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1995 XJR with 280K km. Newcastle. Australia.
Recently new to me, she is impressing me and driving me to distraction.
A deceased estate car, she had not been run for two years. (The odd tootle to the end of the country lane.)
When I initially drove her home she ran fine at partial throttle, but would shudder and shake at WOT.
New fuel, fuel filter, plugs. Cleaned out the oil from plug recesses. She ran better, but decided to test me by loosing all power and stopping. A tow truck ride home and I finally isolated the issue to be caused by stainless exhaust pipes working their way down the stainless headers, enough to allow leaks. O2 sensors not getting enough gasses and the ecu threw a wobbly.
Jacked the pipes back up on to headers and she would start but stall. I eventually got her to run by starting with MAF unplugged, then plugging it in. A few cycles of this and she started and idled consistently.
Now, a week or so on, she is over fueling. Start Up and a relatively nice idle, the odd miss here and there, but black smoke issuing from tail pipes.
Get her up to temp and she drives nicely, pulls hard under boost, but still black smoke at idle even after a 50km drive.
I cleaned the MAF with aerosol MAF cleaner. Visually checked for air leaks. There is a high pitched constant noise from rear of engine under intake.(Not compressor whine) Unsure if this is normal or not. (Could other XJR owners Chip in, please?)
The airbox was removed by PO. Pod filter. Air Intake temp sensor is bridged.
Is there a hard reset process for ecu? Should ecu learn/adjust on O2 sensor readings?
I have checked for corrosion on O2 heater circuits, at O2 plug and White connector (AP1?)
Unsure how old O2 sensors are, but they would have been renewed when staino pipes were put on.
The black smoke has only started since the pipes falling off debacle.
I have a OBDII reader, but no codes are showing and am unable to connect to lambda voltages.
Is there a recommendation for a reader that will connect with XJR?
Cheers.
The O2 sensors on the X300 are different in they generate a changing resistance to O2 content so they are feed 5 volts from the ECU and this 5 volts is modified
They are titanium-based technology and not the more common other
Your reader may not recognize this and default to the more common giving erroneous readings
With a ELM - 327 live data reader your short term fuel trim has a target value of 0 % ( in practice + or - 3 .0 % )
your MAF ( correct part ? ) probably will be the factor to getting there , the inlet air temp also plays a role and easier / cheaper to address
There is a manual calibration of the current Inlet air temp sensor to verify correct readings
See page 86 of the 801s Doc
The O2 sensor connectors can get easily crossed as both connectors fit on each other
Do you have 2 or 4 O2 sensors ?
Last edited by Parker 7; Oct 26, 2022 at 12:09 PM.
The O2 sensors on the X300 are different in they generate a changing resistance to O2 content so they are feed 5 volts from the ECU and this 5 volts is modified
They are titanium-based technology and not the more common other
Your reader may not recognize this and default to the more common giving erroneous readings
With a ELM - 327 live data reader your short term fuel trim has a target value of 0 % ( in practice + or - 3 .0 % )
your MAF ( correct part ? ) probably will be the factor to getting there , the inlet air temp also plays a role and easier / cheaper to address
There is a manual calibration of the current Inlet air temp sensor to verify correct readings
See page 86 of the 801s Doc
The O2 sensor connectors can get easily crossed as both connectors fit on each other
Do you have 2 or 4 O2 sensors ?
There are two O2 sensors, on this vehicle. One has been marked with red electrical tape. So, I presume that the PO was aware of orientation and that they are how that were when I took possession.
I presume that the MAF is original, but will check the part number. I am aware that they are unique to XJR.
Forgive my ignorance, but I am not sure what 801s doc is. I will do a search.
Again, thank you for your time and consideration in sharing your knowledge.
As long as the O2 sensors have been in the current connector hook up for a while they should have learned after a while the in-service performance parameters of each
If you swap them now the ECU will be off until it relearns the new installation configuration
The O2 sensor return wires to the ECU are shielded with a small ground post on the left and right side of the rear engine firewall , there will be many wires on each post
The large ground strap between the starter mount bolt and the car frame should have the mating surfaces cleaned
Last edited by Parker 7; Oct 26, 2022 at 04:48 PM.
Mulling over my experience so far, with this vehicle, I am wondering what effect I had on the ECU when I started engine with MAF unplugged.
When she broke down, she would crank, start but not idle. (Stall immediately after first fire).
Clutching at straws, I tried to start with MAF unplugged and she fired right up and idled.
Could I have somehow set new parameters, with the ECU reading O2 sensors that were not getting full gas flow, when I plugged MAF back in with engine running? ECU was reading very lean emissions (O2's not getting full gas flow) and has enriched mixture?
I might try to start with MAF unplugged again,(now that O2's are getting full gas flow) and see what happens.
The expected range of MAF return signal to ECU is between 1.2 and under 5 volts dc ( this voltage value with the correct MAF is a way to verify and compare your engines performance to the SC AJ16 engines )
By unplugging the MAF sensor, you are at 0 which is out of range and rejected by the ECU
once it is rejected after a certain amount of time the ECU will use a default set of data maps and not optimal mode performance , this mode is different the ECU open /. close mode
Once the MAF value is in expected range the ECU will go back to optimal maps mode
This time delay is another variable of consideration complicating troubleshooting
The O2 sensors will not be used until the ECU is in closed loop mode ( 88 C engine coolant temp )
If you have the wrong MAF installed and at idle instead of the 1.2 volts it is reading, say 1,4 volts it will not be rejected....................................
So you have 2 open / closed loop ECU modes , and 2 default ECU maps modes during the point in time of your different observations
once the engine is shut off the O2 sensors may have cooled off and be too cold to read correctly even though your coolant temp can quickly recover to the 88 C
The heaters in the sensors must recover the O2 sensor operating temp
So you'll have to take a piece of paper and catalog yourchanging variables against observations
By the O2 sensors getting full gas flow would be more like the O2 sensor gas flow is not contaminated by unconsumed O2 being drawn into into the open exhaust system
Last edited by Parker 7; Oct 26, 2022 at 09:25 PM.
Going back to your original problem of poor performance at wide open throttle, remember that the XJR has a second fuel pump, as the main fuel pump cannot keep up with demand in wide open throttle conditions…..
Going back to your original problem of poor performance at wide open throttle, remember that the XJR has a second fuel pump, as the main fuel pump cannot keep up with demand in wide open throttle conditions…..
I suspect that the initial drive experience, upon first picking up car, was a combination of factors.
The exhaust leaks probably caused the most problems, until they got so bad that she shut down.
Since finding and rectifying that problem, she has improved in her driveability remarkably.
Once warmed to temp she pulls like a steam train. Sport mode will hold her gears through the rev range and no hesitation or stumbling.
From this I conclude that the fuel delivery is up to par from both pumps.
The over fueling that I am experiencing is at idle.
I suspect the MAF to be the issue.
If you're off by a little bit on this test point I have doubts the numbers between the supercharged and normally aspirated are the same with a little bit of blower at that low idle speed
Your MAF pin connector connections with the current sensor installed can be a miss match and this happens on the later Jaguar V8 putting in a replacement MAF sensor from reading
The center wire or Green / Pink should be the ECU return wire
Last edited by Parker 7; Oct 29, 2022 at 06:00 PM.
If you're off by a little bit on this test point I have doubts the numbers between the supercharged and normally aspirated are the same with a little bit of blower at that low idle speed
Your MAF pin connector connections with the current sensor installed can be a miss match and this happens on the later Jaguar V8 putting in a replacement MAF sensor from reading
The center wire or Green / Pink should be the ECU return wire
Excellent. Thank you. This is the type of info that I need to start to determine if the MAF is the culprit.
On a side note, I have a OBDII reader that reads everything in my Subaru, but has a lot of "this function not available" when plugged into the Jag.
Is there a recommendation for a reader?
I am currently searching forum for a general consensus on what works.
Cheers.
Black smoke
