I have a 1995 Cherokee SE, 4.0, auto OD, 3.55:1 axles, & I’m running just slightly larger tires, 235/75R15. I’m trying to get the fuel mileage up to something better than 13 / 14 MPG.

I drove this rig as my company vehicle from new until it was about 4 years old and had about 120k miles. I bought the vehicle and drove it up to 152k miles. I sold it to my mother who had to for 14 years and put 9k miles on it. I’ve had it back since Aug. 2016 and it now has 172k miles. The first six years, this XJ averaged 20 MPG, meaning it got something between 19 & 21 MPG every tank. It was 100% stock at that time, including 215/75R15 tires.

I decided to replace fuel injectors about three years ago to try to improve power & possibly fuel mileage. I first bought some 4-pintle Ford injectors p/n: 0280150943. These injectors were advertised to work in 4.0 Cherokees from 1989 to 1995. The Jeep started and ran perfectly with these injectors, with the smoothest idling since it was new. I later found out these injectors were lean as compared to the stock Siemens injectors and could cause the engine to run hot. In less than a week, I bought some 703’s and replaced the 943’s. I could tell no difference in power over stock injectors with either set. I didn’t have the 943’s in long enough to know anything about their fuel mileage.. The Jeep still has the 703’s. It also has a new O2 sensor, new catalytic converter, new plug wires, cap, rotor, plugs, cleaned throttle body & has had the ECU reset when appropriate. The Jeep starts and runs well, but today’s fill up - 14.3 MPG. Apparently the 703’s are flowing fuel quite well.

I was considering trying the 943 injectors again since “lean” sounds like better fuel mileage, but I don’t want to harm the Jeep running it too lean. I searched up some info about the injector, but I don’t know the stock injector data, so I don’t have the info to do a direct comparison.

Does anyone have any experience running the 0280150943 injectors more than a week? Any overheating or other problems due to them being more lean than stock? Any improvement in fuel efficiency?

 

I run 12 hole injectors, 62mm TB and ADV CPS using 89 octane. About 16mpg in the winter with a little extra pep.

 

There was a thread on this site that ran actively for a few years, all about getting better MPG. At the end, the guy who was dead set on making 25 MPG finally gave up. He posted what he was finally able to get.

It was the same as my box stock 97 with 4 hole injectors. 18/24, IIRC.

If it's getting 13-14 MPG, something is wrong, or you are a leadfoot. Stop looking for sliver bullets, and find out why your mileage dropped.

 

Start with the basics. o2 sensor and the engine temp sensor can make a huge difference in mileage. Also verify that the torque converter is locking up at cruising speed.

 

Just keep in mind the injectors don't control fuel mixture or mileage. The computer controls injector "on" time to adjust mixture and controls it from data received from the sensors, but especially the 02 sensors. If the injectors flow large amounts of fuel, the computer limits on-time to compensate. The number and size of the injector ports do control fuel droplet size however and the finer the droplets, the quicker the engine response.

 

Install a vacuum gauge in the dash and monitor it. best way.....

 

Did a new Denso O2 sensor about six weeks ago, but I can’t tell it made any difference in MPG. It did change the way the Jeep idled for a couple start up cycles (idled much slower than normal), but that also returned to normal within 4 startups.

Torque converter is locking up at the appropriate speed.

I checked the engine temp at the thermostat housing with a laser temp gun when the Jeep was warmed up. It showed me around 200-205 degrees. I did a new water pump and stat about 18 months ago and I wasn’t sure I got a 195 degree stat. Does showing 200 degrees on that housing verify I have a 195 degree stat? It’s only a few inches around the head from the first exhaust tube which I shot out of curiosity and it showed about 500 degrees.

On the temp topic; being a 1995 model, it has the temp sensor at the rear of the head also. The temp gun showed about 175 degrees on the hex nut portion of that sensor when the stat housing was showing 200. I’m sure the water temp on the tip of that sensor would be some warmer, but the hex nut of the sensor is as close as I could get to the head. The head itself also showed about 175-180 degrees around that sensor. Normal?

I checked other mechanical issues; no brakes are dragging, no driveline binding or resistance that I can tell. It picks up speed when slipped into neutral going downhill....

I believed the MPG of the Jeep dropped during the 14 years it mostly sat still in my mom’s garage. She did drive it weekly, but in the entire 14 year period she only put 9k miles on it. During that time I put two radiators, a distributor, and a few batteries in it along with oil changes and gas.

 

Do you still have the stock injectors?

 

And what's the compression?

 

OMT. Got a vacuum gauge?

 

The supposed "injector upgrade" posts you see on this forum are complete BS. In the case of the XJ, 1 hole, 4 hole, 200 hole, it doesn't matter. They all get the same MPG and power is the same as well. I'm sure someone will chime in on my post and argue about it, but it's true. The power increase or MPG increase after swapping injectors is 1 thing. The fact that your old injectors weren't up to par, flowing as well as they should, or some type of clogging issue.

Usually injector upgrades are done for only 1 reason. Flow rate. To increase the rate of flow in a performance car that has a bigger turbo for example. Or the ability to run E85. In the case of the XJ, this isn't something to worry about. The XJ doesn't respond as well to power modifications as far as how much power you can squeeze out. Very poor performance gain per dollar.

 

Injectors are only 1 part of the "team" Their flow rate has to approx match the airflow Thru the engine. I have had 2 jeeps in the past 25 years totaling over 500k between them One was a 92and now an 01. They were both AT and stock for 100k then both lifted and later stroked. Neither EVER got close to 20 mpg...usually 15 to 17 on mostly highway, and around town 13-15. Mixed normal driving was 15 give or take. My Lifted (31's) and Stroked 01 with 20% bigger injectors just came back from a ski trip to Vermont from NY. Ballpark 250 miles uphill-ish on highway got 16mpg at 65. Coming "downhill" at 65-70 got 17.1 I think thats the best I ever got in any jeep. As soon as I start to drive around town where in revving above 2000 and not in high gear eats up lots of gas. Coolant temp is an important part of that equation much cooler than 190ish the computer rich-ens up the mixture. Remember if you change the tire size from "stock" delivery...the speedo gear will be off if not adjusted to the new tire size and thus your mileage driven will be not accurate. It doesn't take much tire difference to be off 5% or more off or actual speed/distance. Bigger tires rotate slower so your speed and distance driven will be less than actual. If you have GPS drive at 60 on GPS and see what your speedo reads 10 % will be 54 or 55 gauge mph..then add 10 % to your mileage ..15mpg becomes 16.5mpg..may not be your issue but its something to add to the equation

 

. Yes, and the Jeep was running OK with them, but they haven’t been cleaned or otherwise touched since removed.

I have not checked compression. The Jeep does not use enough oil between changes to add any oil & never has that I recall. I know that’s not the same as a compression check, but that’s all I have at the moment.

OMT. Got a vacuum gauge? I don’t have a vacuum gauge, but thinking about the suggestion of installing one.

Anyone know if the temp sensor / sending unit in the rear of the head is the one that sends data to the ECM or just for the gauge?

 

So if you were getting good MPG with them, and 4.0 engineers spent a lot of time figuring out what the best overall injector would be, then why throw arbitrarily selected injectors at it and hoping something good will happen? You can test and clean those injectors yourself, or have the service do it for about 20 bucks apiece.

If your compression is below normal you're not going to increase MPG by changing injectors.

You need a diagnostic vacuum gauge to check for leaks in the system and if the exhaust is blocked. Like if the catalytic converter is clogged, muffler internals falling apart, bunch of rodents cooked inside the exhaust etc.

 

I do calculate an additional 4% greater mileage than I roll up on the ODO for figuring MPG. So if I have 180 miles showing on the trip ODO, I use 187.2 as the miles driven.

As for the past mileage, the Jeep miles and fuel quantity were input on each fill up and on monthly vehicle reports for over 120k miles while it was a company vehicle. The average mileage was calculated by a vehicle fleet management company. The average was 20.4 or 20.7 during that time, I don’t remember which fraction for sure, but the average was over 20 MPG. The driving type was mostly highway, but I drove it pretty hard all the time. I do recall getting 21.x for several tanks of fuel during non-winter fuel additive times.

The replacement company vehicle I received was a 1997 Cherokee & its average was 18.?. It had the same motor and transmission, but it might have had different gears. It was sort of a lemon in several other ways so it not getting as good MPG as the 1995 fit in with its other ailments.