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What is the most important tip you'd share with MJ owners?

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#1 Pete M

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Posted 20 January 2009 - 08:16 PM

I'm not looking for a FAQ here, I'm looking for those warnings or little gems of knowledge that you want every owner to know, but they'll likely not ask about until it's too late. Things like pulling up the carpet to check for moisture, or checking that your master clutch cylinder isn't leaking into your fuse box. For now I'll just leave this all as a regular thread, but later on I'll compile it into a single list.

So what do you wish you knew? :brows:

--When at all possible, do the work yourself! Tools and shop manuals are good investments. Handing over money to the shop guys only helps in their investments.

--Pull up your carpet! EVERY MJ owner should do it asap. I don't care what climate you live in or how little rust is on the outside of your truck, there must be a dozen ways for moisture to get under the carpet and once it's there, it's only a matter of time before the floor rots out from under you.

--Please do not ever spend any money on a Peugeot transmission (manual trans behind 87-89.5 4.0Ls) beyond new gear oil. It is a weak transmission with very expensive parts. Look into an AX-15 swap

--Please do not spend any money on a Dana 35 rear axle beyond gear oil and brakes. It is a weak axle and not worth upgrading or heavy repair. Look into a Dana 44 or 97+ Jeep 8.25 or Explorer 8.8 swap if you want to upgrade. Or if you just need the truck running again, look for another Dana 35 or a 96-earlier 8.25. Don't forget to take this opportunity to get some better gearing. :thumbsup:

--Better gearing in your axles will give more kick-in-the-pants acceleration than any muffler/airbox could ever dream of.

--If you have a manual trans, check your fuse box with each oil change for any evidence of the clutch master cylinder leaking into the cab and dribbling down the firewall into the fuse box. Brake fluid will disintegrate the plastic.

--Lube you hood release mechanisms! Including inside the cable and the center pivot. With every oil change if not more often. If it breaks, look here: http://comancheclub....c.php?f=2&t=872

--Use a hose to spray up in front or behind your rear wheel well to clean off that little shelf above the tire that collects dirt, which collects moisture, and rust is inevitable. There's a reason why our trucks rot there first and it's very preventable.

--Clean out the drain holes in the bottom of your doors. Dirt collects in that pinch seam and that attracts moisture, etc.

--Add rocker guards if you wheel. And do it before you smash your rockers. We have a long wheelbase and the rockers are extra susceptible to contact with rocks, logs, even simple mounds of dirt.

And lastly: Be careful when contemplating your first MJ purchase. These trucks have proven to be highly addictive to certain individuals!

Keep on Jeepin' on!



1988 MJ with a 4.0, TJ ax-15/231, 78 Bronco dana 44/9", bumpers, rollbar, blah, blah blah...

A quick synopsis of my current and past MJs: Click here!!

Swap in a relay harness for your headlights before it's too late!!


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#2 jtdesigns


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Posted 20 January 2009 - 09:00 PM

Mj's and XJ's are the same from doors forward. (not a problem, but wish Id knew it before looking for mj parts.)
"Back in Black"
1989 2wd 4.0L 5spd MJ Eliminator
1996 4wd 4.0L AW4 XJ Classic

#3 Akula69


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Posted 20 January 2009 - 10:39 PM

#1 - Always check the body grounds first when strange electrical problems start appearing.

#2 - If it won't start check the CPS (crankshaft position sensor) first.

It's OK to be brutally honest...sometimes it just becomes more brutal and less honest...

"People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf." - George Orwell

87 2WD MJ SWB 4.0 AW4 "Junior" - In conversion to 2K MJ
99 4WD MJ LWB Metric Tonne 4.0HO AW4 242J - Son
03 2WD WJ Laredo 4.0HO 45RFE - Daughter
04 2WD WJ Laredo 4.0HO 45RFE - Wife



#4 james750


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Posted 21 January 2009 - 12:06 AM

Do NOT use Fram oil filters. (they have a history or failures in Jeeps)

Check your battery box for cracks/breaks if the hold down is broken out all it takes is hitting a bump for the battery to come up and hit the hood, causing a severe short.

Check your CAD (central axle disconnect) b4 you go offroad for the first time, and lock it over if necessary . (or permanently bypass it and never worry about it again :thumbsup: )
'90 mj, 4.0, ax15/231, 6.5" front 10" SOA rear, RE coils with 2" spacer up front. d30 non-disco/8.25 29spline aussie ,4.10's JCR prerunner front bumper w/hitch, JKS swaybar quicker disconnects...

#5 Geonovast


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Posted 21 January 2009 - 01:40 AM

1. The AX-4/AX-5 will NOT bolt up behind a 4.0
2. 4wd swaps are a lot easier than they seem.
3. Dana 35 axles suck. They are a weak axle for sure. I'm fairly sure the one in my 2.5 DD is on its way out.


99 XJ, 4.0 HO/AW-4/NP 231, D30/8.25 - Parked The MJs formally known as mine.

88 MJ, 2.5 TBI/AX-4, D35 - DD                             CC on Facebook!
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Do I have an AX-15 or BA 10/5? What's my factory axle ratio? Common Jargon definitions.

#6 tazjeeper


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Posted 21 January 2009 - 06:54 AM

buy 2 or 3 the same if you can that way you have parts when needed.
Look over the frame realy well for cracks or signs of weld repairs.
look for broken wires under hood and dash or wires that have been taped or replaced
as stated before clean and keep clean to prevent rust.
over 30 and counting. j10, cj's, Xj's and Mj's, full size cherokees
Just Empty Every Pocket

#7 chunks6067


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Posted 21 January 2009 - 11:07 AM

A bad oil filter adapter gasket ring can be misdiagnosed as a bad rear main seal :doh:
(i cleaned the hell out of my engine before searching for the leak) quick and cheap fix :banana:
{CJP} 90MJ 4x4 Auto LB
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Powermaster alternator upgrade!

#8 Ed in North Ga.

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Posted 21 January 2009 - 06:16 PM

Know how to diagnose your jeep. Get a self-ranging multimeter. :thumbsup:

know the OHMs values for the CPS, the IAC, the TPS, the Ballast Resistor....don't pay money to shotgun fix it, TEST it before replacing it.

For the Renix owners, a lot of those values can be found using this site:
http://www.lunghd.co... ... ostics.htm

learn how to clean the throttle body and IAC bore, and reset the TPS to spec . Understand an old MJ will REQUIRE you to clean the throttle body, or suffer.

learn how to clean the bulkhead connector.

Carry in the glovebox, 1 spare CPS, 1 spare fuel line quick connect kit (fuelrail to hose repair kit/MOPAR), 1 ignition switch, 5 feet of wire +/- and tape, and at the minimum 2 pipe connectors with straps.

USE IT- don't let it sit, and don't baby it. Let it sit too long, you will suffer the consequences....Jeep MJs hate to be left alone...you were warned.

understand the 4.0L, when properly used past 200,000 IS a carbon creating monster- accept blowby- its a fact of life.
and always remember, the volt gauge LIES.
:) Jeep spoken here

#9 project88mj


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Posted 21 January 2009 - 08:19 PM

a picture with highlited or colored coded tracers for vacume lines

and a list of the ones you don't need
i miss the comanche... hell i miss jeep

#10 vzehler


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Posted 21 January 2009 - 08:22 PM

*Contrary to popular believe, some dana 35's have a metal plug opposed to the rubber plug most people identify them by.

*Invest in PB Blaster (a rust penetrant) and use it several times starting a few days before you plan on wrenching on your jeep. WD-40 is NOT the same thing.

*Use locktite on bolts.

*Know torque specs and do not over torque a bolt or use air tools on lug nuts.

*If you remove the bed on your Jeep, you must reground the wiring harness or it will not start.

*97-up front end is easily swappable to a Comanche.

*97-up doors will also fit on a Comanche.

*97-up mirrors will fit on 96-down doors with minor trimming.

*If you do a 97 up front end swap. upgrade your flashers to heavy duty jobs.

*Jeeps will potentially consume all of your excess money.

*Your wife/girlfriend will get pissed because you work on your Jeep to much.

#11 Pete M

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Posted 21 January 2009 - 09:47 PM

The proper procedure for bolting on a rim is to torque to spec in a star pattern, then drive around the block and re-torque. At least that's what I do. Haven't lost a tire yet (knock on wood).

Keep on Jeepin' on!



1988 MJ with a 4.0, TJ ax-15/231, 78 Bronco dana 44/9", bumpers, rollbar, blah, blah blah...

A quick synopsis of my current and past MJs: Click here!!

Swap in a relay harness for your headlights before it's too late!!


the new DIY master search index: CLICK HERE!!

#12 Str8OuttaBallard


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Posted 22 January 2009 - 12:54 AM

If your a city-slicker and like to wheel in the woods or ORV park always remember a spare door key...

If your a city-slicker and park on the street buy a steering wheel club and use it...

If you blow through ball joints switch to Moogs...

If you have the Renix cooling system get rid of it! it's easier to fix than a newbee would think!

for wheels and tires Discount tires has been good to me...

If your truck gets fender bendered and the person that hit you leaves a note get a written estimate for repair and see if the person that hit you will pay out of pocket... then do the the work your self and put the money elsewhere into your rig!

Working A/C! '89 MJ 5" RE Kit, Rancho My Ride w/9000xls, 32x11.5 BFG KM2's, '92 HO 4L and a bunch of other mods

#13 maddzz1


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Posted 22 January 2009 - 06:32 PM

Certain parts are getting harder to find. If you get a chance to grab them, get them even if you don't need them right now.

The airtex sending unit does not work on an MJ; even if they say it does.

There is a website called comancheclub {SMILIES_PATH}/jamminz.gif

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We got our sights set straight ahead but I ain't sure what we're after

#14 hogelectra


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Posted 26 January 2009 - 12:51 AM

Locate now the junk yards in your area that either have older MJ or XJ - become friends. Got a lot of good advice, help and parts that way. Drive your rig when going
86 MJ, 2.5L 4spd. longbed
2" lift, Mud Retread Tires
Rock Sliders - own design
Front Bumper - Own design
Ford Explorer 88 on rear
Aussie Locker on newer Front DANA30

#15 comancheman


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Posted 30 January 2009 - 11:39 PM

always carry a spare fuel pump ballast resistor and then a spare for your spare.
or carry a jumper wire to get you home.

#16 Jerry


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Posted 31 January 2009 - 07:03 PM

Before replacing your thermostat, check and clean the contacts from the temp sender unit and while you're in there check and clean any other reachable electrical connections :thumbsup:
1986 Pretty Blue 4x4 2.8L V6 Long Box "Champ"
1989 Flamin' Red 4x4 4.0L S6 Long Box "Diablo"

#17 hogelectra


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Posted 03 February 2009 - 07:18 PM

No matter if you find no rust anywhere when you checkout the vehicle - you can count on having to do a restoration job on the rusted floor when you remove the carpeting.

If buying a 2.5L then look for a gear ratio of 4.1 or 4.56 you will thank yourself later

Replace the lower shock mount on the rear immediately with a axle universal mount $20 for the mounts and a little welding. Otherwise you'll be fighting bent mounting bolts every time you go out.
86 MJ, 2.5L 4spd. longbed
2" lift, Mud Retread Tires
Rock Sliders - own design
Front Bumper - Own design
Ford Explorer 88 on rear
Aussie Locker on newer Front DANA30

#18 ren


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Posted 04 February 2009 - 10:26 AM

If you are having taillight troubles, then check and most likely rework the ground connection inside the drivers side taillight pocket.

If you the fuel gauge doesn't work and the fuel pump is having trouble, check the chassis ground back at the tank. I have had to re-ground this on 3 different MJs' so far... :headpop: I just go to the frame rail, or bed, depending on which is closer to the break in the wire.
"When life gives you nothing but RAIN, then GO PLAY IN THE MUD." qoute by me.

#19 MancheKid86


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Posted 08 April 2009 - 12:29 AM

engine running badly?
sounds likes the timing is off?
before you buy a timing chain/timing light
replace/connect your vacume hose right above your engine

we're far too lazy to click links. :D

..............or read.

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#20 87ComancheLB


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Posted 28 April 2009 - 11:18 AM

If your 4.0 is idling high or your constantly blipping the throttle to try and get it back down, try changing out your old single port fuel injectors for the 4 port high flow injectors, engine will idle very smooth plus increase in power and better fuel mileage I think this was one of the best mods I did.