It could be bad cat(s) too. Or PCV. Or ...

Chances are it's an air leak.

What are fuel trims at idle & 2500rpm in Park, engine warmed up?

What are last 6 of the VIN?

 

Mines the same as USA 2003 onwards, so no hose under manifold

How could 'back to the gas cap' cause this fault?

 

Oh, could be cats?
Fuel trims are 5% and 7%.
It's the later engine.
I did a DIY smoke test today, at 10psi no leaks but at 25 psi the manifold pressure sensor started to leak a every small bit but it does not get to this pressure does it?

 

5 & 7% won't set those codes.

But, you're getting something that does.... maybe a leak triggered by something else (say, EVAP or EGR active) or it's not a leak. A misfire also looks like a leak, due to the unburnt air (it can't see the unburnt fuel) but usually you get a misfire code.

Cats can upset the system.

If that was +ve pressure, it's not the same as -ve. May or may not have been good enough.

It's got the right plugs & coils and all believed good?

 

Sorry the fuel trims are +ve.
There's no misfire and drives like a jag should.

What do you think I should try next?

 

The vacuum system goes the entire way to the gas tank.

What exactly are you doing when this fault occurs?

 

My +ve etc was - as I said - about pressure. What did you do to get 25psi?

Worth checking the other items which activate and there are a lot.
And the cats and other things I posted.

It doesn't drive right because if it did it wouldn't set codes.

Maybe the freeze frame data would help.

 

Just driving it, it can be at 70mph on cruise or 20mph in town, there's no pattern. But it does not happen in the 1st 5mins from cold start.

 

To get the 25psi in my DIY smoke test was by useing a self bleed clutch/brake kit connected to a spare wheel.

Then the codes/RP comes up it still drives/feels fine.

 

Hi all,

Ive been looking into maybe a have a leak in the fuel tank emission system, i as understand the system is-
A vacuum pipe from inlet manifold to Evaporative emission valve (which is opened by the ECU), which connects to a resonter which then connects to a canister in/by the fuel tank.
As i understand it works- Then the valve is closed, the fuel tank is vented into the canister which absorbs fuel vapor, then the valve opens (which is opened by ECU to calibrated data tables) the canister is then exposed to the inlet manifold and fuel vapor is pulled into the cylinders.

Is this right? If yes then does the valve open/close every quickly? If it is opened for too longer time then the engine would go lean every time it opens?
Also it has a roll-over valve in the tank so if the car rolls fuel will not run down this pipe into engine bay, could this limit the air flow to stop the engine going lean?

 

no a leak from the evap system into the intake will show as a rich condition(like it the purge valve was leaking internally, would aslo throw a evap leak code) because youre inducing fuel vapor not air. the only way it would show as a lean condition as a result is IF theres a leak in the pipe from the PURGE valve to the engine a very short run.

 

Cheers.
What if theres a leak between the purge valve and tank, so its not pulling fuel vapor but air?

 

Then it still pulls air and fuel vapor and still messes with afr's because it doesnt coincide with mafs reading and injector pulses. Its just like spraying carb/brake clean at a vacuum leak. Its always pulling in air and when you induce a fuel it still reads a rich condition at that point and no longer a lean condition. This is how you find vacuum leaks with short term fuel trim monitoring

 

Ok cheers.

Where next do you think i need to look at?

Thanks Simon.

 

I'd try the freeze frame data a few times looking for a pattern or at least clues.

 

Freeze frame will not help to identify a source jv.
I just found vacuum leaks on a car that was restricted perf and customer said ran fine. Had mafs put on and air intake tube. Still a fault. I got the car and hooked up to monitor short term fuel trims and sprayed the intake area and other spots and it immediatly show the intake gaskets leaking and the oring behind the throttle body adapter to intake manifold. And when i pulled it in the next day cold it sat there and chugged. I dont see how the customer said that was normal and it ran fine except that once it warmed up some it quit doing that.

 

It won't show the source but he says he has no leak parked, whatever revs, hot or cold. (Not sure I believe it but hey.)

 

Don't forget i have done a smoke test on the inlet manifold and at 10psi no leaks.

 

I will yield to Brutal and agree that it is a vacuum leak. One of the reasons I asked what the driving conditions were when the fault appeared. On my car it did not come up as long as I was at speeds above 50mph.

 

alright then try this one on for size
i had a 2011 xj 5litre that was over heating and seemed to loose coolant under the intake. I pressure tested it several times and held pressure to 15 psi everytime so i decided to vacuum the system. And low and behold itsucked air big time, you could see it coming into the coolant reservoir and hear it too. It was coming from the outlet pipe under the intake. Would hold pressure and had minimal coolant loss. But as the engine cooled down it sucked air into the system and created a air lock and then would overheat. New pipe and all fixed.. The moral. Just because it didnt leak under pressure doesnt meen it doesnt leak. Remember it runs under vacuum not pressure unless boosted and then only when rpm is up. Again if it were me, ide look at short term fuel trims and spray potential areas. And even do it when cold and seals are at their smallest and more prone to leaking
one other thing I just noticed, youre dual fuel and I dont know that system, I can only speak from gasoline system experiance on Jaguars since thats what we have here in the US