528i-- Vacuum leak

Hey everyone, I am really frustrated right now, my car is not passing inspection and Im not sure what is wrong. I was hoping someone could give some advice or answers. My CEL light has come on and its the codes for my pre-cat sensor. I decided to do a tuneup and changed all filters, oil change, new spark plugs, new sensors, new MAF sensor and still the CEL light comes on. It is now starting to overheat too.

When I first start it in the mornings it is rough, and you have to press the gas peddle a bit so it doesnt turn off. The Other I was doing this and I noticed the Catalytic convertor was bright red and glowing. Also the car is now overheating sometimes. Both of my mechanics say its a vacuum leak and they cant find it, someone mentioned its my head gasket. Any ideas? Iv been driving a ford explorer and I drive about 400 miles a week, its killing me on gas I need my 528i back.

Originally Posted by archciaa

still the CEL light comes on. It is now starting to overheat too.

The way to make sense out of multiple symptoms is to take 'em one by one - but do the most critical first (e.g., overheating will KILL your engine whereas a non-blinking CEL misfire won't).

For example:
- What to look for when your KTMP (1) or coolant temperature gauge indicates overheating (1) & what happens if you drive one mile too far with an overheated BMW cooling system (1).

Originally Posted by archciaa

Both of my mechanics say its a vacuum leak

Hmmm... two mechanics? And they haven't fixed it yet? Methinks there is bad news in your future ... (or they already told you the bad news?) ...

Anyway ... as per the title of this thread, if it's truly a run-of-the-mill vacuum leak (which every one of us will face on the E39 eventually), then these threads will help:
- How to diagnose a typical BMW E39 engine misfire (1)

But, I would wonder about the logic of assuming that a vacuum leak misfire could/would cause overheating in and of itself.

Originally Posted by archciaa

someone mentioned its my head gasket

Ah. Now we get to the potential real culprit.

This set of threads was written for people who suspect this type of overheating:
- Summary advice to provide users who suspect a major engine repair due to overheating (1) (2) (3) (4) & how to test an engine for a blown head gasket, cracked heads, a warped block, stripped head bolt threads, cam seizures, contaminated bearings, coolant hydrolock, or piston, ring, or valve damage (1) (2) & what are the major factors in deciding whether to rebuild the engine, replace the engine, or sell the car (1) & a DIY for replacing the I6 M54 head gasket (1) (2) & replacing the V8 M62TU head gasket (1) & why these engines are so prone to heat-related damage in the first place (1) & welding the crack between cylinder #3 and the water jacket on the exhaust side (1) & what engine swaps are most recommended (1) (2) (3) & where to obtain a new or rebuilt head (1) replacement short block or long block (1) (2) & how to lift & remove the engine (1) & the most recent real-world results from the last 50 people faced with similar blown engine problems from which this advice came from (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) (40) (41) (42) (43) (44) (45) (46) (47) (48) (49) (50)

Just had to say bluebee is like the Data of this e39 starship.

Originally Posted by archciaa

Hey everyone, I am really frustrated right now, my car is not passing inspection and Im not sure what is wrong. I was hoping someone could give some advice or answers. My CEL light has come on and its the codes for my pre-cat sensor. I decided to do a tuneup and changed all filters, oil change, new spark plugs, new sensors, new MAF sensor and still the CEL light comes on. It is now starting to overheat too.

When I first start it in the mornings it is rough, and you have to press the gas peddle a bit so it doesnt turn off. The Other I was doing this and I noticed the Catalytic convertor was bright red and glowing. Also the car is now overheating sometimes. Both of my mechanics say its a vacuum leak and they cant find it, someone mentioned its my head gasket. Any ideas? Iv been driving a ford explorer and I drive about 400 miles a week, its killing me on gas I need my 528i back.

Umm....

What are the codes?

Are you loosing coolant? You need to find out if your head gasket is gone--a red hot exhaust is not good and never heard of a vac leak causing such. On Vac leaks--go to the search engine and type in Vacuum leaks revisited and then scroll down and click on link--that's for a m54 engine--but it may help you find the spots for you to check--there are a few more vacuum hoses on your car that the m54 doesn't have--would suggest that you start by replacing all of them--hoses are cheap--unmeterd air plays havoc on fuel mileage and power and vacuum leaks --well thats unmetered air entering the engine. Hope that helps

As others have said, it sounds like you have a large vacuum leak. The usual place for a vacuum leak is the rubber intake boots between the MAF and the throttle body. You need to remove and inspect these boots as it is almost impossible to thoroughly inspect them when they are on the car. FYI a lean running engine will run very hot and will be damaged if forced to run lean for extended periods. Lean means too much air & not enough fuel usually caused by a vacuum leak.

The other thing you can do is take the car to a trusted BMW shop. Not a shop that is unfamiliar with these cars. The car should be smoke tested for vacuum leaks and the fault codes should be read and diagnosed correctly. There are many fault codes for pre-cat O2 sensors but in most cases the sensor is telling you that there is a problem-the O2 sensor is the messenger and not the problem. It is also essential that your overheating problem is diagnosed and solved. Overheating an aluminum engine will kill that engine dead if not taken care of.

Guessing and throwing parts at these cars can get very expensive and usually does not solve the problem.

Originally Posted by johnstern

A lean running engine will run very hot

I've always wondered about that.

I understand that a lean mixture is a hotter mixture - and I understand that, in the cylinder itself, a hotter burn can damage things - especially since the cooling system is the oil 'in' the cylinder and the coolant 'near' the cylinder ... but - doesn't the cooling system have enough of a margin to remove the excess heat such that the temperature measured on the temperature sensor (located even further away) might be close to normal?

Caveat:
I don't have any first hand experience with this - so - consider that a newbie question as I think I understand the theory (lean is certainly hotter) but I wonder why the cooling system doesn't handle it (within its margins)?

Originally Posted by johnstern

The car should be smoke tested for vacuum leaks and the fault codes should be read and diagnosed correctly.

No wiser words were spoken to the OP.

Without the current codes and a smoke test, it's just a guessing game.
- How to make, borrow, or buy lean-condition misfire test tools to test for vacuum leaks & lean conditions (1) (2)

Originally Posted by johnstern

Guessing and throwing parts at these cars can get very expensive and usually does not solve the problem.

I agree - yet with one caveat.

For a decade-old BMW, prophylactically replacing all the rubber hoses isn't necessarily a bad idea.

The OP should read these for details:

- How to locate all problematic (between 1/8" & 9/32" ID) 3.5x1.8mm, 3.3x1.8mm & (between 17/64" & 9/32" ID) 7mm ID vacuum tubing (single material), vacuum hoses (multiple material), 3.3mm OD curved vacuum pipes (rigid tubes), 3.5mm & 7mm ID vacuum endcaps (closed end) & 7x3mm manifold o-rings (1) & 7.52X3.52mm and 9.2X2.8mm fuel injection o-rings (1) & gaskets (1) on the M54 engine & where in the USA to get new vacuum tubing & vacuum caps (1) & what SAE sizes to get for all the metric M54 engine vacuum tubes, hoses, pipes, and caps (1) & correcting the F-connector errors in the realoem diagrams (1) & finding the ends of hard-to-locate vacuum tubes (1) & sorely needed clarification on how the M54 CCV vacuum port works on the M52 CCV valve connection to the fuel pressure regulator connection (1)

Originally Posted by bluebee

I've always wondered about that.

I understand that a lean mixture is a hotter mixture - and I understand that, in the cylinder itself, a hotter burn can damage things - especially since the cooling system is the oil 'in' the cylinder and the coolant 'near' the cylinder ... but - doesn't the cooling system have enough of a margin to remove the excess heat such that the temperature measured on the temperature sensor (located even further away) might be close to normal?

Caveat:
I don't have any first hand experience with this - so - consider that a newbie question as I think I understand the theory (lean is certainly hotter) but I wonder why the cooling system doesn't handle it (within its margins)?

Bluebee, I guess I was not specific enough. You are correct I that a lean mixture will, most likely, not cause the cooling system to overheat but rather the temp in the cylinders will be very hot and can also cause the CAT to be overheated, i.e. glowing red. Lean mixtures can also cause piston damage such as a hole burned through the top of the piston in a racing situation where the racer is trying to extract the most power from an engine without the mixture becoming so lean as to cause this. This does not usually happen in street driving but my fear was that the OP would be running the car for extended periods on the highway at high speeds with this large vacuum leak. The cooling system would not allow the engine to overheat but the in-cylinder temps and, hence, the exhaust gasses would be extremely hot.

Thanks for the replies. I have not dared to drive the car around anywhere. I changed out the whole coolant system during summer because of overheat issues and it had no problems. The problems started last month, when it started getting cold. I will pass this information along to my mechanic, I guess my next stop will have to be the dealership. I had plans to vinyl wrap my car but I guess I rather have a working car rather than a pretty car.

Originally Posted by johnstern

a lean mixture will, most likely, not cause the cooling system to overheat but rather the temp in the cylinders will be very hot

Thanks for clarifying. That's how I understood it to be so now I'm no longer confused.

Also, I would think a red-hot cat would also trigger some kind of blinking CEL?

Originally Posted by archciaa

I rather have a working car rather than a pretty car.

Yep. Without the engine, it's just fancy leather furniture.