hgeranium

Are you 100% sure that it’s the computer? A 4.0 has many causes for the symptoms that you’ve explained. You can buy reman ECUs from any big box retail or online store, or preferably grab one from a junkyard. There should be a few years that have the same ECU that you need; someone smarter than me can tell you.

Thanks for the graphic! When tightening my bolts I just used a picture of a manifold gasket and referenced the holes on the bottom I needed to find with the top holes lol

After some independent research I did see something about slower logic from the ECU means it takes longer to verify crank position, so I'm sure you're right.

Great to know! It makes me feel better knowing it's a 'quirk' of the renixes rather than something I need to diagnose. Thank you

I wanted to get a little survey on how long it takes to turn your XJ/MJ over when cold and warmed up. My MJ has consistently taken 7 to 10 cranks cold, and 5-8 when warmed up. This is the oldest vehicle that I've owned (2nd oldest is a 94 GMC C1500), so I'm curious if it's just a 4.0 being a 4.0. It's not like the truck has trouble starting up, just more cranks than I would be expecting. I feel like I've seen online people starting up their XJs with 3-5 cranks. My GMC always started up quickly, but I suspect the TBI played a part in it. My only in-person friend with an XJ has a chevy 3.4 swap, so I don't have any IRL comparisons to make.

I agree with eagle on the manifold bolts. I made a post a few weeks ago about an intermittent high idle/rev on startup (eagle might have been the one to tell me to check it), and I tightened all the bottom manifold bolts that needed to be snugged. I'll never actually know if the problem is gone, only if it comes back, but as of now my startups have been much smoother and less aggressive.

My friend spotted this jeep back in San Antonio! Looks quite different to that auction picture.

Thank you very much! I’ve read about that happening to people but stupidly never checked myself.

An occurrence that has been happening for almost as long as I've had this MJ, about 3 years now, (88 4.0 AW4) is that, on occasion, during cold starts (sometimes when warmed up too, but more seldom) the motor will rev up hard to ~2000-2200 for a few seconds and come back down. I also had another issue paired with that where the revs would go up and get stuck there, even while driving. This happened seldomly through the last 3 years but really ramped up last month. The throttle would get stuck open. Super jumpy, hard to brake, etc. like the throttle plate was cracked open. I cleaned the TB (no major carbon deposits), ran a can of sea foam, and replaced the IACV a few weeks ago and I haven't seen this problem come back thus far. However, even with the throttle body cleaning and IACV replacement, that high revving phenomena still regularly occurs. I guess I would like to know if this a common occurrence for anyone else and I should just ignore it as an old vehicle quirk. It is my daily driver, so that's why it's more of a concern to me than if it were just a project. TPS is brand new, voltage tested perfect and within that specified resistance range (Cruiser tip #8). Vacuum lines are solid all around, no leaks there. Resetting the IACV does nothing to change it. The truck runs flawlessly other than that. In park it idles steady at around 900rpm and in drive stays steady at ~700. The fact that the truck runs so well otherwise leads me to believe that it's just an old vehicle quirk but wanted to run it by y'all with much more 4.0 experience than I. Thank you!

Not sure how appropriate this is considering it's not a cruiser-appointed tip, but a very quick DIY fix that eliminated a great bit of my wind noise is found in this old BleepinJeep video: All you do is stick a line of 1/4" poly rope between the door seals and the frame itself. It puffs just enough to seal up any gaps. This also helped stop a leak from the top of the doors during heavy rains or when washing the truck for me. Another thing that is well documented for MJs/XJs with the older style metal trim around the front windshield is to swap it out for the rubber one piece molding when replacing the windshield. I'm sure that none of this is new for many of us but I figured it's better to have something than nothing in regards to the tips that cruiser never got around to writing up. Hopefully any lurkers browsing cruiser's tips on the forum will find this helpful.

What was your price on that? I was planning on using a six foot tarp with magnets along the bed, but that is a much better idea!

Ah, that’s unfortunate to hear. Some junkyard vent window assemblies will have to do, then.

Woah! Good find!

1988 Jeep Comanche Eliminator 4.0, AW4, 4x2, D35 rear, SWB Build date: n/a, that door sticker is long gone.. South Texas Bought it in 2022 with 176k on it. As of 8/2025 I have put just over 10,000 miles on it. I daily drove it all of 2022, had a second car from 2023-early 2025 so drove the jeep less frequently. As of March 2025, it is my one and only daily driver again! This is my first Jeep, being heavily inspired by my good friend who has an engine swapped 1984 Cherokee Chief. I happened to come across it on marketplace only a day after my previous truck was totaled in front of the house by a texting driver. It runs and drives fantastic, I frequently have to make ~400 mile round trips and never get any complaints from it.

Both of my vent windows have now suffered the same fate of that bottom rivet, specifically that black rod, connecting the window to the door completely rusting out and breaking in half. I'm wondering if anyone has any experience with a DIY fix without fabricating/rebuilding that mounting? Or would a full window replacement be the best way to go otherwise? Attached isn't my picture. No AC or vent windows in the Texas summer is going to get old quite fast, so I'm willing to try even the jankiest fixes. My jeep has had its fair share of them.