I've got a MacBook Pro but none of that should causing issues. Don't know why it came up owner protected but since you don't have a password protection on it must be something on my end.
As for K&N I've heard/read pros and cons for them on the Land Rover forum but figure, why mess with it. No sense in causing issues if you don't have too!
Thanks again for the info and help.

 

SAAB turbos switched from AMM meters to absolute barometric pressure sensors in the mid 90's. Minor air leaks on those would not throw a code and the engine would run fairly normally until boost was called for. I don't know why everyone didn't switch to these sensors.

 

The real reason everybody has gone to Mass Air Flow (MAF), instead of using various atmospheric and manifold pressure sensors (a speed/density system), is because MAF is significantly more accurate than speed/density, and with the strict emissions standards, along wiht high fuel mileage reauirements. it is necessary to control the engine as precicesly as possible. The speed/density systems are simpler, and probably more reliable, but not precise enough.

 

Please excuse me for digging this old tread up, but this morning I noticed something strange and I can’t find reasonable explanation for it.
I have ’98 4.0 XJ8 with AJ26 engine. My car have only upstream narrow band O2 sensors (a little bit strange, but it doesn’t have O2 sensors after cats).
Few days ago I noticed that my long term trims are quite negative on both banks (-13.3 and -15.6). I looked at MAF readings and they seems to be just as they must be. O2 sensors looks “alive” (beside that my OBD scanner is quite slow).
However today I decide to play a little bit and to see what will happen if… I pull engine oil stick out of seat. And the result is that nothing happened.
After that I decide to provoke huge vacuum leak, by disconnecting part load breather. When I done this I noticed that MAF reading goes UP.
Really I expect exactly opposite reaction for the MAF. In my understanding, plastic PLB hose is connected bellow throttle body directly in the manifold, by disconnecting it I put a lot of unmetered air directly in the engine, however I saw 6.5g/s reading of MAF. What can cause this?
Also I can swear, I heard small vacuum leak on bank 2 somewhere between 1st and 2nd cylinder, and Bank 2 LTFT looks more negative (running richer) than Bank 1.
I already measured lambda values with wide band sensor (innovate LM-1), and on idle and part throttle everything looks ok – lambda 1 for both tailpipes. On Full throttle it seems to be a bit richer than needed – around 0.75, but I suppose this is also normal for factory tune (too much on the safe side).


Regards,
Christo

 

Not an engine I know but -ve trim means it is subtracting fuel as the O2s are saying it's otherwise running rich.

I suppose it could be due to MAF wrong readings, but no doubt other things (bad injectors etc).

Causing an air leak is just going to confuse things, I suspect.

I REALLY think you should have started a NEW thread and in the correct forum!

 

Forget exact problem mate!
I suspect leaking injectors (they are quite old now days) as a reason for negative trims. I'll solve this sooner or later.


I’d like to draw your attention to other part of my post.


What confused me most was, that with disconnected PLB, I get raised MAF readings.


From this I can suppose there is some routine in the ECU, to go from direct MAF readings to calculated MAF (load), based on speed/TPS, when ECU thinks direct MAF readings are quite off.


For sure this is only my guess trying to explain why I saw higher MAF readings through OBD, while I expected to see quite lower.
Maybe there is other more evidential reason for this.

 

I don't think you should concentrate so much on the MAF signal and disconnecting the PLB. Everything starts with the negative fuel trims. Negative trims are a rarity for the most part, so we need to find a possible cause for the perceived rich running condition.
I would suggest checking the voltage drop between the car body and the engine itself. Connect a voltmeter to clean spot or bolt on the engine, and the other lead to a good spot on the body there in the engine compartment. Start the engine and let it idle. Anything more than .15 volt is trouble. More than .6 volt is real trouble. Poor engine to body grounding will drive the O2 sensor signals falsely high, which is what happens when the engine is running rich. The ECM won't know any better and will drive the trims negative in response.

Worth a look, and easy to do.
Good luck!

 

Thanks for this advice Steve!

It is logical, but I’ll never think about this

Unfortunately that wasn’t my case – just measured 0.02v between aluminum thermostat tower and left shock absorber top mount bolt.

I didn’t mentioned that I already measured fuel pressure and proper operation of fuel pressure regulator and everything is ok.

So until now fuel pump & FPR – excluded, MAF – excluded, O2 sensors – excluded (every time I saw failed O2 sensor, it was failed showing lean condition so ECU adds fuel, not subtract).

I’m heading for at least one leaking injector on both banks, nevertheless I already gave them for cleaning (about 6months ago), and I reinstall them with new rubber seals.

I ordered few weeks ago exhaust manifolds from newer type (2 by 2 divided cylinders), and another intake manifold (previous owner was drilled current one to put LPG, but I don’t like position of nozzles, so I’ll relocate them).

While I swap manifolds, I’ll inspect again injectors if I can find some evidence for bad one.

As soon as I know that real mixture is Ok (I already checked with wideband sensor) I know, that I can’t break the engine, and I know I’ll find reason for this problem at some point.



I’m concentrated on MAF readings, while I pull away PLB, because it is not logical for me, and that means that my logic doesn’t follow DENSO logic J

Few years ago I spent so many nights trying to read description of BOSCH motronic ME7 system, because I’d like to know how exactly system operates, what the system takes into account, when switches from one map to another, when apply some fueling and ignition corrections etc.

Unfortunately this document was „auf Deutsch“ J And I know almost nothing in German language. I wasn’t only one person trying to understand this, even one guy was joking that easiest way to understood most terms for injection and duration is to watch an old German porno. J

However at the end I know most interesting strategies of bosch motronic quite well. Btw their strategy for fuel trimming is a little bit different, and maybe better one



Now I saw something that I doesn’t expect, and I’d like to know what happened.

I’m sure there is a reason for these higher readings, and I’d like to find it.


Cheers,
Christo

 

The attached files are excellent write-ups from XJRGUY.


Fuel Trims Part 1 - Primer Rev2 by XJRGUY.pdf
Fuel Trims Part 2 - Using Fuel Trims by XJRGUY.pdf

I wanted to put them both in one place and renamed them slightly so others could easily find them.

Thanks XJRGUY!

 

LOTS of great information!
Do we know what PC Scantool is used here?
I recognize the IDS/SDD but not the one that generates the fuel trim tables.
Many thanks to all.
Patrick

 

The one that generated the Fuel Trim tables is one that is no longer supported, called ScanXL. Was put out by Palmer Performance, but they were purchased by Auto Meter some years back. That outfit just let it languish. I believe you can still purchase it, though, and when you learn to use it, it's one of the best out there.

Cheers,

 

Thanks. I'll see what I can find.

 

I was just looking at mine!