cold start failure

[whippetpaul]

Hello, my XJ-S 3.6 has lost its cold start assistance. It used to start instantly, but now will only start after numerous attempts, despite the exceptional hot weather. My garage had the car for 9 days, attempting to find the problem but said they could not and they managed to start it.
I do not know where to start my diagnosis ?

Can anyone suggest the cause ?

Paul.

[poprivet]

Hi Paul,
When you turn on the ignition, but before turning the engine over, you should hear the fuel pump run for a few seconds then stop, (not to be confused with the ABS pump).

Then look at the temperature sensor in the thermostat housing behind the top hose, if it has a white plastic body it needs changing to an updated one with black plastic body although I expect it has already been changed before now.

I think your car had the crank position sensor changed a while ago so that should be ok although it's worth checking that the sensor head is free of muck (it's magnetic).

Failing all that, assuming once it is running it is running well, is the normal spark plug gap checks, is there a spark, are they wet with fuel etc. etc. One last thing, is the fuel fresh. Some low mileage cars with a full tank may have been last filled a year ago.

I'm sure you will find the problem, the later 3.6's like yours are usually very well behaved.

[whippetpaul]

Hello, thank you for your reply.
The sensor appears to have a white body.... is this a different sender than the one operating the temperature gauge ?
I was not able to tell if the pump ran before starting.
Once the engine catches it steadies to idle quite quickly, runs perfectly afterwards.

How many elements are there to the cold start system? Could some component have failed ?

Kind regards Paul.

[poprivet]

Hi Paul, there are two sensors there, the one closest to the cylinder head has one wire and controls the gauge, ignore that one.

The one furthest from the cylinder head has a multiblock connector and is the one that gives information to the computer. This is the one that was modified some time ago as it caused cold start problems.



http://www.jagspares.co.uk/Manners/part ... DBC3728%23

Cheap part to replace for a change!

[whippetpaul]

Hello, I agree a surprisingly cheap part. I will change that and see what happens.
Thank you again for your help.
Paul.

[whippetpaul]

Hello, I changed the coolant sensor and the car started instantly as usual. A great relief after weeks of frustration.
Many thanks once again for your suggestion...
Paul.

[steve_m]

I suggest that you use a different garage!
It's always worth coming here first.

[poprivet]

Looking good Paul, I may be biased but the later 3.6 models (Microfueling and Sportspack) are brilliant in my opinion, more then enough performance in real life driving, far easier to maintain then the V12, cheaper to buy, rarely overheat and have a very reasonable fuel consumption. (I've no wish to upset the V12 lovers, each to their own. I've had a SIII V12 Sovereign myself and although silky smooth it was a nightmare to live with).

I would agree with many that the 4.0 AJ16 engine is even better then the 3.6 but I really prefer the looks of the pre-facelift models.