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96 4.0L xj lost its power

ktm racer 419

ktm racer 419

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here is the deal. I got too used to my 4 cyl comanche. Now that i threw 33's on my stock geared 4.0 auto 99, it has WAY more power than my 5.38 geared 96 on 35's

something is not right here.

its a 96 4.0 aw4

the power only kicks in around 4250 rpms and even then it isn't too impressive. other than that it just kinda lugs along. I can still get it up to highway speeds no problem and cruise along just fine.

new parts:
plugs
wires
cap
rotor
cps
o2
air filter
fuel filter
alternator
battree

tps,map,and iac are all good
coolant temp sensor is good

cat is fairly new (could see through it one month ago)

Hooked it up to the scanner and everything looks fine, no codes.

Not sure where to go from here.
any ideas?
 
Last edited:
First, I would check the fuel pressure, static and driving (tape the gauge to the windshield--I do love duct tape!).

Second, test the TPS (throttle position sensor).

Post back with results.
 
joe_peters said:
First, I would check the fuel pressure, static and driving (tape the gauge to the windshield--I do love duct tape!).

Second, test the TPS (throttle position sensor).

Post back with results.
Click to expand...

i was gonna do that today. but i opened the box to my fuel pressure guage at work and it was missing.

i should add that tps,map,and iac are all good (i played around with swapping them out with the ones on my 97)
 
gonna add that coil is good (had a good spare, problem persists)

gonna see if i can pick up a fuel pressure guage and maybe do a compression test today
 
OKAY

narrowed down my issue here

fuel pressure is at 38 running

stock calls for 49 + or - 5 psi

so its a fuel delivery issue

is it safe to say it's my fuel pump or are there a couple more things i could be checking

can't be the regulator as that would give me too much pressure correct?
 
Normally I would expect excessive pressure when the regulator fails.

Is the fuel filter external on the 96? If it is I would change it and retest.

If the filter isn't external, you are going to have to pull the pump assembly to check the filter and/or replace the pump.
 
the fuel filter is a few weeks old
 
Last edited:
Starting to sound like pump time.

One other thing--get a bright spotlight and check the fuel lines from front to rear to see in there is any damage.
 
Pumps in 96's ( I have two of them), depending on when they were built, are notorious for giving trouble. Although its usually a connector issue (easy fix), but sometimes its the pump itself (not so easy fix) and its in the tank. Typically the problem is the pump wont work, but I suppose it could cause a similar problem to what you are having.

Have you used the same pressure tester on your other XJ just for comparison purposes. (make sure the gauge it good)
~James
 
i just went ahead and replaced the pump and strainer

all is good now

thanks for the help guys
 
Glad you got it taken care of! :roll:
 
stumpXJ said:
Pumps in 96's ( I have two of them), depending on when they were built, are notorious for giving trouble. Although its usually a connector issue (easy fix), but sometimes its the pump itself (not so easy fix) and its in the tank. Typically the problem is the pump wont work, but I suppose it could cause a similar problem to what you are having.

Have you used the same pressure tester on your other XJ just for comparison purposes. (make sure the gauge it good)
~James
Click to expand...

You mention a connector problem. Which connector(s) have you seen this on. Having some weird issues myself on my '96 and will be checking fuel psi in the next few days.
 
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