Just Bought 86' 2Wd 2.5L 5 Speed, Has Engine Problem

[tonemj]

this motor just causes a ruckus idling, its loud and clangy like lifter slap or maybe a loose timing chain hitting against a bad timing tensioner?? i don't know, it runs great when going, pulls decent as a 2.5L will. but when idling it just sounds like crap. it has 333,000 on the odometer, previous owner said he got it from a dealership who said that the guy that sold it to them had a newer engine put in, but its still a tbi 2.5L, so i think this is a lie, but i have wire connections that lead nowhere all around the engine bay. its like I'm missing tons of connections but i have no idea what theyre for, tried tracking them down and I'm a decent electrician and have worked on many 4.0L cherokees so i figured the harness couldnt be too different for this comanches 2.5L. i mean even the wire w/ plug coming out of the distributor doesnt have anything to attach to, how does this work? how can the timing advance during higher rpms with no input from the computer or anything? also its not blowing out any heat, only outside air temperature through the vents or windshield, so i know i have vaccuum and its okay in that department but I'm not getting heat. what could this be? thanks for any input guys

 

here's the truck:

 

 

[Geonovast]

The fact that it has a connector coming from the distributor tells me it likely is a newer engine.

 

The 2.5 didn't change much over the years, when it comes to the actual block and head. It most likely has a newer engine, but has the original TBI intake manifold, because whoever did the install didn't want to change over the entire wiring harness, and also almost everything else in the engine bay, to a newer system. Also remember the TBI 2.5 was used from 86-90.

 

The plug coming off of the dizzy tells me that it could easily be a 91 or newer motor. In 1991, it went to an MPFI system and there's a sensor inside the distributor that's used for deciding which injector to open. Since your truck is TBI, the computer doesn't care which piston is firing, since there's only one injector. The timing advance is done electronically, by the computer. It gets that sort of information from the CPS, which is mounted on the driver's side of the bellhousing. If that's not connected, it will not even start.

 

As far as your problem, what you're thinking may be the case. The 2.5 does use a tensioner, and it could have easily worn out. What I would do, is take the distributor cap off, and turn the motor over by hand to tighten up the chain. Then you can turn the motor backwards, and see if it hesitates before the dizzy turns again. This will show you if there's slack in the chain.