I have got a Jaguar XJ6 4.0 Straight Six X300 on a 1997 plate. I noticed a strong smell of petrol coming from the exhaust also its using too much fuel. Its giving me less than 200 miles to a full tank of fuel. I was suspecting either a coil pack or spark plug but was not sure. Also the car seems to run slightly lumpy but It's hardly noticeable. I did not want to spend money on things that are not necessary. I have a Maxi scan OBDII/EOBD error reader which comes up with p1621 $11 1/1 other Manufacturer control but do not know what that means. But this error has come up for a long time anyway so may not be linked to the problem.

 

Maybe the O2 sensors and/or temperature sensor are toasted and have fed the engine with wrong data, and the over-rich mixture has fouled some or all of the spark plugs?

 

I wondered if i got a garage to put it on a diagnostics computer would it show up with a error if the sensors are faulty ?. Also does anyone have a idea what spark plugs I should put in my car ?. I think NGKR BCPR6Eare the correct ones but not 100% sure. Any suggestions would be appreciated!.

 

Also does anyone have any idea how many 02 sensors would be on my car ?.

 

Hi! I had some similar issues with my 4.0. A new/used maf sorted most of the issues though. You'll find cheap ones on ebay.co.uk . Worth a try in my opinion.
Regarding spak plugs I would go for NGK BKR6E. The BCPR6 plug will fit, and I am actually using it in my car, but it is NOT the correct size.
The BCPR6 is a so called JIS plug. Designed for Japanese cars, and a few millimeter height difference from the BKR6E which is a ISO size. (international) The XJ came originally with champion plugs with ISO size, so I would stick to that. (I'll probably change mine later to the ISO sized NGK.


I also believe there are 2 sensors on your car if you are in Europe. American cars had 4.

 

Hi I really appreciate your advice and it sounds like good advice to me. I had a old car and once changing the air flow meter it was better. Do you recommend changing the maf first and plugs ?. Someone suggested that its best to change the plugs as well because they may be dirty because of rich fuel mixture. Do you think one of the 02 sensors or temperature sensor would cause this also ?. I want to fix the problem but do not want to spend more money then i need too. I will order the maf on ebay then if that does not solve the problem where do you think I should go from there ?. That way I can take it step by step till the problem is solved.

 

I recently changed the MAF after the car had been running very poorly. Stuttering and smelling of gas. I did not change the plugs as they were rather new, but now covered in soot, because of the rich fuel mix. initially the symptoms were only marginally improved but after a few minutes of driving I guess the soot on the plugs just burnt away, and it started running smooth again. Now I just have the occasional issue of the idle dropping down to 400-500rpm but it doesn't choke completely. I am guessing new O2 sensors might improve this but they seem like a hassle to switch. So for now, I'm happy with it.


Having said all this about the MAF, I know that the P1621 code also might be related to the coils, and or the Crankshaft position sensor. Some have also said that a simple mis-start of the engine will give this code. And it will stay there until you delete it with a OBD tool. I bought my obd tool from ebay for 5 dollars and it works fine. I can also delete codes with it. Good luck, I'm curious to hear any solutions

 

Wait; I just did a research on fault code P1621. They all point to possible problem with the ECU:

P1621 - Control Module Long Term Memory Performance/ Immobilizer Code Words Do Not Match
JEC BB Index

P1621 is the code for engine control unit failure
Jaguar: what causes fault code p1621..cylinder..circuit malfunction

P1621 is ECM immobilizer circuit malfunction-out of range voltage for diagnostic line
Jaguar Fault Code 1621

P1621 Engine control module engine immobilization input circuit malfunction
OBDII diagnostics. Trouble code definition for code P1621. Causes of error P1621

Is there any chance you have a faulty, corroded ECU or one with loose or poor connections, or a weak battery and or grounding point giving rise to weird codes?

As for the suggestion of a bad MAF, probably cleaning it would be a more practical option, or would replacing the O2 sensors and or an engine temperature sensor be a cheaper alternative?

 

I have ordered a second hand MAF hopefully this does the trick!. Does anyone suggest I change the ECU or is it a better idea to change the 02 sensors and engine temperature sensor ?. I believe there is 2 02 sensors and are they easy to change yourself ?.

 

Does anyone know where I can get a diagram of a Jaguar x300 engine bay so I know what each sensor is for ?. I tried finding one but could not find one.

 

I'd leave the ECU for now. I'd change MAF first, the O2 sensors.

Does your OBDII reader have a data stream? Then you know what the ECU is seeing. For example if the engine is up to temperature and the ECU is reporting a temperature lower then the thermostat temp, then you know you have a problem.

It will also show if the O2 sensors are open or closed loop, as well as their voltages. Be aware, that there can be a mismatch between the refresh rate of the scanner and the swinging of the O2 sensors, so you'll have to watch for a while to make sure they are swinging form high to low voltage. If one ) or both ) are not swinging then you know you have a dead sensor. Use an NTK 25018 sensor. If you buy it from Jaguar that 's what will come in the box and at about 10x the price of somewhere else.

The sensors can be a pain to change. I think you'll need a combination of a 17mm wrench and various deep sockets, swivels and extensions. Not easy, but it can be done. Do them one at a time so you don't get the wires mixed up.

 

I have not seen one. Coolant temperature sensor is on the left side, at the front thermostat housing where the hose goes to the right side to the radiator. The single wire one is for the dash gauge, the bigger one is for the ECU.

O2 sensors are on the right, on the exhaust downpipes.

 

If it stinks of fuel, then it just means that there isn't enough air in the engine... BUT the fuel to air mixture is calculated with a few parameters...:

- engine temperature
- air flow
- lambda

The spark plugs don't have much to do with it, as any spark will do to ignite. A weak spark of course can cause some problems. So you could simply check if all coil packs with plug inside spark. Should be a stronger, blue'ish spark.

Otherwise you can try a few things:

- start the engine and remove the air flow meter. The engine should run lumpy or better said recognizably different and maybe even stall. If it doesn't you've found the fault.

- does the temperature gauge reach it's middle position quickly or does it take for ever? Maybe it doesn't even get there? Then you can check the thermostat. If it is dead (open), then the engine is not getting warm enough and is stuck in the "cold start" trim resulting in a huge increase in consumption/huge drop in economy. Check the temperature sensors for proper function (voltmeter/multimeter and measure resistance).

- are the lambdasonds working correctly? You can unplug them and see if that changes anything. It CAN cause the CEL to turn on, but then you know, that they are working.

- if all of that above doesn't work, you'll want to check your injectors. One or two can be leaky. Maybe even all of them.

It would be easiest though to use a Jaguar IDS diagnostic system. A normal garage will have troubles getting into the depths of the car's electronics, as the IDS is the only way an OBD II computer will be able to communicate... My XJ8 is the same... Normal fault code readers said "fault free". IDS said "4 codes are stored".

 

Will I need to order 2 02 sensors ?. Also are they both the same or different I always order on ebay but sometimes its hard to get the part you actually need.

 

I removed the air flow meter wire and the engine tried to stall. So it may seem ordering the MAF was a waste of money already lol. The temperature gauge runs half sometimes when in traffic but when driving it stays fairly low like less than a quarter I thought maybe that's because its cold at the moment. When you start the car the heating seems to get warm quickly though. Someone suggested that the sports mode may be stuck on but I'm not sure how to check this ?. When you put sports mode on the light comes on the dashboard but there is no drop or increase in the revs. On older cars when in sports mode the revs would drop. Also where are the lambdasonds ?.

 

The sonds are both the same as they do the same job, just one for cylinders 1-3 and 1 for 4-6.

Regarding the MAF: okay, if the engine stalls or tries to stall, it isn't the problem. If it didn't change, then that would be a problem.

Regarding the temperature gauge: IIRC (my XJ6 has long gone) it has a extra heating pump, located on the intake side of the engine. This has - IIRC - an additional heater in it. So it should heat the interior up quicker (the X308 has the same setup). So heat inside the car isn't the best indicator. I think the gauge should be steady in the "12 o clock" position and not dive up or down... Someone else will know better.

Regarding sports mode: Sports mode is only on the transmission. It only acts on the tranny, not the engine. It isn't an "adaptive" transmission, like in later XJs. It is simply hydraulic and the only thing the "S" does, it holds the revs longer before it changes gear. There are no connections between the 4HP22 (aka your transmission) and the engine ECU. As said, later cars (from X308 onwards) have a connection between tranny and engine (electrically) but that isn't to worry about in your car.

 

The temperature gauge should be straight up, 12 o clock position when fully hot. if it takes a long time to get there, or never gets close, i.e stays quite a bit to the left of center, then you need to replace the thermostat. Other way is if you have one of the IR thermometers, then take a reading of the top radiator hose. If it's not in the 85-90C range, replace the thermostat.

Outside temperature shouldn't matter too much, since it never gets cold in England, relatively speaking. Even at -40C the gauge will come to the center position, it takes a bit longer.

 

As I said, unless you have a data stream, it hard to know if they are working properly or not. Code readers shouldn't be that expensive. Isn't there an autoparts store locally that you could buy sensors if necessary? If you want to order online, I'd use SNG Barratt, they are Jaguar specialists.

 

Sport mode simply changes the shift points higher. It's not your problem.

Daim means the O2 sensors, also sometimes called Lambda sensors, as the shorthand Engineers use for the air-fuel ratio is the Greek letter Lambda .

 

A typical problem for the xj6 is the thermostat failing in the open position and the engine not getting hot enough to run in closed loop, so the ECU will use the startup program resulting in a rich mixture. Oddly, the v8 thermostat often fails in the closed position, resulting in overheating.