You can take the voltage (DC) readings on the end pins - I guess they will be somewhere around 6V, one side somewhat higher than the other. Otherwise, you should look at pages C69 to C95 of the manual for M2.7 intake adjustments and balancing.
Yep I read through those, you sent them to me months ago, thanks for that. Thats where the specs are for tpc and geometrical balance. One side on the bench is 11 ohms and one is 6. I have 5 Bosch iacs, 3 are new, I tested them on the bench and picked the 2 with closest values to each other to stick in. Some were 6.4 some 6 some 7.1 for example for the same pin measuring ohms. Not sure it makes a difference but I feel better with the 2 closest match. Sent from my SM-G990U using FerrariChat.com mobile app
Does anyone know were 383 ohms for MAF comes from? I have WSM and sections below but I find no reference for the 2.7 ignition/injection in any of those, I may be missing a section? Image Unavailable, Please Login
I feel its come from someone just measuring one assuming its never been adjusted since leaving the factory? Or measuring a new one off the shelf. This thread has got me curious as to whats going on with the AFR in these cars, I think I will shoot up to my friends place and do some Dyno runs...
Been thinking through it..... The MAF adjustment sends trim signal to the ECU, but that is only read when cold or in open loop, or if you unplug the O2 sensor when warm as understand it. Which I will do to verify that's the case, the car should go from nice idle back to total train wreck. So the MAF being off coupled with out of balance intakes can really affect starting and cold idle. I seriously doubt my IACs are off or the cause I am 90% sure it the MAF setting layered with intake balance issue, manual is clear if there is too much variance between at 20, 24, 60, 80 % throttle open with TPS it can cause idle instability. Even slight MAF CO2 screw changes can have a large effect. Once I get the car it just idle I can dial it in open loop with my PLX wide band. I can hopefully determine where the MAF's are, to do that I can pull voltage from the O2 power wire and block the air injection since > 450mv is rich and 450mv < is lean. That "should" give me direction on which way to adjust the MAF screw to try and get the car to idle, so I can adjust it from there. If it was 1 bank it would be easy but its 2 so cant just arbitrarily make both richer or leaner. I screwed up one of the pins by crimping it wrong, so I have to order another set of plugs, UGH, here is the first harness. Need 2 so I can synch the banks. Harness into the male end and the female end into the TPC. Then I can tap voltage from the alligators in real time. Miroljub gave me the idea for the harness. Image Unavailable, Please Login
If the IAC's weren't opening it probably wouldn't start at all. I am not so sure about this theory of disconnecting the O2 sensors. I have tried this on my car, and it makes no difference to the idle at operating temp. Also, I noticed adjusting the MAF did not make any difference to the voltage coming off of the O2 sensors, which are both brand new BOSCH replacements which tells us it is not affecting the idle mixture. So I left the MAF adjustments alone after that. The biggest difference and improvements were made by adjusting the air bleeds on the throttle bodies. But I am going to shoot up to my friends shop and run the car on the dyno with the gear on it and look at its AFR on light throttle cruise, idle, and full throttle just to see what its doing. I feel there is a lot of urban myths going on here, some useful info some misleading......
Takes about 2 min for a change to register. Blip the throttle and let it settle about 2 min, the changes are not instantaneous. MAF screw is irrelevant to when in closed loop, so unless you unhook the 02 sensors you wont see any change at all as far as I know. Sent from my SM-G990U using FerrariChat.com mobile app
I understand that, it still makes no difference. I'm just suggesting there could be a misunderstanding about how this system actually works.
Few links talking about this. https://www.ferrarichat.com/forum/threads/how-the-maf-co-screw-does-not-matter-in-closed-loop-operation.201174/ https://www.ferrarichat.com/forum/threads/wrong-maf-co-settings-on-a-motronic-2-5-car-can-cause-fires.204039/#links https://www.ferrarichat.com/forum/threads/how-to-set-the-maf-screw-accurately-on-motronic-2-5.202083/#post-137893700
Nice to have them all in one spot, I have read these over and over.......lots of info in those threads.
I don't know where exactly it came from but the 383 Ohm of the pot on the MAF is considered "baseline setting", not only in the case of 348 but also in the case of Saabs, Volvos, Porsches etc. which use similar generation ECU-s and MAF-s. Some years back, I bought a new Bosch MAF (same generation as the 348's) for my Volvo with the CO pot factory set and capped - it measured exactly 383 Ohm. In any case, the MAF pot resistance is applied between the ECU Pin 43 and ground meaning that function of the Pin 43 is mixture trim. It is possible that the 383 Ohm was derived from what the ECU requires to have its mixture trim at "baseline", i.e. to be neither on the rich nor on the lean side.
Makese sense thanks. Making them both 383 likely puts the banks out of synch as well until its adjusted per car. I know my cold start issue started years back when I set them to 383. And it's real cold here now. After a rebuid you can assume they would need to be reset. My friend will measure his car after Christmas when he's at that house and I want to get a sense of how much it was adjusted. Not relevant to my car I know.. but just a data point. I'll bet one is below 383 and one is higher. Curious is all as I am 100% sure those pots have never been touched. Sent from my SM-G990U using FerrariChat.com mobile app
I'm also going to take my 348 up to my friends dyno, we'll look at this in detail, I wanted to do it yesterday but he has two cars to get done (race cars for tuning) so I can't get on the dyno until maybe Friday which is a rolling road type, not a cheap Chinese hub dyno. For the idle, again I will try this disconnecting the O2 sensors and instead of trying to read the narrowband ones on the car, we'll have the dyno's wideband connected and look at that and see what we can achieve by adjusting the MAF trimmers. In fact I can probably just remove the ones on the car and use two wideband in the headers in place of the factory ones. But before we do anything, we'll just look at where the car is at as a base point. I'll do a couple of pulls. Obviously cold start we can't look at but my car cold starts really well. I agree with your theory that the MAF trim wont be exactly the same for each bank, will be interesting to see what your friends car reads on the MAF trimmers. And there is a clue right there, that's valuable information with when the trouble started.
ust recording progress. I reset both TB's to .05mm clearance, its trickier than it seems. Then I checked the TPS both banks, I did not touch them, I just measured to see where I was. The spec is 400-600 mV with 80 mV max difference. Mine are 451.8 and 455.0 so well in spec from the last time I set them using OHMS 18 months ago. I also put in 2 bench tested IAC that were also very close to each other with resistance and voltage using the same harness, but just function test can be done like shown below with a 9v. Courtesy of Pelican parts forum. Have not started it yet, I need to make a second harness and measure both simultaneously at various throttle openings to ensure they are synched through the range. MAF's are both set at 384.x as well. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
With that tiny tweak the car started and idled acceptable, remember the air screws are not set they are just at a default of 1 turn out. Was good for about 20-30 seconds then the air injection came on and it started bogging and fighting. Hmmm...
There we go, at least you're heading in the right direction. This is interesting with the EGR affecting the idle like that though....For grins and giggles, what if you were to open the air bleeds up some?
Ok so.. cold air, dense oxygen, hunts and surges, when its warm its fine but air is less dense so its less lean. Ok so its a lean condition. When it gets warm is fine but closed loop seems to handle that. When cold its lean, has to be... Here the symptoms again: Turn the key 2 seconds, it cranks, no fire but some poof sort of sound echoes from exhaust. Crank it again it fires after a few cranks but bobbles then catches until injection comes on this its totally unstable. Almost dying and knocking and shaking surging but never actually an idle more just flailing. Decided enough is enough, the MAF C02 is the ECU trim for open loop or cold. Its a cold idle issue, the MAF has to be set right or it wont work. Doubt it? Turn your MAF's to 375 and try starting it and you see if its any different. Cold weather makes it worse due to density so if you live on the equator may not be as huge an issue. So... I unplugged battery and cracked off the red MAF screw caps. Set both MAFS to 385.0 up from 384.2. Higher number is richer btw. Plugged battery back in. Ok it idles better, still had to key it twice to get it to fire, still has some surges alright but not as bad. Unplugged battery. OK so that that MAF CO2 pot change seemed to have made a slight difference in the right direction. So set both MAFS to 386, plugged battery back in. Lit of much faster on first key definitely better WAY less hunting almost legit idle but its not correct. Unplugged battery. Set both MAFS to 387.5 plugged battery back in. Lights up instantly when keyed now. Idles fine, no surges, no stalls, its not exactly right but its good enough that the idle is stable so I can put wide band on it and set bypass screws and synch throttle etc etc. Unplugged battery again. I will wait 8 hours and see if it starts again, the water temp gauge is not registering yet but the engine is warmer than stone cold, so will wait for it to be stone cold again to confirm. But... it lights off instantly and idles fine, so I can set the bypass screws too next round when it gets to temp and ECU has learned first cycle. It's the MAF setting, lean condition, no vacuum leak, but I wanted to confirm TB settings and IAC's before changing the MAF, not that its an issue or I am afraid to do it, I mean just put it back if you don't like the change. The REAL issue for me, is every time you unplug and plug those MAF's connectors in and out to clip on the alligators for the multimeter test, you risk the it not seating on pins and getting loose female connections from male pin wear and reduced female spring tension.
Engine is cold. Bumped both MAF's to 390 even, idles exactly like it does when warm now. Tomorrow I will set the bypass screws once the ECU learns and radiator fans come on. Then synch banks next week when I get new Junior Power Timer plugs to make second harness in a few days. REAL cold expected this weekend so will have to see what next week brings. So progress but not complete until its all timed and then wide banded. Probably wait for spring for that, its freaking cold in the garage. I'll fire it up in the am and see if its still working as expected.
Great progress!! I'm not sure I understand this "learning" thing, I would have thought the ECU is ROM.......
Its adaptive thats why you can go up and down mountiains with no changes or why a 348 works in Phoenix az and Denver Colorado.etc. When ecu unplugged it takes 30 min for the ecu to relearn basic paramaters and needs it all all engine temps. Nothing can be on, not radio not ac, not heat, nothing. After 10 min it's drivable but it takes 30 min after an ecu reset to relearn before your supposed to even touch the gas pedal after an ecu reset. It's all in the wsm actually. So it's a rom with table values that are calculated and persisted. Until you reset it. Just like cel's unplug the battery and plug it back in a week later the cel is still there. Persistent. Calculated closed loop values are wiped when ecu looses power. Has to relearn. Cels are not lost. Learns all the parms and settings like tp butterfly angle etc and that gets fed into algorithm based on temps, 02, fuel etc and stores that so it does not have to constantly calculate it. Now today that happens instantly but the moronic chips are slooooow. there is short term and long term fuel trims that adjust over time based on how the car is driven. Is why there are cels for short and long term lambda conditions. The open loop stuff is hard coded tables but closed loop is adaptive. Also if there is some value whacked out like a maf at 50, it ignores and uses default table values which may or may not work well but will be better than a whacked out maf as an example. Sent from my SM-G990U using FerrariChat.com mobile app
Ohhhhhh, okay, but this is typical of engine management, which is why I was confused, I do not recall anyone referring to it as adaptive until now. Just reading around here it sounds like something which was exclusive to Ferrari, but its common, any car made since the 80's with EFI does this.... We learned about this in our fuel injection courses in the 1980's when I was a mechanic. And yes, the processing is absolutely slow, which at the end of the day is why I am going new ECU and taking advantage of modern fuel injectors and modern processing, these systems in our Ferraris is so archaic, there are much better options to get the best from these engines if you have the means to do so....
Yes new EM in the car would be great.. a few have done it all ready. I think there are adapters that convert the ecu plug to other systems. Really look forward to that if you write it up.[emoji106] Sent from my SM-G990U using FerrariChat.com mobile app
You can buy those connectors which are on the end of the loom that plugs into the ECU, although my friend is saying it might be easier to make another loom, there are a lot of things we wont use, like the MAF's, one TPS, one crank angle sensor and so forth, but we'll see.... Also I think its going to be a lot easier just to take the engine out too which is why I haven't been racing out to buy the ECU and get onto it...I have time.... Did you do another start up? As soon as you said the trouble started after you set the MAF's to 383 I wondered if that might have been the key.... Hopefully I can get my car on the Dyno tomorrow and get some numbers (AFR) and see where we are at.....
3 years ago I set mafs to 383. Every winter since, this is the third I have issues till spring again. The maf affects start up for sure, I turned it down to 370 and it would not even run, fires and dies instantly. There is actually a thread on maf for start issues when cold somewhere. 383 may be fine for balmy Italy in summer or florida or arizona but not in NJ winter with dense air. Works fine for NJ spring till fall. Air injection leans out gases for emissions or what not. Blindly setting them to 383 when there is no issue is plain bad advice. Now if you have an issue set it there the go up and down to resolve it. Of course with a new engine it's simply worse, went from rough hunt idle to basically no idle. Needed to be reset, new engine.... Everyone including me is sick, son has covid so just dont feel up the the cold garage today. Btw the maf screw is funny, you can turn it clockwise a hair and change value then go counter clockwise 1/2 turn and nothing or numbers go up. Have to keep turning till it drops then go back up. It's not some well timed gear drive. It's why people change it and say there was no change. You have to set it low, turn clockwise until it responds then make adjustments in one direction, up, a tiny tiny, I mean 1/2 screwdriver tip or less width tweaks. I suggest you play with it with ohm meter to understand it before anything. Sent from my SM-G990U using FerrariChat.com mobile app
I hope you get well soon, that doesn't sound ideal to be sick at this time of the year. I wont do much to my adjustments without an AFR analyzer on the car, that is how I used to working....
