I have a S type 2001, 4.0, low number at the clock (49 000kms), automatic and blue…
I have misbehaviour since now close to 4 years without finding the issue. The car did not provide any fault message.

The initial event was when I turned on right, and the engine operate like a motorbike when you reach the bottom of the fuel tank and when you have to turn the “reserve”. It is the same with a carburettor when the carburettor tank is not full.

I Removed the fuel tank, clean it and verified the pumps. No finding.

I bought a scan tool and monitored the fuel pressure. It was stable, even if the engine did work properly (average 272kpa, min 255, max 294).

I thought about electrical connection issue on the fuel control controller but as the ECU is able “to speak” to the OBD bus, it is powered properly.

Since this time, I use the car only to go to the village to buy my bread (I am French!) and now the problem seem to have evaluate as the idle is unstable and I have a lack of power. I had time to change all the sparks (the right one, the OEM), all the filters and the chain tensioner.


I had recorded lot of measures. As said previously, nothing is reported by the maintenance system, no fault detected.

At the beginning of the week, I had found in this forum a Jag trouble shooting procedure. I went to the short term fuel parameter and had recorded this following plot.
The engine is at idle, the idle is unstable and the engine had reached his operating temperature. Is seem that the engine control is trying to adjust the fuel quantity and when the drift is to mluch, it recover. During this record, the lambda was between stable 0.73 and 0.75. The mass air flow was measured between 5.68g/s and 8.9.

Air leakage?
Some idea? As I found nothing
Comments please
Thanks,
Richard

 

Try hot engine, parked, fuel trims at idle and rev to about 2500.

There are multiple networks as well as the OBD one so you might have a fault on one. Not likely. Also, fuel pumps are driven over yet other wires & signals - but not much to show what might be wrong yet.

Lambda should be near 1.0 so something is wrong, as you know.

Start with the fuel trims and let's see what they show.

Oh - and check the car is running CL (closed loop) on both banks (OBD status). With lambda so bad it may not be.

 

Thanks,
I had attach a plot of fuel trim. Did you went on it?

 

Can't you just post actual numbers?

 

the fuel trim is unstable, in the same manner in boths ranks. Il decrease from -1 down to -13% and sudently come back to -1%. In the same time the idle is unstable.

 

And at the higher revs?

You're making this slow and much harder than it is!

 

Its starting to become somewhat humorous.

 

"Try hot engine, parked, fuel trims at idle and rev to about 2500.".
I did it and had recorded the fuel trim and O2 parameters. They are consistent. I start the engine and went to differents rpm steps to 2500. When the O2 is over 0.9, teh fuel decrease and the O2 decreased. Then the fuel increase and O2 also..... The loop is closed but instable.
I had attached the XLS tabs.
No fault reported.
At least, the values bank 1 and 2 are consistant. If I have an air leakage it is common to both bank, before the metal part (Don't know the name in English).....
Idea are welcome.
... xls file can't be uploaded....sorry

 

Copy/paste the data into the body of a reply.

 

Plug the OBD reader in and drive the car and see if the reader captures a code.

 

Well,
I had try copy/past. The curves are hidden. They are in the word file attached.


The red curve is the O2 mesurement on bank1 at the output of the engine.
The blue curve is the fuel trim balance on bank1.
The engine was hot, the measurement is at iddle (700rpm) and unstable. No fault reported by the engine health monitoring.
The record between the plots 200 to 235 is interesting ( I assume) as it reflect that the engine control loop is working. At 200, the lambda is very low (close to 0) and the control react by increasing the fuel from -7% to +4% making increasing the O2 parameter.
The system work but not properly. It is like if the engine does not behave as it should (engine maping in computer memory).

Others measurements below (engine sart) reflected that the bank 1 and 2 (each side of the V) are operating in the same manner and are synchron in term of fuel trim balance and 02. Therefore I had reported only one side of the engine.



Do you know how many temperature sensor are in this engine?
The temperature measurement used to report the temperature ate the dashboard seem to work, but they are car with other temperature sensor for the engine control. It is the case for this?

I had driven the car this morning, added new fuel (octane 98), recorded the parameters and no faults reported....

Thanks for your thought

 

I give up. Getting a few numbers is so hard.