I’m at my wits end here. The car runs well. Uses too much fuel though. Plugs look normal when I pull them.
Jag specialist shop checked the fuel pressure. It’s good.
Where else can I go?
I did send the injectors out for cleaning, but this problem existed before then.
Coolant Temp Sensor seems to be trading correctly…through the OBD2 port.
What else? Oxygen sensors have been replaced within the last 2 years.
I think there is also an air temperature sensor, though it doesn’t alter
the fuelling much.
Best regards
Jim Brighton UK
1984 XJSC 3.6 Manual
Veekay,
How do you know it is running rich? What was your fuel consumption in MPG when you calculated it after several fill ups and hundreds of miles of driving? Do you smell unburnt fuel in the exhaust? If you have, have you had your emissions tested to verify that something is wrong? Is it possible that you are driving the car aggressively or perhaps spending a lot of time in traffic so that is affecting your fuel consumption? If you are getting your fuel consumption from a trip computer, those can be inaccurate.
Regards,
Paul M. Novak
1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA USA
My LTFT is +10.
The shop I just dropped it off at conformed it. They checked the fuel pressure and even noticed that I have swapped injectors…
Shop mentioned that even STFT were high.
I think there is also an air temperature sensor, though it doesn’t alter
the fuelling much.
Best regards
Jim Brighton UK
1984 XJSC 3.6 Manual
Do you run the a/c regularly?
If you don’t use the a/c and don’t have a lot of fuel in the tank then you can quickly raise the temperature of the fuel to the point of evaporating it. Significantly.
Ask me how I know.
I’d like to ask. My 6.0L does not have the fuel cooler (deleted from the factory). Please tell is what you found out.
What temperature thermostat are you running? Maybe the engine is running slightly on the cool side?
I found that at average temperatures, not particularly hot days, the fuel acquires quite a bit of heat circulating through the fuel rail.
Pumping at around a gallon a minute through the ~190F engine bay, the fuel simply gets hot. Without the A/C fuel cooler running It only gets hotter.
I noted my sealed and closed gas cap in the rear view after a 15 minute drive spewing fumes. Regardless of your cars fuel vapor venting system, heated fuel is going to evaporate.
Your car had no fuel cooler from the factory? What year do you have?
This is a subject for another thread, but I’d argue here that gas tank venting and engine rich running are not related.
BTW, my 6.0L is from the last production year - 1995 - in my avatar. The 4.0L also doesn’t have a fuel cooler
I had this happening in my 95 which caused the check engine light to come on and I could smell the gas. Three dealers could not sort it so I took it to the dealer in Charleston, SC and the tech found the problem was the air pump. I changed it and problem solved.
I have been out and about the last few days, so I really appreciate the reponses.
I have monitored air temp sensor, through the OBD2 port, and it seems to be functioning. Well enough it seems. The numbers do move and they seem to be in the right range. When the engine is hot, the temps are in the 110sF.
I don’t run the AC usually often, but since this is a daily driver, its been used plenty over the summer. There is no fuel cooler.
I have a 187F thermostat I installed perhaps two years ago. The original one in the car was failing. I replaced the coolant temp sensor at the same time just because I was there and it was cheap.
I have a 1996 XJS with the AJ16 engine. I am not aware of a fuel cooler option.
Lastly, I thought the air pump was only used briefly at startup. After 45 seconds or so, it shuts down and does nothing. Am I wrong about that? The car runs well and smooth. You wouldn’t even know I had a problem unless you knew the miles per gallon wasn’t right.
I did replace the air pump when I first got the car. After a few months I got a code, so I replaced it, and that was that.
This is correct. Secondary air injection is emissions equipment. Any shop that is claiming to fix running issues by repairing/replacing the smog pump should be avoided as it speaks to a gross incompetence (or worse).
My unsolicited advise, if I may – if it is running well, don’t mess with it.
Steve
Try driving without roaring around for a tankful or so (I know, difficult …) and see if old lady style (no offence intended old ladies) gets your mileage up.
After the tankful trial, if your mileage does improve, weigh up the cost savings against the thrill of the drive … and if you’re like me, you’ll say to hell with economy - have fun!
That’s true on the V12. As I understand it, the AJ16 uses a completely
different arrangement of air pump, but I’m sure it still has oxygen sensors,
and frankly I don’t see how oxygen sensors and an air pump can ever be
compatible. An air pump would HAVE to shut off for the oxygen sensors to
work.
– Kirbert
I’m kinda pissed because the shop told me they ran the oxygen sensor reorientation and that seemed to fix the overfuelling issue.
Dammit. I have a WDS that could have done that.
After initially dropping to a LTFT of 8.6, I have not seen any more of a drop. Its been a week…
I finally got to the bottom of this!
After driving for too long of a time with the LTFT at 10.something, it was the TPS that was the root of the problem!
The car drove fine, it just had really bad fuel mileage. No check engine lights, no smoke, not really any other symptom, other than poor fuel economy.
I replaced the TPS, with a brand new one, a week ago and my LTFT is at 0.0! I had a spare old TPS that I inherited as part of a used bin of XJS parts and it did not help. I will take this TPS apart and see whats doing.
I do want to note that the new OEM TPS no longer carries the Ford branding that the original parts bore. Also they come with silver pozi screws, instead of brass torx screws. The plate that holds them in also is silver in color, not the old brass color. Thought I would mention that. It was purchased directly from JDHT.