M50 Injectors in an M20?

[DmcL]

hoping there might be a few out there with some tuning experience with motronic and varying size injectors.

ive already got the car running sweet on 19lb (200cc ish) M30 injectors but im trying to get it running on some E36 323i injectors and have had a few snags along the way. first was a lean spike and hitting a wall at about 5000rpm which the engien would not rev past. i sorted that out but its a bit dodgy below 2000rpm and wideband indicates lean off the scale (above 18:1 or 19:1, forget top of scale on my AEM) even when i give it throttle. runs fine everywhere else tho.

ive tried a few things that have affected the problem area slightly but nothing that seems to directly affect it. im going to try loading up some ignition/fuelling values from other tunes ive done and copy them over to this tune. the engine generally doesnt want to pull below 2000rpm, most notable when pulling from a stop and it doesnt matter if im giving it light throttle or moderate throttle, might even be happening if i give it full throttle tho not 100% on that yet.

anyone have any ideas? car doesnt want to pull and will buck slightly and engine sound will change a bit, sort of burbly on and off with the bucking, when it s not burbling/bucking there is like no power then it all comes in and hits u crossing about 2000rpm and runs fine the rest of the way up. i would think its a part throttle ignition/fuelling issue but given the other issues ive had with these injectors i wouldnt be surprised if it was something in a correction/injector lag/pulsewidth related map either..

[DmcL]

dont think i mentioned im running a home brew MAF conversion also

ive just pulled the MAF conversion out along with the modded ECU for it and popped in the good ol AFM and a standard ECU with a chip in it tho chipped for standard injectors. idle was high initially but adjusting the AFM dropped idle and leaned out part throttle areas from what i can tell, no issues revving with no load on the engine so going to see how it does on the road and if any of the problems i have encountered with the MAF and these injectors happen with the injectors on their own without the MAF conversion to further complicate things. hoping this will be like taking 1 step backwards in order to take 2 steps forward and help me figure out wtf is happening with the MAF and this specific set of injectors but well see..

[DmcL]

right.. same thing happening with the standard AFM and a "normal" performance tune for it. its not happening quite as heavily but still moderate and still below 2000rpm under mild to full load.

since its happening with both my MAF conversion and the standard AFM its leading me to believe (as is wideband readings) that there is a lean spike on moderate throttle from low down due to the 64mm BBTB. im going to have a fiddle with some of the fuelling maps and probably the acceleration enrichment map to see if i cant iron it out.

if ant or anyone fancies shedding any light on such problems they have faced tuning M20's with larger than stock TB's id appreciate the help.

[DmcL]

finally figured it out.. had to tweak some injector/pulsewidth related maps. runs perfectly on them now

[e301988325i]

So the BBTB made a noticeable difference?

[eta]

I don't it has made a noticeable difference on my 2.7i. Ant re did the chip afterwards as well.

I think the main difference for me has been the sound. Given the cost of the mod I don't regret it. It may make a difference with other modifiactions as they come but I am unlikely to refit the original TB I will not know.

[DmcL]

hard to say tbh.. it sounds more throaty with the BBTB but without a dyno before/after its hard to tell. im pretty sure it has freed up a few more ponies higher up the revs on the butt dyno tho.