New to me MJ

[ComancheX2]

Hi all,

 

New member here.  I recently picked up an '87 Chief and am starting to get to know it and figure out what I need to do.  It's a 4.0, 4WD, BA10/5 manual.  

 

First question.  It came with a spare AX-15 along with the appropriate crossmember and NP231.  As I was cleaning up the crossmember there's what I believe to be a mouse nest in the center accessible by the lightening holes.  But just to be sure, since it looks like compressed cotton rag, they didn't come with any insulation inside it did they? I'd think it would just be a moisture trap, but stranger things have happened...

 

Next question.  It has a 3" lift and 31x10.50 tires.  Driving home it only got about 16 mpg. It runs really smooth, so I don't think there's anything significantly wrong, but I was surprised at how much less it got compared to my H.O. era AX-15 XJ.   I ended up pulling the wheels off the XJ and putting 235/75's on the MJ.  Still didn't make much improvement, only getting about 17 mpg.  My XJ would get at least 21/22 and occasionally up to 24 mpg.  Would the lift cause that much of a drop in mileage?  An alternative, or maybe additional factor based on some searching, the temp gauge didn't get anywhere near as warm as my XJ, only about 150/160 at 60mph.  Haven't been able to test yet to see if the gauge is accurate or if it really is operating that cool. If accurate would that be the primary cause rather than the lift?  The prior owner said that he'd gone thru Cruiser's tips.  I'll start doing the same and may find something, but if anyone has any suggestions on what to look at first, I'd appreciate the guidance!

 

Oh, and the turn signals stopped working too.  They worked on the test drive, but driving home after turning on the headlights, the left turn in the instrument cluster stayed constantly lit. Then when turning the switch the actual turn signal wouldn't flash.  Right turn signal did flash however.  After getting home, two days later neither worked.  I'll have to dig into that too.

 

Other than that, it's got a few things where the prior owner(s) had little dents here and there with a largeish one on the bed sidewall where the paint was knocked off and it's starting to get some surface rust.  I'll get those places taken care of to protect it from becoming bad. In the mean time, I'll have some fun with it.

 

Thanks,

Robert

[MagicJames]

Lets see some pics my friend, gotta love a Chief. 

The poor milage is probably just a bunch of little things inmy option. The lift won't help, running a bit cold doesn't help, the throttle body and the whole system could need  going through. 

The turn signal issue is a bad bulb or bad ground. The sockets for the bulbs also get pretty corroded and do that too.  

[ComancheX2]

Thanks James,

 

I actually tried to upload a picture into my profile, but something didn't work.  Then reading thru the rules it talked about 3rd party hosting.  I'm somewhat of a luddite, so I'll have to get my nephew to help me with where to host pictures. 

 

I'll get busy and start going through things one system at a time.  I was able to learn some working on my other Comanche (Not an MJ) but I don't have a lot of experience with automotive maintenance.  Part of the reason for getting this was to have something I can work on and learn.  The PO had commented that on occasion it would have a high idle and I did experience that once so far.  Said he'd replaced the IAC but it would fix it for a while, but always come back.  I'm wondering if it could be a small vacuum leak.  So I'll get the experience to learn.

 

Today I've got to go get a load of top soil to address drainage issues at my mother's house, then get down to my farm to do some work.  I'll get some pictures to have ready to post.  It's definitely not a show truck, but it's a good starting point.

 

Maybe this will work to post a pic...

[pizzaman09]

Check to see if the manifold header bolts are tight where the exhaust and intake bolt to the head.  That can cause all sorts of weird idle issues.

[ghetdjc320]

Nice looking truck! Always liked the look of the “Chief” graphics. I’ll take a crack at some of the questions:

1. There is no insulation in the crossmember. The cross member design does have several sandwiched pieces of metal that can indeed get moisture and oxidation traps, but the crossmembers were typically galvanized (one of the very few pieces on MJ’s) and normally hold up decently. They are fairly lightweight and still solid enough for their use. 
2. First off, your XJ is getting rather phenomenal MPG so the comparison might be a bit off. 16 mpg for a lifted 4x4 MJ with a 4.0 is very normal and typically within range. What is interesting though is that you noticed it wasn’t getting as warm as your XJ. If indeed the gauge is accurate, a rich running engine will get lower MPG & typically runs cooler. A renix engine monitor or REM can be a really handy tool to help you see what the ecu is doing and can sometimes help track down issues. 
3. If the turn signals were working then went out as you drove with the headlights on, my bet is that it’s the sockets and/or bulbs themselves. I’d remove all the sockets, clean them, add some dielectric grease and swap in some new incandescent bulbs. 

[ComancheX2]

Thanks Pizzaman and Ghetdjc,

 

Good to know.  Knowing that the FOD in the crossmember isn't insulation, I'll pull it out before I put a coat of paint on it.  I was going to look at cleaning the throttle body and IAC, I'll check the header bolts while I'm at it.

 

For full disclosure, my mpg values are highway at 60-65 mph.  In over 250K miles, my stock AW4 XJ would easily get about 20 on the highway, and the AX-15 slightly better.  So that's what my frame of reference is based on.  It's probably due for a tune up and I've ordered some new higher efficiency parts.  Hopefully that and doing (re-doing) all of Cruiser's Renix tips will help.  I was also looking into the REM the other night. Found it kind of interesting that he talked about the ability to get component parts and the tariffs. I deal with that to a small degree in my day job. I can only imagine how much of a pain all this would be for a small entity like that.

 

In the mean time, made my first trip testing the payload.  Got a 1/2 cubic yard of top soil to try and fix the poor job the county did when installing a new water main.  It squatted pretty good, but handled it okay.  

[89 MJ]

Were both of your XJs 4wd?

 

The best my MJ has done is right around 20 mpg. It has only done that on one tank, every other time has been in the 16-18 range for highway driving, so I think you're right in line with what you should be getting.

 

I think there could be a number of factors for the worse fuel economy. Needing a tune up, like you thought, the lift is a big one, and MJs are naturally a little higher than XJs it seems and probably less aerodynamic too. From my experience, 4.0s actually like some RPM, so the factory 3.07 gears are hurting you some. 3.55s would probably yield better mileage. It is also worth nothing that the cylinder head, intake manifold, and exhaust manifold (possibly the cam too, I don't remember) changed in 1991 when the HO Jeeps came out. All of those let the air flow better, which will help gas mileage.

[ComancheX2]

Yep, both stock HO era 4x4's, so the HO may definitely be a factor.  If they like a little more RPM's then that does make sense as it was doing about 1600 or so at 60 mph.  I know my IO-320s liked to be at 2400 RPM, but that's a different beast.  At the moment I'm driving about 115 miles per day.  So with 17 mpg and $3.69+ fuel it's creating a little more of a hit than I expected.   Looking for a decent FWD KL for the daily drive until I can get out of that situation.

 

While talking to a co-worker, he told me about "Kansas Rocks" and said he wanted to take his kids sometime.  I'll likely go along with him sometime before deciding if I want to keep the lift long term.  Right now I don't plan on doing a bunch of rock crawling, so not totally necessary for me.