Pre HE V12 running poorly when hot
 

Hello all.
I have a pre HE V12 XJC.
The car runs and idles fine when relatively cold, but say 10km into a drive when the engine temperature gets up, the engine starts surging, almost stalling and doesn't idle confidently.
I know some of the injectors are a little sticky but I have recently replaced the coil and the Lucas amplifier system with a Crane Cams system fitted and tuned by a professional Jaguar workshop. Full service and tune too.
Any thoughts please?
Manifold pressure sensor? Evaporation in the rails....help !

First thoughts are:

Fuel pressure regulators are unballanced, and set TOO high. They are a mongrel to get right, and I run 29PSI on one of the PreHE's, and 30.5 on the other car, and both are SWEET. The book, NAH, I use my ears for that "sweet spot" sound, and it tooks years to perfect. She calls it selective hearing, whatever.

The cold start injectors are NOT switching off, and/or are dribbling fuel, VERY, VERY common.

The PreHE is prone to flooding, so all and sundry must be RIGHT, even down here.

When it starts this nonsense, feel the coil, is it HOT, or the same temp as the rest of the bits. If its HOT, there is your problem, so the cause needs finding.

What Crane system is used, I have had terrible issues with the XR3000, so have swapped the box for the XR700, and a Bosch GT40R coil, with external resistor, removing that big ballast thing totally.

The list goes on.

Thank you Grant.
The coil has been replaced in the last weeks with a Crane Cams coil. The ballast resistor looks to still be in place though.
Yes, the XR700 was the system installed so that's OK.
I'll go for a spin this afternoon and test the temps etc.
Have you had any issues in Adelaide with the fuel evaporating in the fuel rails - that seems to get a bit of internet chat for the pre HE injection system.

In a word, NO.

Sir Arthur (in the garage) is just over 500K kms, and the thing will NOT stop unless the key is in the OFF position.

2 Summers ago, as you will remember, we were hovering at 47c, and NO issues with any of the Jags.

Nothing seems overly hot including the coil. Repairer seems to think it may be the manifold pressure sensor so he will experiment with one from his own car. will keep you posted

I'm having exactly the same issue with my coupe. The problem has only become apparent with the recent spate of hot weather we've had in the UK. After about 10 to 15 miles the car with start to misfire, progressively getting worse until even moderate acceleration causes a loss of all 12 but the car still runs around town fine. I've also got a non standard ignition system fitted mine being the AJ6 system. I'm going to try and run thought the suggestions made by Grant and will report back thanks.

Success - problem solved !!!
It was the manifold pressure sensor which is a round unit and sits above the radiator - apparently there is a copper diaphragm inside which can degrade. The part is not available new these days so my mechanic sourced a working second hand unit.
The car hasn't run better and I'm very happy !

SWEET.

Always something simple.

That Manifold sensor is getting old now. I remember repairing one a very looooong time ago on a DS21 Citroen, same D Jetronic system, and I used some Brass shim, as that was all I had laying around on a long weekend. She is still driving that thing today.

Hi boxa, just added you to the Qld Roll Call list.
Are you interested in the All British Day?
See link below.

https://www.jaguarforums.com/forum/a...nsland-122181/

thanks Grant - hopefully running as reliably as Sir Arthur now !!

Hey Clarke
I will be coming for a look - but don't have time to bring the car and hang around all day. Maybe I'll see you there !

I'm still trying to tackle this issue, it's driving me mad! I've tried replacing the trigger board,Coil,Spark amplifier, Plugs plus leads and as boxa mentioned the Manifold sensor with no avail.

The car seems to run really well until about 20 miles of driving and then the first signs somethings not right hits, when you push the car to about 5000rpm it starts to not pull, you can feel the cars stopped accelerating it struggles likes this until the gear change and everything's fine again until higher rev range is reached.

One other thing that I believe is linked to this issue is the car struggles to idle confidently, with a slight misfire and then occasionally hiccuping as if 3 or more miss in unison. If anyone has any more ideas I would greatly appreciate them thanks.

What pressure are the 2 FPR's set to.

One of mine ran sweet as at 29PSI, and the other was sweet at 31.5PSI.

I have NO idea what the book says, I just did it by ear, obviously WITH the gauge (2 actually) connected, and just kept fiddling until the engine/s sweetened up, and did so with them at the same pressure each side. Since the PreHE has 2 fuel rails with an FPR on each rail. VERY messy and complicated, and a MONGREL to set the FPR's at the same (or very close to) pressure.

Yours sounds like the pressure are out of whack, and when at the top end of the rev range, is running too lean, and when changes up a gear, the revs drop, the required volume of fuel decreases, and away you go.

Another factor that creeps in (runs actually) is the integrity of the fuel pump, and the age of the fuel filter, then the venting of the fuel tanks raises it ugly head.

Tank venting is easy to test, simply lift the fuel cap, and go for a blast.

Fuel pump, well if the age is unknown, simply replace it, and the filter, they are not that expensive.

The FPR's cannot be set correctly if the supply pressure AND volume is too low.

Thanks for the reply. That all looks like really good advice, I will be replacing the pumps and filters as soon as possible. Another factor that may give credence to a dying fuel pump is in the rear you can hear a slight vibration when ticking over, though it might have been the exhaust rubbing but then again it may be the pump. Thanks again.

maybe a cheap first step is to check the auxiliary air valve. this sits at the rear of the left hand water rail. the workshop manual suggests removing and testing in hot water to ensure it closes nicely. maybe as the engine warms up it isn't closing hence too much air and the engine runs lean?

Will see you there boxa, just look out for the Silver Series one with faded paint and a Jaguar forums Banner close by. Make sure you sign the banner.
:icon_beerchug:

my x type has been having stalling out problems for two years. But only when its warm out. it never acts up in the winter. Ive been searching all over the net, hearing a lot about the Mass air flow sensor, cracks in the antifreeze reserve, I
and intake tuning valve, intake manifold are all possible problems. my secondary fan hasn't been working so were check that tomorrow. good luck