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6 Posts
4.0 ZJ Tips....For what it's worth.

Hey All,
I'm new to the forum format but I like what I found here. I'm 37 with 20 plus years as a ASE Cert. Master Tech. and 5yrs in a dealer. I have going thru posts and found stuff that was cool and some was hogwash. I bought my 97 ZJ 4.0 about a year ago and heres what I have done so far in no order.

I mounted a second battery in the rear. It's wired with a solenoid so when the truck starts or runs, The two batteries are connected. But if you leave the lights on or play the radio you can kill the front battey and the rear remains charged and with a push of a button it jumps the front (I also built a 190amp alternator for it)

I removed the engine driven fan and radiator (leaking) and replaced it with a spiffy aluminum unit. Then I mounted a Lincoln town car (01?) fan to the new radiator by making two small brackets to the upper and lower header. I also used two of those clips you mount trans cooler with for extra support. I wheeled it pretty hard and it don't budge. I took the original fan shroud and cut the bottom of it so you still see the caution fan if you understand me. This way it looks bone stock. I wired the fan using a thermostat that the sell next to the add on fans. I have a three position switch. Center it comes on where I set it. Down is off for water crossings OFF, and up is override on high. I mounted the adjustable thermo stat in the grill and can adjust it at any time with a screwdriver.

I removed the dist cap and removed the pick up. I removed the ears and modified the spot where the wires go thru. Now you can manipulate the timing because the pick up is set in on spot and the electrodes are in another. I went two degrees over stock without detonation. I did try further but I had to put the 180deg thermostat in and run shell premium.

I line bored the throttle body...nice to have friends with cool machines :)

I made up a intake with a K&N cone and a electrical conduit plastic pipe. It was the exact size and bend I needed and it is on the shelf at Home Depot.

The best mod was relocating the IAT. It really tied the other mods together belive it or not. True it does enrich the mixture but I am stolic (14.7/1) just above idle. When you increase airflow you also have to inrich the mixture. Just to be a nut I mounted a second IAT in the intake so I could compare on my snap-on scanner. Even more nuts with a 3 position switch and access to you ambient air sensor harness you can make the read out in the display up top tell you the intake air temp with a flip of a switch.

It is a MUST that the cone air filter doesn't pull engine air. The heat kills any gains you got. I use a piece of cardboard for a templet and the make one out of sheet metal. I haven't made mine yet but I'm surprised at what a good job the cardboard is doing :)

Make sure you take the air intake behind the grille out and remove the flap (that keeps the bugs out) and open the rear up so it feeds you "box" with cold air.

I also removed the stock charcoal canister out and replaced it with one from a 98? Couger (small one) This canister has all the ports you need and fits nicely where you airbox was and next to your K&N cone.

I also have front and rear quick connect jumper cable ports and 25 feet of cables under the back seat.

I made a docking station for my Zune (Microsoft Ipod) that ties it into my pioneer din and a half head unit.

Another interesting one was I had my amp meter out and I decided to check voltage drop at the injector/coil feed. I had a major loss of volts and amps under load. I wired a 30 bosch relay piggyback to the factory harness and man it help my power search. I never dynoed but I would say 5 hp and a much smother delivery of power.

I remover the front marker lights (Under the Headlight) and replaced the sockets with 2 filiment sockets and put clear bulbs in. Now the front lights go on with the parking lights and blink when signaling. Looks got with the front lit up. You can also add bulbs to the tail lights to eliminate the dark spot below the brake lights.

I put in the hid headlights...the real ones with the ballists...BRITE

I use my truck for side work and have about 40grand in tools in it so I alarmed it with a Omega alarm with a page and a mile of coverage. I can also have it call my cell and I added 6 different sensors.

I saw a guy in a post 'adjusting' his throttle cable with split shots....From what I saw he was taking up slack in the cruise control cable. If you want to adjust the throttle cable put a adjustable wrench on the bracket between where the cable pass thru. Just lean towards the pass side and don't go too far. You should be able to hear the throttle snap closed. Make sure you readjust you TV cable (trans)...pop the tv cable off and remove the white clip. Adjust it till the cable is even with the linkagi e. Maybe a hair shorter for quicker downshift.

I know alot of these tweaks may seem silly but when your low on funds you can do most of these for peanuts. I am cheap and I like doing with what I have.

Well thats all I can think of right now (tired) but there is MUCH more. If anyone wants pictures let me know. After this they may not let me post LOL thanks for listening. Anyone know the temp specs for 4f trans?
I just did an upgrade to 4 hole injector on my 99 gc 4.0l. Now I'm getting a p0172 fuel sys rich code.
any ideas why. computer relearning? thanks

525 Posts
I just did an upgrade to 4 hole injector on my 99 gc 4.0l. Now I'm getting a p0172 fuel sys rich code.
any ideas why. computer relearning? thanks
Had the same on mine after fitting 4 hole injectors and after running for a few days I cleared the codes with a reader and its been fine since
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