• 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.

4.0xj???

O

OZNAD

NAXJA Forum User
Location
pennsylvania
i know its been asked 1000 times before i just think this is ridiculous... i have 90xj with renix4.0, starts after a try or two runs at least idles fine, rev it up to 4-5000rpms smooth, kinda backfires but not bad. once it warms up to about 110-150degrees, starts idling funny and will eventually stall, as with driving it will seem to lose all power,more noticeable on a uphill grade, it would probably stall if i didnt pump the gas pedal, until it gets to 2-3000rpms, then seem to run ok above 3000rpms, i have only driven short distances cause it sucks and it would leave me stranded... i've already replaced: egr, air filter,plugs, wires, cap, rotor, fuel filter, vacuum lines. so what do you think about this turd? i'm takin a break on it for right now...
 
also i replaced the tps today... set it with the test i read on here.. i had 4.64volts between A-D, so i set it to 3.80 between B-D... is that how its set?? anyway i'm still having the same problem as my first post....​
 
has it had a tune up?
prime the fuel pump, and take a fuel pressure reading....
leaving the gauge installed, start it up, and rev it, watching the fuel pressure.
if the fuel pressure drops significantly under high revs, your fuel pump is having trouble keeping up under load.
 
Your tps, harness disconnected, key in run position, approx. 5.0 volts between D ground and A power.

Your tps, harness connected, key in run position, approx. 4.15 volts between B power and D ground.

This is assuming an auto trans.
 
xcm said:
has it had a tune up?
prime the fuel pump, and take a fuel pressure reading....
leaving the gauge installed, start it up, and rev it, watching the fuel pressure.
if the fuel pressure drops significantly under high revs, your fuel pump is having trouble keeping up under load.
Click to expand...

my '96 XJ is experiencing similar issues that the OP mentions. I tested my fuel pressure this evening (before seeing this thread) and it idles at 42psi.. off-idle, revving the engine, it drops to mid 30s.. saturday, i'll pull the pump and check the sock, and possibly replace the pump & sock. 233K miles, it's prolly due.. :)
 
i didn't run the pump capacity test. I pulled the pump, since I felt compelled to do it right after work..

Here are the findings...




 
Easiest check any time you XJ starts acting up is to unplug and replug in your CPS (crankshaft postion sensor) the connector is located at the rear of the Valve cover on the driverside. I am not saying replace it although that may be needed in the future. Just unplug it and plug it back together. You would be surprised at how many different faults can arise from the CPS.

Here is a lil illustrated pic from the rear of the engine.

Crankshaft_Position_Sensor_diagram.jpg
 
spoony did changing the pump work? i just did the ignition coil today and that wasnt it... so.. map, cps, and fuel pump?? i cant seem to find anything about the iac on the renix? testing the tps i got 4.64v(A-D)so i set it at 3.80v(B-D)... correct? on the ballast resistor for the fuel pump was 12v on one end and 14v on the other..
 
XJ Stryker said:
Easiest check any time you XJ starts acting up is to unplug and replug in your CPS (crankshaft postion sensor) the connector is located at the rear of the Valve cover on the driverside. I am not saying replace it although that may be needed in the future. Just unplug it and plug it back together. You would be surprised at how many different faults can arise from the CPS.

Here is a lil illustrated pic from the rear of the engine.

Crankshaft_Position_Sensor_diagram.jpg
Click to expand...
nice pic on the location of the cps
 
OZNAD said:
spoony did changing the pump work? i just did the ignition coil today and that wasnt it... so.. map, cps, and fuel pump?? i cant seem to find anything about the iac on the renix? testing the tps i got 4.64v(A-D)so i set it at 3.80v(B-D)... correct? on the ballast resistor for the fuel pump was 12v on one end and 14v on the other..
Click to expand...
Mine wasn't so much the 'pump', but the sock-filter on it. It was absolutely clogged.. I replaced the pump, as well, only because I had it apart, and there's 233K mi on the original one..

And yeah, it seems fine now. The fuel pressure is steady 49-50psi, idle/revving, where it was ~42/35, before.
 
Could be many things or a combination of things. But what the heck, take a look at the EGR. Things will usually be just fine at higher RPM's if it is hanging open.
Also do a cold and warm ohm test on your CPS. Eventually starts get problematic, but until then it can cause a litany of grief.
Loosing power on an uphill grade may be the O2 sensor, they tend to act up worse at low vacuum for some reason. A bad O2 sensor will eventually lower your top RPM's to around 3500-4000 in my experience. And may cause bucking at around 2000 RPM's.
 
In addition to fuel pressure, fuel capacity can be tested. You should do a capacity test to pump at least 1/4 liter in 7 seconds. Failure of test would indicate kinked line or dirty filter or fuel pressure regulator failure
 
i installed the fuel pump today after pumping my friends mom(he drives a yota), both turned out pretty good. haha... im going to drive around some more tomorrow because i still havent regained confidence in the jeep just yet, but it wasnt doing what i originally described . . . thanks
 
8Mud said:
Loosing power on an uphill grade may be the O2 sensor, they tend to act up worse at low vacuum for some reason. A bad O2 sensor will eventually lower your top RPM's to around 3500-4000 in my experience. And may cause bucking at around 2000 RPM's.
Click to expand...

Plus a bad O2 sensor will show up once the engine warms up and switches to close-loop mode. Maybe try unplugging it altogether and see if it behaves better or worse.
 
You must log in or register to reply here.

Similar threads

N
Severe stumble, misfire and no start issues
2
Replies
27
Views
4K
maxbraketorque
M
M
96 XJ stumbles then shuts off when warmed up. P0171
4 5 6
Replies
113
Views
11K
Unclewolverine
U
L
Fuel Pump Check Valve or leaky Injectors?
2
Replies
23
Views
5K
Lost_Wrench
L
B
Jeeper needs Help !!
2
Replies
22
Views
3K
denverd1
denverd1
J
XJ wouldn't run on a hot start unless I reset the ECM
Replies
5
Views
936
pearlheartgtr
P
Back
Top