bought my first mj, 86' 2.5L 5 speed, problem need help with

so its a 86' 2wd 5 speed comanche i got for $800 with a 2.5L i believe from an 88' the previous owner didnt know the exact year but someone put in a newer 2.5L for some reason. and im not 100% sure it had the 2.5L from the factory but its a classic edition, all manual inside no power, nothing special really but this motor has so much wiring hanging around the engine compartment im guessing it had a 2.5L before otherwise it would've been quite difficult to wire up efficiently. but i mean the wire with the harness plug coming out the distributor has no plug nearby to connect with, how does it know when to advance and all that? it runs great but idles rough and very loud. i hear a mechanical clanking when its idling i am not sure where its from, took a stethoscope to the valve cover dont hear any lifter slap or anything from the water pump/alternator/power steering pump. do these have timing gears and chains on the cam that may be slapping? im unfamiliar with the 2.5L and i have even more plugs near the firewall on the passenger and driver side that arent plugged into anything. im worried its gonna be a b1tch to smog this thing. when previous owner bought it the dealer smogged it at probably a shady smogger and got it to pass and he said hes had it stall out occasionally and had to turn it off for a while then get going again, happens intermittently. i have no idea what to make of any of this, could the renix system that was swapped in be all these wiring loose ends? this 2.5L has TBI which i thought was only 86', i have no idea please help me im clueless. thanks guys

edit: i bought it yesterday drove it home 5 miles. parked it over night. checked all my fluids and drove it around all day today without any fumbling or stalling issues, just loud engine noise starting out in first and idling. but once im going it sounds very clear and solid. it gets bad death wobble from a totally worn out track bar but ill fix that. this engine is worrying me. by the way the odometer says 333,341 miles but he said hes unsure of the motors mileage in it now. i figure the price and clean body and no rust and fact it was running was worth the motor questions..

Yeah, you're correct about how unusual it'd be for that truck to have been changed from a 6cyl engine to the 4cyl. Also, '87 was the first year for Renix AND the in-line 6. '84-'86 had either the 2.5 cyl or the 2.8 V6. The 4cyl was fuel injected where the V6 was carbureated.

Easiest determination is to look at the emissions sticker on the firewall above the master cylinder. That should tell you what engine it originally came with (assuming that sticker wasn't removed) but they generally are more work than they're worth to scrape off.

Yes, the wiring for the 4cyl was a mess from the factory. Many plugs are for the different accessories such as the idle boost switch for the power steering system (if yours has manual steering, you'll have a loose connector for the switch it doesn't have.) Same for A/C and other smog controls that may or may not still be on the engine (or were but removed by a prev. owner).

Given the large mileage numbers, I'd definitely suspect that the timing chain is what's making the noise. I had a 4cyl that sounded like the #1 piston was slapping or the lifter was loose and banging around..... but it turned out to be a loose chain with a busted tensioner inside the timing cover. I posted some info and pics in one of my MJ threads :

http://www.naxja.org/forum/showpost.php?p=244165968&postcount=24

I don't envy ya about dealing with emissions out there in CA...... it's bad enough here in Colorado.

Looks like a nice, clean bodied truck though! :thumbup:

well im loooking thru the wiring diagrams and noticing a lot of things undone. and i believe the knock is coming from inside my timing chain cover too, probably a bad chain and bad tensioner (hopefully). then its got weird bugs like power to the dome lights, new bulbs, but they dont work. fuse is good. i dont know i gotta test if this things drawing power when its ot running too cause my batterys dead every morning, alternators shot too.

Yeah those OEM dome lights in the rear pillar panels were junk from the start. Brittle plastic holding the brass contacts ..... All likely broken.

ComancheClub.com has lots of good MJ specific info as well. A few good posts about fixes and replacements for those lights.

YELLAHEEP said:

Also, '87 was the first year for Renix

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Actually 1986 was the first year for Renix. The 1986 2.5L TBI is a Renix system.

1986Comanche said:

Actually 1986 was the first year for Renix. The 1986 2.5L TBI is a Renix system.

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Correct.... the 84 and 85 xj and mj had the carb still.

Actually 86 was the first year for the MJ, it never had the carbed 4 cylinder. Just one year of the V-6 that had a carb.