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Matt
Matt, Mechanical Engineer
Category: Jaguar
Satisfied Customers: 22001
Experience:  BEng hons Mech engineering, in auto industry 22 years
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1998 xj8 4 liter it fires up then stops fires up then stops

Resolved Question:

1998 xj8 4 liter it fires up then stops fires up then stops then just cranks over coz its flooded.
Submitted: 1 month ago.
Category: Jaguar
Expert:  Matt replied 1 month ago.

Hello

This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion ill make a leak worse) so leaks can be better or worse as the engine heats up.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth cleaning out the idle speed control motor / valve as these get clogged up with carbon and some brake cleaner washed through helps free things off.

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.
if the engine condition is the same then chances are the meter or the connection to it is faulty

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading
Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile

Matt and other Jaguar Specialists are ready to help you
Customer: replied 1 month ago.
i have disconnected the crank case vent pipe and sealed the hole it is connected to.Now it starts on second or third go.It would not start at all before i did this. So it is better, but not right. It had a new fuel pump about six months ago. Once it starts it runs on a fast tick over and slows as it warms up. So it does every thing it should. Accept start first time. Any further ideas ? Thanks for your help.
Expert:  Matt replied 1 month ago.

Hello

the next step should be to plug in a scan tool that can do monitoring and see what the engine coolant temperature is sitting at and if the signal is steady and not jumping around? As if its not steady the chances are the sensor needs replacing and this has a strong effect on starting performance

Customer: replied 1 month ago.
The scan tool showed 22 deg steady, then gradually to 85 when started. On looking at other systems found a DTC P1336 which showed as cam shaft sensor. It had a new crank shaft sensor fitted about 8 months ago. I deleted it. Then it started first time. but the engine was hot. I will try it again tomorrow when it is cold. Has it got a cam shaft sensor.?
Expert:  Matt replied 1 month ago.

hello

yes there's a cam position sensor on the end of the cylinder head

see the attached image

Expert:  Matt replied 1 month ago.

Hi
do you still need help?
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Customer: replied 1 month ago.
Tried to start it the next day, would not start. So I got 2 cam sensors delivered yesterday but I can only find one at the rear inside of the left cyl head near the throttle body. On taking it off I found the plug on the end is wrong so they have to go back tomorrow. Any idea where the right side one is fitted. thanks
Expert:  Matt replied 1 month ago.

Hello

OK looks like on this year there may only be one cam sensor

this image shows the location which sounds like the 1 you've already found

Customer: replied 1 month ago.
This engine looks the same as mine and the sensor is in the same place I will get these changed for the correct one tomorrow. I have already rated you 5 stars and written a review and added a 25% bonus. Thanks again.