Before I begin I'd just like to say I've read a lot of threads about misfires and (so far) only one of them seems similar to the issue(s) I'm having;

X300 4.0L annoying misfire - Jaguar Forums - Jaguar Enthusiasts Forum

With that said I'll move on. A few days ago my car began to misfire in traffic, the idle became very rough and there was a complete loss of power. As a result I had to get it towed. I decided to check obvious things first and as a result have temporarily removed the intake piping and connected the maf straight onto the throttle body with a silicone joiner, this is to ensure that the main intake pipe isnt leaking and causing issues.

So far I have checked:
-Coils
-plugs
-cleaned throttle body

I decided to start unplugging the various sensors and here are the results:
-maf; unplugging this caused the idle to rise to 1500ish rpm
-iat; unplugging this had no effect
-cps; unplugging this had no effect

-coolant temp sensor; unplugging this actually improved the idle, however whenever the electric radiator fans come on the idle once again becomes extremely poor. Im not sure what this means (bad sensor?, something in the fan circuit?)

Thats about it, if anyone has any ideas please let me know!

 

Adam,

My 3.2 did that same thing some time ago.

Having recently replaced the CAS (crank angle sensor), it did not come into the thought process.

However, I did notice significant oily gunk in the top of the CAS plug, which is mounted vertically on the timing cover.

My thoughts were that since this looks like a "sealed" connection, little more immediate thought was given, but it eventually bugged me enough to seperate the 2 sections, and found horrid gunk inside the connection. Carby cleaner liberally sprayed in both sections, dried, reconnected, all sweet.

This is NOT a sealed plug arrangement, the top section has 2 holes open to whatever wants to fall inside. This gunk obviously interrupted the integrity of the required signal to do what is required.

 

Thanks For The suggestion Grant it may very well prove to be invaluable information. Come to think of it my car has recently developed Quite the Valve cover leak and it Does drop oil right onto that region....

 

Also, just to eliminate all, were any of the rubber coil boots dripping in oil when you removed them?

 

Unplugged the Crank sensor Today and cleaned it, has Improved the idle quite a bit. However the idle still Degrades when the Fans come on.all rubber Coil Boots were dry.

 

OK, NEXT.

Connect a DVM (digital volt meter) to any +ve post under the bonnet. There are 2 on either side fuse block, with a rubber cover over each one.

Run the engine, observe the voltage, you are looking for 13.8 or better. When the fans switch ON, observe what happens. I reckon it is dropping too low, coz the battery is dying, and the alternator cannot keep up at idle. Not uncommon.

That means 2 things, the battery, or the alternator needs sorting.

These are juice hungry cars and systems.

 

So, one wonders if the problem is related to the electric fans or to engine temperature.

I'll keep a very long story short.....

I battled an idle misfire for about three months. The engine would be smooth for about 20 minutes at which point an idle misfire would occur. The longer the engine was running the worse the misfire became...and it often became quite severe, sometimes to the point of the engine conking out.

Weeks of torment ensued.

Cutting to the end of the story.....

On nothing more than whimsy I replaced six spark plugs which were only a few months old and looked perfect with six spark plugs that were brand new and looked perfect.

End of problem. Period.

I have no solid explanation for this. I did change brands (went from Champs to NGK) but I have no idea if that's significant.

So, consider this as nothing more than a weird story that has been thrown into the mix. I have no idea if your car would benefit from the same whimsical spark plug change. But, considering how cheap and easy it is to replace 'em, one might be tempted

Cheers
DD

 

what are your fuel trims? LTFT in the extreme negative value indicates Lean condition take a check at fuel pressure at fuel rails.

 

Hi from jaguar they recommend useing champion or ngk but deffo not bosch av heard these x300s dont like them

 

I replaced all the plugs with ngks about 2 months ago. I Will Have to get a volt meter but its Strange that the issue is only caused by the fans, the Lights, air con etc have no effect on the idle even when run all at once. Odd

 

If your observations are correct, then either the fans are effecting the engine, or the engine misfires exactly when the temperature comes up to fan on temperature. To make sure, I would run the temperature up, stop the car, then unplug the fans, restart the car and see what happens. You can run the car with no fans for a minute or two without fear.

Does turning on the AC not run the fans on your car? I think that means the AC switch mod has not been done. And, can you tell if the problem occurs when the fans are running in both high or low speed?

If it is the fans running, rather than the engine temperature that causes the problem, I would look for bad grounds on the engine to chassis strap, and on the chassis stud near the fan relays.
Good luck.

 

It's the fans. With the fans unplugged the idle is fine at any temp. Not sure what to do now, fan relay problem?

 

One or both fans are drawing too much current for the system at idle.

This may be the alternator not up to snuff, although the fact its fine with the a/c and lights etc on, I doubt it.

There are postings around about these fan motors seizing, which usually blows fuses?, but maybe yours are just on the edge??, but draining available power causing the stumbling.

 

Adam:
Well, it very well might be the fans drawing down the system voltage, either by them drawing too much current as Grant said, or by the system having a high resistance in the path to the engine that is not there when you ran your load test. I would check the false bulkhead connection, the high current cable connection to the engine fuse block, the battery terminal connections, and all of the ground straps, especially at the battery, the engine ground and any ground points near the fan relays.

You should measure the voltage with and without the fans running at the main power point at the engine fuse block, and even better at the engine ecu power feed.

If it is not voltage drop to the ecu when the fans run, then it is electrical noise. If so, you may have a long fight finding it! Again, grounds could be a problem on this one, or just bad motors. Or bad connections in a connector, ..

And, although I am not seeing the exact interrelationship in my head, head Doug's advice and do not discount a failing coil. Bad coils have had some pretty interesting manifestations of symptoms.
Good luck!

 

the very first post sparkzap stated when the coolant sensor was disconnected that the idle improved. I am confused as traditionally my car would not start nor run with the coolant sensor unplugged. However this has changed as now my car will start with the coolant sensor unplugged. will somebody please shed some light on the subject. I really believed that the car would not start with the sensor unplugged now im wondering if I have a bigger problem.