No power in 4th gear 84 CJ7 - Page 2

poppatello · 11-19-2009, 11:14 PM

No, you don't have to live with it. You need to change your driving habits. Just do what Mike said and let the motor rev out a bit. They love it. My 4 banger never ran so good. Jeeps are like corvairs, if you baby them they give you grief. Run the hell out of them and they treat you good.

scooter · 11-19-2009, 11:31 PM

Quote:

Originally Posted by mastercraftka

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

I couldent even use 3rd in my auto with 33`s probably. Even with 31`s and a 6/ auto and I think the 2.73`s but never checked yet, I need to drop into 2nd to pull 55 climbing the several mile long grade I go up every day.

Big_Pete1999 · 11-20-2009, 12:02 AM

I had the exact same problem. It was that my tires were big and my gears were too small.
I have 33" tires, and I had 2.73 gears (stock). So basically, I was bogging down in 4th gear every time the slightest incline came up.
I changed gears to 4.10 and problem was solved. You have 31" tires, so 3.54 or maybe 1 step up should do the trick. I had the chart, but don't know where it is.

apfroggy0408 · 11-20-2009, 12:10 AM

My tires measured to be about 28 in in diameter and this is how I usually drive on the road. 1st gear is 0-15, 2nd gear is 15-25, 3rd gear is 25-35, and 4th is 35 and up. Is that about right?

**Mike Romain** · 11-20-2009, 07:06 AM

Quote:

Originally Posted by apfroggy0408

My tires measured to be about 28 in in diameter and this is how I usually drive on the road. 1st gear is 0-15, 2nd gear is 15-25, 3rd gear is 25-35, and 4th is 35 and up. Is that about right?

Well...... If you want to up your gas mileage, you need to keep the revs up a bit more than that does I think. A tach is a great thing to have. I find the 258's get the best gas mileage when running about 2300-2500 rpm. If you short shift it like that, you are down in the teens usually which just drinks gas.

On the highway if I run at 2300-2500 rpm I get a nice 21 mpg.

If I use 5th gear with my 33's and 3.31 gears, it drops to 1750 rpm and I get closer to 15-16 mpg, a Big hit.

Same for around town, if I use 4th under 50 mph, it just drinks gas and is boggy.

**Mike Romain** · 11-20-2009, 07:08 AM

Quote:

Originally Posted by mastercraftka

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

Then see my driving style as mentioned. I can get 21 mpg.

RVC · 11-20-2009, 08:36 AM

My Jeep gets about 10mpg on the highway and will only do about 65mph top speed, 3:42 gears TF999 trans and 33" tires. It's a gutless pig. My engine compression is 150 psi from cly 1-6 so that's good, it's just slow but I don't mind.

**mastercraftka** · 11-20-2009, 09:27 AM

Ya I am getting about 13 mpg and driving in 4th with the 33 inch tires. I will try staying out of 4th and see what it does. I guess long term if I wanted to I could change gears. I do need to get a tach.

apfroggy0408 · 11-20-2009, 01:24 PM

Quote:

Originally Posted by Mike Romain

Well...... If you want to up your gas mileage, you need to keep the revs up a bit more than that does I think. A tach is a great thing to have. I find the 258's get the best gas mileage when running about 2300-2500 rpm. If you short shift it like that, you are down in the teens usually which just drinks gas.

On the highway if I run at 2300-2500 rpm I get a nice 21 mpg.

If I use 5th gear with my 33's and 3.31 gears, it drops to 1750 rpm and I get closer to 15-16 mpg, a Big hit.

Same for around town, if I use 4th under 50 mph, it just drinks gas and is boggy.

Yeah this is my first manual vehicle so still learning how to drive it well. I think you are correct I need to get me a tachometer so I can watch them rpm's.

Pog · 11-20-2009, 04:54 PM

Quote:

Originally Posted by mastercraftka

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?

I see that you are in Texas, so I am not knowledeable of your state inspections / emissions laws. With that being said, research the following topics:

1. Nutter Bypass
2. Team Rush Ignition Upgrade
3. Carter BBD Carburetor Problems

The highly likely wornout, 1984 smog computer and related components you have in your Jeep restrict your top-end revs / power curve big time. I did these upgrades / fixes on my '84 with 258 and it was like dropping a new motor in. I have zero issues with 4th gear on my T5 tranny with stock gears and 31s. Finally, go over every vacuum hose connection under your hood checking for leaks and dry-rot. Replace or repair these hoses as needed. That alone can make a world of difference.

Regards

**mastercraftka** · 11-20-2009, 08:42 PM

PogMoThoin, I have very few of the orignal vacumn lines still attached the pcv and some others. Most of those lines aer missing.

Pog · 11-20-2009, 09:32 PM

Quote:

Originally Posted by mastercraftka

PogMoThoin, I have very few of the orignal vacumn lines still attached the pcv and some others. Most of those lines aer missing.

This website:

Jeep Adventures Under the Hood

Should be part of the late '80s model CJ owner's bible. It will give you a ton of guidance on all the emissions stuff and vacuum lines. Sounds like your CJ may already have a bunch of the emissions stuff removed or disconnected. The problem with that is if the old computer module is still active under the passenger side dash, it won't be getting all the signals it needs to behave properly. Thus, your motor will lose power at higher RPMs (like shifting into 4th). Add to that the notoriously flakey, computer controlled Carter BBD carb and you will have more issues than you can shake a stick at. The Nutter Bypass will cure many of these issues.

Hope this helps some.

**mastercraftka** · 11-20-2009, 09:45 PM

This is awesome, I do want to get this thing all stock under the hood as soon as possible and this will definately help. thanks, Mike

yobtarf56 · 06-27-2011, 12:18 PM

1980 cj5 Original 4cylinder engine and stock tranny, I dont have any power in her up hill at all. I read thru this thread and one said to run in 3rd at 55. I dont care about highway miles because she is my jeep for town and fun but she has to go on highway sometimes. I have 31 in tires on 15 in rims. I just dont care about speed and they can pass me all they want here in washington state and I will smile and wave and know they are saying "Damn he looks like he is having fun!!!"

**mastercraftka** · 06-29-2011, 12:16 PM

Quote:

Originally Posted by yobtarf56

1980 cj5 Original 4cylinder engine and stock tranny, I dont have any power in her up hill at all. I read thru this thread and one said to run in 3rd at 55. I dont care about highway miles because she is my jeep for town and fun but she has to go on highway sometimes. I have 31 in tires on 15 in rims. I just dont care about speed and they can pass me all they want here in washington state and I will smile and wave and know they are saying "Damn he looks like he is having fun!!!"

Welcome to the forum! What tranny do you have and what rearend ratio?