Hello I have a restricted performance fault on dashboard and i need to disable it for a day, it may be a head gasket leak but the fault displays at times only , when it does display the car shudders badly on acceleration, fine when fault is not displayed on dash... Can I disable the display for a day easily, perhaps a fuse or relay or similar???? Also radiator fans are not working , where do I begin .. I like to check the obvious Stuff first ... All advice is greatly appreciated thanks, I'm just an amateur so go easy 😁 thanks Trevor

 

There will be DTCs logged in the ECM for you to determine the cause of the Restricted Performance. What are the codes in the module????

bob

 

There are 2 ways in which the fans turn on . One is by the coolant temp sensor and the other is a command on by the A/C pressure switches . We'll test it by the A/C method .

Fuses first : # 12 / 30 amp Engine Compartment fuse box

# 14 / 30 amp Engine Compartment fuse box

# 14 / 10 amp Engine Management fuse box

Then run with A/C on and see if you get both fans .

If not you can swap the right fan connector over to the left and see what you get .

 

First off Trevor why do you think it could be a head gasket?
It sounds more like an electrical fault if it comes and goes.

Can you give us more info on the car, what year and is it XJ8 or XJR?

You can read the fault codes stored by using an OBD reader, there's plenty of info on this forum, basically connect it to the car and pull the DTC's as Motorcarman (Bob) has suggested - an essential little gadget when you own one of these cars...
Once you've posted the codes we can at least suggest a fix so you can rid of it permanently instead of just for one day.

 

The auto parts store will read the codes for free as they want your business . Write the all the codes down ( don't rely on your memory ) and have them reset the codes to erase them .

 

Hi codes are and have repeatedly been P1316 missfire rate exceeds emissions and P0308 cylinder 8 misfire detected ..

Loosing coolant regularly... 1998 xj8 4.0

 

Hi Bob thanks for replying codes listed below

 

The first thing to do in troubleshooting is to pull coil number 8 and swap it with number 7. Drive a bit and check the codes . Are you now getting P0307. If so then the coil from number 8 is bad and needs to be replaced. Since you are going to pull coil 8 to swap I would go ahead and change the spark plug while the coil is out of the way. The coil may be good and the plug bad.
When you pull the coils check for oil around them. If it is there is oil the plug could be shorting out. The cure for oil in that area is new cam cover gasket.
For your coolant loss problem the only way to good a good resolution is to have the system pressure tested. Your leak could be where the coolant is contacting a hot surface and evaporating off and you can't see it.
Biggest culprits are the heater feed and return underneath the intake manifold and the "Octopus" hose under the throttle body.

 

Are the fans supposed to run all the time ??? Thanks

 

No the fans should not run all the time unless it is VERY hot (yeh in N Ireland? Hehe)

 

They often run when a/c is on, including auto (so try with it off).