Hi all, sorry for my first post being a request for help, but I'm sure I'll have more to contribute in the future!
I've had my x300 (3.2) for a couple of months now, and have a few issues still to sort out... the two most pressing of those are the car often stalling when coming to a stop (need to swap the spark plugs & clean the TB before I ask for any help there, I suspect!), and being difficult to start from cold:

From cold, 9 times out of 10 it will take ~7 seconds of cranking before it will fire.
The remaining 10% of the time it will start instantly.
Once started, it will re-start instantly.

I've swapped the CPS as it seemed a reasonable precaution on an item that's likely to fail at some point, but no difference. Not too surprised on that, as it shows the expected ~200rpm when cranking & not firing, suggesting there is a signal being produced. The battery's nice and new too.

So has anyone got any ideas on a cause? The temp gauge shows cold when it is indeed cold, but is that on a separate sensor from that used by the ECU?

Cheers for any tips - I'm new to Jaguars in general, & will hopefully be able to enjoy the experience a bit more once the more serious niggles are resolved!

 

If once it starts, and it is shutdown immediately then restarts again without a problem, then a prime suspect would be fuel pressure that has dropped while parked. The ~7 seconds of cranking is what it is taking to build up pressure again. If you are able to start by turning the key to position 2 several times to prime the pump without going to the cranking position, that would be another sign of lack of fuel pressure at startup.

 

I would also recommend that you check that the half engine speed sensor (often called the cam position sensor, though it isn't mounted anywhere near the cam shafts) is correctly timined. At TDC cylinder 1 a hole in the cupped disc inside the sensor should either line up with the dot in the middle of the little perspex window, or be 180degrees out, depending on whether you are on TDC firing or non-firing. If the hole looks 180deg out then turn the engine over 1 rev and check again.

 

Thanks, but I have tried that one! No difference...
I fully expected it to work too - sounded like a good explanation. But then it didn't explain the occasions when it fires instantly I suppose.

 

I'll have a look - ta! But wouldn't that give issues all of the time rather than on just 90% of cold starts?

 

I'd be tempted to check the coolant temp sensor for the fuel injection system. If it is skewed "warm" or "hot" the ECU will not give the fueling enrichment needed for that initial cold start.

If this was the case I'd also expect poor running when cold but, hey, not all faults follow our logic.

I'd definitely clean that throttle body before getting too involved with in-depth trouble shooting elsewhere. You might kill several birds with one stone.

Cheers
DD

 

So the temp sensor is indeed separate from that used for the temp gauge? As per my admittedly rather lengthy original post, the thought had crossed my mind! Can it be tested at the ECU (to test the wiring too)? If so, do you happen to know which pins, and what resistance it should be showing?

I've been putting up with it for weeks - a 4 month old and a house move mean free time is something I used to have! I'm sure the new spark plugs are working wonders in the boot too...

 

Yes, separate from the sender used for the temp gauge

The coolant temp sensor can be tested with an ohm meter. I don't have the specs at hand. I can look it up tonght if nobody chimes in sooner

Cheers
DD

 

Thanks Doug - the specs would be great.

I'll hazard a guess that it could well be the wiring to the sensor - if it's a dodgy connection that would explain how it can work perfectly on occasion! So if anyone knows which pins on the ECU it goes to, that would be most useful...

In the mean time I'll try again to get my OBD reader to work - that may well give me some clues!

 

I spoke too soon. The resistance/temp graph in my manual is cobbled up...partially illegible and the resistance side of the graph totally non-sensical. Hopefully someone else will chime in.

At minimum you could check the sensor resistance (across the pins) on a cold engine (high resistance) and check again on a fully warmed up engine (low resistance) to determine if the sensor is at least fundamentally operational. Not very precise, though, without knowing the correct values....especially the values at the cold end of the scale.

On the manual shows ECU pin P1105-14 for the blue/yellow temp sensor wire and P1105-31 fror the black/brown temp sensor wire (ground). These are in the red ECU connector. I'm sure the "P1105" identifies the connector and the "14" and "31" identify the pin. That's how I interpret it, at least.

Cheers
DD

 

OK, did a little checking and cross referencing. Multiple aftermarket sources show the same replacement part number for the LHE1600AA coolant temp sensor used on the X300s and the EAC3927 coolant temp sensor used on umpteen older Jags.

If that's correct, and I'm fairly sure it is, then this should apply:

Testing the Coolant Temp Sensor


Cheers
DD

 

Great stuff - thanks again Doug! Tempted to just order one (hardly expensive!) but as you've gone to the effort I'll do things properly...

 

Right, well I've not had a chance to check the resistance on the sensor yet (having just moved house, my multimeter is 'somewhere'!), but I have got my OBD reader working.
It reports what look like fairly sensible coolant temperatures - I'll confirm that when it's properly cold, but I'm tempted to believe that's not where the fault lies.

One interesting thing that it does report, is a throttle position of ~10% when there is no throttle applied. The cable is well adjusted, so I have to suspect there's something funny going on with the TPS / throttle body. Can anyone confirm that the 10% reading isn't what it should be saying?!

 

FWIW, that's about the same as mine. Not sure if it's correct....but I have no starting problems.


Cheers
DD

 

Bother! Was sure I was onto something then...

 

I know, I know - I still need to do the plugs, clean the TB and check for air leaks.

But the damn thing has started instantly the last 3 times - it seems to like the cold/damp!

 

Since temperatures have dropped around here, it's now starting instantly more like 90% of the time. Bonkers.

 

Plugs swapped & TB cleaned - it started instantly yesterday and this morning, but as it had started doing that more often anyway I can't really get my hopes up yet! Hasn't yet stalled when coming to a stop either though...

I'm sure the couple of loose plugs and coil bolts were really helping matters!

 

Yup, I spoke too soon. Just popped out on my lunch break to return the incorrectly-supplied cam cover gasket (see my other thread!), and it was back to starting after ~6 seconds.

 

So... which temperature sensor is it that I need to change?! Looks like there are two at the thermo housing - one with a 2-wire connector and one with a single wire...?