Engine Power Issue after Regear

I regeared to 4.56 and notice on the highway going up fairly steep hills (elevation ~5000 ft above sea level) I still lose speed even though RPM is 2800-2900. This happened on Hwy 80 from Evanston WY to Cheyenne, for those who know this road. Is this normal with 5.5" lift and 32x11.50 tires? That is, does it cause enough drag to slow my XJ down to 55 MPH? How about you Easterners who drove to Moab...how was it going through some of the passes for you? For me, it feels like the brakes are dragging, even though I know they're not. My buddy had no problem driving the same highway in his stock Dodge w/ 6 cyl engine. Actually, his tires are slightly larger than stock. I'm wondering if I have a tranny problem. I mean, it feels like I have stock gears again, tho' the RPM gauge shows otherwise.

Also, for those who regeared and run ~2600-2800 RPM on the highway, did you notice your engine heats up higher than before the regear? Mine stays between 2/3 and 3/4 on the gauge, which is too high for me. Everything in the cooling system was replaced, so I'm thinking a plugged radiator. Looking for input from similar setups on what you're getting on temp gauge. Hope this made sense.....I'm in a hurray. Thanks for any input you can provide.

Tom

Not sure on the power loss issue. Have you tried the climb in 3rd gear?

When I regeared to 4:56's w/ 32's there was no temp change.

How many miles?

Flowers

A couple of times I ended up going into 3rd gear, but at ~ 3300 RPM, I didn't want to leave it there too long.

Just under 172,000 miles. Head was rebuilt about a year ago.

Tom

I can pull any hill in the mountains out here (4,000 - 7,000 feet) in 4th gear (manual trans) in any RPM between 2,500 and 3,000 rpm.

88 4.0, 212,000 miles, header, 2.5" exhaust, 4.88's, 35's, 4,500 pound rig.


CRASH

Tom, how old is your cat converter?

Jes

Jes said:

Tom, how old is your cat converter?

Jes

Click to expand...

Good One Jes! I didn't think about the cat.


Flowers

Cat is fairly new and emission test done last week with great results. Thanks,

Tom

.......and my neighbor was telling me last week "Boy, I'm glad I got rid of that green XJ"............ So the "3 Sisters" were mean to you, HUH?

Does your tranny shift down into 3rd when you head up these hills or does it hang out in 4th and lug? It should kick down and pull strong in 3rd......stop worrying about reving your engine above 3500 rpm's!! You should pull it down into 3rd on big hills anyway. The 4.0L HO makes it's best power up in the 3-4K range, so why wouldn't you want it running there, especially when you need the climbing power? If you are building heat as well as power loss, and shifting is sluggish or not happening when it should..........reminds me of a Trans Fuse that was blown on my 89 for a couple of months before I realized it was even there. Replaced the fuse and it shifts like a champ, kicks down when I nudge the throttle, just like it should.
Hope this helps, the hills in Big Wonderful are steep indeed, especially since you always have a 20 mph headwind......no matter which way you're driving.

You still chasing this gremlin Tom? Actually, shifting into third for some of those climbs sounds perfectly normal. Always did it to me even when I had stock tires and no lift. You probably just need to lose weight or something.

If you are worried about the engine...take it to a good shop and have a leakdown test performed..it will point out any potential problems with how the engine is sealing..such as leaking valves or cylinder/piston sealing problems, head gasket, etc...if it's ok...make sure all the tune-up stuff is ok. And yes a 4.0 HO can easily run at 3,500 if it's in good shape.

Also how good is your clutch fan? If its bad you'll heat up at those rpms and running warmer is going to also hurt your power to a point.

I have almost the same setup as you - 6cyl, 4spd auto, 32's, 4.56
I have never had issues on 80 (I lived in Laramie) except for the pass outside of Laramie on the way to Cheyenne. That pass your lucky if you stay in 3rd and not 2nd.
The overheating thing -- I had some of the same problems you are having (I consider 210-225 normal operating range) even after doing a full cooling and exhaust rebuild.
I replaced the radiator, got new electric fans, convered to the open system from the closed, new K&N air cleaner, new exhaust(including high flow CAT, Flowmaster 50, and new pipes).
The problem was these were cooling the engine, but all the heat was staying under the hood. I devised what I jokingly refered to as RAM AIR cooling like on the old hot rods. (Take a look at the link). This was a temporary fix, but I drove for 15 days around Southern Colorado (big uphill climbs) and it worked fine. So now that I am back I am going to vent the hood. I am not sure what I am going to use as the grate (probably an XJ cowl) , but I am going to cut on the 2 sides of the hood to let this hot air out. FYI the Jeep performed much better, got better gas milage, and pulled the hills in higher gears with my radiator fluid breathing concoction.
Maybe this is a similar problem you are having
Steve

http://photos.yahoo.com/sander74

Thanks everyone for the responses. I have replaced everything in the cooling system except for the radiator, which was new when I bought this XJ a couple of years ago.

When left in 4th gear, my speed went from 80 to 55 MPH during several of the hill climbs. About 2-3 times I had to downshift into 3rd. Since arriving in Colorado I noticed the trans is shifting a bit harsh from 1st to 2nd, so I'll adjust the cable.

Jeff, where's this trans fuse? Thanks again.

Tom

Tom, the transmision fuse is under the front passenger side dash in the footwell. There is a little cover that is held in by two screws. Drop that cover and you should see it.

Thanks

For any that don't already know this, it's better to manually downshift from 4th to 3rd on steep hills rather than letting the trans downshift itself. The difference is that in the downshift mode the torque converter stays unlocked, which increases the engine rpm and raises the trans fluid tempurature. When manually downshifted the torque converter locks up, bringing down the rpm and not creating extra heat in the trans.

Tom, like everyone else said, the 4.0L can handle the rpm, so downshift and don't worry about running 3300-3500 rpm on the hills.

What brand/type of tires? Some tires like TSL's are pretty heavy and the chunky tread also causes a lot of rolling resistance. Both of these factors will really pull down performance when going up hills. Also one thing I never hear discussed is the fact that taller tires effectively "spread out" the transmission gear ratios and that changing axle ratios does not effect that aspect.
Mike B.

Thanks for that tip, Richard.

I don't mind running that RPM range, but I have no doubt there's a problem. Yesterday I had to nearly floor the go pedal just to keep up with traffic in the city. Weird. It's tuned up, fresh oil, T-body cleaned, emissions are great, newer cat, smooth at idle, etc.

By the way, I run BFG A/T tires.

Tom