S-Type Running Lean - running out of ideas!

[david27]

Hi,

 

I'm new to this forum, I'm actually writing this on behalf of my dad, I've been trying to fault find an ongoing issue with his car for the past few months and I'm running out of ideas.

 

His car is a 2003 Jaguar S-type 3.0 v6.

 

Basically it manifests itself with a system too lean on both left and right banks. Sometimes just an engine management light, other times restricted performance also.

 

Below is a storyboard of what I've tried:

- New lambda sensors (all 4)

- Leak test inlet etc for obvious leaks (found 2 small leaks, both fixed)

- Noticed, while monitoring fuel pressure that under harsh acceleration it drops to 35/40 psi. Looking into it, apparently this should hold at 55 +/- 5.

- The above prompted me to try changing the fuel filter - this improved it, the car went 500 miles without showing a EML.

- In the last 2 weeks this has come back, worse than before now, every journey will result in the EML.

 

To save keep throwing money into things I dont necessarily need, I was wondering if anyone could give me some pointers to try next. For instance, what about the fuel pump in the tank, or is there a regulator in the system that might be at fault?

 

Many thanks,

 

David

 

[thathawk400]

Hi have you got a good obd2 scanner a good one should be able pin point your problem as your car would have several fault codes stored a good reader would be able to read fuel trims check fuel pressure I have had problems faulty coils I had a lean problem the codes I got I looked up on the internet and managed to solve my self instead of going to a main dealer or an indie could be a weak or failing fuel pump

[Simjag]

Has the spark plugs been changed?

[Claws]

Clogged filter?

[JOE-DOT-COM]

Hi David

as its common to all cylinders, possible fuel pump or fuel pump pressure regulator

if the fuel pressure low, you could check with a gauge like I think you have, but you could try clamping the return line off slightly to get your fuel pressure up to your 55psi

with say some mole grips and then drive it, could be something as simple as the fuel pressure regulator, if you cant achieve the 55psi with clamping the return hose, it could be the fuel pump

it has to be something common to all cylinders, I think there's also a fuel pump ecu, that lowers the voltage to the fuel pump when idling, could be this, some people hot wire the fuel pump to get more power as fuel pressure will be raised, hot wiring is just basically bypassing the ecu/fuel pump control unit, with a ignition supply

common fault with running lean is usually air leaks, split hoses, inlet manifold gaskets etc, but you said you have checked this, you could try some easy start around the hoses, inlet manifold area, if theres a leak, it will suck the easy start in and the revs will raise on idle

could also be airflow/maff sensor, this also can effect mixture of engine

cheers

Joe