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[just-boot-it!]

On the way home from work my 97 4.0 xj shifted into top gear abour 45mph as normal but as you increase throttle it started to hestitate off and on quickly and sometimes it was so severe i thought the diff was fooked??
So i managed to get home by keeping it in 3rd and keeping the revs up and thinking it was maybe the fuel pump I parked on a grass bank about 30 degree slope upwards and crawled up very slowly and the same symptoms occured?? No dash lights, no leaks or unusual dial readings?
Any ideas guys?

[Panic mechanic!]

tps?

[just-boot-it!]

Not sure, it accelerates fine upto top gear then any amount of throttle around 50mph it no likey likey!

[Panic mechanic!]

yup I would swap it out and try another if you can get your hands on one

[just-boot-it!]

Ive read somewhere you can check the fault codes manually if you have a digital odometer? something about turning the ignition on and off, any ideas?

[Panic mechanic!]

[just-boot-it!]

Thanks for the vid, spent a couple of hours research and it sounds like either the tps or cps, just as the snow is about to fall the xj gets a cold 

[Mike Pavelin]

I would check plugs, leads, dizzy cap first

[just-boot-it!]

Bit of an update, been to a mates garage and checked the voltage and resistance of the tps, cps, both fine, used his obd2, no fault codes. the distributor cap contact points and rotor contacts show signs of wear, like fine scratches? On the drive home like before it starts to shake the engine into top gear around 50 mph.
I will give lighthouse a call and order a dizzy cap, rotor and new leads.

Thanks for the info.

[tag]

Fuel pressure...........

[JamesH]

I would consider changing the rotor, cap, leads and maybe plugs and even coil too. They should be seen as fairly frequent service items imo and aren't normally too expensive.

[Jeepjedi]

tps could still be bad, it is usually the fault, the turning/contacts bit in the unit goes bad voltage is not that much of an indicator, but i may be wrong but it is a cheapish item and worth for peace of mind

[gazjeep]

Cheapest place for TPS was rockauto.com & very quick delivery too 

[just-boot-it!]

The jeep is my weekend / bad weather car as i have a tdi golf for the commute in the week but dont really want to drive it regular as the hesitation and banging noise is so severe it cant be good. Fuel pressure is ok I think as when you boot it and it kicks down and it takes off as normal, would the car be hesitant all the time if there was low fuel pressure?

Thanks

[Jonny Jeep]

Try unplugging the upstream O2 sensor. If the sensor is causing the rough running the Jeep will run fine with the sensor disconnected. You may get a code and check engine light with it disconnected but if it runs OK replace the sensor. NTK is OEM.

[just-boot-it!]

I take it upstream means manifold?? Hope not what a pain in the arse that was with my borla manifold only took two weeks of faffing to cure that! Its ran fine for a month since the new 02 sensor was fitted tho.

[tag]

the fuel rail needs a constant pressure, if its low or too high it will affect performance, last year i worked on a vw golf that would not pass emissions but not showing any codes after checking all the obvious  it was the fuel regulator over fueling the rail  and the car ran rich,  if the rail is low the symptoms would be lean running  both these conditions can lead to poor running , alot like a bad lambda sensor........ .  

[just-boot-it!]

Its just passed its mot two week ago, without 1 advisory ( 52 plate golf had 3 !! ), although they did say the exhaust was blowing, got my dizzy and new plug leads, gonna fit them saturday. Damm faults have eaten into my lift kit fund!

[isle of man]

Kat blocked/breaking up...

[just-boot-it!]

Cats only 6 month old but could be blocked.....

[isle of man]

Hey, Ive just got my finger in the air, trying to help.

[Jonny Jeep]

Yep, upstream is pre cat in/just below the manifold. It may not be the cause of the problem but unplugging it from the loom can be used for a free diagnosis.

[isle of man]

Do this when the engine has reached normal operating temperature as before that it's NOT part of the loop.

[Jonny Jeep]

I'd unplug it when it's cold. The engine won't switch to closed loop with the O2 sensor disconnected. If the O2 sensor is the cause the engine will run fine with it disconnected but may trip a code. Disconnecting the sensor when hot/in closed loop will just put the computer in open loop.

[just-boot-it!]

Many thanks, ooh look more snow on the way friday and the jeep is almost an ice block! Yipee!