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Matt
Matt, Mechanical Engineer
Category: Jaguar
Satisfied Customers: 21366
Experience:  BEng hons Mech engineering, in auto industry 22 years
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My 2002 Jag X Type 2.1 auto has a persistent misfire. Diagnostic

Resolved Question:

My 2002 Jag X Type 2.1 auto has a persistent misfire. Diagnostic computer just returns misfire on cylinder x. Different number each time. Something is obviously causing misfire but not being picked up.
Submitted: 2 years ago.
Category: Jaguar
Expert:  Matt replied 2 years ago.
Matt :

Hello

this sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,

Ideally measure the pressure at the injectors and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

Matt :

hi, does this make sense?

Customer:

Sounds plausible. I will have to get my garage to check. If that's not the problem any other ideas?

Matt :

Well random misfires, can also be a poor earth connection for engine sensors

Matt :

so well worth checking that the main earth strap connections are clean and tight

Matt :

do the same for the small earth wires that runout of the engine bay wiring loom and terminate onto the engine with ring terminals

Customer:

I'll have to get back to you, how do I re-contact you?

Matt :

just get back to me on this post, I'll pause the timer

Matt :

This could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;

Airflow meter

Crank position sensor

Cam position sensor

O2 sensor

Throttle position sensor

Customer:

Someone (without too much technical knowledge) suggested it may be an air leak?

Customer:

it makes no diff whether engine cold or warm

Matt :

an air leak is possible

Matt :

but these do tend to be effected by temperature

Matt :

however there's a an easy and cheap test for air leaks

Matt :

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane 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.

Matt, Mechanical Engineer
Category: Jaguar
Satisfied Customers: 21366
Experience: BEng hons Mech engineering, in auto industry 22 years
Matt and other Jaguar Specialists are ready to help you
Expert:  Matt replied 2 years ago.
Hi

do you still need help with this?

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