• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

loss of power

matt hurtado

NAXJA Forum User
Location
austin,tx
OK this is what is going on I am not getting a good response out trying to accelarate in fifth gear and I also am getting a slight hesitation and shudering while accelerating in fourth gear. and I am also losing speed while going up very small inclines while in fifth gear I always have to down shift to get alittle more umf to keep the speed regulated. I just recently added a k&n air filter and new plugs and wires I had the compression checked and that was at 125 per cylinder the guy said that was about right. also when I changed the spark plugs they all had like a whitish residue on them. A friend mentioned that ment that not enough fuel was getting burned.
Also I've got a 4.5" lift with 32x11.50x15 tires .In conculsion why am I lossing power and whats with the hesitation and shudering
 
Might be a dumb question, but have you re-geared the axles??


Mike
 
matt hurtado said:
no I have not regeared the axles.does a size 32 tire really effect the get up and go
yes it sure does ;)
 
Was this lift done recently and was the power loss immediately noticable after the larger tires and lift? Its very possible (it probably is) that this is the cause of your problem. If not, it could be a clogged catalytic converter.
 
I looked at the tech specs for a BFG AT tire to find out how many revolutions per mile does the tire make, here what I found:

LT215/75R15 748 rev
LT235/75R15 717 rev
32x11.50x15 656 rev

On my 88 XJ it came with tires from P195/75R15 to P225/75R15 so if we use the LT215 number in "stock" to travel 1 mile the wheel rotates 748 times.

Now with the 32s to travel a miles the wheel rotates 656 times.

To go down the road one mile the engine is turning, 656/748 = 87.7% of what it use to. If you have the 3.08 gears this means your engine speed in 4th gear, 1 to 1 ratio, is:

215 tires = 748*3.08 = 2304 rpm
32s tires = 656*3.08 = 2020 rpm

That would explain why you are having problems, not enough power/troque.

To get a rough idea what gear ratio you need just ratio the revs/mile numbers and mulitiply them by your gear ratio. (748/656)*3.08 = 3.51

With that you may just want to get a set of gears out of an automatic transmission XJ (gear ratio 3.54) to solve your problem. I am no regearing expert but this what I'd do to try to get the engine back to the RPM range it had with stock size tires.

Until your regear I'd drive around as if it a 4 speed and not use 5th gear, that will help keep your engine RPMs in the right range. Use 4th as your over drive and 3rd as your normal gear. If this fixes your problem then save up your $ for the gear change. I only suggested the 3.54 since it is a commonly available gear set for our XJs. I am not sure what other gear ratios are available.
 
Last edited:
Other available ratios that might come in handy would be the 4.10 available behind most 4-cyl XJs. I'm going to be pulling a 3.55 8.25 next week since with the 32s and auto tranny it just doesn't provide the get-up n'go that I used to enjoy
 
do you all think that I could just find an 8.25 rear that allready has 3.55 to 4.10's in it ,I could just do an even in and out swap and remedy this issue
 
3.55s in an 8.25 would be most post-91 XJs with a 6-cyl and automatic and no ABS. 4.10s would come from a 4-cyl
 
matt hurtado said:
do you all think that I could just find an 8.25 rear that allready has 3.55 to 4.10's in it ,I could just do an even in and out swap and remedy this issue

dont forget that you have to swap the front axle too... so the gear ratio is the same.
 
Back
Top