3.4 swap running very rich
 

Looking for some insight here..
The car is a 2000 986S. I've swapped in a 3.4 from a 2000 996. The car fires up and runs well for a couple of minutes, but within 10 minutes, all of the plugs are fouled and it stops running.
The 3.2 ECU has a Softronic flash for the 3.2. that engine ran fine 4 years ago, but died due to intermix.
the 3.4 has new after market fuel injectors (possible culprit), 996 intake manifold, original 3.2 MAF housing and new 124.01 MAF.
thoughts or questions??

Put fresh plugs in and read the air fuel adaption, it is out I would also suspect the injectors.

The 3.2 and 3.4 stock fuel maps utilize different sized maf housing sizes. If you are using the 3.2 MAF housing, your DME is thinking that you are moving MUCH more air than you actually are, hence the rich running. Replaced the MAF housing with a 3.25" diameter housing and this should fix it.

What aftermarket injectors is it running? If it is a bosch, just double check the flow rates to ensure they are equal. I forget off the top of my head but I wanna say the stock rate is 240cc/min (thats for the 2.7, 3.2, and 3.4). I run the 03-04 MY injectors on my 2000 and they work flawlessly with a stock 996 tune and 3.25" MAF housing.

Edit - I just reread that again. If you're running a 3.2 tune, your 3.2 maf housing should be correct b sorry about that.

Have you measured afrs at all? And are you running in open or closed loop when this is happening? (Any elm/obd logger should be able to tell you that). If you're in closed loop operations (which you should be at idle) and the exhaust o2 sensors are the same from when your last motor died, they may be driving your problem.

On a side note, is would be very careful about running a 3.2 tune on a 3.4. When you go WOT be and you kick into open loop mode (supposing that there is one still with the flash) you may go lean. Again, a wbo2 would be helpful there.

These are the injectors I've installed:
https://www.ebay.com/itm/293054016510
sys 22 LBS. Not sure what that converts to as metric.
I went with these because they were new, advertised as flow matched, and 4 hole. The stock injectors from both my 3.2 and the 3.4 are 2 hole. Is there much of an advantage of the 4-holes over the 2-holes???
I've had the car running and on Durametric, which showed thing running normally, no misfires. It was definitely a misread, as the car was stumbling along. I'll give it another shot, though.
I'm tempted to put the old injectors in to see how that goes.

That translates to 230ish, so your on a good ballpark there. I drove normally trust "import" products like that though but that's just me. If they are calibrated properly though they should be fine

Bosch (and the rest of the world followed suit) developed the ev1 style because the 4 hole designs gives better fuel atomization, leading to better fuel delivery and a bunch of other benefits. Porsche switched to these injectors in 2003. They are the ones I run in my 2000 (Bosch branded) 2.7 without issue.

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