That's what my mechanic told me. 80psi front and 70pdi on the two back cylinders. Now I know why the engine shakes and the loss of power. Now Imm scratching my head because I installed new pistons rings, timing chain kit, head gasket, heads resurfaced, valves were turned to seal better etc etc... The machine on Jaguar is not giving any engine error that can explain. What other options do I have?

P.S: My mechanic told me because of the lower symilar compression values on all cylinders (70-80) that its possible the timing is wrong, even by one tooth. I really dont know

 

I’d be very suspicious of this most recent compression test. In post #17, you said a compression test was good then. It’s not like the engine has suddenly worn out in this short time frame.

Why the sudden change? Lots of factors can affect a compression test and give misleading low numbers. Starter cranking speed is huge, so make sure the battery is fully charged.

You’ve mentioned the engine seems to be running rich. If excess fuel is present, this will wash oil from the cylinder walls and reduce compression.

Have any of these mechanics tested the fuel pressure at the injector rail? Connect a mechanical gauge and compare it to the scanner reading. This is a very basic step in troubleshooting, but I’ve heard no mention of this yet.

 

First time, few months ago, I went to a mechanic near my house and they said that the compression was okay. But went to another mechanic last 2 weeks and said compression was very low now. So I dont know whom to believe because last week I also went to the Oficial Jaguar dealership and they didnt mention any kind of low compression or any error on the computer that justifies the symptoms. Never made a fuel pressure test yet. Maybe its my next step to do! What is the normal range for the fuel pressure for this car? What should I do?

 

Ive had a neighbor with a 2.5 '04 s type.
He had some of the codes you mentioned and missfires on certain cylinders, on both banks.

In his case, problems were caused by some of the exhaust valves. They were broken and obviously had created bad compression.

He claims the problems have randomly appeared.

why did your headgaskets go bad?
If you said your compression is low, you might have spotted the issue

good luck, keep us posted

 

Mine had a headgasket failure. Bubbles in the coolant reservoir, sweet smell water coming from the tailpipes. Removed both heads, installed new headgaskets and head bolts etc and that problem was solved. Valves were turned and intalled just a new one.

 

Did you overheat your car? Why did the headgaskets fail?

 

He overheated sometimes yes because of the thermostat, before engine rebuild

 

Reading from the beginning of this long thread, it seems we are no closer to a good fix. One big question:

Has the engine run properly at any point since the rebuild?

Just trying to get an idea about valve timing or similar issues during assembly that could cause trouble.

Was the engine running okay before the overheat that led to all this trouble?

You mentioned the injectors have been replaced. What brand was installed? Stock specifications? I'm wondering if they could be defective or "performance" models that flow too much fuel.

And I keep stressing you need to measure fuel pressure with a mechanical gauge. Proper fuel scheduling is highly dependent on having the correct pressure. You could be chasing your tail without this very basic check.

 

The engine never ran properly, it got slowly worst over the years, before and after the overheating and the rebuild, same symptoms but now is worst than ever.

All new injectors were Denso brand, exactly as the originals and same side code (green S-type&X-Type Denso injectors), that I bought from England from a worskshop specialized on rebuilding injectors only. Also changed all the connectors of the injectors (every one of them was either broken or loose), didn't do anything.

I didn't measured the fuel pressure yet but its my next step to do(I dont know what is the correct pressure range). But I remember 2-3 years ago, when the car was better (but not perfect), I drove to Lisbon and before that I filled the petrol tank full(I never do that because the car is LPG), and the car struggled and stuttered a lot that once time, dont know why but never filled up full tanks again. Also a question, suppose this was a problem of high fuel pressure, that would only affect while driving "Gasoline mode"? or also when driving LPG mode?

Last week I went to the Oficial Jaguar Dealship to do a complete computer diagnosis/analysis. They have the Jaguar sofware and are the only ones able to give me some "holy grail" answers I thought. Nothing, they said the car didn't had any errors, didn't talk about compression pressure or fuel pressure or valve timing etc etc.

 

I wonder how in-depth this diagnosis really was. They may simply hooked up their official scanner and checked a few basics. A few areas may have needed further investigation:

Compression: The computer compares the relative power output from each cylinder. A fault code(s) is set if one or more are low compared to the others. But if all are equally low, there’s no differential and thus no fault code. This is where you need a mechanical gauge to be 100% sure. I would suggest double checking the recent findings of low compression. This strikes me as odd as previously all was good.

Fuel pressure: The computer adjusts pump output to maintain a target pressure at the injector rail. This value is displayed on a scanner. But if the sensor is inaccurate, the computer will happily adjust to this inaccurate value without setting a fault code, because it thinks all is good. That’s why I keep saying to check the pressure with a mechanical gauge. It’s a very preliminary step in troubleshooting.

Fuel trims: Did the report list long and short term fuel trims? If the actual fuel pressure is out of range, the long term fuel trim may be high or low as the computer tries to maintain the desired air/fuel ratio.

 

Check valve timing. Incorrect valve timing could cause low compression and incorrect vacuum pressure. The ECU sees the reduction and thinks the engine needs more fuel so opens the injectors for too long. But first, Check for inlet leaks, anything that could cause a reduced vacuum. Leaky vacuum pipes, accidentally disconnected pipes or pipes connected to the wrong place. Disconnect the brake servo pipe and block it off just to see if the servo is leaking inside.
One other thing. Check your intake pipework isn't damaged. The plastic resonance chamber has a habit of disintegration. The plastic vacuum pipe that runs between the middle of the inlet manifold branches also has a habit of splitting and leaking.

 

Any of those things will set a code for a vacuum leak and he says the car has no codes??
Now you tell us it's a dual fuel vehicle which complicates things even more? How is the jaguar dealer going to troubleshoot the car when Jaguar never offered an LPG version? I just don't think they have any experience with that?

The list of codes you started with in your first post are they from when the engine was running on LPG or gasoline?
With the long history of this engine NOT running correctly are you sure the LPG conversion was done correctly and is still operating correctly?
If it was my car I would get rid of the LPG stuff UNTIL you can get the car running properly on gasoline THEN convert it back.

I have much experience with Propane vehicles as my Dad had a shop that specialized in this. He mainly got into that business because of the poorly done conversions which has given Propane a bad name in the US. But he always started with a properly running gas engine first. Otherwise too many variables and you end up chasing your tail as apparently you have been doing for quite some time?
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I'm old school, I don't rely on codes. They can sometimes be useful but are often misleading. In my experience a car can run like poo, but still not show a fault code. Example: Audi A6 ran like crap which got worse when the engine got hot. It had no fault codes, but it didn't take me long to realise it was running rich due to a faulty temperature sensor. Replaced sensor, car ran fine. Happy customer! Should there have been fault codes? Yes, in theory, but there weren't. I was taught to use logical process of elimination and it usually works.

The point about LPG or petrol is valid. I agree that you should get the car running right on petrol before switching lpg on. However, if we are talking about the same car as mentioned in my lpg installation post. I think we have established that the installation was done in a hurry. There is a possibility that it could have caused problems.
For example, gummed lpg injectors may not seal fully. Poorly installed nozzles may leak. So for the purposes of diagnosis, I suggest that you leave the lpg system turned off until we have found the problem.

To be extra cautious, you could try disconnecting the outlet pipes from the lpg injectors and blocking them off. At least that would discount the possibility of dodgy lpg injectors.

 

I've just realised. To our collective shame (myself included) none of us have suggested the obvious. Engine management coolant temperature sensor. A faulty sensor, or sensor wire, fools the ecu into injecting too much fuel causing all the symptoms you explained. Also bore wash caused by excess fuelling could explain the slightly lower compression.