Today my throttle seemingly cut out completely for like 30-40 seconds. No CEL, no warnings, engine idled completely normally. There was nothing out of the ordinary. It was as if the throttle had become disconnected is the only way I can describe it. I had come to a stop and was kind of stabbing at the pedal trying to figure out what the problem was and it came back. I drove around for a few more minutes with no further issues. Anyone else experience this before? Mine is a 1998.
This is why we ask members to put in their signature their MY, Model and where they are in the world. We don't know if yours is a standard XJ8 and XJR (which has two fuel pumps), are you in England or Australia with the option for other fuel types (petrol, diesel, CNG, LPG) and different motor size. All this helps clarify who can and how we can help.
This is why we ask members to put in their signature their MY, Model and where they are in the world. We don't know if yours is a standard XJ8 and XJR (which has two fuel pumps), are you in England or Australia with the option for other fuel types (petrol, diesel, CNG, LPG) and different motor size. All this helps clarify who can and how we can help.
Off hand, I question if the fuel pump cut out.
You're absolutely right, that's my bad. This is a 1998 XJR with the AJ26. I'm in the USA. I just had the entire engine apart for head gaskets, chains, etc., etc. Throttle body was completed disassembled and reassembled (bored out with a new throttle plate). The bearings inside are immaculate. I can't imagine it's anything with the throttle body itself. It seemed vaguely like an electrical issue, just one that wouldn't trigger any kind of warning or anything. The idle was perfect, so probably nothing with fuel etc. The throttle pedal itself also seemed fine and never felt any different while I was trying to make it work. It was literally like there was no one home at the other end, and then bam it came back completely in an instant. I had been driving for roughly 45 mins when this happened. Basically the first long drive after getting it all back together.
Fuel # 1 pump dropping out is a good tip and can be jumper'd to stay on jumper Ing between socket 3 and 5
Use blade type connectors and medium gauge wire for best current flow , the auto parts store may be able to make one for you with a kit under the front counter
This will have the pump stay on at all times so will drain the battery with keys in pocket
See throttle for your AJ26 supercharger engine page 43 bottom right corner but I would expect that would give codes ( ? )
Both fuel pumps are brand new. I replaced them two days ago, so I don't think that's the issue. Could be worth throwing a gauge on it if it happens again. If it was fuel it probably would have stumbled or had some other symptoms though, so I'm not sure. The new pumps could be faulty but it's highly unlikely.
When I lost my pumps, it was instantaneous and I just coasted to a stop. Yours being new, there could be a connection issue, but start with the fuse (simplest) being secure in the socket, continuity on the tabs and meter the power. Heck, I'd replace the fuse (cheap) just to eliminate the possibility of a bad bridge.
“I can't imagine it's anything with the throttle body itself.”
Throttle bodies have a less than stellar reputation on the AJ26/AJ27 (N/A & S/C) platform. When I had my 98’ XJR, I learned a lot of their fragility when I replaced 3 of the 5 or so throttle shaft bearings. The swiping action of the TPS brushes inside needed to be reshaped, gently cleaned and repositioned for a more positive contact on the board that it rides on. In my opinion from what you described your experience was, it sounds like the brushes of the TPS needs to be cleaned, reshaped and repositioned. Heat will always be the enemy and when you have a thin brass/copper brush, heat will warp it and heat will add resistance. However, especially the AJ26 (N/A & S/C) ECM is susceptible to failure. I believe it was due to the capacitors. First things first, check to make sure the 3” PC fan in the passenger front floorboard just in front of the glovebox is debris free and actually running with the key on. If that’s fine, at least we ruled out that the ECM is likely not overheating from a dead fan. Make sure your TB connectors are clicked in place and using a small flathead screwdriver, gently but firmly push in on the wires towards the sensors for a more positive contact. There are other things that can cause this also but, I listed enough things to check for now.
“I can't imagine it's anything with the throttle body itself.”
Throttle bodies have a less than stellar reputation on the AJ26/AJ27 (N/A & S/C) platform. When I had my 98’ XJR, I learned a lot of their fragility when I replaced 3 of the 5 or so throttle shaft bearings. The swiping action of the TPS brushes inside needed to be reshaped, gently cleaned and repositioned for a more positive contact on the board that it rides on. In my opinion from what you described your experience was, it sounds like the brushes of the TPS needs to be cleaned, reshaped and repositioned. Heat will always be the enemy and when you have a thin brass/copper brush, heat will warp it and heat will add resistance. However, especially the AJ26 (N/A & S/C) ECM is susceptible to failure. I believe it was due to the capacitors. First things first, check to make sure the 3” PC fan in the passenger front floorboard just in front of the glovebox is debris free and actually running with the key on. If that’s fine, at least we ruled out that the ECM is likely not overheating from a dead fan. Make sure your TB connectors are clicked in place and using a small flathead screwdriver, gently but firmly push in on the wires towards the sensors for a more positive contact. There are other things that can cause this also but, I listed enough things to check for now.
I am intimately familiar with the insides of the throttle body and I have a spare on my bench. I will check all of these items and report back. Thank you as usual for the in-depth response, I appreciate it.
Maybe I can even throw up some photos of what you're describing.
It did it again today. It was right after a long pull onto the highway. After coasting to a stop it was already back by the time I got it park. I am thinking it's something with the fuel now. I need to complete all of the checks everyone has suggested in here, I just haven't had the time. I will report back with what I find.
“I can't imagine it's anything with the throttle body itself.”
Throttle bodies have a less than stellar reputation on the AJ26/AJ27 (N/A & S/C) platform. When I had my 98’ XJR, I learned a lot of their fragility when I replaced 3 of the 5 or so throttle shaft bearings. The swiping action of the TPS brushes inside needed to be reshaped, gently cleaned and repositioned for a more positive contact on the board that it rides on. In my opinion from what you described your experience was, it sounds like the brushes of the TPS needs to be cleaned, reshaped and repositioned. Heat will always be the enemy and when you have a thin brass/copper brush, heat will warp it and heat will add resistance. However, especially the AJ26 (N/A & S/C) ECM is susceptible to failure. I believe it was due to the capacitors. First things first, check to make sure the 3” PC fan in the passenger front floorboard just in front of the glovebox is debris free and actually running with the key on. If that’s fine, at least we ruled out that the ECM is likely not overheating from a dead fan. Make sure your TB connectors are clicked in place and using a small flathead screwdriver, gently but firmly push in on the wires towards the sensors for a more positive contact. There are other things that can cause this also but, I listed enough things to check for now.
I have a throttle body disassembled on my bench and do not see the brushes. Are they actually on the side where the cable itself attaches?
Jaguar addressed the throttle body issue decades ago.
The problem was 'stalling' at speed because the plate was programmed to close and wipe the bore every so often and and a VACUUM could keep the throttle locked closed until the engine stalled relieving the stuck plate.
We replaced throttles and re-programmed ECMs under a RECALL/SERVICE ACTION.
From what I remember, the newer throttles had a throttle plate stop moved to prevent the blade from closing entirely.(no total vacuum)
Some ECMs could not be re-programmed for this fault and the throttle bodies were just replaced.
The ECMs that were able to be reconfigured had the original throttle left in place.
Don't know if this is your issue and your car missed the service action/recall?
I still have a few old throttles that were part of the recall but Jaguar just wanted them 'scrapped' so I rescued them from the dumpster.
Jaguar addressed the throttle body issue decades ago.
The problem was 'stalling' at speed because the plate was programmed to close and wipe the bore every so often and and a VACUUM could keep the throttle locked closed until the engine stalled relieving the stuck plate.
We replaced throttles and re-programmed ECMs under a RECALL/SERVICE ACTION.
From what I remember, the newer throttles had a throttle plate stop moved to prevent the blade from closing entirely.(no total vacuum)
Some ECMs could not be re-programmed for this fault and the throttle bodies were just replaced.
The ECMs that were able to be reconfigured had the original throttle left in place.
Don't know if this is your issue and your car missed the service action/recall?
I still have a few old throttles that were part of the recall but Jaguar just wanted them 'scrapped' so I rescued them from the dumpster.
Here is some info about the problem/solution.
Thank you! My XJR is an 1998 and the vin falls within this range. It's possible that it travels too far and can get stuck closed as the TSB suggests. I can remove the throttle body and adjust the stop so it cannot close all the way, but it seems very unlikely that I can get the ECM flashed so many years later.
The phenomenon described in the TSB does seem to mirror what I am experiencing. If it happens again I can try putting it in neutral to see if that works.
The throttle replace or re-program is dependent upon VIN so I don't know what your car falls under.
Good luck and let us know what you find.
If you are in the North Texas area, I can re-configure the ECM with WDS or IDS if your VIN is in the range?
Unfortunately I am located in CT and it would be very difficult for me to get to Texas lol. I will have to call some local dealerships and see if there is a chance someone can do it.
I do have an update on this issue. So it happened again and this time I was able to react in time and put the car in neutral while coasting down the highway. This seemed to solve the issue and the throttle came back. This seems to jive with the idea that vacuum is holding it closed? Perhaps the idle control valve relieves the vacuum at idle?
Then if you want to try an Inde' shop, you may try phoning someone off this list and defo ask if they have Jag service Tech training and ask if they are familiar with the scenario Bob provided. https://www.jagshops.com/cities/connecticut
