I just got an '88 Cherokee... I know not to expect good mileage, but I was wondering what to expect and if there are ways to improve it. For now it's my daily driver, but eventually I might just make it a toy.
It's got the 4.0 6 cylinder, auto tranny, and I think NP242 TC...the select track one...
I've already done the full tuneup, oil and whatnot... Working on all the other fluids soon.... Thanks everyone!

 

I get 15.5 around town/rural road 50 MPH driving.

Clean the throttle body.

Refresh the grounds on your 87 along with cleaning the C101 connector and making sure your sensor ground circuit is okay.

 

I drive 90+ miles a day to work..well, 46 each way..2 miles on each leg is thru town rest is highway..I avg around 20mpg..there have been times where I wondered if I was doing slightly better but I think it still is about 20 on the hwy..with city, there is sooo many variables..the weight of your foot, in traffic or not, number of lights on your route, etc..not counting mechanical variables..
Im not sure about after market add-ons that will improve economy as Im a relatively new XJ owner (3-4 months) but a few simple things will definitely help you NOT lose mpg..keeping your tires inflated properly, oil changes regularly, your tune up helped, good air filter, etc..keep in mind you're literally driving a brick..it's CoE drag is just a tick above that of a parachute lol..

 

Where do I find info on the c101 connector? I'm not doing well with the search.
What grounds do I concentrate on? I'm sure there are a million of them

 

Nvm on the c101.... Found that on google... Lol. Still looking for info on what grounds to tackle.

 

My 88 4.0 stock gets 20 highway, 15 in town.

Check the tire pressure, tune up, etc... Before I did a tune up it was never that good. What are you getting now?

 

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 11-28-2011

 

Renix Jeep C101 Connector Refreshing
　
The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of almost 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

Almost every critical signal between the engine sensors, injectors, and the ECU travel the path through the C101.
The C101 is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the bolt and pull the halves apart. You will find the connector is packed with a black tar like substance which has hardened over time.
Take a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.
If you have a small pick or dental tool tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter. Apply a true dielectric grease, not the stuff that came with your brake pads, to the connection and bolt it back together.
　
　
Revised 11-29-2011

 

8-)... Well that will help for sure. Thanks!

 

On my stock '87 I've gone from 12ish to 17.5 mpg in town since owning it. I've done injectors, fuel pump, coolant system, electrical grounds, etc. to get those gains. I think the biggest single contributor, though, is in how heavy my right foot is...

 

Here's a little test that's simple to do and simple to fix if the results come back negative:

Cruiser’s Renix Sensor Ground Test
Set your meter to measure Ohms. Be sure the key is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.
Revised 05/03/2012

 

I know that I need to replace my brake booster... Is that gunna kill my mileage because of the vacuume leak?

 

Ain't helping it.

 

Get the skinniest tires you can find and lightweight, keep them fully inflated, coast a lot, keep the RPMs low.

 

I drive like a grandma... Well on paved roads anyway. ;-)...
Now that I have most of the mechanical issues fixed its getting better. Last thing to do is the brake booster. Then I can start fixing the stuff that ain't broke.