Hi,
Ive got a Jaguar X300 4.0 Supercharged. Unfortunately I have an ongoing problem with my car.

Its currently got 170,000 miles on the clock. A few years ago I had the head rebuilt and another major service.

It is difficult starting from cold. It turns over and won't fire. Then when I start it again, it cranks over very rough. It does run ok, however it does have a slight misfire, but still fine to drive. I did put some redex in the car last week and it has slightly helped the start up.

Whenever the plugs are removed, they are always black. Once the plugs are cleaned, the car runs brilliant for the first drive. Then the next time I take it out, it starts up rough again. Im guessing the car is over fueling, however I can't source the problem.

Due to this problem, I'm loosing a lot of power. The kick down is no where near what it used to be. Before, the power was savagely quick (for me.) It runs ok but there is very little power no matter how much throttle I give.


Ive changed:
Air mass sensor
Temperature sensor
Crank position sensor
Coil packs
Cooling temperature sensor

Could anyone shed some light on the situation please ? If so, I would be very grateful.

Many Thanks.

 

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https://www.jaguarforums.com/forum/n...-intro-must-5/



My first guess would be an O2 sensor issue or some leaky injectors. But it's just a guess at the moment.

Did you replace all of those parts on a hunch or is there some diagnostics that led you there? It's not a pointed question just trying to understand if there is any more background information.

You will need to get some diagnostic info from the car. Do you have the tools to do that? If not, a cheap ELM 327 scanner from Amazon/ebay connected to your phone will do the trick.

As a first step I would want to see what the STFT (Short Term Fuel Trim) figures are and what the O2 sensor voltages are and how they are swinging.

 

I'm not a proponent of just throwing parts at a problem versus diagnosis..... but in this case at 170k miles and 20 years of age a lot of parts are reaching the end of their lifespan so it may make sense to continue replacing some of the fuel system.

I agree that it sounds like you are running rich. If it were running lean, I'd suggest checking the fuel pumps, but running rich I doubt that is the issue. But I'd still look at the fuel pressure, which may be too high if your fuel pressure regulator is defective. That is a relatively inexpensive replacement, and frankly it's probably time. The Bosch unit is about $90.

I'd also suspect your fuel injectors. Have they ever been cleaned? Also a relatively cheap task, esp for a 6 cylinder car. The going rate is about $15 per injector.

I'm sure others may have suggestions about specific sensors that may make the car run rich too. For example, I wonder if a malfunctioning coolant temp sensor could cause a rich running situation? Again, a cheap part.

There's an air intake sensor too, but on the XJR6 is it located on the underside of the intercooler and is a real PITA to get to. So I wouldn't recommend replacing it without cause.

O2 sensors are another suspect, but I'd definitely try to troubleshoot those before just replacing them, as they are not in the cheap and easy "why not" category.

Curious to hear if anyone else offers suggestions on other sensors to check.

Have you had a chance to pull any codes with an OBDII reader?

.

 

Observe ELM327 video around 2 min mark the see your values as live data . A link to an example of it's use on a X300 below . You can record a data graph log as you are driving around and reveiw it at home . Don't think of this as the only tool in your toolbox for you have advice from more experienced people . Takes time to spool up on the ELM327 live data reading out of the ECU and it's controlling devices and final computations ( O2 sensors, TPS , STFT , ect. ) . Champion spark plug RC12YC are the Jaguar preferred plugs for this engine is sensitive to off plugs ( fouling complicates matters as well as I think you're observing that ) . Bosch # 13789 oxygen sensor is a connector ready cheap substitution for the expencive original Denso . X300 O2 sensors are titanium resistance changing and not the more common zirconia voltage generating . Look for corrosion of the 2 aft sensors connectors behind the top left side valve cover as in a row of 3 connectors , don't cross positions .

https://www.jaguarforums.com/forum/x...ong%5D-184729/

 

You say you have a slight misfire. If there is a misfire with new plugs I would identify which cylinder and change the coil ( or swap with another to see if the misfire follows the coil). If you have a frequent misfire there will be excess oxygen in the exhaust and the ecu will add fuel to compensate, which is going to make the mixture too rich.
Also, After starting rich and running rough as you describe, the o2s will be sooty and probably won't work properly. I would consider replacing at least the lower ones.

 

Are Rest of World AJ16 normally exasperated engines 2 x O2 sensor configurations ( North American has 4 ) located forward of the forward Cat ? Mine has the 4 sensors so I can't say . But the All of World wiring schematic for the supercharged AJ16 engine always has 4 . Does this make the forward sensor the ones responsible for the fuel trim and the aft ( if installed ) only responsible to verify the Cat is functioning in it's outgas conversion as a thrown code 420 ? Forward O2 sensors are easier to tinker with if that is the case . They can be removed and soaked in gasoline ( not the wires ) overnight to possibly refresh them and read accurately without being clouded

http://www.jagrepair.com/images/Trai...20-%202000.pdf

Although the Jaguar Engine Management Systems document 801S page 80 says the aft sensors controls the trim are they in error , Boeing documents were not always correct .

Cracked exhaust manifolds and damaged downpipe donut gaskets / flange ( as you recently had them removed ) will draw in fresh higher O2 and bias the sensors to make the engine trim rich . As well as a intake manifold vacuum leak in the idle area of operation .

Correct plugs and clean sensors would be a foundation to build from as you correct the engines regulation .

 

If you read my recent thread about XJR emissions fail, you will see a worked example of how even a minor exhaust leak pushed the mixture much too high. Earlier comments re checking your short term fuel trims and O2 readings is a good and inexpensive way to pursue the issue.

 

[QUOTE=Lady Penelope;1726682]Are Rest of World AJ16 normally exasperated engines 2 x O2 sensor configurations ...

Hey Lady Penelope, I think it is the OWNERS of AJ16s who are "normally exasperated"!

 

Spelling is not english's best forte

 

Hi,
Sorry if Im using wrong topic.
Winter and cold is coming, in freezing cold (-20*C..and more) when I start the xj6 in the morning the fuel is leaking somewhere from engine very badly until it gets warm, if its warm, there is no leaking at all.
Guessing, could it be injectors some kind of old O ring fault? Probably problem should be with some kind of rubber sealing ting, that is old and shrinks in a cold, but where to look?

 

Viesis , Take the plastic fuel injector / rail cover off and clean around the upper portion of the injectors and wipe off dry . Repeat cold soak conditions and wipe around the area with pieces of white writing paper to observe a leak . Same with the fuel line connections including the fuel pressure regulator