Misfire when cold, and high CO and lambda during inspection

[ed323i]

I might be imagining things, but it really seems like the M52 engine is running smoother and smoother as the days pass. One theory is that due to the very clogged injectors (now cleaned) there was quite some carbon build-up and it's now slowly disappearing. Also read, where an E38 730i owner experienced the same: #6 .

My wife today also told me that the engine feels happier, that it makes the car feel like it wants to fly (it feels very effortless) when you hit the accelerator pedal on the highway.

Still haven't connected INPA, but will do that soon to see where the adaptation values are now.. Will probably also start using the RomRaider logger and/or Test-O logger.

[ed323i]

Alas, car started to misfire a bit again.. Connected INPA. Bank 1: -27 additive, Bank 2: -15 additive. Nothing to worry about, those values..
Then I checked the 6 cylinders roughness/balance in INPA and I saw that cylinders #1,2,3 and 5 were at zero. Cylinders #4 and #6 were at a couple hundreds (+400 to +700) if I recall correctly.

As I have 6 new coils, perfect 11 bar compression in all 6 cylinders, and supposedly cleaned injectors, I now start to doubt if the injectors were indeed in perfect condition after the cleaning.
I paid 80 euro for it, because they were really, really dirty, the guy said.. I took him 2 days on the ultrasonic cleaning machine to get them clean. Before they reinstalled them, I asked if it wouldn't be better to find a new set of injectors, and the mechanic said: "No it's good enough now". Now I wonder if #4 and #6 still have a bad flow deviation or a bad spray pattern.. I should have asked for a detailed report on the injectors, with exact flow measurements (with photos) and spray pattern photos.. It's Spain out here, so people are not real perfectionists, and that's an understatement.. I don't even know if he changed the filters and o-rings..

Perhaps I'll unplug the fuel rail, and then use INPA to trigger the injectors one at a time, and measure the output and look at the spray pattern.
Alas, the guy in the US that sells a fully tested, flow-matched, rebuilt set of injectors for less than $100, won't ship to Europe.. Out here I haven't been able to find an offer anywhere near that..
Or perhaps I can find two good injectors and just swap the #4 and #6 and see if that improves things.

I'll let you know how it works out.

[ed323i]

Just had a WhatsApp chat with a guy who lives 15 kilometers from here. Tomorrow I'll collect his 6 M50B25 injectors and the complete fuel rail included for 50 euro. So that seems like a good deal. M50B25, S50B30US and M52B25 luckily share the same injectors.

I'll just swap the complete rail (or probably swap the 6 injectors, as rail is not 100% compatible with M52 I think) and see if that improves things. If not, I'll give a good mechanic a batch of 12 injectors and ask him to clean them, refurbish them, and then select the 6 that have the best spray pattern and equal flow. And then be done with it (I hope)..

[ed323i]

SOLVED!!!!

Today I went to buy the 6 injectors. Turns out the seller is a mechanic. For 20 euro more (70 in total) he would also install them. I don't really fancy the jobs where I get gasoline all over me (once, while replacing a fuel pump on an E28, I got it on my arm, and next on my armpit and chest.. no fun, quite toxic also with the benzene and stuff), so it was a no brainer.
Some 20-30 minutes later (it's a good mechanic, seemed like he had done it a 100 times), the 6 injectors are in and he asks me to start her up. In the beginning it wasn't running so fine, due to lack of fuel pressure, but then, after a few minutes, the stick wasn't shaking anymore! Virtually all resonance had disappeared by installing 6, probably 25 year old injectors that had been lying on his shelf for a couple of years! It ran better than the injectors I had the previous mechanic ultrasonically clean!

To put it to the test, I also asked for a exhaust gas test, and both at idle and at 2000 rpm CO was at 0.0% !
Amazing! Last year it almost failed the government inspection due to very high CO at both idle and 2000 rpm, and it only, and barely passed after heating the engine at 4000 rpm for 15 minutes..

On the way back home, I noticed the engine felt a lot smoother. Also, no more exhaust backfires/pops with throttle body valve closed.
And now I know I don't have to be afraid of the next government inspection of the car, due in January 2019.

I'm VERY VERY HAPPY!

I will have a serious talk with the other mechanic that charged 80 euro for cleaning the old injectors, a few months okay. I explicitly asked him if it wouldn't be better to buy another set of injectors, and he said: "No, they are okay now" (NOT!).

I will wait until the gas tank is a bit low, and then add a bottle of injector cleaner, but with these perfect exhaust gas levels, that shouldn't even be necessary.

P.S. I will soon connect INPA and see how the values have changed. And I fully expect all cold start hick-ups, stumbles and misfires to be gone now..
So: If your cylinders register very healthy compression (all 6 @11.0 bar +/- 0.2 in my case), and you've installed 6 new coils, and the oxygen sensors seem fine in INPA, and the engine still has trouble (high CO), then first suspect are the injectors (perhaps after excluding vacuum leaks, but those should have no effect on a static idle exhaust gas measurement as the oxygen sensors and DME compensate for that).