348 MAF adjustment and open loop?

At least for a 348 with 2.7 the MAF screws are ECU trim for fuel I assume in closed loop in conjunction with the 02 sensor. I know the 02 sensor generate voltage regardless of loop mode. But when in open loop the ECU runs off a fixed table and ignores dynamic values.

To that end:
1) The 02 is ignored ion open loop but does the MAF screw adjustment have any effect on AF in open loop?
2) Is the threaded plug #35 supposed to be for a wide band, seems odd as its on 1 cylinder port if so. Definitely can't use tail pipe as the muffler shares banks and there is is no other port to use.
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Threaded plug #35 definitly not for a wide band, I spun mine off with an impact and the threads are way to small more like a thermocpuple probe as it has a needle hole in a cup under the #35 plug.

Still left with the question does the MAF screw adjustment have any effect on AF in open loop?

 

The power of search... apparently the MAF screw is open loop setting meaning I can swap the 02 sensor for a wide band sensor then when warmed up set the MAF's correctly for AFR 14.7:1 at idle.
https://www.ferrarichat.com/forum/threads/how-the-maf-co-screw-does-not-matter-in-closed-loop-operation.201174/

 

Just electronic copy, no paper copy.
In response to what I'm trying to do, yes understanding. I was thinking of tuning idle AF and I thought about the MAF screw but then I thought it would not work in open loop since in open loop it runs of table values not dynamic values so I was looking to understand if the MAF screw had effect in open loop. So understanding of MAF screw and open loop is all. When I found that thread I realized I can unplug 02 sensor and plug in wide band and tune idle AF once warmed up. Or so I will try.

 

Yep the PDF version of the WSM stops at C68. Thanks!
I ordered a wide band, should be here in 2 weeks or so, back logged. I'll write it up assuming the MAF screw affects open loop that I am still not certain of. We'll see

 

Interesting I have never seen the "Ferrari tester adapter Motronic 2.7".

 

Right, I will set the AFR at idle since closed loop has no effect on MAF resistance setting. The MAF setting is open loop which is presumably below 2K rpm and a WOT. In between is closed loop so driving with AFR reading may provide interesting information but nothing changeable noting the manual states you cannot control that as it is under ECU control. The issue is "I think" the banks need to be balanced first as the air screw affects idle AFR as well. I tried with vacuum gauges, did not work need Mercury ones. I may take it to factory dealer and have them balance banks since apparently there is a Motronic 2.7 reader they can use to do it.

 

Since this is one time idle tuning (maybe 2 times) and not dyno or road tuning across the whole band I went with this. I'll set the power supply with alligator clips and clip to charging posts of the battery, basically use it like a portable unit. Units like the LM1 run off cigarette lighter but the displays are primitive. We'll see how it works.


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Yes definitely saw it, thanks for the reference for others as well. I decided to use wide band instead.

 

Interesting yes, will definitely work better than a temp gun on the cats! You said you had Zietronix ZT-3 and wide band sensor, why not use that?

 

I am assuming we can use a wide band to tune the CO screws on the MAF to match AFR to each other thereby equalize the banks at idle, at least as it relates to fuel not air using air screws.

 

Exactly, this is why I asked the question up front, the system uses table values for open loop begging the question what does the MAF CO screw then do? Everyone says it affects open loop but I am not so sure at all.

Regardless I will try and I will as you say equalize the banks with 383 as a reference as opposed trying to hit an AF number. But I suspect 383 is on the rich side. Who knows I may need to richen up a bank perhaps one bank is lean at 383. I am quite ok with richening up a bank to meet an AF bit not so keen to go below 370 or so. In the end I will see what it is then try to equalize them using (370-400)ish as the operating range and the numbers are the numbers once equalized using the lowest banks number as the floor. Equalizing is the key.

btw I have never seen 383 as a setting in the manuals. I have yet to read where someones was actually 383 before they touched it.

The flip side of fail safe rich at idle mode is it fouls plugs when idling and cold . It's also only open loop while cold once warmed only (about 300 degrees on cats) way before water or oil temp come up to normal. Once it hits 300 its closed loop which begs the question, why even bother with MAF screw if it only does something when starting and cold. Although I thinks its open loop at WOT. Its just odd...

Marco clearly said it affects it in the thread but a guy at the end posted he tried and nothing happend. maybe did not wait for the effect to materialize its not instant. Ehh we'll see.
https://www.ferrarichat.com/forum/threads/how-to-set-the-maf-screw-accurately-on-motronic-2-5.202083/

 

Makes sense, very similar with Wide band except waiting for closed loop, that wont happen. The EGT method may actually be better but will take longer for changes to reflect plus you can drive in closed loop and see whats happening. Its tempting to pull the cats and weld a new bung for wide band.

I plan on trying the air screws again, mainly because the posts out here talk about blocking the IAC ports into the plenum to do this test. I can tell you if you do that the engine all but wants to die and throws a CEL. I did it, it was VERY clear that write up was a guess, as it simple does not work, block the IAC port into the plenium and listen in horror to what the engine does. The actual by the way manual has no mention of blocking ports only to stop the IAC from working presumable by unplugging them. So I will retry with what the manual says.

It also talks about disconnecting the Compensation Solenoid Valve. I assume that clamping the hoses from the Depression tank #2 will have that effect.

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Right I read that, I assumed at idle it was in a position that that is triggered differently when unplugging it. Like perhaps unplugging it opens it, it is odd that the manual goes out of their way to call out disconnecting it so I assume disconnecting it changed its state when the car is running. But it is a Ferrari manual so perhaps it is not needed to do so.

 

PLX wideband with phone BT connect arrived. Going out of town but will detial what I did and how it worked and what the 383ohm maf settings did, dead sure they are way off and what they were adjusted to of different on my car. I'm in NJ if anyone wants to use it. Image Unavailable, Please Login Image Unavailable, Please Login

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