YJ FI and Gearing

[PhattyX]

I'm debating buying a 4 cyl YJ as a commuter to keep some mileage off my car. I had a couple questions before I start looking...

Did the 4 cyl get Fuel Injection in the YJ (or just the 6 in '91)?

Do ALL 4 cyl have 4.11 gears or just certain years?

Ultimately, can I get more than 22 mpg out of the 4 on 87 octane? I understand the electric fan and a few assorted other mods have a great effect on the mileage. I'd be doing almost all highway driving. I didn't seem to do well with the TJ on the highway. You know, "box on wheels" aerodynamics and all.

Thanks,

-X

 

[90growler]

The 4banger has Fuel injection from 1990 to present. However, the 90 YJ has Throttle body injection and most of the aftermarket parts will not work for it (air intake, TB Spacer, Ect.). The 91-95 has MPI FI just like the 4.0 to the best of my knowledge. I wouldn't reccomend it for the interstate if you didn't care for the TJ on the highway. You would be lucky to get it to 70 and forget about 5th gear....can't see how that could save gas.

Regearing would be different........I would like to know as well.

 

[Bounty__Hunter]

Pretty sure the 2.5L started with FI in '87 with TBI, then switched to MPFI in '91. They have 3.73 gears in the auto and 4.10 in the 5spd.

The most I've seen is 21-22mpg, and that's with a lot of mods. I don't think any higher is realistic.

 

[Jeepr]

They all had 4.11s. If you are looking for mileage, don't go that route. My 95 4cyl, auto, with 235x75s, got about 17 mpg at 65 mph and 19 mpg at 55 mph. It was great around town, but way underpowered on the e-way. My 4cyl, stick, XJ got like 25 mpg.

Good luck.

 

[TwistedCU]

I know for certain that BH is correct on the 87-90 being throttle body injected, and the 91-95 have multi-port FI.

As for gearing the 5 speeds definately all have 4.10 gears. That's the route you want to go if you want to get 20+ mpg. The automatics are 3 speed autos and will do poorly at highway speeds.

I think 20-22 is quite doable if everything is in good conditioned and properly tuned. I got 20 mpg pretty consistantly in my '92. The electric fan conversion will give you the best bang for the buck. Taking the drag of the mechanical fan is a big factor for the 2.5L. Mine had manual steering, and I am sure that helped too.

Gas prices are coming down, and 20 mpg wouldn't be too bad for a commuter if your commute isn't too long. Having a Jeep for some of the ugly snowstorms we'll probably see here in PA this Winter is priceless.

 

[Bounty__Hunter]

They all had 4.11s.

No, they didn't. See post above ^^.

 

[90growler]

Didn't know that about TBI. I would like to reagear to gain power. What should I switch to and how much should I expect to pay? All YJ 2.5 5 speeds have 4.10 right?

 

[Bounty__Hunter]

I would like to reagear to gain power. What should I switch to and how much should I expect to pay? All YJ 2.5 5 speeds have 4.10 right?

What size tires?

Yes, all 2.5L 5spd have 4.10 gears. You may find a rare oddball or two, as jeep made exceptions to every rule when it came to throwing parts together.

 

[90growler]

What size tires?

Yes, all 2.5L 5spd have 4.10 gears. You may find a rare oddball or two, as jeep made exceptions to every rule when it came to throwing parts together.

I run 31x10.5's so I guess I would need 4.56 gears for dana 30. Is that right? Does transmission matter? What should I expect to pay.

 

[Wrangl3r93]

I have 31x10.5's on my 4banger 5 speed(4.10 gearing). With nothing done to it except for the air restrictor taken out i generally have no problems with power. Unless you plan on getting bigger tires i'd say use the money on less expensive engine mods to regain the little power loss resulting from your tires.

 

[TwistedCU]

I run 31x10.5's so I guess I would need 4.56 gears for dana 30. Is that right? Does transmission matter? What should I expect to pay.

31's shouldn't bee to bad if the motor is tight. You can do some power mods to help compensate but yes, regearing will give the best result. If you don't ever plan to go any bigger than 31's then 4.56 will bring it close to stock performance. If you plan on getting larger tires then consider waiting until then and going with 4.88's.'

Oh, and that would be a yes on the Dana 30 (your front axle), but don't forget the rear - Dana 35. Obvioulsy you need to do both at the same time if you want to be able to use 4WD.

 

[Bounty__Hunter]

I run 31x10.5's so I guess I would need 4.56 gears for dana 30. Is that right? Does transmission matter? What should I expect to pay.

Yes, transmission matters, as the auto doesn't have an OD and the 5spd does. They both came with different axle gears so your starting point in gearing will be different.

If you have a 5spd, then 4.10 to 4.56 isn't much of a change to justify the money and time involved. Consider gearing to 4.88 if you make the change, acceleration and crawl ratio will improve, and you'll be ready for the inevitable jump to 33". Mileage won't suffer much between 4.56 and 4.88.

If you have an auto, then 4.56 won't be too bad with 31" tires, if you never plan on going bigger.

What transmission do you have?

 

[90growler]

What transmission do you have?

Funny you should ask...I changed the transmission oil yesterday and was stumped at what I found. Assumed I had an AX-5 but when I refilled it it didn't take as much gear oil as I thought. It only took about 2.5 quarts instead of 3.5. According to the haynes manual that means I either have a NV1500 or NV3550. I tried to find some sort of ID on it, but I didn't have any luck considering the amount or grime and mud on it. I don't know what I have. It's a 1990 if that helps.:???:

What would be a good price for 4.88's? Do you know where I can find some used?

 

[Bounty__Hunter]

It's an AX5 in the '90, the NV trannies were only available in late model TJ's. 2.5 sounds about right.

Check out www.completeoffroad.com for a good price on gears, search national forums like www.jeepsunlimited.com/forums for used gears.

There's a shop near here that'll set up front and rear axles with new 4.88's for around $880, tough to beat that for shop labor.

 

[Wrangl3r93]

Funny you should ask...I changed the transmission oil yesterday and was stumped at what I found. Assumed I had an AX-5 but when I refilled it it didn't take as much gear oil as I thought. It only took about 2.5 quarts instead of 3.5. According to the haynes manual that means I either have a NV1500 or NV3550. I tried to find some sort of ID on it, but I didn't have any luck considering the amount or grime and mud on it. I don't know what I have. It's a 1990 if that helps.:???:

What would be a good price for 4.88's? Do you know where I can find some used?

Yeah in my 93yj i was changing the fluid and it specifically says to get to it on the ax-5 it's on the passenger's side and on the ax-15 it's on the driver's side. Even had pictures. Mine was driver's side. The dealer said the engine had been replaced but it's still a 4banger and i just don't know about this transmission. I was told if it's an ax-15 it won't match up to the 2.5L. What are the other possibilities?

 

[TwistedCU]

I gotta warn you, 4.88 gears mated with 31" tires will result in the Jeep being geared very low. Around town and trail use will be great, with lots of power. It'll be fun to drive, but at highway speeds the engine will be screaming.

While it is true that 4.56 gears isn't much of a change from stock gears, 31's arent that much bigger than stock tires to warrant 4.88 gearing. If you plan to step up to 33's then that's different.

 

[Jeepr]

No, they didn't. See post above ^^.

What? are you quibbling over 4.10 or 4.11? It's basically the same gear!

 

[Bounty__Hunter]

What? are you quibbling over 4.10 or 4.11? It's basically the same gear!

No, quibbling over 3.73 and 4.11, as the 2.5L Wrangler came with both.

 

[PhattyX]

Thanks for all the info / input. I'm going to keep my eyes out for one. The goal is to keep mileage off the car and frankly I couldn't afford my rent if I had to put gas in the CJ. I can live with ~20 mpg. Something with FI to wheel should prevent me from having to be dragged up a hill again, too.

Thanks again,

-X

 

[Jeepr]

No, quibbling over 3.73 and 4.11, as the 2.5L Wrangler came with both.

Oh, I didn't know. I had a couple of 4cyl YJs, one auto and one stick, they both had 4.11s. I know 3.73 was an option on the TJs with the 2.5, but I didn't even know you could option it on the YJs.

See, you learn something new every day.