https://www.jaguarforums.com/forum/x...-fixed-233152/
That's how I fixed it

 

Here is an update if anyone can figure it out. The short and long fuel trims do not change by revving the engine 1500 2000 2500 RPMs the long fuel trim is at 19.5 and fuel trim as at 25 at all times. The motor has been smoke check twice and apparently nobody sees any leaks... if anyone out there can help me sort this issue out and find the correct fix I will pay them $100 via PayPal or whatever that ends up in pounds if you're overseas I'm serious I can't even drive this thing

 

I just went through this on a 2005 XJ8L. The LTFTs were +25 at idle, but settled down to under +5 by 2,500 rpm. STFTs were 0 to +5 at idle, falling to maybe -20 at higher revs. P0171 and P0174 were persistent.

I smoke tested the intake via the main intake hose by removing the MAFS and taping over its port, and propping the throttle butterfly valve open. I inserted the large smoke machine cone into the air intake hose and filled the system with smoke. By this method I found a small crack in the vacuum hose for the fuel pressure sensor. Very easy to replace that hose. While I had the MAFS out I cleaned it thoroughly with about half a can of CRC MAFS Cleaner spray.

I disconnected the main intake hose from the throttle body and cleaned the butterfly valve and bore as well as I could without removing the TB, using a small plastic-bristle bottle brush and throttle body cleaner spray.

I then disconnected the crankcase breather hose and connected the smoke machine to test that hose and the Bank 1 camshaft cover. No smoke leaked anywhere, but there was oil around the base of the crankcase vent (the circular disc that looks like a PCV valve), and around the VVT solenoid. If oil can get out, air can get in. I replaced the two O-rings on the stem of the crankcase vent that fits down into the cam cover, and I replaced the VVT solenoid seal (both very easy jobs).

I did the same thing for Bank 2 by smoking via the full load breather hose, and by this method I found a leak at the base of the oil filler neck. I should have already known from the oil seepage there. There is a small metal tab that locks the neck in place. Carefully pry that up with a small flat-blade screwdriver and the neck un-threads counter-clockwise. (The supercharged engines do not have the oil filler neck - the cap fits directly to the cam cover). I didn't have any O-rings in stock that were as large in cross-section as the original, so I just added a second O-ring to the existing one and when I threaded the filler neck back in it felt nice and snug and no more leak. I added another thinner O-ring to the oil filler cap for good measure. The VVT solenoid gasket was leaking on Bank 2 also, so I replaced it.

I replaced the O-rings on both breather hoses/pipes even though the smoke machine didn't show any leaks from those connections.

After the above work, the fuel trims were improved, but LTFTs were still around +20 and STFTs were about +1 or +2 at idle.

Fuel pressure was good at 55 psi or so, but I replaced the fuel filter just to rule it out. The old one was full of black gunk, but replacing it had no noticeable effect on fuel trims.

All along, the MAFS signal had looked plausible on the scan tool, at 0.01 lb/4.5 gm per second at idle and climbing with throttle. But I began to suspect that the MAFS was a bit lazy. So I ordered a cheap SKP MAFS from Rock Auto and installed it in the car just to see if it would make a difference. Surprisingly, the fuel trims were WORSE! But this made me ponder whether the original MAFS might be out of spec. So I ordered a genuine Denso MAFS from Parts Geek and installed it. I watched the fuel trims at idle and, amazingly, the LTFTs began falling from +20 to +18 to +15.... I took the car for a good test drive, and by the time I got back, at idle the LTFTs were at +2 and the STFTs were at 0. P0171 and P0174 did not recur. Problem solved!

Parts Geek has two Denso MAFS listed. I think I ordered the one that is slightly cheaper and is listed as First Time Fit. The Denso part number is 197-6030, but unfortunately that doesn't show up in the Parts Geek listing.

I hate swapping parts experimentally, but at this point in time probably all X350s could benefit from a new MAFS. I would highly recommend a genuine Denso.

Cheers,

Don

 

Wow, well done!

 

Thanks Don mine is an 04 so I don't have VVT so that is all ruled out. From what I understand when the fuel trims do not come down when revving it is probably not a vacuum leak correct me if I'm wrong on that. I did change the mass air flow sensor so the original one might have already been good but the second one was a Denso and didn't change anything please advise thanks

 

Hi viper1996,

Is your car supercharged?

You originally reported that the fuel trims came down at higher revs, but now they do not. What has changed between those two points in time?

Cheers,

Don

 

I fixed a couple of vacuum leaks that's about it doesn't seem to make any sense.

 

Hi viper1996,

In looking back to Post #10, I see that your engine is a 2004 supercharged. This is the reason you don't have VVT. Also, I see that you have an aftermarket intake pipe installed, and the rubber hose that connects to the ovate air intake tube does not fit well and is not secured with a clamp. That connection appears to be entirely inadequate. It is very likely that once the engine begins inhaling air, the rubber hose deforms and allows unmetered air to leak into the intake. It might not leak during a smoke test at <1 psi, but under engine load it surely needs a better fit and a clamp.

P.S. It helps others if you will edit your signature to include the year, model and engine of your Jaguar so this info shows up in all your posts.

Cheers,

Don

 

Viper did you see my thread on high fuel trim fix?

 

Yes I did Alex. Nobody has worked on the car other than me so I know that wouldn't be the problem on my particular vehicle.

 

What I got out of it is that anything you do before the MAF , if screen is sitting incorrectly , larger diameter pipe and such can screw up MAF reading so it might not be a vacuum leak at all. At this point if I was you , I would compare MAF signal readings from a similar car this will tell you if MAF sensors are the suspect

 

Alex,

viper1996 has a very obvious leak point in his air intake hose where it is slipped on to the ovate air pipe that goes back to the throttle body. The hose is not fitted well, and there is no clamp. See his photo from his post #10 that I copied in my post #28. The hose is in the upper right corner of his photo.

Cheers,

Don

 

Wingrider. do you remember who you ordered the gaskets thru?

 

Wingrider,
Where were you able to source these internal gaskets from? My shop has found the leak but cannot find these internal gaskets.

 

Okay I finally had some time to look theJag over really well I put my scanner on it and the fuel trims do come down under a load while driving. High and low trims come down at least 10 points depending on the RPM as I go higher even more. So now I am thinking it would be a vacuum leak correct? Now the hard part would be finding it it's been smoked check twice even by jaguar and they say there are no vacuum leaks but I'm guessing there is. As Don noticed I may have a potential leak in a couple of spots on the intake which I'm going to seal off and retest but I believe that will not be the problem but I want to rule it out. When I spray carb cleaner on the breather hose nothing changes and I did have the intake strapped down previously but have left it off because I keep messing with the whole system but I am going to double-check for sure

 

Just park with a hot engine. Look at all 4 trims at idle, then rev. If they come down then yes.

 

Okay I will try that tomorrow and post results thanks

 

Viper did you ever get yours sorted?

Going through the exact same thing with my 2004 XJR. Every time I post about it people constantly tell me its a vac leak. Had the smoke test done 3 times by 3 seperate Jaguar garages and none of them can find a leak. Really frustrating.

Just a thought, what should the MAF read range wise? Like what is the maximum reading you should get?

 

XJR_hunter
When my 04 XJ8 was having a similar issue.
With no apparent vacuum leak, even with a smoke test.
The solution was, the eight rubber gaskets, inside of the intake manifold.
Easy fix AFTER the manifold is off the car

 

Hi XJR_hunter,

Here's a case study I posted in another thread. I was working on a normally-aspirated car, but the procedure is very similar on the supercharged cars:

"I just went through this on a 2005 XJ8L. The LTFTs were +25 at idle, but settled down to under +5 by 2,500 rpm. STFTs were 0 to +5 at idle, falling to maybe -20 at higher revs. P0171 and P0174 were persistent.

I smoke tested the intake via the main intake hose by removing the MAFS and taping over its port, and propping the throttle butterfly valve open. I inserted the large smoke machine cone into the air intake hose and filled the system with smoke. By this method I found a small crack in the vacuum hose for the fuel pressure sensor. Very easy to replace that hose. While I had the MAFS out I cleaned it thoroughly with about half a can of CRC MAFS Cleaner spray.

I disconnected the main intake hose from the throttle body and cleaned the butterfly valve and bore as well as I could without removing the TB, using a small plastic-bristle bottle brush and throttle body cleaner spray.

I then disconnected the crankcase breather hose and connected the smoke machine to test that hose and the Bank 1 camshaft cover. No smoke leaked anywhere, but there was oil around the base of the crankcase vent (the circular disc that looks like a PCV valve), and around the VVT solenoid. If oil can get out, air can get in. I replaced the two O-rings on the stem of the crankcase vent that fits down into the cam cover, and I replaced the VVT solenoid seal (both very easy jobs).

I did the same thing for Bank 2 by smoking via the full load breather hose, and by this method I found a leak at the base of the oil filler neck. I should have already known from the oil seepage there. There is a small metal tab that locks the neck in place. Carefully pry that up with a small flat-blade screwdriver and the neck un-threads counter-clockwise. (The supercharged engines do not have the oil filler neck - the cap fits directly to the cam cover). I didn't have any O-rings in stock that were as large in cross-section as the original, so I just added a second O-ring to the existing one and when I threaded the filler neck back in it felt nice and snug and no more leak. I added another thinner O-ring to the oil filler cap for good measure. The VVT solenoid gasket was leaking on Bank 2 also, so I replaced it.

I replaced the O-rings on both breather hoses/pipes even though the smoke machine didn't show any leaks from those connections.

After the above work, the fuel trims were improved, but LTFTs were still around +20 and STFTs were about +1 or +2 at idle.

Fuel pressure was good at 55 psi or so, but I replaced the fuel filter just to rule it out. The old one was full of black gunk, but replacing it had no noticeable effect on fuel trims.

All along, the MAFS signal had looked plausible on the scan tool, at 0.01 lb/4.5 gm per second at idle and climbing with throttle. But I began to suspect that the MAFS was a bit lazy. So I ordered a cheap SKP MAFS from Rock Auto and installed it in the car just to see if it would make a difference. Surprisingly, the fuel trims were WORSE! But this made me ponder whether the original MAFS might be out of spec. So I ordered a genuine Denso MAFS from Parts Geek and installed it. I watched the fuel trims at idle and, amazingly, the LTFTs began falling from +20 to +18 to +15.... I took the car for a good test drive, and by the time I got back, at idle the LTFTs were at +2 and the STFTs were at 0. P0171 and P0174 did not recur. Problem solved!

Parts Geek has two Denso MAFS listed. I think I ordered the one that is slightly cheaper and is listed as First Time Fit. The Denso part number is 197-6030, but unfortunately that doesn't show up in the Parts Geek listing.

I hate swapping parts experimentally, but at this point in time probably all X350s could benefit from a new MAFS. I would highly recommend a genuine Denso."

One thing to check specifically on the supercharged cars is the air intake pipe with the integral Helmholtz resonator chambers. The lower cylindrical resonator is ultrasonically welded to the pipe, and that weld tends to fail. Remove the pipe and inspect the weld, gently pushing the cylinder side to side to see if the weld has come loose. I also had one S/C car on which the right upper resonator (left when viewing the engine from the front) had deteriorated at the corner of the plastic and had very small cracks that were leaking. I found that with the smoke machine.

Another thing to be aware of is that most smoke machines produce very little pressure, typically about 1 psi, to reduce the risk of damaging fragile EVAP system components. Engine vacuum at idle will typically run around 20 in. Hg., or 10 psi, so some leaks can be difficult to find with a low-pressure smoke machine.

Cheers,

Don