TJ can not maintain 75 mph in overdrive

Fishtaco said:
1.Why Not! Well I personally would say they are not the most practical or even safe vehicle to be constantly travelling in the higher speed ranges given modifications and the reason I asked.
But If its fine and common practice then it gives me reassurance when I am cruising at 70MPH.
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It's a lot of fun having a Jeep on 35s that can be tossed around and driven hard without much care. And it climbs over big rocks, too.
 
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rasband said:
As long as you’re the guy in the slow lane, I’m fine with that. The worst is when traffic gets bogged down by someone that doesn’t realize the left lane (at least here) is for passing.

You're describing a bit of a utopian state - we won’t be far behind sadly.
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Dont worry I have driven quite a bit in US but after a few years of low level speeding fines from fixed cameras in Oz people tend to change their driving habits fairly quickly, Its easy enough for delivery drivers to loose your license in one day, going through speed cameras 5- 6MPH over will gain you 2 lost points out of 10 points and the points stay off your licence for 3 years (pro rata) as well as the fines, loose all 10 anytime during a 3 year period and you get an immediate 3 month driving suspension.
So I suppose my driving habits have changed through force and time and the reason maybe maintaining 75MPH in a TJ seemed a bit excessive?
 
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@matkal I'd go with a cat or other non-gearing issue to begin with. When I first got my jeep it was practically the same setup as yours and had no issue going 90+. Obviously going to a lower gear would help but I don't think that's what's limiting you to 75mph or at least struggling at 75mph.
 
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Oh that was only stock for maybe 3 months, then death wobble kicked in and I got a lift and 33s. My jeep gets REAL pissy when I go over 75mph now with 33s and 4.88s. Basically only can get to 85 on a downhill and a backwind pushing my Jeep. I mean I've been told I'm suicidal for driving my Jeep with no doors before so...? That guy also told me his Subaru was more capable offroad than my jeep so I don't take him too seriously..
 
imahnu17 said:
@matkal I'd go with a cat or other non-gearing issue to begin with. When I first got my jeep it was practically the same setup as yours and had no issue going 90+. Obviously going to a lower gear would help but I don't think that's what's limiting you to 75mph or at least struggling at 75mph.
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I agree. After I get the presumably stuck injector(s) fixed and change the oil I’m going to look into the cats.
 
Got the injectors back, guy said one of them had a slight drip that went away after cleaning. He also said that the injectors where ...... a bit dirty. (I assume the spray pattern was bad). Changed the oil and got the injectors back in and went for a test drive, it still cannot maintain 75mph in OD. I didn't expect it to but I was hoping. Also checked the trans fluid and it was nice and red and at the proper level.

I guess my next step is to take it to my mechanic and have him see if he can figure out if it's the cat(s) or something else and go from there. This is all very frustrating because it seems as though its "always something" that either prevents me from driving the Jeep(was planning a wheeling trip up north) or from doing some upgrades( suspension, axles, etc.) I'm just fortunate that this is not my DD and was always going to be a long term project.
 
I thought we had made it clear that with oversize tires your 3.73 axle ratio isn't quite enough gear to give the performance the engine is easily capable of providing. The reason the engine's not able to produce that power now is the 3.73 axle ratio is restricting its rpms. You were barking up the wrong tree with what you tried above. If you really want to be able to cruise at 75 without problem you need to regear your axles to a slightly lower ratio. 4.10 to 4.56 would do it for 31's. Or go with a smaller tire.
Again, your 42RLE's Overdrive ratio is lowering the engine rpms so much that the engine can't put out enough power to do what you want to do. Regearing will raise the rpms back up just enough to overcome the larger tire's added leverage against the engine.
 
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Just to +1 to what Jerry said, you really do need to re-gear to get any kind of power when in overdrive. My 99 WJ with the same 42RE transmission has 3.55 gears and 30" tires, and at 75mph it's barely pushing 2k RPMs and I have almost no power. I'm downsizing to stock tires when the current ones run out.
 
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Jerry Bransford said:
I thought we had made it clear that with oversize tires your 3.73 axle ratio isn't quite enough gear to give the performance the engine is easily capable of providing. The reason the engine's not able to produce that power now is the 3.73 axle ratio is restricting its rpms. You were barking up the wrong tree with what you tried above. If you really want to be able to cruise at 75 without problem you need to regear your axles to a slightly lower ratio. 4.10 to 4.56 would do it for 31's. Or go with a smaller tire.
Again, your 42RLE's Overdrive ratio is lowering the engine rpms so much that the engine can't put out enough power to do what you want to do. Regearing will raise the rpms back up just enough to overcome the larger tire's added leverage against the engine.
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Up until a hundred miles ago it didn’t have a problem going 75 not that I did it very often but it was very capable of doing so. Regearing is on my list but I’m not ready for that yet.
I’m trying to figure out what changed in the last hundred miles.
 
I'd be very surprised to drive a Wrangler with the 42RLE with 31" tires and 3.73 gears that could easily maintain 75 mph with the OD on.
 
I’ve put (unfortunately only) about five or six thousand miles on mine since I’ve owned it and it never had a problem going 75 in OD the few times I’ve done it. That’s why I’m trying to find out what’s wrong. Otherwise it would have been the same old same old and I wouldn’t have noticed a problem.
Maybe it’s not common but nonetheless it WAS capable.
 
So, I get that it used to work and something probably degraded. Mine has the same setup. It is marginal with the gearing and 31s. That means anything in your engine or trans that degrades in the slightest will take you out of OD. After you spend the money cleaning or replacing the Cats, cleaning the injectors, rebuilding the trans, etc. you could have put some 4.10s or 4.56s in and get much better performance.

It's good to get a mechanic to look at it. However, you are sending him on a hunt for a very slight drop in performance. It could get expensive.
 
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I know my post above doesn't help you find the problem, but you are looking for a 5 HP problem. My advice is just to try and save you some money.

Options:

You can back off the speed and drive it until whatever degraded fails hard so it's easy to find.

Send your mechanic to look for a 5 HP problem with a pile of cash.

Or, change the gears and enjoy the hell out of your Jeep!
 
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If you must go on the hunt...Something cheap to try: Maybe something in the intake system loosened up since the rebuild. Spray some engine start around the interfaces and any vacuum lines to look for a vacuum leak.
 
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