Hi guys, great website you have here, hope you guys can help me too?

Car:

1996 XJ6 X300 3.2 automatic 121k

Symptoms:

When the car has been left for some time and the car is cold, say first start of the day she takes some 5-6-7 seconds of cranking before she starts, once started if then stopped straight away she will start up prompty just as she should.

Checked:

I have checked the camshaft timing and all is good.

I have checked the coolant temperature sensor (CTS) by two methods both by reading the live data out of the diagnostic port. The CTS reads ambient when cold agreeing with the ambient air temp sensor on ther dash, and secondly when the CTS is unplugged I get a reading of -40c so the wiring is fine.

I did wonder if I have a fuel rail pressure issue I think the rail pressure should be 38 psi? Be good if someone can confirm this?

She drives faultlessly once started, idles fine, she runs wide open throttle fine with a very strong engine indeed.

One issue she does have is a battery light always on, I think this is red herring as she charges fine on dash display and by measureing volts at the battery with everything possible switched on loading the alternator... I have seen this before and it was a faulty resistor pack in the alternator, annoying but not a job stopper. She has been like this since purchased 5 weeks ago.

I bought the car with this cold start fault thinking it would be mis-timed camshaft sensor but hey ho, she was cheap and I'm guessing the seller knew she had an issue.

I have had oodles of XJ-40's & X300's but only a few X308's so I know these models reasonably well, but to be honest never had too many issues with any of them....Mercs and Beemers yes but Jags not.

For my sins I used to work for a Japanese company in the late 90's, early 00's whom used to supply all the tailpipe emissions measurement equipment for both Jaguar R&D at Whitley and the Conformity Of Production site at Browns Lane which is now mostly closed I believe?
Jaguar was one my favorite customers, always a happy place to be and real enthusiast engineers, many of which seem to be into motorsports, classic cars or performance gear.
The guys were both fussy but easy to deal with and lived in the real world with not a lot of business posturing and/or internal politics going on.
The X350, X400 and later X200's were being developed when I was there, alongside quite a few Aston's.
Ironically I wanted a X400 as my replacement company car but they were too expensive and had to settle for a C-Class Merc!

cheers guys

 

that should be camshaft sensor timing!

 

and no error codes!

....how do I edit a post?

 

rev counter shows 200 rpm during no start crank too

 

Hmmh. It seems like you have covered about everything. I do not remember the parameter, but I am pretty sure there is there is an Intake Air sensor in the MAF that is involved in fuel mapping and can be read with mode 1 OBD.I do not know the 3.2 liter engine, but if you have an EGR, I wonder if it might be leaking by the port?

Your fuel pressure number is about right, but there is no factory installed test port on a X-300.

Look down in the bottom right corner of the box around your post when you are logged in. You should see a "edit" click box.

And... welcome to the forum. For us dumb *** Yanks, you might add "England" to the "Norfolk" designation so we don't think you live on the coast in Virginia.

 

Thanks for prompt reply. For want of something easy to do I may just pull the crankshaft position sensor and give it a clean and check for excess gap, also pull the plugs for a looky see, nothing to loose.
Both fuel trims all look good so I know she thinks she is running well...indeed a strange one.

....I did have a Corvette C3 with a similar issue that was down to fouled plugs and stuck EGR valve...just mentioning I know they are chalk 'n cheese

 

The fuel pump will run for a couple of seconds when you "Key On" the ignition.

Suggest you try Key On/Key Off a few times before next cold start. If that helps with the starting then it would indeed point to fuel pressure loss.

 

Yes, I tried that, no change....

 

Have you had a chance to read PID 0F, "Intake air temperature"?

Assuming you are not noticing a decrease in crank speed at low temperatures (which I doubt), then one would assume the problem is related to fuel mapping at low temperature crank conditions.

 

well that typical, just went to move the old girl and tried turing the ignition on and waiting for 3 seconds and she started straight up....could be a one off but I'll try again tomorrow.

Just read the air inlet temp and all OK...but...


I found a code 1621.....ran it around without clearing, then decided to clear that code after a drive and now I find the central locking is bouncing 3 times before locking....!!!

Think I may make a new thread on that one!

 

OK, I tried the key on in ignition mode and wait three/four seconds method and then went to crank and she started straight away again.....hmm.

Tomorrow I go for a quick start and see what happens?

 

tried to start without a pause.....long crank time!

ABA test will be tomorrow with the pause again

I may fit a noid light to an injector to see if the injectors are acutally being told to inject during this null crank period....I believe sequence goes.

1/ key on
2/ assuming immobilisor is 'off', then the fuel pump runs and primes to pressure
3/ crank the engine and the crank shaft sensor (if working!) gives the ECU an rpm signal to say "hey I'm turning here" then the system cycles the injectors.... injection will not occur before the crank rpm is noted.

cheers all


all the best.

 

If I am following the thread correctly, the significance of the few seconds pause is that it allows the fuel pump to restore pressure in the system, the implication being that it has ebbed away as the vehicle has become cold overnight. When it is still hot, there has not been time for the pressure to ebb away, hence the vehicle starts immediately. A tiny leak could be the culprit, but I would imagine you would have seen or smelled fuel if this was the case. I dont believe there to be any one way valving in the fuel pressure regulator, so the only other way for fuel pressure to be dissipated would seem to be via a leaking injector or a tired fuel pump. If all it takes to start the car from cold is a few seconds pause with the ignition on, it might be worth living with it, at least for a while to see if any more clues emerge?

 

thanks for the reply, yes I know this seems logical, I agree with it. It's not a big issue and as you correctly say, I can live with it

...but my old head keeps telling me it shouldn't take that long for a fuel pump to build up to 38psi, even if the fuel rail was empty...I've had other fuel pipes off other cars and the time from zero to 'run' pressure is almost instant....can't be the fuel filter as it runs wide open throttle OK...I can't help thinking I'm missing something, you know how these things niggle away.

puzzled & content and very thankful of your help

 

Question: do these cars run a fuel return to tank system or non return system?

I'm guessing its a return system as I can see what looks like a manifold pressure sensitive fuel pressure regulator?

 

Return to tank is right, and yes, the pressure is vs manifold pressure.

 

So weak fuel pressure regulator allowing pressure to dissipate into the return pipe maybe?

 

thanks for the reply.

Are you sure the fuel pressure regulators have a non-return valve? Would be a good shout if they do

cheers

 

As I understand it, the fuel pump runs continuously when the ignition is on. Once the target pressure is reached in the supply system, the pressure regulator opens, and the excess fuel goes back to the tank via the return pipe. At wide open throttle there won't be much fuel going back to the tank, but at Tick Over there will be a lot more. When you switch off, the system should retain pressure in the supply side, and the theory I have in mind is that your car gradually loses this pressure, necessitating a few seconds to allow the fuel pump to restore pressure. The only places the pressure can go would seem to be out, via a leak in the pipe work, back into the tank via a weak fuel pump, back into the return pipe via a weak fuel pressure regulator ( and hence back into the tank), or into a cylinder via a weak injector. The fuel pressure regulator is probably the easiest and cheapest to address, and at this point would also seem like the most likely culprit. I hope this helps.

 

thanks for the excellent reply, I work on more non-return systems nowadays for my sins.

Yes, one would assume the fuel reg should 'close' in an effort to retain fuel pressure after key off....I believe the fuel pump is designed to be a non-return?

I have the kit to check fuel pressures but its frustrating that Jaguar did not fit a fuel pressure take off point....I may need to be creative and look into tapping into the fuel rail to check for fuel pressure decay and FPR response.

I have now noticed a slight lumpiness to the cold start and just have a 'feeling' I may have a weeping injector, although as with all these quirks once noted the 'internal' radar can pick up on things that one would normally think as normal

cheers again