It is not necessary to check voltage, ecu interprets that for you and returns it in form of % open on your scanner
just play a bit with lever at the throttle body and watch the result on the tool, it should suffice
Not sure what exactly you wanna clean in tps but cleaning throttle contacts is fine but i wouldn't embark on cleaning tps internals

 

So here is my plan:

- Adjust throttle cable. Test drive.
- Clean MAF. Test drive.
- Clean throttle body if dirty. Test drive.
- Fuel pressure test to discard pressure regulator and fuel injectors leak.

If everything is as always, then I might have issues with the spark plugs, vacuum leak, coils, pump, clogged fuel injectors or fuel filter.

The mechanic changed spark plugs and fuel filter, he did not raised the flag on fuel signs in the spark plugs, so in principle I can discard fuel injector leak, fuel filter clogged and spark plugs.

I put fuel cleaner in the system, so I could also discard that I guess.

This will leave me with vacuum leak, pump or coil.

Vacuum leak, I believe the effect should be seen it idle, which is no the case.

Coil plugs...how can they be tested?

Last option is the pump...or change the fuel filter again!

​​​​​

 

- Adjust throttle cable. - is a must, fix it first
- Clean MAF. -good anyway
- Clean throttle body if dirty. - look for butterfly sticking or not opening fully
- Fuel pressure test - is a must
Observing long term trims at the moment of failure will point you in the right direction (rich or lean) otherwise you are all over the place with you tests
You don't want randomly fix things but rather use the tools at your disposal to isolate the issue, so first test and only after that think about replacing anything

 

LTFT can be done at first test drive. No issue!

 

Hi again,

Did adjust the throttle cable, or rather not adjusted, since it was already perfect. Just by turning one quarter idle went to 1000 rpm (could have lowered with time but it was a high start I believe) and it did not properly contacted the reel stop.

Test drive and...this time I got a proper set of data but no LTFT, probably because I added it to the log too late.

Anyway, next step is the MAF cleaning. By the way, in forecast of the fuel check, does anyone know if this is the pressure regulator? I can't seem to find the vacuum line, there is one line that would look like it but goes all the way back to the firewall, why would it do that? It looks like it has a Tee shape, I marked it on the second picture.





Thanks,

 

Yes it is fpr and line you marked is a vacuum, it should be straight connection not a tee and certainly not open to outside,
while there check if vacuum line smells petrol what would mean failed regulator diaphragm

 

Thanks,

These pressure valves are still a mystery to me, it looks like on every car they're different (I know design changed) and it's location also changes . Probably is just the perspective of the photo, but does not make things easy.

Scrolling the forum has not changed my situation, there was a thread where somebody asked the same question and the answer was honestly not clear to me. At some point somebody describes a fuel pulse damper... https://www.jaguarforums.com/forum/x...or-xj8-187025/

I think I'll skip the MAF cleaning and go directly to the fuel pressure, I think I'm beating around the bush too much.

One thing I should have mentioned, is that I have some fuel smell inside the cabin when starting the car, specially today at high idle after the throttle thingy. I know, injector leaking? I feel ready to do the test. One practical question from a novice, once I finish the test, relieving the pressure with the button on the manometer will make the fuel go out the transparent tube of the fuel manometer? Should I expect any fuel spillage?

 

Yes it is fpr, early type


And i was wrong, there is tee piece indeed. Pull that hose our and look if there is any fuel or excessive odour coming out, don forget to plug it back

Smell of fuel at start up, especially in cold weather is normal i wouldn't worry about that much unless it is somehow excessive or don't subside after some warming up
Cleaning maf takes few minutes and is nice to have it done so for your own peace of mind you should do it and yes pressure test is definitely thing to look at next

 

Hi again,

I did a fuel pressure test today.

1. Manometer connected and key in position 2: 2.6 bar (37.5 psi). Yeah, a bit on the limit.
2. I did not fully check the pressure dropping at this stage, might repeat the test this weekend.
3. Engine started, same pressure as point 1.
4. After some minutes, it looks pressure drops to 2.4 bar (35 psi).
5. Tried to rev to 2000 rpm just briefly, pressure did not seem to rise much, maybe I should have kept it there for 2s or so?
6. With engine almost hot, I tried going to WOT, I stopped pedal halfway because I do not know how risky it is for engine (and the sound is deafening, since I work in a small garage box). Pressure DID NOT MOVE, manometer needle was cold dead.
7. Tried removing the vacuum line from FPR, impossible, it is like glued. The only one I could remove was the one joining the tee and going to the firewall, but that is useless, since there is still a vacuum path from the FPR to the engine. Pressure was always 2.4 bar (35 psi).
8. Engine off, pressure rises slightly with time (0.1 bar after 5 mins or so). I guess this discards fuel injector leak or pressure system loss.

I can repeat the test if needed, this first time I notice I was sloppy in some points.

Another point, there is a violent noise like a firecrack from time to time as engine heats up. I thought it was coming from the engine front, but with the engine plastic covers removed, it is clearly coming from the area of the injectors/air intake manifold. There can be a crack noise every 30s or so.

Thanks to everybody for your help.

 

As long as engine is hot and you are not keeping it at red line for more then few seconds it is all right to rev high
Your pressures looks ok
Did your car misbehave any more after you started this topic or it was just a single event ?
As for firecrack i will let others chime in as i don't have a clue, ?engine backfire? maybe try to record the noise and post it here

 

Yes, I can repeat the issue on demand, WOT and high revs.

I need to disconnect the vacuum line from the FPR, tomorrow I'll try. I don't understand how it is so stuck, I want to think it is due to something sticking (fuel).

Did battery test, not sure if a bad battery can make the pump go weak, at least alternator can I guess.

12.2 V engine off, after car sitting whole night. Low but the car can go a week untouched and start on demand no issue.

14.25 V engine on, all accessories off.

14.15 V headlights on, AC on, radio on.

12.8 V after switching off engine.

12.5 V after 10 minutes.

Yesterday when I tried to go WOT, I saw the map reading light dim, so I was suspicious.

This tells me that my battery is weak, but holds power (after a week in the cold it can start the car) and the alternator looks good?

Took a video of the noise, I'll edit and post later. Sound is there when engine shuts off as well and cooling.

Driveability fault tree from Jag says pressure should go up to 3.2 bar at 2000 rpm, I could not test it yesterday, will try also tomorrow along with the LTFT.

Wish me luck.

 

The car has a rev limiter so you can't go above usually 3000 rpm in P or N.

ALL rubber/plastic hoses will be stuck and immovable because of heat and time. Try rotating the hose first. I use these types of pliers to help.




These are really nice because they are double jointed and I find they help a lot on installing rubber hoses in places you can't reach with your hands. Since they grip the hose 360 degree's they are way less likely to damage the hose or the nipple it's attached to.

.
.
.

 

Ok, today I finally got to disconnect the vacuum line from the FPR. I used some pliers with duct tape rolled over it to make the grip softer. Took some time but I got it out, once out it was really easy to put it on and off, such a drama for nothing.

Bad news is that the second pressure test is useless, the pressure gauge is rubbish I believe. It was measuring 1 bar at key position 2, no movement from the needle afterwards.

The pressure regulator does not leak, so I guess that discards it as the culprit.

By the way I broke (broke by itself of course ) one side of the plastic tee, the one that goes into the vacuum line routing to the bulkhead. Are these plastic tees standard? Will search for it. The nipple is stuck inside the plastic hose, but I manage to keep it in place and conencted.

At some point after removing the vacuum line, it seemed like pressure was raising slightly, but go figure with this pressure gauge.

Test drive after everything was finished. This time I think I got the good stuff. This is a 10 min drive, with the shaking at 288s or so.








It looks like the LTFT stabilizes short after the start of the trip and does not vary much during the shaking that I notice?

The STFT however, it looks like it goes negative (rich condition)?

I'm lost, I think I'll clean the MAF as next step and take it to the shop for a proper fuel test and maybe reading some codes if any (my OBD says zero). As I said, the poor goes to the shop twice. At least now I know I can do this myself, assuming I have the right tools.

As always, thanks so much for your help and comments.

 

It is unlikely that your gauge is rubbish, it may be few psi off but should give you an approximate idea of pressures in the system, does it stay at 1 bar with engine running?
Your stft got quite negative in bank 2 and i guess from graph stayed there at least for few seconds, it point to the problem in that bank and not a fuel pressure or maf problem
So here are some ideas
Dirty clogged injectors - did you run cleaner through? it may take some time, may also be not enough and you will have to send them for cleaning
Fouled spark plug well, they like to fill with oil and then misfire
Spark plug itself, pull them and inspect condition and colors
Ignition coil - dunno how to test them other than resistance which doesn't tell much anyway, but clean the contacts and inspect them, you can also swap them between banks to see if rich condition moves with them (same applies to injectors)

 

Pressure was around 2 bar (29 psi) with engine on. But the needle was stuck afterwards, no difference if I accelerate, remove vacuum line...
The other day it did the same thing, but the needle was alive at the beginning, jumping and bouncing. Once it starts showing that frozen state, I do not rely anymore.

I'll stick to plan and clean MAF, then do the rest, step by step, motivated, relentless.

 

Assuming gauge is ok, 2 bar is way to little especially under load
Hang your gauge to the tyre valve and see what pressure comes out, you will have an idea if it is working or not

 

First test was 2.4 bar idle and 2.6 at rest.

Cleaning injectors sounds quite good to discard that and come back to the pump later with more boxes ticked.

Saw this morning a guy replacing the pumps on an XKR on YT without even moving tank.

Except unbolting the 7mm screw from pump bracket, he did the rest between the space between the tank and thank ceiling. I guess the XJ has less clearance? Otherwise, has anybody tried it? Maybe a long extension and a camera probe connected to the phone? I would like to be first to try and succeed.

 

on xj8 you either pull the tank or cut through shelf and end extract pump from there, in both cases not a fun job

from workshop manual:

8. Start the engine and record the fuel pressure reading.
As a guide, the fuel pressure should be approximately 3.0
bar (44.1 psi) with the regulator disconnected.
9. With the engine still running, reconnect the vacuum hose to
the pressure regulator and record the reading.
 The pressure should drop to approximately 2.6 bar (38
psi) when the vacuum hose is reconnected.

 

Ok, I got 2.6 the other day on first test. Taking out vacuum today had no effect today but nothing had. Maybe the Schrader valve was dirty or damaged, I found the car without cap on it.

 

Removed air pipe, pretty straightforward and w/o hassle. Just to comment, the two parts (air pipe and MAF) split on the jubilee clip as I was trying to remove the air pipe, as if they were not properly attached.

I got out of light so I will proceed with cleaning tomorrow or on the weekend.

Here are some picture of the before.