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What Engine Computer Do I Need?


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I have a 1988 Comanche Pioneer 4.0L 5-speed manual. It's the only vehicle I own so I'm in a rush to get it fixed. The guy I bought it from took a lot of short cuts that I've been fixing but this latest fix has got me a bit uncertain.  I took it too a local NAPA, they hooked up an OBD-1 (?) and said "the computer is not getting any communication." They recommend getting a new computer. I'm looking for one online and I'm at a point of uncertainty. I understand that jeeps are interchangeable but I don't know what range of computers or varieties of computers are acceptable for my vehicle?

 

 

Additional Info:

 

The problem started with my KC lights. They weren't done right and one broke off of the top. I shunted the wires and the next morning when I turned them on while driving to work (I take dirt roads)  the switch got really hot, melted, and broke. I disconnected the battery, removed the switch, taped the wire ends. Roughly a week later my starter goes out and I replaced it. Then a week after that, while driving down said dirt road, my radio goes out and a few miles later my engine starts humming and loses power. It jerks, pops, stutters, spits, and is sluggish in every gear. I almost stall out every time I go up hill and I can't get over 25mph on dirt roads. It's my daily driver so it's been a real pain in the @$$. I bought it in March and drove it for 6 months with no problems whatsoever but a lot of seemingly random things when to $#!& all at once and I'm wondering if there's an underlying problem that they're all connected to.

 

There were 5 blown fuses that I replaced today and fixed a vacuum leak, it runs a little better but that's every last bit of info I can think of at the moment. I apologize if this is overkill but I'm really new to this game and need as much help as I can get, as fast as I can get it. 

 

My main dilemma is what engine computers I can use. All advice is appreciated. 

 

Thanks in advance.

 

 

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There is no OBD on a 1988 Comanche Pioneer 4.0L 5-speed manual.  I really doubt it's the computer.  But if you want to get a new computer, I'd get one for a 1988 Comanche Pioneer 4.0L 5-speed manual.

 

Considering the KC lights started the problem, that's kinda where I'd start.  Were they wired in with a relay...or just a switch?

 

I'd start by checking cables, grounds and connections.  Sounds like you need to go directly to Cruiser's tips.

 

Cruiser's Mostly Renix Tips (over 26 of them) can be found here:
http://comancheclub....tly-renix-tips/
 
 Refresh*Connections*Before*Replacing*Components
My Jeep Technical photos can be found here:
http://comancheclub.com/topic/43691-jeep-technical-photos/

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They weren't done right and one broke off of the top. I shunted the wires...........

 

What does this mean? You tied the two wires together on the broken KC light mount??

 

Then the next morning when you switched the lights on things started burning?

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Paradise is correct. Your NAPA guys don't know what they're doing. I don't know how they even connected an OBD-1 scanner to an '88 MJ, since there's no OBD port.

 

Start with the basics -- to run, it ned fuel, air, and spark. We'll assume that it gets air -- but you should check the compression. Then check fuel -- but for testing purposes you can dribble a SMALL amount of gas directly into the throttle body, and that will make it fire IF you also have spark.

 

The most complicated to trouble shoot is spark. But first figure out what you have and what you don't have, then post more info and we'll keep making guesses until somebody gets it right.

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Of course, all that's Captain Obvious stuff.

 

My guess is that the OP tied together a hot and ground wire together on an aux light that was tied directly to the battery, and created a dead short when he turned the switch on the next morning and things started shorting out possibly all the way back to the Renix box. Let's see what he has to say before diagnosing..........

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Of course, all that's Captain Obvious stuff.

 

My guess is that the OP tied together a hot and ground wire together on an aux light that was tied directly to the battery, and created a dead short when he turned the switch on the next morning and things started shorting out possibly all the way back to the Renix box. Let's see what he has to say before diagnosing..........

I'm with you. 

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If your Comanche starts and runs, the computer sounds OK.  If things are burning out, melting, fuses blowing etc sounds like the previouus owner has connected some ground points to electrical power.  I'd get a maintenance manual, like Chilton or Haynes and go completely through the wiring diagram from stem to stern with a VOM meter or have a local auto electrician do it.  Your computer is a DRBII machine not an ODB 1 or 2.  Napa didn't do you any favors except show their lack of smarts although it does point out how Renix maintenance is becoming such a dark ages project.

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The problem started with my KC lights. They weren't done right and one broke off of the top. I shunted the wires and the next morning when I turned them on while driving to work (I take dirt roads)  the switch got really hot, melted, and broke.

No, the problem started when you "shunted" the wires together.  :)  That's actually called SHORTING, not shunting... you hooked positive and negative together to create a short circuit as soon as you turned on the switch. 

 

Figure out where that switch got it's power from and start from there...  Look for more melted wires and blown fuses... Five blown fuses means there's a lot more damage somewhere else most likely.  You may have burned a wire across several others.  Check the fusible links near the battery too.  (The mess of green really flexible wires just behind the battery on the firewall.  Pull on all of them individually.  Any that are stretchy are in need of replacement.

 

It's likely that not all of your problems are related, and highly likely that your problem is NOT your engine controller, but rather some melted wiring that you just haven't found yet...

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I have absolutely no idea what I'm doing. I bought the MJ so I could learn to work on cars, however I ended up totaling my other daily driver before I had a chance to get too crazy with it. I had a feeling it was a wiring issue because the guy I bought it from had $#!& going everywhere, but I know nothing about that sort of thing.  I have the Haynes book but I'm dumb to the trouble shooting process and I feel like my speculating is running me in circles. Would pictures or videos help?

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Pictures or videos really won't help. You will either have to find someone who knows automotive wiring and proper troubleshooting procedure to get things right, or learn it yourself. Lots of community adult education centers offer basic electricity courses, as well as local community colleges. If you don't have basic electrical knowledge and know how to logically identify and repair electrical problems you will do more harm than good; I think you realize that.

 

So if you don't have time to get "electrically smart" because you need your rig running now, you'll either have find a competent individual to do the repairs while you watch and learn, or find something else to drive while you are learning to DIY. Don't feel bad because you screwed up; we all have a time or two. Sorting out a simple auto electrical system like our trucks have isn't difficult if you have a basic understanding of how DC circuits work and know how to use a multimeter.

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Not helpful for your questions, but possible encouragement:

 

1.5 years ago I had enough knowledge about trucks to change the oil and air filter at regular intervals. That was it. Then my old truck died and I bought my MJ. Just read this tech board everyday and google anything you don't understand. Read through the DIY Forum on this site as well. Again, google anything you don't know. Eventually it all falls into place and starts making sense. To date I have remade the wiring harness for the front lights, switched the front clip, installed different axles, and fixed some wiring hack jobs left from the PO. It just takes time, patience, and lots and lots of reading. If I can figure this stuff out then almost anyone can. Good luck!

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It might help if you put your location in your signature.  That way anyone local might be able to give you a little direction and help, and lay eyes on your problem...  or join a 4wd club, or car club and get help that way...   You've already learned an important wiring lesson the hard way, and the curve is VERY steep if you keep learning things by doing it wrong first...  :)

 

Nobody was born with the knowledge of any of this stuff, it's all learned.   You just need to find someone who can help you quickly solve this problem, and it's not going to be done at a keyboard...

Good Luck!!

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I did a lot of reading in here and in my Haynes book and went to work. So here's my update.

 

1) I disconnected all of the after market lights (KC's, Hella's), checked all fuses, and exposed wires, and cleaned up every ground I could find.

 

2) There was a loud humming in the fuel tank so I took the tank off, cleaned it out (there was a lot of $#!& in there), I let it completely dry in the sun for a few hours. I gave it a new fuel pump w/strainer and fuel filter.  The humming was gone, there was a lot more giddy-up in the first three gears but I couldn't get past 50 mph. When I drove it home I lost power once I hit the dirt road and basically crawled along at 15mph on dirt and 30mph once I hit pavement again. I noticed the oil pressure dropped to around 20-25 and the exhaust was making a popping/thudding sound up near the manifold.

 

3) There was a leak in the oil pan gasket so I took it off, replaced the gasket and used that opportunity to replace the oil pump and strainer. It all went back together fine.

 

4) I replaced the sparkplugs, spark plug wires, distributor cap, rotor, and the coil along with the wire that goes to it. I didn't mess with the distributor base at all. The wires are ACCEL Hi-Temp super stock spiral core 8mm.

 

5) I replaced the crank shaft position sensor.

 

Result? It won't budge.

 

The battery sat on a trickle charger over night. The starter was diagnosed as being good. The starter fires up nice and strong, radio and head lights come on, the fans come on, the serpentine belt moves. I'm probably gonna get yelled at for this but I even left it in gear for a starting attempt and it'll roll forward an inch or two. We tried a push start, we tried starting fluid, there's just no combusition other than one instance of a backfire. We pulled the sparkplugs wires with the spark plugs one at a time and they are all firing but they're weak yellow sparks.

 

These fixes seemed simple enough. Take pictures as you pull one thing off, put the new thing on in reverse order, yet somehow I made matters worse. Any ideas?

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I had mobile mechanic come out and look at it this morning. He said that everything I did was correct, but the problem was compression. The 1st cylinder was only reading 60psi (well into the red). He said I need to get the head redone. There's a local place called car quest that will do it for a few hundred. I'm gonna go ahead and do it just because it most likely has never been done.

 

What are y'alls thoughts and experiences with this BTW?

 

PS I'm in Navarre Florida. On the panhandle between Pensacola and Destin.

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A "few hundred" to do a head? Is that if you carry it in, or does that include them taking it off and reinstalling it? What's included in their price? Is that a valve job, valve guides, and decking (truing) the head surface?

 

"A few hundred" is a very imprecise number, and to me it sounds a bit on the high side.

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A "few hundred" to do a head? Is that if you carry it in, or does that include them taking it off and reinstalling it? What's included in their price? Is that a valve job, valve guides, and decking (truing) the head surface?

 

"A few hundred" is a very imprecise number, and to me it sounds a bit on the high side.

 

I spent all day yesterday taking it apart and marking everything. I've never ever done this with any vehicle so naturally, I feel a lot more familiar with the way things work and a lot of things make sense now. 

 

Anyway, I'm taking it to get it fixed/milled/machined/what ever it's called today. I don't have a price estimate yet. But is there anything specific service I should ask for?

I feel like I have a unique opportunity to make some awesome improvements/changes/upgrades while everything is already off. I'm just limited by my inexperience to know what to ask for or what is available on the the market.

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  • 2 weeks later...

Valve job (lapping the valves to make sure they seat properly) and decking the head (making sure the head is completely flat) is what I would recommend asking for.

 

Fwiw, I don't have much experience with jeep motors but lots with inline 6s and 8s. Valve guides may be a good idea as well(usually a brass or bronze guide to keep the valves moving in up/down direction and eliminate any side-to-side movements), I'd Google and see what the general consensus is.

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  • 1 month later...

It is how it starts, learned myself in similar fashion. Traded my good running car for a "better car" with overheating issues. My cousin said, "sure I can fix it, but you're gonna do the work and learn.

Slight overheating issue, became complete head/gasket swap. New fuel system, and it just kept going ... Been fixing my own junk ever since. Started to like the fight really, and the satisfaction of winning that fight. Keeps me sane as I see it.

Really, being able to save on repair costs, and being able to troubleshoot/diagnose/repair on the fly (sometime in the middle of nowhere on the side of the road) is a true life skill.

I look at my MJ "Ratmanche" as a labour of love, sometimes she loves me a little less than other times.

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