Beginner guide - Jag XJ8 - please help!

[Brian_H]

As said in the other thread, work out what its like on petrol and get that right, then move from there to getting the gas running right.

Note that gas will show up ignition problems you may not notice on petrol. Also note that a badly tuned or poorly working LPG setup will likely cause fuel trim issues which may not clear immediately on reverting to petrol.

Compression test would tell you if anything is wrong with the engine side likely down to the lack of valve saver. Presume this is an automatic rather than manual gearbox? I've known when I've had issues on a Disco that it would go into limp mode (fautly gearbox xyz switch) and lock it into 3rd which made pulling away somewhere between a challenge and embarassing and very slow in all cases. So comparing on both fuels might allow you to narrow down the fault a bit more. I'd suspect from what you've said that the lpg side wants looking at, There are filters in the lpg side, but these rarely get changed unless someone has a problem (and then its rarely helped, I've only known it to make much difference on a couple of occasions, one of them was on a forklift which ran off bottles, where the filter was caked in flakes of rust and debris, and the other was a vapour filter that had been on for around 50k miles and was significently blocked with heavy ends to the point of it being difficult to blow through).

Getting hold of the lead may help give some clues whats going on with the gas side. If its not had much attention in that time, I'd be suspecting either injectors or vapouriser could be a bit past their best (possibly leaking slightly causing your performance issues).

Do you have any access to the obd side of the Jaguar? Any fault codes or trim data your able to access?

[v8vroom]

As said in the other thread, work out what its like on petrol and get that right, then move from there to getting the gas running right.

Note that gas will show up ignition problems you may not notice on petrol. Also note that a badly tuned or poorly working LPG setup will likely cause fuel trim issues which may not clear immediately on reverting to petrol.

Compression test would tell you if anything is wrong with the engine side likely down to the lack of valve saver. Presume this is an automatic rather than manual gearbox? I've known when I've had issues on a Disco that it would go into limp mode (fautly gearbox xyz switch) and lock it into 3rd which made pulling away somewhere between a challenge and embarassing and very slow in all cases. So comparing on both fuels might allow you to narrow down the fault a bit more. I'd suspect from what you've said that the lpg side wants looking at, There are filters in the lpg side, but these rarely get changed unless someone has a problem (and then its rarely helped, I've only known it to make much difference on a couple of occasions, one of them was on a forklift which ran off bottles, where the filter was caked in flakes of rust and debris, and the other was a vapour filter that had been on for around 50k miles and was significently blocked with heavy ends to the point of it being difficult to blow through).

Getting hold of the lead may help give some clues whats going on with the gas side. If its not had much attention in that time, I'd be suspecting either injectors or vapouriser could be a bit past their best (possibly leaking slightly causing your performance issues).

Do you have any access to the obd side of the Jaguar? Any fault codes or trim data your able to access?

So, I’ve been testing petrol. It works perfectly fine!
I’ve been to one LPG mechanic, and they’ve mentioned starting off with the spark plugs as he could smell unburnt fuel.

So that’s potentially a first troubleshooting route.

The car yielded no codes when I gave it a scan.

A new finding is my tank.
I’ve let the tank run to the brink to the point where it automatically switches to petrol.
Both times, I’ve topped up to 33L. (£25)
The capacity is 42.4L (£32)

The tank is 15 years old. What could this be?

[Brian_H]

Thats progress.

Tank sounds about right - they are only supposed to fill to 80% of the water capacity, your registering about 78% so its about right where it is. I would say it seems the tank is a bit on the small size for the car though to me. To "fix" it would be to make it fill above this, There is a float inside the tank on a arm that operates the shutoff valve, you'd adjust that if you wanted to change it. Changing the tank long term might be a better bet once you get it working properly for one of larger capacity (depends what you currently have and how the pipework gets to it as to how easy that may be)

Starting off with spark plugs isn't a bad idea, you don't have much else to go on just yet. It may also be worthwhile checking if the system holds pressure if you switch back to petrol, you can roughly gauge this with squeezing the pipe that leads to the injectors and comparing after a couple of minutes. Its more accurate if you can get the software sorted though.

[v8vroom]

Thats progress.

Tank sounds about right - they are only supposed to fill to 80% of the water capacity, your registering about 78% so its about right where it is. I would say it seems the tank is a bit on the small size for the car though to me. To "fix" it would be to make it fill above this, There is a float inside the tank on a arm that operates the shutoff valve, you'd adjust that if you wanted to change it. Changing the tank long term might be a better bet once you get it working properly for one of larger capacity (depends what you currently have and how the pipework gets to it as to how easy that may be)

Starting off with spark plugs isn't a bad idea, you don't have much else to go on just yet. It may also be worthwhile checking if the system holds pressure if you switch back to petrol, you can roughly gauge this with squeezing the pipe that leads to the injectors and comparing after a couple of minutes. Its more accurate if you can get the software sorted though.

Sorry, 42.4L is 80% of the 53L tank. I’m short by nearly 10L! I’m ok with the tank size for now, but may upgrade it in the future.

The spark plugs were looked at last year and were fine. I guess I’ll have to now undo the car to view them for myself. If I’m idle and switch to petrol, the car stalls at times.

[Brian_H]

Well that gives you two options on the tank - either its not fully empty when the pressure is dropping off (restriction in outlet possible but unlikely) or its underfilling. Underfilling would be down to the float mentioned earlier. You'd want to empty the tank before trying to investigate that. Might be an idea to identify if its a 4 hole or single hole tank as well.

Given you say it stalls when switching between fuels at times, I'd look at what the fuel trims are doing then if you are able to view them with whatever you have for diagnostics?

[v8vroom]

Well that gives you two options on the tank - either its not fully empty when the pressure is dropping off (restriction in outlet possible but unlikely) or its underfilling. Underfilling would be down to the float mentioned earlier. You'd want to empty the tank before trying to investigate that. Might be an idea to identify if its a 4 hole or single hole tank as well.

Given you say it stalls when switching between fuels at times, I'd look at what the fuel trims are doing then if you are able to view them with whatever you have for diagnostics?

Thank you for the advice.

My tool shows no error codes when using it. This is not on top of my list of priority just yet.

I am looking into what sparkplugs are best suited for the car. I could go for Iridium plugs, but I have learnt of the NGK LPG LaserLine plugs. They are awfully pricey.

[Gilbertd]

and they are nothing more than standard NGK Iridium plugs. Either stick with what it originally had or the NGK Iridium equivalents.

[LPGC]

You may need plugs changing but I doubt worn plugs are the reason for stalling during changeover or any other driveability problems you may be having... more likely there's something(s) wrong with the LPG install and/or fuel return if fitted.

I know the standard plugs work well on LPG in these engines, I don't know (or at least don't remember... I probably have changed plugs on these in the past and might have fitted iridium) if/what equivalents will. If I were changing plugs on it I'd stick with standard for now, at least until you've got the LPG system working properly then maybe next time they need changing (if you've still got the car) swap some iridiums/equivalents in. If you fit plugs that no-one has confirmed work well in that engine (standard work well) and can't get the results you might be a long time wondering if the problem is plugs. It's unlikely it wouldn't run well on LPG with NGK iridium equivalent plugs but why even make scope for extra doubt.

A 50 litre tank should normally fill to 40 litres (80% of 50 is 40)...

[v8vroom]

and they are nothing more than standard NGK Iridium plugs. Either stick with what it originally had or the NGK Iridium equivalents.

yes, I came to that conclusion too. I will be purchasing these tomorrow - NGK PFR5G-13E.

[v8vroom]

You may need plugs changing but I doubt worn plugs are the reason for stalling during changeover or any other driveability problems you may be having... more likely there's something(s) wrong with the LPG install and/or fuel return if fitted.

I know the standard plugs work well on LPG in these engines, I don't know (or at least don't remember... I probably have changed plugs on these in the past and might have fitted iridium) if/what equivalents will. If I were changing plugs on it I'd stick with standard for now, at least until you've got the LPG system working properly then maybe next time they need changing (if you've still got the car) swap some iridiums/equivalents in. If you fit plugs that no-one has confirmed work well in that engine (standard work well) and can't get the results you might be a long time wondering if the problem is plugs. It's unlikely it wouldn't run well on LPG with NGK iridium equivalent plugs but why even make scope for extra doubt.

A 50 litre tank should normally fill to 40 litres (80% of 50 is 40)...

so, I am attempting what I can do with troubleshooting. As of now, the sparkplugs are the only job that I can tackle (anything else is away above my skillset. I have a liking to learn, but if something goes wrong on this car then I've had it) I have booked myself with an LPG Jag Specialist in Lincoln, but that's in 2 weeks. So, in the meantime, I am doing what I can in hopes that it resolves all issues and a hefty bill.

My troubleshooting route:

• See if sparkplugs need changing. If so, change them to the NGK PFR5G-13E iridium ones (I managed to pick up 8 for £37 which is an absolute bargain; even cheaper than regular plugs)
  If the problem is fixed, amazing.
  If not, head to the local LPG specialist who does not particularly like working on old Jaguars, but I will get service from him and see if he spots anything.
  If that does not fix anything, off to the Jag LPG specialist it goes.

Yeah, I'm not getting above 33L but hopefully, I can get this resolved after the acceleration problem is resolved. Are LPG cars meant to have slow acceleration? My local mechanic owns an LPG converted LS400 and he mentioned he tried everything to fix this and deemed it's normal.

Regarding the car stalling when changing from gas to petrol, it still does this..however only once. When I start the car again and switch back and forth from gas to petrol, the car does not stall.

[LPGC]

It' could be that the tank is fitted with the valve (and float) at the front? If so and if the floor of the spare wheel well hasn't been levelled off then the valve would be at the deepest end of the tank, which could explain why you can only get 30L (60% fill) in the 50L tank.

Not a great situation thinking you may need to visit 2 LPG installers. No reason 'not to like working on old Jags'... it's an LPG converted car. A good LPG specialist is good full stop, no need to claim being an LPG specialist for only one make of car.

A car running on LPG should accelerate almost exactly the same as it does running on petrol. I have converted many Jags and LS400's.

[v8vroom]

It' could be that the tank is fitted with the valve (and float) at the front? If so and if the floor of the spare wheel well hasn't been levelled off then the valve would be at the deepest end of the tank, which could explain why you can only get 30L (60% fill) in the 50L tank.

Not a great situation thinking you may need to visit 2 LPG installers. No reason 'not to like working on old Jags'... it's an LPG converted car. A good LPG specialist is good full stop, no need to claim being an LPG specialist for only one make of car.

A car running on LPG should accelerate almost exactly the same as it does running on petrol. I have converted many Jags and LS400's.

I am an absolute amateur in the LPG world so I would not know where to start to look into this.

Yes, it is not ideal going to two specialists but it's what I'll have to do.

So, a new finding occurred today

I was able to fill 35L - this is a record. My gauge was full of green bars (I only ever hit 3 out of 4 after a top-up.) The car felt just as nippy in petrol, but it did not last for long. I should mention something underneath rattles - I suspect the Cats have gone. The car still runs perfectly fine in petrol mode, though.

At times, the car will get stuck in a gear and choke at 4000RPM, so I have to let go of the pedal for the car to either upshift or downshift.

[Brian_H]

The tank thing is actually simpler to work out than it sounds. If your stuck, take some photos of the tank in the car and upload them here. Press full editor and preview button to see upload options. It's literally a case of looking if the tank is flat or not where its installed with the car parked normally, and where the valves are located on it. Photos might be easier there than trying to explain what your seeing.

[v8vroom]

The tank thing is actually simpler to work out than it sounds. If your stuck, take some photos of the tank in the car and upload them here. Press full editor and preview button to see upload options. It's literally a case of looking if the tank is flat or not where its installed with the car parked normally, and where the valves are located on it. Photos might be easier there than trying to explain what your seeing.

I may not need to take any pictures at all now..the local mechanic fixed the car! The fuel to air ratio was misaligned so all he did was a recalibration and now I have the full power of a gloriously cheap V8!
He mentioned the tank mileage should work well now, so I will give it a week to assess how many miles I can get out of it!

Thank all of you for assisting me with this problem!

[v8vroom]

Hi all,

I've done nearly 8000 miles since we last spoke.

There are two things I would like to understand
1) The Jag takes a few seconds to turn over and sounds like it won't, but it eventually does. Is this normal? This was an issue before I replaced the sparkplugs with LPG-specific ones (NGK PFR5G-13E)
2) Is a service on my Romano system simply just running the software to see if the vehicle is in check? My local LPG specialist said for my vehicle. this is the case and nothing needs replacing.

[Brian_H]

Service you'd normally expect the filters changing. They last a fair while but do eventually clog up.

Is the starting issue still apparent if you run it on petrol for a few minutes before switching off? If so it's likely either the reducer or injectors are leaking gas slightly into the manifold, this fills up the manifold and until that's cleared through to the exhaust it won't start as there's not enough air in the mix and far too much fuel, both gas and petrol.

The lpg spark plugs generally aren't needed, you should be fine with the normal ones as long as they aren't platinum ones. Iridium options or standard copper should be adequate. Better to avoid the multiple electrode ones if you can though.

[v8vroom]

Service you'd normally expect the filters changing. They last a fair while but do eventually clog up.

Is the starting issue still apparent if you run it on petrol for a few minutes before switching off? If so it's likely either the reducer or injectors are leaking gas slightly into the manifold, this fills up the manifold and until that's cleared through to the exhaust it won't start as there's not enough air in the mix and far too much fuel, both gas and petrol.

The lpg spark plugs generally aren't needed, you should be fine with the normal ones as long as they aren't platinum ones. Iridium options or standard copper should be adequate. Better to avoid the multiple electrode ones if you can though.

I’ve not tried running the car on petrol before switching it off. I’ll give a try. At times, when the car is warm, the car will turn over with no issue. Recently, the car has not started to turn over at all. I have to attempt 2/3 times before the car starts.

[v8vroom]

A new month and a new potential problem?

This was a few minutes into my cold start..does this sound normal?

https://www.youtube.com/shorts/xi60qnkA9ho

[LPGC]

A new month and a new potential problem?

This was a few minutes into my cold start..does this sound normal?

https://www.youtube.com/shorts/xi60qnkA9ho

Difficult to tell. Do you mean the regular metallic like clicking noises? That could just be injectors. If it is injectors it could be normal for the type of injectors (I forget what type you have), or it could be that the injectors are touching something (e.g. the petrol fuel rails on the Jag engine, or the plastic engine cover) that acts like a sound board (the injectors may be a lot quieter if insulated from such sound board), or could be that the injectors are louder than usual (for the type you have fitted) because they're worn.

What does it sound like when it's running on petrol?

[v8vroom]

A new month and a new potential problem?

This was a few minutes into my cold start..does this sound normal?

https://www.youtube.com/shorts/xi60qnkA9ho

Difficult to tell. Do you mean the regular metallic like clicking noises? That could just be injectors. If it is injectors it could be normal for the type of injectors (I forget what type you have), or it could be that the injectors are touching something (e.g. the petrol fuel rails on the Jag engine, or the plastic engine cover) that acts like a sound board (the injectors may be a lot quieter if insulated from such sound board), or could be that the injectors are louder than usual (for the type you have fitted) because they're worn.

What does it sound like when it's running on petrol?

I lost access to my account for a few months so I couldn't log in.

I sold the car not long ago and bought a '99 XJR.