TYPICALLY....Contaminated MAF sensors will under report at idle and over report at higher speeds..

 

All,

For anyone interested in raw data I have attached another OBD report here.
Tab 1 was City & Highway before I cleaned my MAF
Tab 2 was B-Roads/Highway/City after cleaning.

I think, it made a difference, but when you are in a "car induced heightened state of sensitiveness" one "feels" a lot of stuff, that might not have itīs roots in reality.
However, fact is, that my highest MAF reading, after cleaning the sensor (and not only the temperature one :P) was 300g/s which would result in proper 375 HP - which would be nice.

So here are the next steps of my "make it work, and make it proper" to do list:

1. Order a new MAF (just in case)
2. Do a Dyno run with the old MAF (to see whatīs what)
3. Do a Dyno run with the new MAF installed (letīs see what difference that makes)
4. Install new exhaust (hope itīll arrive next week)
5. Do a final Dyno run to see what the exhaust has changed (apart from the sound)

Happy to share the results, if anyone is interested.
Thank you all for your support, hints, tips and pointers so far - what a great forum!
Cheers!

 

TL;DR: Your Long Term Fuel trims (all of them, the entire matrix) should be close to zero, or at least below, say, 5%. OBD Codes trip at 25%.

Speaking in general, there is a base open loop fuel table per bank in the ECU. It is a matrix of numbers (boiling down to how long to keep the bank injectors open), indexed by Load and RPM. The upstream wideband O2 sensor (and the downstream Lambda to a lesser extent) offer the possibility of closed loop feedback, and adjust the base fuel table based on what is actually happening in the exhaust in terms of O2 content. That adjustment is another table, called the fuel trims, added on top of the open loop matrix, also indexed by Load and RPM. There is a 2 part adjustment for each Load/RPM "cell". One is short term number (what is happening now) that typically fluctuates quite a bit, and a long term number which is the average of the short term numbers over the last 2 minutes. The actual fuel table becomes the base fuel table + long term trim + short term trim. Trims can be positive or negative. On a perfectly running engine, with "perfect" sensors and no air leaks, all trims should be close to zero (the base table is great as is, no adjustment are necessary at any Load or RPM). On an aging car, these trims can develop over time, and eventually trip a codes when any one fuel trim hits +25% or -25%, meaning the feedback mechanism has to add +/-25% more fuel on top of the base table. I am sure there are complicating scenarios, e.g. when the purge valve is cycled to burn fumes, or when the OBD monitors run.

From there, there are general diagnostics scenarios. The most common test is to check the trims at idle (high vacuum). If high, it likely means air leaks, i.e. the sum total of all air leaks, is getting noticed by the ECU and will affect the drivability. Another is high trims at higher Load/RPM which points to the AFM. Negative trims can also point to the AFM, or the purge valve stuck open. Of course things can get more complicated: air leaks developing while the engine rocks at high torque, plugged fuel filter loosing pressure at high flow, poor reading of manifold pressure, or air temp, etc, etc.

Hope this helps.

 

^^^^^ +1

I'm relatively new to the world of fuel trims, but from what I've learned you want the two long tern fuel trims to add up to no more than 10%, i.e. not more than 5% each. Certainly zero would be best, but the cutoff for acceptable is 10% combined.

Z

 

Thank you both for your input and explanation.
So with 10īs on both banks my LTFTīs are telling me, is that I have an air leak in need to be found and fixed. Oh Joy!

Well, Iīll keep you posted and thanks again.

 

More than likely several leaks, all adding up to 10% extra fuel (not great, but not terrible either). There are so many opportunities for air leaks, you might want to look into a smoke test (injecting smoke under light pressure into the intake and see where it comes out). The fuel pressure vacuum line might be a good spot for injecting smoke. Best is to not remove anything and test everything while in place. You can of course reach out to a shop, or buy your own smoke tester. You can even make one with an old soldering iron and a bicycle pump.

 

HI , AN example of fuel trim for bank 1 ltft +10.......stft -4.... your having 6% fuel added this is under 10% so should be ok, Its best if both banks are running under 10%
You need to look at each bank on its own and dont add both banks to get your fuel trim.
Best to give your fuel trims for both banks at idle and at 2500 rpm when parked and engine up to temp this will show what if anything is wrong and lots of members that can point you in direction.

sorry but i didnt look at your file as my security advises against opening un known files.
Hope this helps............

 

Today I have:

• Ordered a new MAF (OEM @ local Jaguar dealer)
• Ordered Airduct Seals NJA3553AA & NJA3554AA
• Scheduled an inspection at my workshop, where we will do a smoke test

I would have ordered this accordion tube as well, but I could not find itīs part number - anyone can help out on this?


I WILL get to the bottom of this and Iīm not only expecting proper power delivery but better fuel economy as well (because it seems to me, my car is just burning fuel to compensate wrong air).

BTW -. would this mystery part tube be a good connection for a smoke test? (Blocking off the upper hole that goes to....errr....the motor )

Thank you all!

 

From SNG Barrett catalog.

 

Perfect - thank you, sir!

 

See if you can find the fuel pressure regulator at the end of the fuel rail. The vacuum line is great for this. It goes to the throttle body.

 

Makes sense. Thanks for your support, sir!

#15?

 

I would say #13, this way you can even test for leaks down #14 as well.

If you are paying for a smoke test, and end up with extra time, you can also inject smoke in the evap system (testing the purge valve, charcoal canisters, and all the lines front to back). Take pictures of the leaks for future repair. For the evap system, there is typically a valve with a green cap somewhere. The valve core has to be pulled, and smoke injected. I believe these valves are the same as tire valves, so a simple cheap tool is used to extract the core.

For power, have you checked the inter-cooler pump is operational?

 

Great suggestion and I will forward to my workshop (hoping they know HOW to do this properly)

Havenīt checked the inter-cooler pump yet and will search the forum to see how this is done.
Thanks - great input as always!

 

It's on the fender below the air box, and runs as soon as the ignition is on (engine off) so should be easy to locate. It's failure is a fairly common problem apparently, and folks have found a replacement Bosh pump for the job.

 

Dear all,

Hereīs an update on my endeavors:
- I scheduled a smoke test with a Jaguar dealer
- The smoke test showed, that the engine itself does not have any leaks (which was great and a bit disappointing too, as I thought it might be a seal or hose which could be easily fixed - case closed)
- Thanks to fmertz suggestion, I asked them to test the EVAP system too.

What they did is this:
- remove the driver side front wheel
- remove the wheel lining
- disconnected a hose that led into the purge valve and put pressure to it via a hand pump
-. no pressure was retained and so they said "Itīs not working. We are going to order a new one"

Fine, I thought - maybe the purge valve is stuck open and that explains my too high Fuel Trims.
Yesterday I had another appointment with the workshop and while they were disassembling the wheel lining I took a look at the part they wanted to install.
It was this one:






This sits somewhere beneath the compressor.

So, they had to order the next. hopefully correct part.
It was readily available and so I could come in today.
The part should be: LJB 1515 AA, however this part has been changed by Jaguar to LJB 1515 AB - no other purge valve is available from Jaguar.
Now, what I have found is, that it seems to be the same part, with one, outstanding difference:


On top of the valve, there is a small outlet/inlet/tube that the old valve did not have.
I donīt think it should be connected to anything, as usually, any hose connector widens up a bit, but this one is plain straight.

Well, I had it installed and OF COURSE (this is not my day) my OBD2 Scanner stopped working exactly then and there, so I could not check if Fuel Trims are down. Gaaahhhh
They applied the same hand pump pressure test and....no pressure was held.
We turned the ignition on, even started the car - no difference and I expect, that this is NOT the way to test the functionality of the purge valve, is it?
Generally, itīs frustrating to have these "Millanics" (Millenial Mechanics) fumble around your car and you need to tell them exactly where is what and what you want to achieve. Most of them have no clue.

However, back at home I was able to get my OBD2 Scan working again and....Trim levels have gone UP.
But I need to gather more data during a longer run and take a closer look at it then, comparing to data I have from before the exchange.

So far, so...whatever.
Does any of you know what to do with the mystery tube? Should I block it off, so it works like the old one?

This is getting tiresome, I know.
Thanks for your time and support.
Cheers,
Berglmir

 

The original part above is the supercharger purge valve, completely different purpose.

For the evap, you should really ask them to inject smoke to find the leak. Fresh air with a hand pump is ok for a pressure test, but defeats the purpose of locating the leak(s). Normally, if the purge valve is stuck open, you get a code (P0422?), and you normally tend to run too rich (it's constantly releasing fuel vapors in the intake), so trims trend negative. I am with you on the purge valve. They are computer controlled (they cycle on and off quickly), tend to be noisy, and a source of complaints, hence the multiple versions over the years. There was even a blanket available for sound proofing at some point, which trapped moisture and rusted the valve. FWIW, don't throw the old one out just yet, it seems like the root cause is still to be discovered.

Best of luck, keep us posted.

 

As always, thanks for your constructive feedback, sir!

The question is: Should the purge valve retain pressure when applied during testing? Ignition ON/OFF? Engine running?
The new one does not! (The Millanic even blew in the low tube before installing it and he could just breath through)
Itīs all very confusing....and a bit fascinating

 

Since you believe you have lost midrange punch is it possible ( your engine would be going from vacuum to positive pressure) that the mechanics stressed a plastic/rubber component while doing the prescribed work and thereby created a slight crack which only opens with the rush of positive pressure?

Good luck on your search.



wj

 

A possibility for sure.
I will book a session on a dyno soon and see, what power the car actually has right now.
I have installed a new exhaust last week (I will share in the Forum as soon as I have some video/sound samples) and the new purge valve installed.
I know there is something amiss due to the high Fuel Trims, but my feeling of lack of power might be totally subjective.
If the dyno run tells me the power is almost up the OEM specs then I might be a little more at ease - but somehow I doubt that.