I don't want to buy injectors to fix misfire

cgoat328

New Member
Dec 27, 2022
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Hello, I don't want to replace my index 1 injectors since they are 900 CAD (665 USD) each now. I own a 2007 335i it's RWD and manual but it shouldn't matter. I have just passed 200k km (124k miles). I bought the car just over a year ago at 180k km.

I run stock tunes from MHD with DCI and DP. I have done a valve cover replacement during the summer and replaced my coils but not the spark plugs. I just looked at my PCV blow-by hose and it definitely has a light brown liquid going through it and might even be leaking on the ignition ground closest to it.

Now for what happened. I was eating lunch and noticed my fuel economy was poor. Before it was 12.6L/100km and is above 15L/100km now and keeps fluctuating.
I thought it was bad gas and ignored it until my next fill-up, but didn't do anything. Then I noticed that the nut holding the ignition ground was loose and tightened it.
Nothing changed and kept getting poor fuel economy so I ordered spark plugs cause I might as well change them while looking at them.

Now here's the fun part. Before I installed them, It was just poor fuel economy and nothing else. Then my car started to misfire constantly at every RPM at every gear, no matter what as if I lost a cylinder. I checked MHD DME codes and I got 29D2 (combustion misfire, cylinder 6) Limped home to check the spark plugs. All the plugs looked the same and couldn't visually tell any faults from the spark plugs. Installed the new spark plugs and made no difference, still constant misfire and 29D2. Swapped coil from cylinder 6 to 1 and no difference, constant misfire, and 29D2.
Note: I did notice that the misfire got worse the warmer the car got. I made it down the road with a small misfire and it got worse the longer I drove.

Gave up for the night and wanted to see if I had a leaky injector by seeing if the spark plug was wet in the morning. Pulled all spark plugs and cylinder 6 looked no different from the rest of the spark plugs. Now I was confused thinking if I had a wet spark plug in 6 it would be the injector. So I tested to see if the spark plug was even firing and it was.

Now I have confirmed it wasn't the spark plug, coil, or injector that wasn't at least leaking overnight (confused about how this affects my idle, is it blocked completely?)

So I pulled my intake manifold off and I believe this car never got a walnut blasting. cylinder 6 wasn't even the worse cylinder but Im thinking if I can pick at and brake clean and scrub it with a soft brush enough I should be able to tell a difference if it was just terrible carbon buildup. I cleaned it, started the car, and didn't do anything, constant misfire and 29D2.

Im planning on moving the injector from 6 to 1 and seeing if the misfire moves with it. I'm wondering if it's even worth trying to replace the seal and decoupler while doing this just to see if it moves or if I can swap them and if it doesn't move, replace the seals and decouper and swap them back.

Or am I missing something?
 

Stevo585

Lurker
Dec 16, 2022
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I would start with the obvious and easy.

Since you replaced spark plugs, have you tried moving cyl 6 coil and see if the misfire moves?

If that does nothing, I would swap the injector with cyl 1 injector. Just make sure you re-code it.

If the injector seal is not destroyed, you should be ok to put it back in for testing purposes, then change them when you find your issue.
 

Stevo585

Lurker
Dec 16, 2022
24
7
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@cgoat328 I did what Stevo585 is recommending to confirm I had a bad injector. I did, and also didn't want to spend thousands of dollars, so I bought a used one from here: https://specializedgerman.com/search.php?search_query=n54 injector&section=content

Hopefully they will ship up north to you. Don't forget to replace the seal once you confirm.
Wow! I bet you could still get a set of index 12 used here and get them sonic cleaned for less then the price of brand new ones.

I will be favoriting that link!