Misfires after new injectors

[Redd]

I recently installed 8 new Bosch injectors in my M3 and its been running like crap since. Low rpm small throttle inputs cause random misfires in all 8 cylinders. Logging afr thru OBD2 shows random afr spikes and dips with no pattern. Runs fine when WOT tho.

Do new injectors need to be coded? If yes, what information is needed for coding?

[Etansinsta]

no they don't need to be coded. maybe check that they are properly seated and you didn't forget to plug anything in. did you touch anything else while you were in there?

[mapster37]

normally injector bores are filled with all sorts of debris, possibly some fell into the bores during removal/ install causing your misfire issue

[tdott]

Did you buy them from a reputable vendor?

There are some fake ones on ebay that will do that. Not sure about in your part of the world but I imagine it could be the same issue.

[Redd]

Originally Posted by tdott

Did you buy them from a reputable vendor?

There are some fake ones on ebay that will do that. Not sure about in your part of the world but I imagine it could be the same issue.

Bought them from ECS. They were $25 a pop and Bosch branded, doubt ECS would sell fakes.

The mech I used is a BMW specialist so I don't think it's install error (but will get them to check again). Plus unlikely its dirt or install error if all 8x cylinders are misfiring.

The symptoms are really weird. At mid to WOT, it runs fine. It's only at low rpm, low throttle - like feathering throttle while slowing down - that it misfires. There is no CEL, but the car lurches and I have misfire codes on OBD2 and also stored in DME. Logging afr shows weird spikes and dips in afr. Occasionally it would misfire so bad to the point the engine would stall.

Even weirder, when I press the Power button, the misfire happens a lot less or none at all. This suggests to me it's something to do with the electrical signal to the injector. The new injectors don't like very low voltage, but the higher signal on Power mode is OK. I'm going to try coding the new injectors today. Will update how that goes. Worse case scenario I'll swap back the old units and send these back to ECS.

[Johal E32]

Swap back to the old injectors if possible, see if the symptoms are still there?

[Redd]

Update - Swapped back to the old injectors and problem persists. So it's not the new injectors.

Also E9x M3 S65 injector change does not require coding. The injectors don't have the 6 digit code. Injector coding is required for direct injection engines.

So I'm back to square one. Sigh. Below is afr logging from Torque app. Top is throttle pedal, afr (measured) middle, afr (commanded) bottom. As you can see as I slowly lift off throttle, afr suddenly dips, then spikes. This is random, I can make it happen like 50% of the time.

[amrazM]

you left something unplugged/disconnected, recheck your work.

[Redd]

Originally Posted by amrazM

you left something unplugged/disconnected, recheck your work.

At this stage, the mechanic has removed and reinstalled the plenum twice, injectors twice. Same problems. Tomorrow a stock plenum is going on (currently it has a Carboproject plenum).

[amrazM]

Originally Posted by Redd

At this stage, the mechanic has removed and reinstalled the plenum twice, injectors twice. Same problems. Tomorrow a stock plenum is going on (currently it has a Carboproject plenum).

Check the rear hose that runs to the ICV

[Shrm4n]

What solved this one for you? Just had to recheck your work?

[Redd]

Originally Posted by Shrm4n

What solved this one for you? Just had to recheck your work?

This was a couple years back. If remember correctly, I had just installed a new Carboproject plenum (my 2nd one). Carboproject re-uses stock bottom half of the plenum and this particular one I got had a small air leak at the IAT sensor hole. It was this air leak that caused the misfires under high vacuum conditions (2-3k rpm, part throttle).

It didn't occur to me at first that the plenum was the problem as I had also installed new injectors at the same time and my 1st Carboproject plenum ran perfectly for several years. In the end, we found the problem by removing the plenum and letting the engine run in alpha-n mode which eliminated the misfires. So we knew the problem was in the plenum.

Sealing up the air leak and new O2 sensors (the misfires damaged the O2s) fixed the problem.

[Shrm4n]

Originally Posted by Redd

This was a couple years back. If remember correctly, I had just installed a new Carboproject plenum (my 2nd one). Carboproject re-uses stock bottom half of the plenum and this particular one I got had a small air leak at the IAT sensor hole. It was this air leak that caused the misfires under high vacuum conditions (2-3k rpm, part throttle).

It didn't occur to me at first that the plenum was the problem as I had also installed new injectors at the same time and my 1st Carboproject plenum ran perfectly for several years. In the end, we found the problem by removing the plenum and letting the engine run in alpha-n mode which eliminated the misfires. So we knew the problem was in the plenum.

Sealing up the air leak and new O2 sensors (the misfires damaged the O2s) fixed the problem.

Ok, interesting. I’m using stock plenum so I’m assuming I left something loose and will start there. I immediately thought my new injectors were my trouble but will check out the plenum first. The car had only misfired for 30-40 seconds before I killed it so hopefully o2s will survive. Thanks for your reply all these years later, I appreciate the help sir

[spammysammich]

It is very easy to fold the ITB couplers when you reinstall the plenum or to not get the air/oil separators properly seated. Doesn’t hurt to have inspection mirrors or a bore scope to help double check.