Hope someone can help me as i'm at my wits end!
2002 XJR 100 with full history and 82K - starts on the button when hot and cold BUT when the engine has been running for 20 mins or 4 hours stop and leave it for 30 mins and it takes 7 sec of cranking before it fires up.This fault is 100% consitent day in day out and makes no difference if the car has ben run for 5 mile or 500 miles.
So far i have changed the throttle body and purge valve. Very good Jag garage has run all computer tests on nothing has come up.
When its started its perfect - no oil use or blue smoke at any time

 

I'm sure someone will chime in -- this is a classic crank position sensor failure on a Mercedes Benz.


When you say "starts on the button when Hot and Cold" -- are you talking about the outside temp. Because obviously the engine and all the sensors are hot when it is sitting after a run.

 

My car does the EXACT same thing! It has been doing that for the past 7 years! 100% consistent on warm starts too. My takes maybe 3-4 seconds to start though. When yours eventually starts, does the engine feel like it could stall for a second and then slowly climb up to a normal idle speed? I have now trained myself when to give it some extra gas when it starts slow like that. My car makes buzzing sound with a sound of water rushing only when I get the warm slow start. Must sound must be the fuel pump. It shouldnt be a fault because the problem only occurs during a warm start.

My hot starts are normal but my cold starts are strange because the car almost starts too fast. It only takes about a 1/2 second crank in the morning followed by a strong smell of a rich gas mixture from the exhaust.

I have an inconsistent 'small vapor leak' CEL.

 

You might start by cleaning the throttle body inside around the butterfly, and part load breather and MAF sensor. There's a sticky in the XK8 forum for how to go about cleaning these. Fuel pressure check, there's a valve just outside of the fuel rail. Throttle body connection, electrical contact cleaner on the connections.
Disconnect the battery if you do the points above. I'd do a hard reset too, letting the throttle body reset fuel trims.

Crank position sensor could be faulty, but would it throw a code?

It's as if the fuel once up is good, it's getting it to the injectors while the engine is warm, it takes time....a weird one. Fuel pumps getting long in the tooth? I'm guessing out loud here, sorry!

 

first think in the morning when the engine is cold it fired up straight away and if you stop and re start in 5 mins its fine - when you leave it 30 - 45 mins it always takes extended cranking to fire up

 

how old are the fuel filter and plugs?

 

thanks sean B - i have cleaned the MAF Sensor before and no change, fuel pump sound possibile -

Does anyone know what regulates the fuel pressure ?

thanks

 

On the MB's you often do not get a code. I remember it has to do with a partial failure of the sensor - but I forget the reason why -- sorry.

I remember the reason for the failure -- heat -- when you turn off the car. The area around the sensor gets too hot as heat moves from the cylinders no longer cooled by circulating coolant.


I was not clear above: The MB sensor uses a magnet on the engine and inside the sensor is a coil that is affected by the magnet as it spins by - this "wave" effect on the sensor coil is what the engines computer uses - this is a typical design. Excessive heat takes its toll on the sensor - I forget what it actually does to the sensor but they they do not work correctly when hot. My Nissan V6 has three of them - crank and both heads. Only thing on the engine I have ever replaced in 130k. On the Nissan they are linked together and since you can not test them -- just replace all three ($125)

Does anyone know what the sensor looks like on the JAG?

 

think i might change the crank sensor as its onlt £22 ish from what i can see online - at least that 's a cheap way to cure/eliminate that option

Thanks

 

How long has your car been doing this? Mine has stayed the exact same for 7 years! Hasn't gotten better or worse for the past 50k miles.

 

Describes the symptoms of our s type 4.0 perfectly. Been doing it for many years. Fires immediately when cold and have to crank it 7-10 seconds when warm. Replaced all plugs and coils, cleaned maf and new fuel filter.

 

Did those repairs help you? I also did that on my car a few years ago and nothing changed for me.

 

Its been doing it since i bought it - no better no worse as time goes on
Very annoying!

 

No change at all. Asked the dealer about it also. He acknowledged that it was a common problem on those years with no suggestions for a fix. Only stated that they run a rich mapping leading to the warm start problem.

 

That would explain my rich smelling exhaust. I spoke with a mechanic about my prob and he had no idea what the problem could be.

I read somewhere (I think the XK forum) that the problem could be a evap valve sticking?

Anyone heard of that causing this?

 

Yep i have! changed the evap valve which made no difference however the set up on 2001 onwards was different,it was bolted on the bulkhead and electoniclly controled. whereas earlier cars it was based near the tank and had a valve that would open at about 1 bar - this valve would stick open and cause starting issues

 

Smithy,

I posted this on you intro post and not sure you saw my post. Turn the key on count to ten then start the car and see if it starts quicker.

 

outlook is looking good in terms of finding the cause of the warm start issue - TL Jaguar Nr Reading UK 01189 9762899 have spent the last week or so fault finding on the Jag ( when the car is warm the fault is only there for 7 sec then its need leaving for 30 mins so very time consuming ) and it is down to fuel pressure. whats has been noticed consistently is when its warm it losses pressure by 50% (Should be 40psi ) the cause is looking like the Fuel damper in the engine bay which is not working when heat soak takes effect ( The fuel damper keeps pressure but also helps with the noise prodcuced from from the fuel lines )

Option 2 is 1 of the fuel pumps not working correctly when warm but as they dont get that hot its not as likely as the fuel damper

I have hope and will update again next week

Already we have an XKR within 5 miles of where i live with the same issue so hopefully TL Jaguar can provide an answer to all !

 

Thanks good info, keep us posted on what Tom finds, he's knows his stuff - why not get him to install a quaife while it's there?

ATB

 

I'm willing to bet you it's the battery! I had the same problem that was resolved with a new battery.