One more comment - mine also has the metal gasket TB shape. When I asked the dealer for the right gasket for my vin, they gave me the same paper gasket that does not fit. The gasket that works is the metal one (that from what I understand comes on the XKR).

 

Thanks for all of the feedback capitaineInsano, the symptoms do sound very much alike.

I went on an extended drive today, mostly interstate, and noticed that my fuel trims while driving are actually very much improved. I am well below +5 on both banks during most highway driving, with pretty much four zeros when accelerating. It's just so weird that when I am idling the fuel trims fly up into the positive teens and sometimes also do so when coasting. Sometimes coasting does not effect trims, sometimes it does. It wouldn't be weird if I could find a vacuum leak, but since I can't....it's weird.

What about the purge valve? Would that cause fuel trim issues if it was malfunctioning in some way?

 

I think the short answer is yes. If the valve is stuck open it allows effectively unmetered fuel vapors and air into the intake at times when the ECM doesn't expect it (if I recall correctly, idle and overrun are two of those times). On an X308 there is also a canister close valve - I don't know what might happen if it misbehaved.

You've made progress and I think you are going to figure this out!

Cheers,

Don

 

Evap purge valve part number...

LNG1515AA

or

LNC1515AA

I am at the beach for a couple of days and we drove the XJ8, so I can't check the part number on my XJR purge valve. I thought I might have one shipped to the house so it would be waiting for me when I get back. Depending on where I search I get one of the two above part numbers.

Anyone able to shed some light on that?

 

Does resetting the ECM first change the LTFT?

Don't forget, it is LONG term fuel trim, which is
derived from averaging STFT.

A reset causes the usual learning from base trims.

There is a longer thread on blocking off the EGR
where Avos is either the OP or a frequent poster.
It is blocked off on his XKR.

There are also the duct seals leading to the supercharger.
Sometimes they just get old, or earlier ones deformed by
getting sucked in. Air introduced after the MAF and TB
would certainly lead to high LTFT.

 

FWIW, when I first bought mine, the numbers were like that.

They came down when I switched permanently to using
ethanol free Shell V-Power Premium.

My idle is smoother when I dose the fuel with TC-W3 marine
two stroke oil at 1:500.

 

Doing a reset causes my LTFT to be at zero for a while, and the STFT run +15 or so until the LTFT learn that value and the numbers switch, with the STFT being zero and the LTFT being +15 or so. Until I start driving on the highway that is when they all get much better, normal in fact.

I though about deleting the EGR, but haven't looked into it. My understanding is that the EGR valve reduces the combustion chamber temperature, and the rest of the cars tuning is designed with that parameter in mind. I would be concerned it would somehow put undue stress on the engine by raising the combustion temperature above specification. But, like I said...I haven't actually looked into it.

Smoke testing and spraying....extensively, did not show any leaks anywhere around the supercharger or TB or intake pipes etc. etc. etc. That doesn't mean I didn't miss something, but I looked really thoroughly.

 

I am not where I can access my XJR, but I remember the purge valve has the external connection point with a green cap on it. The LNC1515AA picture I see does NOT have this connection point. The LNG1515AA picture I see DOES have that connection point. Jagbits is where I saw these pictures.

I guess that means my car has the LNG1515AA part number purge valve solenoid.

 

Sounds exactly like an air leak that still hasn't been found, sadly.

 

JagV8, could that as yet undiscovered air leak be the purge valve? Potentially?

One more piece of diagnostic information...
When I raise the RPM with the car in park the fuel trims are terrible, way positive; higher even than at idle. If the RPM are raised while driving, under load, the fuel trims go down to where they are supposed to be. In other words, there seems to be a leak when NOT under load that's not there under load. If I am understanding those results properly...

 

I suppose it could (but of course it may not be).

 

I got back from the beach today, a little sunburned but happy.

I decided to hook my mityvac vacuum pump to the purge valve to see if it holds a vacuum. Well, it's old and brittle. The little plastic vacuum line connection snapped off like a twig. Stellar engineering there....

Plus, the two other lines are on there SO tight. And, as always, there are extremely fragile lines connected so you have to use atomic force while at the same time not breaking papier mâché vacuum lines.

I did get those lines off, but there is no way to repair the vacuum connection to even test it. I tried liquid plastic cured with an ultraviolet pen. I tried epoxy. The connection is just too small and has to endure too much force to be repaired.

Now my car is down until I can acquire a new purge valve. Whether the old one was bad or not, I guess I'm getting a new one!!

 

I guess this was telling you to replace that thing.
I really hope it will solve your problem, you spent enough time on it.

 

The LTFT is expressed as a percentage of the baseline.

If you have a constant air leak of X, but the air otherwise introduced to
the intake is Z or 10Z, then the effect is X/Z or X/10Z. The percentage
of fuel over baseline to compensate is less when it is X/10Z.

Simples no?

 

Thanks plums.....I think.... haha

I'm guessing you're saying that the percentage of compensation needed is lower when X is a smaller percentage of Z?

Anyway, I want a new purge valve NOW! lol.

We went to see my mom while we were at the beach this week and she asked me to remove a small convex mirror from her passenger mirror (2007 Mercedes E350). I proceeded to break the mirror. I went to amazon.com and got a replacement shipped overnight and fixed her mirror the next day (making me $100 poorer, but that's the cost of clumsy). I want that kind of solution to my purge valve problem but I am not finding a good source for that. Amazon is no help. In the morning I'll call the dealer, worth a shot. If that fails I'll pay the crazy next-day-air fees and get a new one delivered Saturday.

 

I managed to perform a vacuum test on the old purge valve. I made a connection with epoxy and hooked up the mityvac pump. The valve would not hold any vacuum whatsoever. I put the air compressor hose at the connection and with a low flow I could feel air coming out of the side of the valve.

I don't know how conclusive my test was, but I lean towards thinking the valve was bad. I guess we'll see when I get a new one.

 

Hi Jeff,

As I mentioned earlier, on your '03 there are two valves in the evap system. The purge valve (EVAP or EVAPP) is on the left firewall near the shock tower, and the canister close valve (CCV) is down beneath near the second carbon canister. The EVAPP is normally closed, but the CCV is normally open. If the valve you tested was indeed the purge valve, then it has failed. But if it was the canister close valve, your test may be inconclusive.

The AJ26 / AJ27 Engine Management System manual has diagrams of the system. If you don't have the manual I think it is available from Gus at jag-repair.com. If you don't find it there, PM me your email address and I'll send it to you.

Cheers,

Don

 

It is the one up on the firewall (LNG1515AA per heritage site). The canister close valve (LNC1525AC) is not visible from where I am working.

The local Jaguar dealer was not terribly expensive, maybe 20% above online prices. They did not have it in stock however. I am getting one over-nighted and even with the next-day-air charges it comes out a little cheaper than getting it at the dealer. I should have it by noon tomorrow.

 

The purge valve came bright and early this morning. Interesting thing though, when I did the vacuum pump test, the new one didn't hold vacuum either. Perhaps there is some design difference on a Jaguar purge valve that renders the vacuum test useless for diagnosis?

I did a hard reset and installed the new purge valve. Upon initial start-up the fuel trims were perfect, all four of them. As the car approached operating temperature the trims climbed a little to between +4 and +9.

On a 10 mile test drive the trims are excellent on the highway, but still hover around +7 to +9 at idle and during coasting. The STFT will still occasionally jump to +15 or so during coasting, but they correct fairly quickly and the LTFT is only slightly effected.

This is certainly an improvement over the trims with the old purge valve. Also I never saw a crazy negative (-25) STFT like I saw occasionally with the old purge valve. It was either a positive swing or it was near zero.

I will drive for a few weeks and see how it all works out.

My conclusion? The purge valve replacement helped, but I think I still have a small vacuum leak somewhere that is preventing my trims from being perfect. But, they are probably better than the fuel trims of 75% of the cars on the road. I'm going to drive and enjoy until I get bored one afternoon and feel like poking around again to see what might be leaking. My leading suspect is still the EGR valve, but with LTFT below +10 I can't justify buying a $250 part.

 

The trims are one thing...but how about the shake? Is it still there\different?