As some of you know I am a professional British car technician, specializing in Jaguar vehicles. This problem has me scratching my head a bit.

I have 3 Jaguars, all showing the same symptoms, a hot restart misfire. It only happens for about 15-30 seconds, and only under the following condition.

Car driven about 20 minutes, park for 15, restart, and there you go. An irritating and rather strong misfire, randomly across all 8 cylinders.

All three vehicles show the same codes, and number of 300-308, and excess emission codes like p1316 etc.

No other codes found present in any of the three cars, all three have had recent major services (our version of a tune up) and all 3 have new ignition coils. 2 of them have a new throttle body for an unrelated symptom.

vehicles affected-

(1) 03 Jaguar XJ8 4.2L NA
(1) 04 Jaguar XJ8 4.2L NA
(1) 03 Jaguar XKR 4.2L SC

Before you say it, I checked for vacuum leaks on all three, no leaks were found after smoke testing the vehicles. All show fuel trim values of less than 10% either rich or lean. Just for kicks we ran fuel injector cleaners on all three, all three have new crank sensors, 1 car we reprogrammed the ECM and 1 is getting fuel pump installed (The XKR, this car may be having a problem with the fact that the fuel pump is putting out 80lbs which is well above spec. It also causes the vehicle not to start when this symptom occurs, so in the interest of making this easier, we can talk about the XK when it is back together.)

Can't say I don't ask about the fun ones! Any ideas would be greatly appreciated.

 

First Thought is that the cats are marginal and or the upstream/downstream 02 sensors

But on second thought the key may be siting for 15min after warmup
It might be the IAT sensor out of spec as the air charge will be very hot

Along the same lines it might be the Pollution Purge system as well

Rather than a smoke test do a vacuum test using a vacuum pump

Make a plug for the airbox and it the vac pump and gauge here
I have a Vac chamber for silicone molding and use the valve/gauge from this
The procedure is to pull a vacuum and lock off the pump
Not the reading on the gauge and leave it overnight
If all is ok the gauge will not drop

If you get a drop you can then go about hunting down the issues

Remember it may be more than one here is where the gauge is very handy
As you can isolate the main systems such as the fuel tank, brake booster, and the 2 breathers and retest

You can then test the engine alone which lets you know if you have issues with the superchager, manifold valves, dip stick ect
Interesting this will even show up ring issues. A quick crank and retest will tell you thats the mix of open inlet vales will change
A Stethoscope will tell you if the dipstick is leaking or if you have anything around the manafolds

Once this is OK start testing the items you blocked off. You can test the pollution purge and brake booster, full load breather ect in isolation this way or add them back in and retest

You may find its the dipstick of full load breather or even the evap line to the tank
I find the easiest way ti to isolate and test the re-add items till i get a difference

A smoke test often hides the issue as the smoke is not always venting externally.
For example if the full load breather is open or leaking into the cover the smoke will be leaking where you cant see it. Same goes for the pollution purge it may be leaking under the car or into the boot cavity near the canister where you cant see it
A vac test will show this up right away

In saying that I have to go though this myself soon

Cheers
34by151

 

Hmm, it sounds very similar to this thread:

https://www.jaguarforums.com/forum/x...-drive-111104/

there is a software update for this - have you tried that? The 10% ethanol for winter gas is interesting...we are in winter - do they sell ethanol % gas in SF?

 

Seeing as how this occurs following a heat soak, it reminds me of vapor lock. I would imagine the fuel system includes a return line to tank. I wonder if pressure is bleeding off from the fuel injector supply while it sits and then it needs several seconds to re-establish steady pressure?

 

This is a return less system, on all 3 cars. Using a fuel temp sensor, fuel pressure sensor and a modulated fuel pump. So the fuel pump has a duty cycle, that is on/off when required. Only the XKR seems to have a fuel pump issue, it is not possible to properly block off the fuel line to the system. I have run a fuel injector balance test on the two XJ8 cars, and all 16 injectors drop 28 lbs on a 5 mil test. Though this tests extremely high, they are equal across all 16 injectors, which pretty much eliminates the idea of bad fuel injectors.

 

Another note;

The car starts fine, normal cranking and start up times for all three vehicles, unless the XKR happens to be putting out 80 lbs, and then the car doesn't start at all. I sincerely doubt that the problem is related to that fuel grade, or quality.

 

Yes, but I wonder what Jaguar did to address the fuel issue? Changes to injector cycle? timing change at start up? sensor turn on time? Hard start problem could be similar to the stumble i.e. same base issue, different symptoms.
Can you look up that ecu update and see what the actual solution was? (I know Mazda was good about telling what their TSB's actually did, but others don't). It might give some more insight.

Come to think of it, mine does this sometimes; seems to be only in warm weather tho. Hmmm, I find if I turn it off and restart it, it usually goes away; which leads me to think sensor...or if I give it some gas it goes away shortly, which feels like a fuel issue. Strange.

 

Rosskuhns;

There is a TSB related to rough start setting misfire codes, and lean codes, that leads to an injector cleaning procedure. Of course, none of these cars set a single lean code, and all have long term fuel trim within spec. There are very few TSBs relate to the engine on the 4.2 L vehicles, and the TSB came out in 2005, so I'm sure while these cars were still receiving service from the dealer they had fuel injection cleaning done as per the required maintenance.

34By151;

Thank you for the thorough response, but I do have to consider billable hours. I don't have any evidence that the vehicles are running lean, even momentarily. I would be hard pressed to start vacuum pumping the system, especially if I have nothing to support a lean condition.

 

what do the fuel trims look like when it's misfiring?

 

The misfire is inconsistent, and only lasts for 15-30 seconds, not long enough to change the fuel trim data.

 

What software did you use to update the ecu Legacy or SDD? There is a known issue on the later 4.2 cars with this exact problem. The fans come on & run for a long time after short distance driving. I had one customer have me reinstall the software from Legacy.

 

A seen a few people use a shop vac for the Avc source. Not as thorough but quick. The trick seems to be to put the shop vac some distance from the car extending the hose to cut down the noise

I still think the most likely cause is heat soak and its one of the temp sensors out of spec. Remember the ECU changes the fueling based on temp High and Low. So check out the obvious ones IAT, Coolant and Trans

Cheers
34by151

 

margate69, did you ever figure this one out?

 

What is the fuel pressure at the rail upon starting when these misfires occur?

I had trouble with a leaking fuel pressure regulator on my N/A xk8, and I've read others having them too.