348 MAF adjustment and open loop?

Went out and got alligator clip test leads from harbor freight. Clipped one end to power wires and other to battery terminals, unit powers up, BT module lit up, connected with the app and bam, ready to go, phone screen shots below. So setnupnis teivila and literally 1 button push. Unit is designed to be a permanent install so the power leads are small. Clips worked great considering this is a one time deal to configure the open loop AF settings. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login

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Looks like fun.

 

I did the EGT readings today, factory non-cat 348, the gauge connected to the L&R Thermocouples, engine idling only, with the MAF pots as set some time ago - both at 382 Ohms. The first readings are before the cold engine start (ambient temperature). The subsequent readings are at approx. 1 min. intervals, total time about 10 min. The difference L-R started at about 8C (the top temp on the gauge is the left bank) then grew to the max. of 18C when the EGT-s were around 200C. When the EGT-s reached about the maximum they will go to at idle (~265C), the difference dropped to ~10C. I guess this was due to some equalisation done when the O2 sensors came into play (closed loop). For the next test (tomorrow, from cold engine), I will turn the pot on the left (cooler) MAF to make the bank run a bit leaner and see if its EGT gets closer to the right (hotter) bank.

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That is an awesome test! The car goes into open loop from cold start in about 3 minutes when the cats hit 300F I think. I assume once in closed loop changes to the MAF screw has no effect? Why not unplug the 02 sensors and keep it in open loop?

If I recall:
Higher number = Richer
Lower number = Leaner

 

I intend to do the tests step-by-step. Higher ohms should be leaner, lower ohms richer. Tomorrow, I will turn the cooler side MAF screw to leaner, say 400 ohms, and see what effect it has during open and during closed loops. With this test, I would like to establish whether to CO screw has any effect in the closed loop or not. If not, then my recorded difference of 10C at around 265C EGT-s should remain the same but I may see less difference during the warm-up open loop. The first observation I have made is that the difference of about 10% during the warm-up (open loop) dropped to just 4% when the EGT-s reached ~265C and, presumably, it was closed loop by then.

I prefer not to disconnect the O2 sensors as the engine will run pretty rich and probably have rather rough idle. Instead, I will do one test per day (no hurry) and see if I can first achieve EGT-s with minimal difference during the open loop. I have read that the difference L to R of the CO pots resistances could be as much as 100 ohms when the L & R banks are equilised using a gas analyser.

 

Mine we're off about 70 total between them before I touched them. But who knows someone could have touched them the caps we're off.

I suspect the maf screws absolutely have an effect on closed loop. That is a great test.

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Unfortunately, I will not be able to continue my EGT tests for some time. Hooked-up the EGT gauge today but, when I started the engine, it immediately produced a fairly rapid sharp metallic knocking sound. Switched it off quickly, probably after 3-4 sec. Cranked the engine briefly a few times (without it starting) and did not hear any knocking. Started it one more time and, after a very brief metallic knock the engine smoothened out, no misfiring, but then I heard a few occasional faint knocks (from one bank, I think) so I switched the engine off and will not restart it until I look at the pistons with a borescope and check the compression.

Checked the belt at one bank (removed the top cover) and it looked good and tight. However, I suspect that it skipped a tooth or two on first start-up. The belt has done just some 4k miles but it is about 10 years old. So, it looks like a major and possibly replacing some valves.

 

Wow that's crazy! Keep us posted.


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So, from now on, you alone have to handle all MAF adjustment experiments.

Thinking back now, my engine trouble (belt skip or something else?) may have actually started some time earlier. Since about 2 years ago, I lost the easy and smooth start of the engine I had before. Instead, it would always start with initially running rough/hesitating, for two-three seconds, at very low rpm and then smoothen-out and idle very well with absolutely no strange noises (14k miles only done). Perhaps today was the next step of something that was "cooking". I will report in a new thread once I make any findings.

 

Good idea to mark the belt and pulley with white paint marker so one can check from inspection cover of it ever is suspected of skipping.
I'll start my test on Sunday.

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Very interesting and valuable thread!!
After a lot of careful consideration, I have decided to go with a fully programmable aftermarket ECU, back when these cars were new the Motronic was top technology, but now we have much better technology, injector technology has moved on.....and I think there is a lot of potential these engines have which can be used with some new technology thrown at them.
I will install the ECU so it is fully reversible to factory if I ever decide to sell the car.
I am going up in injector size as the puny injectors these cars have are only good for about 320hp. 250cc quad spray is what I'm using. No MAF, all on TPS.
We have 98 octane here so we'll be tuning it on that which means we'll get as much timing into it as possible...

I will document the whole thing here, including dyno runs etc etc, I'm looking forward to getting the best from my F119G........

Sorry to derail the thread, back to regular programming.

 

Awesome look forward to it!

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Simple to set up.

 

Had logic reversed above, corrected here.
Got home early ran quick test. It is worth noting I read out here the 383 is a bit lean so it passes emissions and to richen it some for safety. That sounded reasonable. So I set my default to 380 not 383 to richen it a tad. The test unit I have the PLX WideBand 02 does Lambda and the conversion is as follows : Lambda to AFR: Lambda x 14.7. It does Gasoline also but the fuel may have ethanol in it or what ever so I'll use Lambda and convert.

With 14.6 being the industry standard stoich AFR value

• An AFR higher than stoich = lean
• An AFR lower than stoich = rich

MAF CO screw:

• Higher number = Leaner
• Lower number = Richer

Idle from cold

• Drivers Side MAF=380 LAMBDA AF = 1.3 / 19.11 AF
• Passenger Side MAF=380 LAMBDA AF = 1.3 / 19.11 AF

So it seems I am quite lean and 383 is not rich enough, at least not on my car, setting it to 380 made it leaner but not enough. I will let it cool down and set it to 400 and see what happens. Then down to 370/360/350. The nice thing is they are both the same, the exact same, so all seems healthy if one were to use that as some measure.

 

I let the car come up to operating temps, fans coming on and off. When you rev it to 2K ad 3K and 4K you can see AF dropping 17,16,15,14, there is no feedback from O2 so that makes sense.

At idle when cold at 380 the AF is 19.x.
At idle when warm at 380 the AF is 18.x.
At idle when warm at 350 the AF is 17.x.

At a linear rate I would need MAF screw set at 290 or so to get to 14 AF range. NO way I am doing that. So there more to it going on than meets the eye or so it seems. I can't test closed loop as the wideband takes the O2 sensor spots. For now I set MAF back to 383, verified AF is very close to the same on both banks at 18 at idle when warm. But at least I know both banks are acting the same, or so it seems.

Miroljub, on the odd stumble and gurgle at start up when cold for 2-3 seconds before settling in, mine did that too. I turned the air screws in 1/2 turn. They are both set to 2.5 out now (need mercury tube test to equalize them) and the stumble and gurgle for a few seconds is now gone. I realized when may car stalled with AC on when slowing down to a stop a year back and I turned the screws out. That's about when it started. Too far apparently. I turned them back in and its back to normal again.

 

Thanks for the info. I think this is exactly the reason for my "stumble and gurgle" (very good description for it). A few years ago, I decided to remove the idle adjuster screws to clean them up. I remember that one was almost closed and the other 1-2 turns out. It was obvious that the PO had "readjusted" them as there was some damage to the lock nuts. I think I set them both at 2.5 turns out without using a mercury balancer and left them there as the idle sounded good/smooth. The screws are probably out too much as my idle is 1050 rpm but I just found in the manual that it should be 950 +/- 50 rpm.

I will readjust them as per the manual and use a balancer this time.

 

What is telling is adjusting the MAF (on the 2.7 version) had little to no effect at idle. At one point I turned the MAF screw a full turn rich (probably somewhere around 280 ohms) and waited and saw no meaningful change at idle. If I revved it I could see a difference as rpm's climbed to 4k+ but again with 02 sensors plugged it it would go into closed loop. I am not certain those screws have any measurable effect at idle.

The car is open loop at idle(only when cold) and at WOT. Perhaps the 383 is for WOT conditions as its in closed loop every other second when it is warmed up until you hit WOT. It would explain why I see nothing really change at 1k- 2k rpm when the car is warm. It really looks like a predominant WOT setting.

Other threads where people claim to have changed the MAF and saw temp changes or voltage changes, I don't know as I've got Bosch Wide band data that says otherwise. BTW I also tried temp measurement using laser thermometer on the cats and on headers and on 02 bung itself (8 months ago) while changing the MAF screw setting (with different MAF's no less) and saw no effect there either.

So 2 different tests with 4 different MAF's and saw no temp or AF change at idle to speak of when altering MAF C0 setting changes at idle. I suspect one WILL see a difference at WOT but I hate revving the engine to red-line while sitting still, factory says 383, OK fine.

Ohh Miroljub, the car ran, idled, reved, started and stopped running absolutly fine with 02 sensors unplugged. Absolutely zero difference in sound and smoothness between normal 02 sensor operation and with them unplugged. I am sure AF is not optimal as you rev higher and higher of course, but it sounded identical, certainly no change in character or smoothness. (No matter what I did to the MAF screw)

 

After I established (in the other thread) that the compression at my right bank reads 240 psi and left bank 200 psi, I now believe that the reason why my right bank EGT, with both CO screws at 383, is about 10% higher than the left bank is the higher compression of the right bank that I currently have. Probably not only the right but also the left bank compression readings appear to be somewhat on the high side and this is likely due to excessive carbon build-up on the pistons, maybe more in the right bank for some reason. I will continue the EGT tests after I, hopefully, manage to remove the carbon with "Techron Concentrate Plus" fuel additive that I have ordered and bring the compression down to a more reasonable level.

 

I find that Techron does not remove it swiftly, but sea foam does, be advised it will smoke like mad however.

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My findings so far regarding CO screw (open loop mixture) adjustment:

1. Due to over-skimmed right head, I have 20% higher compression in the right bank (150 left 180 right) but the engine idles very smooth and runs well with the CO pots at 383 Ohm. Right bank EGT is 10% higher than the left, I believe due to higher compression.

2. Moved the left CO pot to 400 Ohm (leaner) hoping to bring the left bank EGT a bit higher and closer to the right bank EGT; after starting (cold engine), the engine almost immediately developed detonation in the left bank meaning that the change 383 to 400 Ohm caused quite significant mixture lean-out. What helped starting the detonation was probably also quite a bit of carbon that I have on the piston tops and 1+ year old petrol.

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3. After moving the CO pot back to 383 Ohm, the detonation disappeared.

The EGT gauge which takes simultaneous EGT measurements left-right was a great tool for my diagnosing that my right bank (due to over-skimmed head) has 20% higher compression. The only good result is that both banks have equal compressions between their cylinders - 150 left, 182-183 right.

In view of the higher compression that I have in the right bank, I will not experiment further with the CO pots adjustments based on EGT until I sort out the right cylinder head.

 

Are you talking about at idle or what rpm did it knock, I assume 5K rpm?
I noticed no change in AF at IDLE changing CO pot on my car but when reeving it I could see the AF leaner or richer at higher RPM's which was interesting but it was observational I did not record it I was not testing that aspect but I recall noting it in my mind as interesting, it was open loop (O2 sensors removed). It seems definitively WOT in open loop it has an effect, at idle I could not detect changes in AF. It hovered 18/19-1 at idle regardless of pot changes. As I revved it you could see the AF dropping to 12ish, it drops pretty quickly too. The bottom end of the AF scale was determined by the CO pot, but at idle it was unphased by changes in CO pot.

 

I had the detonation at idle, ~1100 rpm, after I turned the left CO pot to 400 Ohm. However, with quite a bit of carbon on my pistons and with "bad gas" my engine was possibly close to detonation anyway so the change 383 to 400 Ohm probably pushed it over to the detonation side. In view of this, I have to withdraw my earlier statement that "change 383 to 400 Ohm caused quite significant mixture lean-out". I will repeat the EGT tests with fresh petrol and after I have run the engine for some time with the Techron additive.

 

Contemplate using sea foam to remove that carbon.

 

Checked my idle screws today and they were both at 3 turns out (as I set them a few years ago). With this setting, my idle was at 1070, a bit too high. I turned them 1/2 turn in i.e. at 2.5 turns out and the start was immediately better with the idle speed now at 1000 rpm. Will fine tune (synchronise) them tomorrow using two vacuum dial gauges from my vintage 4-gauge carb synchroniser (hope it works, haven't used it for 30 years).

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If you can document it, I tried doing it with existing instructions and the banks almost dies and sputtered and generated no vacuum etc. Unplugging the IAC and blocking the ports into the plenum (as the fchat instructions state) results in an engine that simply does not run.