I Increased My XJ Gas Mileage To Over 20 MPG

[Hammered]

I'm curious to see if switching the battery cables does alot

 

[Blaine B.]

I run 2 grounds and 2 powers to the power distribution center. 4 gauge for each wire. So I suppose that's around 2 gauge total, right?

Helps, I must say.

 

[MudDawg]

There are two ways to learn something....Listen to good advice based on experience or by trial & error.....interesting thread.....good example of good ideas and utterly ineffective ideas....you just have to pick out the good from the bad.

 

[Ecomike]

I run 2 grounds and 2 powers to the power distribution center. 4 gauge for each wire. So I suppose that's around 2 gauge total, right?

Helps, I must say.

First off feel free to call me a grave digger for digging this OLD thread up. I have a thick skin, I grew it in Chem Eng. classes at U of H, part of the Nano Tech Bio-Chem Engr. department research there!

Since I have reached the age where I forget what I had for breakfast today, Hmm, Ohh that's right I skipped breakfast, LOL, , I went and dug up my daily notes on my gas XJ from last year. They are extreemely detailed. I found out that just before I replaced my TPS last year, which helped solve part of my gas mileage and TCU shifting too early problems, that I also found and fixed the day before the following:

"Fixed a bad ground on the TCU side of TPS, was 1550 ohms pin D to ground, now < 1 ohm." Quoted directly from my MS Word file notes. Some how I got so wrapped up in the TPS tests and data and TPS replacement the day after I fixed the ground, that I overlooked posting this trivial little fact back in the summer of last year. I fixed it by running a new ground wire straight from the TPS sensor (TCU side) to the Battery in my case, as I did not want to spend the rest of my life Fking with the wiring harness trying to locate the week wiring connection...

So, since I am still about another 5 mpg away from posted peak MPG performance, according to others here for the Renix 4.0's, I for one am going to go back and check other sensor ground wires like, especially my O2 sensor ground wire because I also determined last year that any wiring or corroded sensor connection resistance in the O2 sensor wiring loop will biass the ECU/O2 sensor towards running Richer (instead of leaner)!

I incorrectly assumed early on that if the engine ground was good enough for the starter, that it was good enough for the electronics, but I failed to recognise that the wiring harness itself could be biasing sensor to ECU readings through failing wiring harness wires and connections themselves.

So the conclusion here is that we should check each and every wiring harness sensor ground, and the ECU and TCU computer grounds for added resistance in those small wiring harness wires that could be killing our gas mileage! Even with 2 ga ground wires from the battery to the frame and to the engine (which is not a bad idea) a single loose connector in the sensor to ECU and sensor to ground connections ( which a 2 ga battery to engine ground might not fix) can cause low power and low Mileage, at least on the Renix controlled Engines. I suspect the same is true of all the 4.0s, including OBD-IIs.

 

[Pharaoh XJ]

Well i asked that question alot of times but never got a straight answer
I have a 94 AW4 3.55 235/75 with 150 kmiles EXPORT version UNLEADED FUEl, so no O2 sensor
best mpg ever 17 mpg
avg is 14 mpg

Does that has to do my ECU & the unleaded fuel setup ?

 

[Ecomike]

Well i asked that question alot of times but never got a straight answer
I have a 94 AW4 3.55 235/75 with 150 kmiles EXPORT version UNLEADED FUEl, so no O2 sensor
best mpg ever 17 mpg
avg is 14 mpg

Does that has to do my ECU & the unleaded fuel setup ?

99% of us have the O2 sensor which allows the ECU to run in a fuel efficient closed loop mode. So since yours does not have the O2 sensor, I would say your getting about the best mileage that is possible. I have seen actual mileage reports for these jeeps that ran from 7 mpg to 25 mpg. Many of us have been lucky to get 11 mpgs when the O2 sensor died.

 

[Pharaoh XJ]

Edit :EXPORT version LEADED FUEL

 

[Pharaoh XJ]

We dont have leaded fuel any more so I m running 92 Octane unleaded.
Any ideas of how diificult it is to swap to an UNLEADED ECU, I know I have a bolt in my exhaust manifold instead O2 sensor, but not quite sure about the wiring ?