one off the used motor was broke. It still has the v6 trans and tourque converter, it all bolted up fine so i left it. I know the v6 trans isnt as tough, its a 42re, but i was hoping i could get away with it. So now that yall have the history, what am i missing? any ideas? Any help would be greatly appreciated.

 

Welcome to the site. I moved this thread to the second generation Ram section,
FF

 

Where did you get your crank sensor, and what brand is it? These trucks don't really care for aftermarket sensors it seems..... also, not sure if the tone ring is in the right spot, or the right diameter for the V-8s...... just a wild guess there though.

The 360 will smoke your trans pretty handily. Gonna have to be REAL nice to it, until you can put in a meaner one.

 

Thanks for the welcome! The crank sensor is a "standard" brand from the local bumper to bumper parts store, ive put these on just about every chrysler product and have never had a problem.. but ya know the saying, new means new, new does not mean good. The tone ring is the flexplate itself.. there are eight square holes for the crank sensor to read for every cylinder, and the flexplate is from a 360, so that shouldnt be a problem.The original flexplate from the motor im using was damaged, so im using another from a 360. One thing i did notice is that the damaged flywheel had no weights on it, but the one im using does have weights, if the tourque converter and flexplate both have wieghts, will that cause my problem due to an unbalance vibration?

 

360 is externally balanced. Now, I am not 100% sure on this... but... I think at one point, the torque converters had the balance weights, and the flex plate did not, then, dodge changed their mind, and the flex plate had balance weights, and the torque converter did not..... Purely guess work, but, something you might want to look into. Probably call up the parts store, and ask them. If they give a year break on flex plates for second gen trucks, that may be your answer.

That said, even if it IS the case, I don't think the vibration would be enough to throw you out of sync. That sounds more like a sloppy timing chain, or, a failing cam position sensor, or, maybe something really simple, like the distributor being loose.... or a bad connection somewhere.

Does the crank signal remain steady?

 

I ordered a crank sensor from the dealer.. took two days to get it and a hundred bucks.. and i was crossing my fingers when i hit the key.. damn thing started right up and runs smooth. Thank yall for the help, i cant believe it. i got three diff standard brand sensors and i was at a loss for the problem. thanks again

 

Awesome! These trucks seem to be overly sensitive to off-brand (non-mopar) sensors...... Especially the cam and crank sensors.

Glad ya got it going.