Quick question about m50 injectors in m42

[bimmer23]

Hi all, about a month ago I replaced my stock injectors with m50 ones while diagnosing a misfire issue. The injectors were not the issue. I read on a forum that m50 injectors would work but after doing more research I found out they are actually smaller then the m42 injectors. Since installing the injectors, I have noticed that the car pulls stronger on the top end but the power curve is more abrupt and less smooth then before. Also, when giving full throttle at ~2500 rpm, the engine has less power then if I were to just give it 3/4 throttle until around 4K and then full throttle. Also when disconnecting and reconnecting the battery the car has absolutely no power for at least an hour. I have a feeling these issues are related to the m50 injectors, but wanted a second opinion before I put the stock ones back in. Thanks!

[e30sh]

Did you use the green or pink M5x injectors? The green ones are defiantly smaller. The pink ones are slightly larger. depending on which flow chart you believe.

For stock replacement 4 pintal, look for the ones that came in the early e36 M42. They have the correct hole size and are not air shrouded like 94/95 injectors.

My guess is the DME is adapting to the wrong sized injectors and it takes some time before it runs better.

[bimmer23]

They are the green ones. I think I’m just going to put the stock ones that I have back in.

[bmwman91]

The DME adaptations from O2 feedback take all of half a second and <20 minutes depending on which ones you are talking about. Short-term fuel trim adjustments occur continuously, on a 1Hz or 2Hz period depending on operating point. It effectively keeps you operating at stoichiometric at all times except WOT and when the engine is cold which is when O2 feedback is ignored.

The long term fuel trim just looks at how much short term trim is needed to maintain stoichiometric, versus what the base fuel mappings call for, and from 15-20 minutes of running (with engine fully warmed up) it will have settled the global fuel multiplier factor. IIRC it can compensate for injector flow rate changes from stock of ~25%.

Anyway, if you swapped in injectors with a lower flow rate then that is likely part of the problem. Sssquid Tuning can clean, refurb and flow-match your stock ones fairly cheaply and I recommend doing that. A stock M42 will run just fine on those.