Hello,

I bought my XJR almost a year ago and it has always driven well so far. But I'm now having a weird problem with my 1999 XJR
that at first looked like a failing throttle body or serious vacuum leak..

It doesn't matter whether the engine is cold or warm, how fast you drive, etc. Randomly the RPM starts acting strangely,
sometimes even resulting in the engine switching off with a message in the odometer: "Engine stalled". The engine check
light is also not on and no DTCs have been set.

Peculiar:
When the RPMs start to fluctuate (650 to just under 1000) and I put the car in Park and get out to listen, it sounds like
the engine is idling very "hard". Not fast, but hard. Louder "V8" sound (noticeably louder than normal) and a very
noticeably high air pressure from the exhaust. There are no messages, a CEL or any DTCs when this happens.

I then cleaned the connectors (which was recommended), went for a test drive and it looked like it was fixed.
Well, it was fixed... for a week or 2. Then the same problem occurred again.

Luckely, because I have a lot of parts from dismantled vehicles in the past, I had a recall replacement vacuum
throttle body lying around, so I installed it and inspected the vacuum lines. I found 1 crack, so I replaced
all rubber vacuum lines (including to and from the supercharger). This helped for a month or so, but now the same
problem has started again. It is not the battery and I replaced it.

Very occasionally on the highway I also feel it, but then it is very short and usually has no consequences for idling.
If this does have consequences, it is usually that I no longer have to accelerate in residential areas. The car
automatically drives up to 20-30 km/h (12-80 mph) from a standstill and on the highway it maintains the same
speed without touching the gas.

It's just a very inconsistent problem and I really don't know how to reproduce (or fix) it.

I also have the following issues with my XJR some of which have been present since purchasing the vehicle but may be (un)related to this issue:
1. Occasionally it will be hard to start (VERY rarely to the point of sounding like hydrolocking) and other times it will start perfectly.
Ordered new spark plugs and an overhaul set for the injectors, but unfortunately these have not arrived yet.
2. Drives fine, but when accelerating hard (after 4500-5000 rpm) it starts to surge.
Frustrating, but I don't do that that often and I have not yet been able to determine whether this is the gearbox or the engine.
3. Brake pedal switch for cruise control is defective.
It doesn't give any errors if I don't use the cruise control, so there's no rush for me.
4. O2 sensor heating element BANK 1.

 

It will be interesting to note the changes after the plugs and injector work
is completed. I would address the O2 sensor sooner than later as that has
a great deal to do with the catalytic converters going south before their time.

 

Could potentially be a throttle body issue, but something that corrected a lot of my throttle weirdness was to replace the connectors for the TPS wiring. I just snipped the wires and added new terminals and it resolved my occasional stalling and throttle hang.

 

Disconnect the maf and start the engine see if any difference

 

Carefully inspect the intake tube. Sometimes cracks form in the accordion section and it allows air to leak in thats not monitored by the MAF and can cause screwy behavior.

 

Car needs working O2 sensors to do proper RPM control.

 

Cleaning the MAF sensor can't hurt anyway, that's what I'm going to do anyway! Yesterday on the way home everything went haywire, which is a good thing because DTCs have finally been set. In addition to the engine, even the gearbox went into limp mode.

DTCs:
P0507
P1229
P1612

Because it was almost impossible to drive properly, I stopped at a gas station. I sprayed the MAF connector and both connectors regarding throttle position with WD-40 (I had nothing else with me, unfortunately), reconnected it several times to clean things up a bit and restarted the engine, which now suddenly started running normally again. The DTCs also stayed away after clearing the codes.

I had also checked the breather to see if it was partially clogged, but after blowing through it, fortunately this was not the case.

The way back home (and then the supermarket) went smoothly. However, this morning almost the same story again, in the parking lot I no longer have to accelerate because he does that himself. Also when I put it in Park and rev the engine, it goes back to idle very slowly.

This leads me to believe that, as Quadcammer also said, it is the wiring or connectors. When I got home I looked at the wires and they look normal and undamaged. I'll de-pin them this weekend and check further.

 

Spraying the MAF with WD40 is the wrong thing to do. The MAF wire will heat up and burn carbon deposits on it making it worse. Always use MAF cleaner.
have you tried taking out the AITS? Air Intake Temperature Sensor. It’s located on the side of the TB. Take plug off, unscrew it and you’ll probably find it’s covered in black deposits. If it is, she will think it’s still cold and tell the ECU to provide more fuel. The overfuelling will cause stalling, lumpiness and higher revs, restricted performance etc. we cured this by cleaning it up. Here is before and after…

 

That's a great tip, Julia700!

For clarification, the Jaguar service documentation usually refers to that sensor as the Intake Air Temperature Sensor (IATS), in case anyone needs to search the schematics or Workshop Manual.

Cheers,

Don

 

Hi Julia700, thanks for the tip regarding the IATS. I'll take a look at that tonight. What did you use to clean it?

I replaced the O2 sensor. Unfortunately the problem has not been solved. Today I did a test drive with another MAF but still the same problem. Sometimes I get a transmission failsafe message and sometimes I don't. It's running / driving very rough.

My cleaned chrome exhaust tips had turned completely black after a drive of 2 kilometers / 1.2 miles.
By the way, I did not spray the MAF sensor itself with WD-40, but only the pins in the connector.

So the IATS is my priority now.

 

 

I would be very suspicious of unmetered air leak(s) beyond the MAF. Given that the engine operates as an effective suction pump, physics demands that air will be drawn in at any unintended leak point, and especially at non-metallic junctions. If such occurs. the MAF>ECM may seek all sorts of weird compensations, including fuel richness . . . and that is what you are seeing at the exhaust tips.

+1 on the O2 sensor, but it may not be the culprit, if you find unmetered intake leaks as above.

As to the BPPS, are the rear and high level brake lights and park-lock solenoid all working? If not, check rear boot/trunk fuses. Any excuse to avoid working on the BPPS.

Finally, I would disregard trans 'limp mode' faults as least priority . . . most often symptom rather than cause in your precise situation of a sick and unreliable fuel/air mixture.

Cheers,

 

Hi,

Small update. As Julia700 recommended, I disassembled the IATS (it wasn't really dirty), but cleaned it anyway. Unfortunately had no effect.

Then I started looking at the MAF sensor again, and I discovered (thanks to another post here on this forum) that I had a MAF for a 3.2/4.0 *NA* engine. The MAF that I installed afterwards simply had the same part number that came with the car when I bought it from the previous owner, but I did not check whether this was the correct one. I have now installed an XJR specific MAF sensor. Unfortunately this made no difference, but it was still a step further.

I have now found something else and that is that the O2 on the left (bank 1) is reading almost nothing..

The STFTs and the LTFTs are all over the place (I took a screenshot of my live data tool while driving).
These results are with the MAF disconnected (otherwise the engine will not run good at all).

Short term fuel trim BANK 1: 19.5%
Long term fuel trim BANK 1: 11.7%

Short term fuel trim BANK 2: -7.0%
Long term fuel trim BANK 2: -15.6%


But what stands out most:
- Bank 2 (with the mostly clean exhaust tip) quickly reads varying voltages between a minimum of 0.030v and a maximum of 0.935v.
- Bank 1 (with the pitch black exhaust tip and sometimes soot in the parking lot) reads almost nothing, despite the fairly high corrections for bank 1. minimum 0.000v and maximum 0.040v.

After some changing of the plugs, I believe that the O2 sensor is broken, or at least transmits incorrect values.

It's not a clogged catalytic converter, I replaced it with a good one from a donor (XJR) engine.

Unfortunately I don't have any working lambda sensors, so I ordered one.

 

Since bank 2 is running rich, I’d pull the plugs out of that bank and see if one spark plug is especially blacker than the other 3 or are they all identical. I’m looking for possibly an injector hanging open.

 

Sorry for the late response, 'life' happened. Now back on the Jaggg!

- Replaced 'bad/dirty side' bank coils with known good *used* ones: no difference.
- Replaced ignition modules (at the brake booster) with known good *used* ones; no difference.
- Replaced spark plugs: no difference. (I did this today, see the pictures for the old plugs. The first cylinder on the right bank has an exceptionally fouled plug.)
- Replaced *all* intake/supercharger related gaskets: no difference.
- Replaced a large number of vacuum lines. Also around and underneith the intake manifold / supercharger.
- Replaced O2 sensor, no difference. Still reading between 0.000V and 0.040V on the right side (dirty exhaust pipes).
- Replaced plastic breather hose on the left bank to the intake manifold and EVAP valve(?) with a brand new one. (unfortunately it broke while removing the supercharger)
- Cleaned *all* connectors with electrical contact cleaner in the engine compartment on the engine *and* at the ECU/TCM.
- Cleaned *all* grounds in the engine compartment. Also the ones at the transmission bell housing. - Cleaned MAF (also checked for correct part number for S/C).
- Cleaned air intake temp sensor (intercooler, right bank).
- Checked intake tube for cracks; none.
- Checked the two small hoses on each side of the intercooler; no cracks.
- Checked vacuum valve to make sure it stays under vacuum; working correctly.
- Checked full load breather (plastic tube at the intake tube of the right valve cover); no cracks, not clogged. I also intentionally blocked the full load breather to see if it changes anything and yes it does.

IMG_01: All spark plugs: bottom of the picture is the front of the engine. The darkest fouled spark plug on the left front is therefore the front cylinder (closest to the radiator) on the passenger side.


IMG_02: The fouled spark plug of the front cylinder of the right cylinder bank (dirty exhaust tip) compared to an average spark plug of the left cylinder bank (no dirty exhaust tip)


IMG_03: Close-up of the fouled spark plug. It's a matte black soot, not wet at all. The same stuff that covers my right side exhaust tip.


I ordered some remanufactured injectors (I couldn't find original Denso injectors, probably no longer available?) and I hope to replace them next week.
I don't think it's valve/valve seat or even valve guide related because sometimes it runs fine.

Maybe, just maybe it's related to timing because the right bank is a tiny bit darker overall, but the front spark plug is a lot darker than the rest. But then again, sometimes it runs fine.

 

I didn't see you mention it, but do you have any smoke out of the tailpipe at all and are you losing oil at all? I had a similar problem, not with any of my Jags, but with my MINI. Tormented me for nearly 2 years quite honestly and I tried so many things. I replaced the PCV valve which is technically built into the valve cover, but is replaceable. The original valve cover was, of course, plastic. Replacing this PCV didn't do a thing, maybe even made it worse. So, something in me decided to redo the valve cover gasket and at the same time replace the cover with an aftermarket aluminum one, just in case there was some sort of micro cracks or something somewhere I couldn't see. Whatever it was that licked it and I was so relieved LOL. My entire career (and hobby) has been spent solving problems and the worst part about solving problems, what takes the longest by a mile, is figuring out what the problem actually IS!

 

Hi Tergitkerd,

YES

No, I don't have any smoke from the exhaust and it's using very little to no oil.
When it's acting up, it does smell like fireworks/sulfur which probably means the catalytic converter is working overtime (very rich fuel mixture).
It just happened again while doing some shopping. Quickly pulled over, disconnected the MAF and drove on. All is fine now, apart from the restricted performance report, but that is to be expected.

 

Front injector for the right bank (with the darkest spark plug) has been replaced (fortunately without removing the
entire supercharger). Unfortunately not the solution. Coincidentally today just before my house again hardly any
throttle response, dirty smelly smell and bad running as described in the first post.

I have checked the timing. Unfortunately plastic chain tensioners and guides, but recently replaced according to the
documentation. No cracks/breaks and the chain is (thankfully) tight.
Still no decent values ​​from the right bank O2 sensor. O2 values ​​for bank 1 at 0.000v - 0.040v. which (I think) results
in a short term fuel trim of 19.5% at all times (also when the lambda sensor is connected).

I have now disconnected both so that I can drive to work normally, because the ECU now
sets both banks to +19.5% fuel trim. This smells too, but not nearly as bad as this unpredictable phenomenon.
I'm going to order the 3 remaining reman/new injectors and replace the fuel pressure regulator with a 2nd hand one I have here.

 

A shot in the dark: how old is the fuel filter? Long, long time ago, I used to get some crazy changes in a 350 Chevy Nova V8; occasionally, it wouldn't even start. Changed the fuel filter and all drivability issues were resolved.

 

Hi Jim,

The fuel filter has been replaced last year around September unfortunately.