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Discussion Starter #1 (Edited)
This thread is intended to help other newbies with things I learned in chasing down vac leaks over the past couple weeks on my 04 325 coupe late production M54 engine - the one that does not have the secondary air pump attached to the intake manifold. Those of you who are much more experienced than me will probably find this thread silly, but hopefully I can help others who are ready to pull their hair out (I don't have any to pull out, though).

I smoked the engine a couple times but didn't see anything. One problem may have been the smoke itself. If it isn't dense enough, you may not see it coming from any leaks. I tried paper, incense and a nasty cheap cigar. None of these worked. Also, I used an electric pump at first that pushed too much air too quickly, so all the smoke I had accumulated in the bottle got pushed out all at once in a second or so. That did nothing. What did work finally - I bought a hand pump and cigarettes. I shoved 3 cigs in the pump intake and taped them in for a good seal. Lit them up and pumped - not too fast and that worked like a charm. I do suggest doing this outside in a well ventilated area, unless you are already a smoker. Also, make sure you remove the MAF - I don't think you want any kind of smoke going through the sensor. To connect the pump to the intake boot. I used a red party Solo cup, poked a hole in the bottom for the pump hose and taped it off to seal it, then slipped it over the intake boot and taped around it to seal it. It all worked great.

If you think you have an idea where a leak is but need to pinpoint it, mix up a bit of dish soap and water in a pray bottle and spray it where you want to check while you are pumping air into the engine like you are smoking it. If you see bubbles forming, that is the leak. Be aware that very slow leaks may not make big bubbles instantly, but may instead create a white froth over a period of several minutes, so be patient.

Things to check, double check and triple check. I say that because I was absolutely CERTAIN I had a few things correct, but I actually did not. I found this out when I triple checked. Clearly, I am not the sharpest tool in the shed.

Use the correct tools, especially the torque wrench. Things like the valve cover and intake manifold have low torque specs, so use a wrench that is appropriate for those ranges. The big wrench that starts at 50 ft/lbs is not going to work. Also, double and triple check your math - smaller torque wrenches are commonly made in inch-pound units, NOT foot-pounds, which makes the numbering system on the wrench completely different. To convert in/lb to ft/lb, take the in/lb number and divide by 12. Pretty simple, but very confusing if you don't know this.

Using the correct torque wrench set to the correct torque, go around all of the bolts/nuts on the valve cover and the intake manifold mounting studs and MAKE CERTAIN they are all torqued correctly. That also means making sure you pull on the wrench correctly and consistently. Using different ways/hand positions to pull the wrench may give you different results. Also, use a star pattern when tightening. On the valve cover (more details below), don't forget to properly torque the 4 nuts on the top between the spark plugs.

If simply tightening things down doesn't help - which is what happened to me when I didn't do it right the first time - here are other things to check:
- the valve cover gasket. Pretty obvious. At first, I didn't think I needed to change mine because from what I could feel around the VANOS, it was still quite pliable. But when I removed it, I found that the spark plug holes seals were hard and the corners closest to the passenger seat showed oil weeping even though I didn't see that on the outside. When you replace it, make sure all surfaces and the groove on the cover are free of debris. Add a bit of good hi-temp gasket sealer on the top corners of the VANOS half moons and those at the rear. Do the same where the VANOS cover meets the engine block - both the right and left sides.
- when you have the valve cover off, inspect it carefully. I found a small crack on the inside of one of the bolt holes. This may not be the best fix, but I used some high temp metal epoxy (not regular JB Weld) to seal it, then sanded it down after 24 hrs of cure time. I also added a small amount of gasket sealer on the block surface around that mounting bolt. Also, carefully inspect the oil cap and where it locks into the cover. Check the plastic PCV connector and its o-ring.
- on the intake manifold, it is easy and cheap to just replace all the flexible vacuum lines. Also replace the rubber plugs on the vacuum ports that are not used. It goes without saying to replace the gaskets and torque the mounting nuts properly. My manifold has a strange unused and plugged port on the top between the 4th and 5th cylinders. You need needle nose pliers to get that out CAREFULLY. Check the o-ring and the inside of the port it goes in. I won't get into details on the CCV system because that topic is covered at length in other threads.
- There are a couple things on the exhaust side too. Check the secondary air pump mounting to the engine block - pull it off and check the gasket. Mount it back and torque correctly. Check the hoses and plastic connectors (and their o-rings) on the secondary air pump assembly.
- Finally, on the front of the engine, there are various bolts on the VANOS housing - check to make sure they are tight and don't forget the banjo connector on the VANOS oil hose.

Yes there are other things to check but IMHO those are more obvious. I intended to throw some less obvious things out there when you can't find the gremlins looking in the normal places.

This forum has been a HUGE help to me so maybe this info will help others.
 
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