No power in 4th gear 84 CJ7

**mastercraftka** · 11-19-2009, 07:23 AM

I get good accleration on 1st through 3rd gears and then when I shift into 4th almost no response. It will eventually pick up speed but any little hill then the speed drops back down. Suggestions?

**Mike Romain** · 11-19-2009, 07:29 AM

What engine?

What sized tires?

What gear ratio?

What speed are you using 4th at?

**mastercraftka** · 11-19-2009, 07:32 AM

258 inline 6

tires are 31's

don't know the gear ratio, but it is stock

I usually shift into 4th at 45 on the speedometer which is about 50 taking into account the larger tires.

**Mike Romain** · 11-19-2009, 07:40 AM

Quote:

Originally Posted by mastercraftka

258 inline 6

tires are 31's

don't know the gear ratio, but it is stock

I usually shift into 4th at 45 on the speedometer which is about 50 taking into account the larger tires.

There you go, I can't use 4th until I get over 65 mph or mine bogs down bad. if I am doing 'less' than 65-70 mph when I hit a hill, I will have to go down to 3rd gear to hold power.

A tachometer tells the story. At 65-70 mph mine is turning 2300-2500 rpm in 4th which is a sweet spot that gives me a nice 21 mpg highway. If I use my OD or 5th gear, it only turns 1750 rpm and is is a dog that just drinks gas.

I run 33's with stock 3.31 gears. 2nd will pull fast to 52 mph @ 4400 rpm, 3rd hauls hard up to 75+ mph, 4th will bury the speedometer and I have no urge to find out how fast 5th will go.

Around town, I never use 4th, just too low a gear that bogs down bad and also drinks gas while doing this. If I stay in 3rd up to the sweet spot of 2300 rpm. that is about 50-55 mph.

poppatello · 11-19-2009, 07:47 AM

I didn't think a 258 would have much trouble. I have the AMC 150 and just like Mike I too must be around 55 MPH to shift into 4th gear. Sometimes I stay in 3rd depending on the winds and if I'm loaded down or not. Most the time if I get the momentum to get to 4th gear if I tap the brakes, I will have to down shift to get it back again. When did you notice a power lost? I just can’t imaging a power lost with a 258 and 31’s. Maybe, I went from stock to 32’s so I can’t help out much. But if it changes when you changed tires, your most likely either going to have to live with it, stay in 3rd longer, or regear.

**mastercraftka** · 11-19-2009, 08:06 AM

I have only had the jeep a few months and it was worse when i got it because for some reason there was two pcv's on it and I was getting blow by. i just vented the back one like it was supposed to be and it seems to have helped i haven't noticed any gas in the oil. i also put a carb kit and changed plugs. I guess i just need to run it up faster before i shift into 4th. I don't have a tach so I was worried running it up that fast was too many rpm's. I do know that the speedometer reads 45 but actually going at least 50 or 55 so I was thinking that was a good speed for 4th gear. Mike

**Mike Romain** · 11-19-2009, 08:23 AM

You may want to use a GPS or find a measured mile because a 'lot' of CJ's will have the odometer and speedometer right on with 31's on it.

The engines roar above 2000 rpm so it is deceiving.

To check your gear ratio, you can just chalk mark a back wheel and the driveshaft, then jack up that wheel. For a normal open differential, you turn the wheel two revolutions while counting the revolutions of the driveshaft. the chalk really helps with the counting. In my case, I got a little over 3 1/4 turns of the driveshaft which means the common 3.31:1 gears.

If you have a traction device in the rear diff, then you only need to spin the rear wheel one revolution while counting the driveshaft turns.

**mastercraftka** · 11-19-2009, 08:56 AM

This is great information I will look into it but you think this sounds pretty common then? I was just thinking that it was carb issues. But I am throwing darts at this point because I have never had a jeep before and wasn't sure if it was common.

**Mike Romain** · 11-19-2009, 09:50 AM

Yes. the top gear is for highway speeds, especially with oversized tires on it. Now if you drop down to P215's or P205's, then the power band drops considerably.

**mastercraftka** · 11-19-2009, 06:26 PM

Ok i was wrong about the tire size 33 x 12.5 i have only had it for a couple months and couldnt remember it when i posted earlier

rodjr · 11-19-2009, 06:48 PM

check your timing also, to much will kill your 4th gear pull.

CaliDaze · 11-19-2009, 06:58 PM

At one point in time when getting up to speed in my cj7 w/304 & 33s I would have to ride 3rd hard up to 3800-4000rpm to get it in to an alright rpm range for 4th. Even still it seemed like 4th had no power whatsoever and would slightly bog down until I would have to shift back into 3rd and ride it back into 4th.

An old gearhead told me to give her a compression check. I had 3 cylinders w/ burnt exhaust valves running less than 20 psi. Like you I had just bought my jeep and thought it ran great in 1st-3rd. Then I did the head and valve job, Holy ****, Now that's what a V8 should feel like.

It's a good thing to check anyways when you buy a new car. And a good place for you to start with you problem.

**mastercraftka** · 11-19-2009, 07:03 PM

Compression check is the first thing i did and all cylinders are good. Ya i have to really give it hec in 3 rd first to build speed but all it takes is one little hill and back down.

poppatello · 11-19-2009, 07:20 PM

No, it's the tires...

**mastercraftka** · 11-19-2009, 07:23 PM

Sounds like it. I geuss i have to live with it or change tires.