More smoke test

[Iforgetalot]

99 540i 6 manual. Been having high LTFT for a while now. I checked for intake leaks and found a couple issues. Fixed them and fuel trims went down from around 17 to 9. Check engine came on last week for a high fuel trim on bank 1. I made a better smoke machine and found some smoke around the throttle body and under the intake manifold.

I used my bore camera and saw that the area under the intake runners gets filled with smoke very fast and with a considerable amount. So yeah I have a significant leak somewhere in there.

So so as far as fixing the leak, what/where do you guys recommend I start fixing? Intake gasket? TB gaskets?

[R Shaffner]

I use an old-fashioned smoke machine, which is a cigar. I'll take in a slow mouthful of smoke and then blow slowly into a tube to the intake (usually a hose attached to the brake booster fitting). I'll repeat that a few times slowly, to fill up the intake with dense smoke, while I watch to see if smoke comes out somewhere. If I don't see smoke, or if it seems to be light in a general area, I'll blow harder while watching closely to see if I can tell where it's coming out. (When you first connect your smoke machine, use a flashlight, look under the manifold and around the TB to see if you can spot the leak. Or see if there's some way to pause and then increase the air flow.)

Other points: Is the high LTFT just on one bank? If so, then it's probably the intake gasket on that side. (Though if you replace the gasket on one side, you'll want to go ahead and do both sides.) If the trim is high on both banks, it's more likely to be from the TB. Though it could be the from both intake gaskets.

And of course, it could be from a loose or split hose to the intake. If so then the high trims would tend to be in both banks.

And finally, if you think it's an intake gasket, there's an easy way to tighten the intake SLIGHTLY to make a tighter fit. You'd remove the nuts holding the intake manifold on, one at a time, add a second washer, and tighten the nuts just a little tighter than they were before. (Be careful not to tighten too tightly, since the head is aluminum and it's not hard to strip those threads.)

Just re-read your post. You said bank 1 had high trims. So it's probably the intake gasket on that side. Since you said the smoke comes out pretty fast, it sounds like you need new intake gaskets.

Good luck!

[Iforgetalot]

Yeah bank 2 is reading high as well but still under the check engine code threshold. I’m pretty confident it’s the manifold gasket. Maybe it’s just loose. That would be an easy fix, but I’m not lucky like that.

[R Shaffner]

Timm Meek has a GREAT site about e38's with the same engine.

Here is his page about how to try tightening the intake manifold. (I haven't done this with an intake, but this trick has worked real well for my leaking cam covers.)

https://www.meeknet.co.uk/e31/BMW_E3...d_Leak_Fix.htm