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Discussion Starter · #1 · (Edited)
Hey folks. I hope that whenever you come upon this thread you're having a good day and doing well.

I have a 1990 Cherokee, with the manual, and the 4.0 I6. I've decided that I adore this vehicle enough that I'm going to try and make it the best possible Jeep (and possibly buy a 1990 Comanche and do all the same things all over again!).

So I figured I'd join up here, share all my planned modifications, discuss details and options, and as things actually happen (this part may be very slow - months or years. I want to do everything myself that I can, and I'm in no real rush.) share the results in photos and experiences.

I feel like I should address a few other basics before getting into specifics.

  • The I6 is an engine I'm particularly fond of. There may (ahem. will.) be significant improvements to the I6 on this list, but I'm not interested in a V8 conversion or anything like that on my Jeep(s), even if you have a very clever conversion that fits well and is amazing, for a variety of reasons.
  • My uses are highway and trails, and there might be some volunteer stuff in my future with these vehicles. What I'm not (at least yet) is a rock crawling fellow, and these vehicles aren't for rock crawling. I like offroading and I like camping, I adore spending time out in wilderness, and I like living far away from, but also making use of, the membership bulk stores, and I like using my Jeeps as primary vehicles.
  • Cost matters much more that project time/difficulty, but cost also doesn't matter that much. So imagine how little project time and difficulty matter to me, if you will. The main thing I want to avoid wherever possible is shop time or professional time - I'll do whatever I reasonably can myself, but certain things are just unavoidable (machining, alignment...)
  • With the neglect that this Jeep has suffered, there will be a lot of repair / replacement alongside upgrades. That's less of a value proposition, I could certainly go out and buy something in better condition. However, that has it's own charm to me. It's not like I'm expecting to get my money out of this Jeep in a sale down the road. I am not, I'll keep this vehicle for the foreseeable future.
  • Despite continuing research, I come into this with the assumption that my knowledge is always incomplete. If you know more, please, share it with me. I'm explicitly going to add that anytime I say "my knowledge is weak", please read that as an active request for more information.

    I'll break these projects up as best as I can, but it may not be the way that's generally done here. Let me know if something's more intuitive for you folks.

    I'll add current photos probably by January. Soon(TM) if you know what I mean. Also, I'll add links to what I intend to purchase in spurts, because there's a lot that I've found solutions for even if I don't know what to buy for everything.

What are your thoughts? I want to welcome all suggestions, opinions, and especially particular part or merchant options that people have had good luck with. Also, sorry if some things aren't indented correctly. The forum and my browser seem to have some minor disagreements.

  • Already done:
    • Battery replacement
    • New terminals
    • New starter relay
    • New steering column
      • Junkyard, but still solid, unlike the old one
      • Needs a little work still, key isn't 'freed' when the vehicle is fully off
    • New rear gate
      • Junkyard
    • New gas cap
  • Current known problems:
    • Very long crank (6-8+s): current priority
    • Gas mileage lower than expected
    • Leaky gaskets everywhere
    • Belt tensioner within PS pump doesn't work, stuck tight
    • Runs a bit rough to my ear
      • Knowledge is weak here. I haven't been around many tuned-and-good I6s in person
    • Heater core is bad
    • Oil pressure and battery gauges don't work.
    • Speedometer is off.
    • Fuel gauge will occasionally "dive" to "light on" after dropping normally down to a little below 1/4.

Project list:
  • Engine
    • 4.6L Conversion
    • Aluminium head
    • HO EFI Conversion
      • I'm told that I have the Renix system, and that that system is significantly inferior.
    • 4-outlet fuel injectors
      • Is that the generally correct term? or is it '4-way'?
    • New block mounts
    • Open cooling conversion
    • 3-row radiator with triple electrical fan
    • Removal of crankshaft fan
    • Rusty's airpipe and filter instead of the airbox
      • Airtube
      • Filter (is there a better cone filter out there? I'd love to hear about such)
    • Switching to separate PS pump & belt tensioner
      • I've noticed that the tensioner on this combo unit tends to fail faster than the pump does
    • New heater core
    • Swap to Evans Waterless coolant
    • Swap to all-year 10W-40 (rotella)
    • Basically every "performance" part that I can get my hands on
      • i.e., Part is still available for whatever seems to come within 2-300% of a "fair price" to my biased and subjective perspective, and that I can reasonably improve might improve something
  • Transmission, T-Case, Axles
    • Swap to an NSG370
    • New T-Case
      • Atlas, is what I'm told, is probably best? My knowledge here is particularly weak.
    • New axles, with new diffs/lockers.
      • Again. Weak knowledge area.
    • Adding cooling to the trans/t-case
  • Suspension, Running Gear, Brakes, Steering
    • 2.5" lift
    • Larger wheels and tires
      • I'm hoping for 32" without major fender mods, but fairly confident 31" will work at worst.
    • Larger steering box
      • Probably junkyard
    • (Grand Cherokee?) Larger / more robust running gear and brakes components
      • Probably junkyard
    • Replacing all bushings/ball-joints
  • Electrical, Lights
    • Supercap for primary electrical storage; battery delegated to backup/failover
    • Isolating switch circuits from light circuits to remove voltage droop
    • Improved (doubled amperage, if possible) alternator
    • Replace & Improve fog lights
    • Add overhead lights
    • Add spotlight
    • Convert tail lights with the Rusty's frame
    • All new lights LED, convert all old lights to LED also
  • Cabin/Interior
    • New carpeting, header
    • 8-gang switch box mounted into dash
    • Possible dash replacement
    • Heated sets
    • New/fixed instruments
    • Much more modern infotainment center
    • New speakers
    • Possibly new dash.
      • I don't know if the plastic has aged well enough for mounting new gang box, new infotainment center
  • General, Unibody, Utility, QOL
    • Valves to replace all drain bolts.
    • Bit of a roll cage
    • Frame stiffeners
    • Running boards.
    • Replacement of several rusted body/unibody panels
    • Any rust welding that's necessary underneath
    • New bullbar
    • New winch
    • Smittybilt IMS for jack, jerry, spare
    • New rear bumber to mount IMS
    • Support hydraulics for hood, replace hydraulics for rear gate
    • Lights on inside of rear gate and hood, lights within cargo area
    • Darkest local-legal tinting
    • Whatever windshield armor is highway-legal here (I've reached out to a local lawyer on this)
    • Replacing rear quarter windows with metal panels
    • Roof rack, custom ladders
    • Rust sealing everything
    • Custom rear cargo organization
      • I'll probably weld some sort of drawer support and "trunk lid" for that cargo area, to hold a good tool box, trauma kit, couple of ammo boxes, water, and then space for groceries and a 12v fridge.
    • Under-hood battery charger
    • Fixing or replacing the engine heater, adding heater for transmission, battery, etc
    • Skid plates
    • The larger side mirrors
      • I think they're off the Grand Cherokee?
 

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1988 Cherokee Laredo, 4.0, AW4, 2wd
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It's not just the EFI. HO's deleted the EGR and Knock sensor, have a different head, exhaust, TB to name just a few changes.
 

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HO myth buster


Renix in 90 made 182 HP. HO in 91 made 190 HP. That's 8 HP difference.

HO only made more HP than Renix at higher RPMs and not a bit more torque. HO had a 58 mm throttle body versus a 52 mm throttle body on a Renix. That’s 20% more air available through the HO throttle body. The HO also had a better design header. See where I'm going with this?

It’s only a 4% horsepower increase…..

The whole 8HP was not mostly from the head, but from the bigger TB and better exhaust manifold.

Put a 60mm TB from www.strokedjeep.com on your present manifold using the Renix head, eliminate the "crush" in your headpipe with proper re-routing, and go for it.

HO stands for Highly Overrated.
__
 

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Discussion Starter · #6 ·
HO myth buster


Renix in 90 made 182 HP. HO in 91 made 190 HP. That's 8 HP difference.
[...]
HO stands for Highly Overrated.
__
It certainly sounds like I need to adjust that plan.

For confirmation alongside those factory numbers, do you have any accurate numbers for post-4.6 conversion as well? Much less likely, but it'd be nice to have nonetheless.
 

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Your not crazy. I'm doing the same thing on an 00' gutting it completely.

  • Current known problems:
    • Very long crank (6-8+s): current priority
    • Gas mileage lower than expected
    • Leaky gaskets everywhere
    • Belt tensioner within PS pump doesn't work, stuck tight
    • Runs a bit rough to my ear
      • Knowledge is weak here. I haven't been around many tuned-and-good I6s in person
    • Heater core is bad
    • Oil pressure and battery gauges don't work.
    • Speedometer is off.
    • Fuel gauge will occasionally "dive" to "light on" after dropping normally down to a little below 1/4.
For the long crank I would check the ignition switch and battery leads +/-. Also possibly a load test on the battery first I know you said it's new but.. If that's not it then move on to check spark on start etc etc as others have mentioned. Had the same on mine and it was the ignition switch. However given all the other issues you listed sound like you may have some cabling or wire issues in the column or harness anyway. A Fluke is your friend there...

If your looking to run larger tires and drive daily I would replace the steering gear box with a beefed up one along with a new brace kit and new PS pump/lines while your doing it anyway. (Going through this right now.) To save your time and effort I would forget about a stock salvage yard replacement as it is not going to make a much of difference with larger tires and lift. There are numerous posts around on beefier upgrade and replacement options.

Also on the rear end, hope have at least a 8.25" or even better a D 44 another option would be a Ford 8.8 however the Ford is also iirc c clip..
 

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Improved. Never corrected.
The Renix ECU must see about 300 RPM for a period of time before it fires off.
The biggest issues Renix had was too much resistance in the ground system. That was followed by poor connections and continuity through connectors.
Go to www.cruiser54.com and see Tips 1 through 5 for 1987 and 1988. Skip Tip 2 for your 89 and 90 as the C101 connector was eliminated in those last 2 years.
 

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Discussion Starter · #14 · (Edited)
I've ordered new/upgrade wires (the JeepCables Big kit, 2GA), and I'm waiting on those to arrive. When they do, it'll be time for a day of going through all the connections and yanking, cleaning, seeking corrosion, yada yada yada - all the stuff cruiser54 recommends, a few other checks I've thought of. I predict lots of terminal cleaner and wire-brush usage in my relatively near-term future (but being out in the boonies, that's relative. Shipping always takes forever out here). Also ordered the quick airtube + filter off rusty's (might do one of those cowl intakes later, but this is a cheap in-between).

I keep seeing the "Mojave Heater" - that seems to be a heater core replacement. Is that better than the OEM part? Or am I misunderstanding it?
 

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On your belt adjuster, are you sure you are loosening all the bolts? IIRC, there are 3 (maybe 4?) bolts/nuts that have to be loosened to move that adjuster. Somewhere on the forum here, there should be some pictures I posted in relation to this, but I can't find it, and can't find the original picture, either.
 

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Discussion Starter · #16 ·
IIRC, there are 3 (maybe 4?) bolts/nuts that have to be loosened to move that adjuster.
I am doing 3 for sure, so if there's a 4th one in the PS-pump/belt-tensioner unit, I've missed it somehow. I'll recheck that when I do the wires. Thank you.
 

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Discussion Starter · #18 ·
Jeez there are a lot of these, and I thought I was only trying to loosen the mount overall, and then loosen the actual tensioning one on the lower right there. I seem to have missed at least the lower rear.

Cruiser54, do you put as much into helping everyone? Thank you.
 
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