It’s a mystery to me????

[rattlesnake]

Just completed a head replacement on 03 m54 engine and noticed this little doo dad lying on my starter when I went to replace the intake. Car is idling rough not sure why yet. But anyhow does anyone know what this is, where it goes and what it does?

[jclausen]

I believe it is from under the intake manifold at the rear, there is the secondary air port and electrical switch for it that valve I think goes in those vacuum hoses

[BimmrMeUpSnotty]

Check valve for one of the vacuum lines

[effduration]

+1.... I believe it has small hoses attached to each side and Conf to to ports at the rear of the intake manifold closest to the firewall.. I’ll see if I can find a pic. I think leaving it unplugged could lead to a poor idle..

look at the pic here:https://forum.e46fanatics.com/showthread.php?t=1074573

[ross1]

It's #6

[jclausen]

Also it could be a one way valve

[rattlesnake]

Completed a compression test today on my 530 I. Results are as follows, #1-160, #2-150, #3-150, #4-145, #5-145, #6-125. Thoughts on causing a miss on the #6 cylinder because of low compression???

[effduration]

Completed a compression test today on my 530 I. Results are as follows, #1-160, #2-150, #3-150, #4-145, #5-145, #6-125. Thoughts on causing a miss on the #6 cylinder because of low compression???

Those do seem low.. but compression #'s can vary a lot due to tester used, #of revolutions, presence of fuel, hot/cold engine.

While I would have hoped to see higher numbers (180psi+) and #6 closer to the rest, I don't think the 125 psi figure on cyl 6 relative to the other numbers shown would cause a mis-fire in and of itself...If it was 80psi or less, yes, maybe..

If all the other cylinders were 180psi+/- and #6 was 125psi, i might also think differently.

my guess is you have an intake leak somewhere. I would run a smoke test on the intake.

Also:

Did you replace the intake gasket?
Did you ever fiddle with/remove any of the injectors ? or did you leave them attached to intake?

[rattlesnake]

I did not replace the intake gasket since it was new a couple months ago when I replaced the CCV system. I left all injectors in the manifold except two (#1 and #6) which I swapped to see if one was bad after getting the miss.

[effduration]

I guess moving injectors made no difference? And I guess we can rule out bad injector o-rings, since it missed before and after swapping injectors...Did you try swapping coils? (worth a try). I would do a smoke test.

[rattlesnake]

I did swap coils and plugs, made no difference. I put new intake manifold gaskets on today, no difference. Got ahold of a vacuum diagram and buttoned that system up real nice, new hoses where needed and caps where required. One thing I find interesting is, with the car running (starts right up every time) is as I disconnect the coils one at a time there is a noticeable difference in how the motor runs. Until I get to #6, which is the one with low compression, when I get to that cylinder there is no difference in the way it idles, which tells me that is the problem cylinder. You can definetly tell it’s missing on that cylinder. Since the piston looked good and the head tested good at the machinists I have to believe when he overheated it he destroyed the rings. I’ve already got about 600.00 in it and unless someone comes up with something brilliant I’m about done with it. Just about ready to cut my losses. As far as a smoke test I have no way of doing that and the shop wants 300.00 to diagnose it since it’s been down so far. I might add you don’t notice the miss at road speed other the loss of power compared to before.

[effduration]

You can't give up now man ....you are so close!! Piston ring failure in these cars due to an overheat is very rare, in fact I have never seen it mentioned. I HAVE seen a piston melt in an overheat, but that is not what we're talking about here. And since you do have 125 psi in that cylinder, I don't think it is a major piston ring failure. Also, you reported only 5 thousandths warpage of the head, which tells me you didn't have a prolonged overheat. I routinely see 11-12 thou or more

I think you have an intake air leak.
How about try spraying starter fluid or WD 40 or other wile engine is running near the #6 cylinder:

- near last fuel injector
- underneath intake near #6
- around DISA valve

Also there is a youtube video on how to use a cigar, a cheap fluid pump, and a rubber glove to do a simple smoke test.