4.0 Liter Fuel Economy Tech

[BadAssEddie]

So, I replaced the injectors in my friend's from work XJ with Dodge Neon, Stratus, etc. (Bosch part # 0280155703). He is reporting 22.5 mpg highway now compared to 16 mpg beforehand. Granted, the number 2 cylinder had intermittent firing due to a bad plug wire, but that sounds like better mileage than most get in 4.0 Jeeps.

Anyone have prior experience with this swap? Seems like a pretty great value for $100 in new parts. I'd be interested if there was any mileage increase on a lifted Jeep. Read as do it and tell me

[turnbull]

The only issue is that I don't know what an XJ should be getting in terms of gas mileage. If we were talking about a TJ, I would be willing to try it out because I've never heard of a TJ getting that high of gas mileage. Maybe one of the XJ guys wants to be the guinea pig on this one?

Did you replace the bad plug wire at the same time you replaced the fuel injectors?

Another reason to be skeptical is that if you go on Wranglerforum.com, people will swear up and down that there is no way to improve hp or mpg on the 4.0. That said, I installed an Edge Trail Jammer kit which consists of a cold air intake, enlarged throttle body, and some programming module. I did 0-60 tests before and after, and the 0-60 time decreased slightly. It's hard to tell whether mpg increased or not because I always get screwed while driving on 81, as in I will hit traffic whenever I am trying to calculate my mpg, so of course that will lower my mpg.

Anyway, point is that if the Trail Jammer kit improved performance despite the forum guys saying nothing works, maybe there is something to be gained from those fuel injectors after all.

[turnbull]

So I found this article concerning the above swap:

http://thexjguys.wordpress.com/2012/12/ ... ctor-swap/

Sounds promising. Now I just need to find what injectors my 4.0 will take, if any at all. I don't know how much different the 04 Wrangler 4.0 is to the 4.0 engines that this article is talking about. This doesn't necessarily mean I'll try it, but it is worth looking into.

[Jeeper52]

i dont think the JF guys are necessarily saying it wont improve gas mileage, just saying the upgrades wont pay for themselves

or at least how i interpretted it (sp?)

[Mr.WJ]

I've been itching to buy the Bosch 4-hole injectors for a while now. Don't know why I haven't. Anyways, the main upgrade is the significantly better atomization of the fuel. WJ people report much smoother idle, better throttle response and a few have gained 1-2 mpg.

[turnbull]

I've been itching to buy the Bosch 4-hole injectors for a while now. Don't know why I haven't. Anyways, the main upgrade is the significantly better atomization of the fuel. WJ people report much smoother idle, better throttle response and a few have gained 1-2 mpg.

I read the same thing for TJs. From what I've read, at the very least one should expect smoother idle and better throttle response; there seems to be no denying that. The question to ask is: are the performance gains due to bad injectors being replaced with new injectors, or do the Bosch injectors actually improve performance?

Physically speaking, the concept is sound. 4 holes as opposed to 1 hole for spraying fuel would increase the surface area of the fuel, so less fuel is wasted. The programming module I have connects to the MAP sensor, which apparently determines the air/fuel ratio. Since the Trail Jammer kit is designed to improve air flow, my theory is that the module is designed to compensate that air flow with more fuel.

That said, if my injectors are using more fuel than stock, then theoretically it would be even more beneficial for me to get the 4 hole injectors. Since I can get them for a little less than $100, I think I am gunna do it. Plus it can't hurt since my injectors have over 100k miles on them.

I make a trip to Richmond once a month, so what I can do is record my mpg both ways one month, install the fuel injectors, then record my mpg both ways for the next month. Hopefully I can get you guys some real data. I might do a 0-60 test as well.

[Mr.WJ]

Right, it'd be hard to tell if the 4-hole injectors are gaining performance based on faulty stock injectors. (clogged, broken, etc). More accurate test would be "new" 1-hole vs 4-hole.

Either way, smoother idle and better throttle response are enough for me.

[BadAssEddie]

He has kind of gotten into hyper-miling since then so that number is exaggerated. He has done some other things as well, for tune up and aero.

I talked to him a little more to get the timeline straight. He went from 14.5 to 18.5 with just the injector swap, then to 22.5 on a trip to Wilmington after everything (roof racks removed, fuel filter, new plug wire, thinner oil, etc.) As a side note lol, he was running 15W-40.

Obviously it is a case of predominately fixing what was wrong, but the engine did seem to run noticeably better with just an injector swap, and I am naturally a skeptic.

[TerryD]

The programming module I have connects to the MAP sensor, which apparently determines the air/fuel ratio. Since the Trail Jammer kit is designed to improve air flow, my theory is that the module is designed to compensate that air flow with more fuel.

That's a very Mickey Mouse way for "correcting" what the computer sees instead of reprogramming the computer and in the long run I don't see it as a very safe alternative. When you start "correcting" the MAP signal, you lose some resolution. It's just their way to cutting cost and corners to provide you with slight gains. It's most likely reporting a slightly higher engine load indicating the need for an ever so slight increase in fuel. A slightly under stoich <14.7 increases power and the piece you have fools the computer into adding fuel in certain MAP regions. Keep in mind that your computer has a set amount it can correct the fuel by to maintain it's desired AFR, so changing an input value rather than a referenced table could affect the ability of the ECM to correct for certain conditions. The company sees this as a calculated risk as most people will never get into the situation and the chances of an average mechanic tracing an engine failure back to their product in one of these instances is very slim, so they are not worried about a few engine failures. You may never get into a situation where you need to worry about it, but I would be interested in seeing what kind of gains you would see at a drag strip or other measurable proving ground (not chassis dyno, those things lie at best) with and without that module in there.

I'm sure someone here is more knowledgeable about this than I am, too much on my plate to focus on the EFI stuff at the moment. Don't grow up kids, IT'S A TRAP!

Anyways, the improved atomization of the multi-hole injectors will account for power gains and mileage reduction because you get a more complete burn of the fuel you put into the cylinder, reducing the fuel wasted into the exhaust system to be burnt in the catalytic converter. In carburetors, annular boosters vs the "dog leg" or drop boosters would be a good comparison. Car Craft or Hot Rod did an article a few years ago about those differences when looking at the Barry Grant Demon carbs. I very nearly swapped out my 3310 for one of their Demons equipped with the annular boosters.

[Matt612]

He has kind of gotten into hyper-miling since then so that number is exaggerated. He has done some other things as well, for tune up and aero.

I talked to him a little more to get the timeline straight. He went from 14.5 to 18.5 with just the injector swap, then to 22.5 on a trip to Wilmington after everything (roof racks removed, fuel filter, new plug wire, thinner oil, etc.) As a side note lol, he was running 15W-40.

Obviously it is a case of predominately fixing what was wrong, but the engine did seem to run noticeably better with just an injector swap, and I am naturally a skeptic.

Hello friends ...had to comment on this one. The trip from bburg down to NC is basically all downhill. I once got 29 mpg going down to ECU in Alex's 4runner packed full of beer, people and shit simply because it was downhill. Mileage on the trip back was like 16

I wouldn't count that 22.5 for much...carry on

[turnbull]

Well I got the fuel injectors. I am not sure when I am going to install them though. I did measure my mpg going to Richmond last weekend; however, the next time I go to Richmond, I should have my new bumper and brush guard installed. I am not sure if I should measure my mpg with the bumper and brush guard installed first, and then install the new injectors and measure the mpg again, or just install the new injectors now and measure my mpg one more time.

I'd like to install them ASAP, but I am afraid if I don't keep the variables as consistent as possible, it might skew the data. Of course, there is the fact that the brush guard and bumper only adds a little less than 100lbs. This last trip I made, I drove 2 additional people, so that is about 250lbs right there (they were both girls), but there is no telling how many people I will be driving next month, if any at all, so the variables might be slightly inconsistent anyway. What do you guys think?

[BadAssEddie]

Well I got the fuel injectors. I am not sure when I am going to install them though. I did measure my mpg going to Richmond last weekend; however, the next time I go to Richmond, I should have my new bumper and brush guard installed. I am not sure if I should measure my mpg with the bumper and brush guard installed first, and then install the new injectors and measure the mpg again, or just install the new injectors now and measure my mpg one more time.

I'd like to install them ASAP, but I am afraid if I don't keep the variables as consistent as possible, it might skew the data. Of course, there is the fact that the brush guard and bumper only adds a little less than 100lbs. This last trip I made, I drove 2 additional people, so that is about 250lbs right there (they were both girls), but there is no telling how many people I will be driving next month, if any at all, so the variables might be slightly inconsistent anyway. What do you guys think?

It's all about averages. Plus you only have so much accuracy without telemetry. Just get a good average over a couple fillups between each change and compare.

[BadAssEddie]

Hello friends ...had to comment on this one. The trip from bburg down to NC is basically all downhill.

I wouldn't count that 22.5 for much...carry on

Yeah, kind of like how I get 25 mpg down highway 12 otw to the beach because it's flat and 55 mph.

He got 18.5 on the way back. I was expecting less so I think that is a pretty good result.

[willhf1011]

I have started using a mileage tracker on my phone that is really useful. Individual trips or single tnk of fuel mileage calculations are good for seeing how well you can do, but do little to nothing to indicate actual improvements to your vehicles mileage.

Alec's note on averages is 100% correct. If you only compare 2 trips, you won't get anything very meaningful. Start tracking your mileage now, everytime, all the time.

Its very easy with the apps. Enter your mileage when you fill up and how many gallons it takes. Next fill up do the same, again so on and so forth. You don't even have to entirely fill the tank eah time, just track how much you put in.

I've been tracking my mileage since mid-july, every mile and ounce of fuel that goes into it. 7000 miles at 18.69 mpg.

Note: Obviously this method is only as accurate as your odometer, which may be pretty far off for many in this club. If you know by how much, track it the same and just apply a correction factor later.

[Mr.WJ]

I've been tracking my abysmal fuel econ for awhile now. City and Highway Averages over the last 40k miles have remained near the same. Speedo has been "correct" since I have been logging, with GPS speed checks with stock tires and corrected with a size up in tires. Of course there are outliers with 100% long highway trips and 100% in the city towing. But it looks like I average about 12 around Bburg.

http://www.fuelly.com/car/jeep/grand_ch ... id07/83984