Won't Start After Vacuum Leak Repair

[Dan Harjung]

I hope you guys can help me out. I have a 94 540i, stock with about 220,000 miles. I do all my own maintenance and haven't had too many engine problems with this car. It was my wife's, but about two years ago we bought her an X3 and gave the 540i to our 17 year old son.


Anyway, the car started running poorly a few weeks back, it would stall at idle, it used more fuel than usual and ran pretty rough. I did some simple diagnostics and found a pretty bad vacuum leak at the the diaphragm on the rear plate of the intake manifold. I ordered a new plate and gaskets and began work to replace it last night. Everything went pretty smoothly. I've taken the intake manifold off several times, trying to fix coolant leaks, so the job was familiar. I replaced the plate and gasket, and the gasket at the throttle plate to intake for good measure.


I got everything back together this morning without any problems, but i'm not able to get it started. It fires but immediately stalls. I checked everything over as well as could, but didn't find any problems. I put a vacuum gauge on it and see almost zero vacuum during cranking. I'm not sure how much I should see during cranking. When it does fire the vacuum only goes to about 5 in/hg.


What do you think I should look at next? Am at bit of a loss. How much vacuum should I see during cranking? Am I on the wrong track looking for a vacuum leak? There is fuel, but could it be a timing issue? Is it possible to mess up timing? Could it be the harness for the crank sensor? Could it fire at all if the crank sensor wiring was bad?


Thanks in advance.


Dan

[whiskychaser]

I dont know much about the 540i and never tried to test vacuum when cranking. You normally do it when the engine is warm and at idle. So you may not be getting an accurate figure. I'd expect you would get 16inHG+ with it running. I dont see how you can mess up the timing. Sounds more like an ICV problem. The car wouldnt normally fire if the CPS sensor or its wiring were faulty. But you may want to check the CPS resistance. Others with experience of the 540i will no doubt chime in with better information

[genphreak]

Reset the ECU (disconnect negative terminal for >15mins) to be sure it is not running the engine too rich in line with previous lambda readings. Verify fuel pressure is a solid 3 bar during cranking- this should not leak down once left idle, unless left for hours on end (even then- it shouldn't). If it does, you may have a pump (or non-return valve) problem, unless there is not enough fuel in the tank...

Also check for a flooded engine: Fuel in the cylinders this can remove oil from the rings causing a low compression state in each cylinder. No seal, no bang- can cause all kinds of no-fire symptoms. I'd suspect this if you have given it too much cranking.

Is the firing you're seeing occurring after a long (30s) or more of cranking? If so this there is fuel present but possibly no spark (ignition happens purely due to the compression building up).

So-
1. It is not EWS as it cranks and fires a bit.
2. It is not timing- this is all mechanical, with a small amount of tweaking done by the ECU.

Sometimes, you can get a bad PCV valve (esp a cheap part). Most of the pros avoid the dogy brands like euro, if you suspect it to be bad, you could do worse than to replace it with a branded one from bmaparts for example.

[Dan Harjung]

Thanks for the help. You saved me a lot of headache.

I reset the ECU, no change. I checked fuel pressure, initial and residual were right on spec. The new part was a cheap euro one, so I put the original one back on and it started right up and ran like it used to. So I'll get a better one and see how it goes.

Thanks again, I really appreciate the help. I'll let you know how it goes with the new part.

By the way, whiskeychaser, I'm not familiar with an ICV. What is that?

Dan

[MBXB]

RealOEM.com * BMW E34 540i Mass air flow sensor

No. 9 in the diagram.
The inner barrel needs to rotate freely. It gets all gunked up.

[MBXB]

RealOEM.com * BMW E34 540i Power brake unit depression

No.7 Vacuum hose the the power brake unit.

[genphreak]

No trouble at all.

Good to know you're on the money with the problem. It is so common to get cheaper non-functional aftermarket replacements these days.

btw, Whiskeychaser was referring to the Idle Control Valve. as MBXB posted.

[miliue]

The new plat probably didn't come with vacuum plugs. For my 530, the plate has two open nipples that need to be capped (came that way from the factory). I didn't cap them at first and my car wouldn't idle after the replacement. Once I capped them the car ran much better, and would idle, but was still rough. Checked again with some carb cleaner and found that I hadn't fully seated the oil return pipe that runs under the manifold when I re-installed. It's the metal pipe that you have to push back toward the back of the engine with a screwdriver to connect with the bottom of the PCV.

In short: check to make sure your new PCV has the appropriate nipples capped right (just compare it against your old part). If everything is capped right, make sure your oil return pipe is seated over the O-ring on the new PCV properly. If both of these things check out, it sounds like you got a bad part.

[Dan Harjung]

Thanks for all the input.

I got new caps for the nipples and new o-rings for the oil return pipe. I was pretty careful putting it together and double (and triple) checked those. It wouldn't run long enough to check for leaks with carb cleaner.

Are there any do's or dont's for cleaning the ICV? Can it be disassembled for cleaning?

I ordered a new "Genuine BMW" part, so I'll let you know how it goes when I install it this Friday.

I took it out for a test drive after I put the old part back in and it burned quite a bit oil (lots of blue smoke) that it didn't do just a few months ago. Is it possible that the oil consumption is related to this PCV problem? On a related subject, what kind of compression tester do you guys use? The one I have doesn't reach down the spark plug hole, so I need to get a new one.

[632 Regal]

Are there any do's or dont's for cleaning the ICV? Can it be disassembled for cleaning?

Take it off and spray the inside where the valve moves with carb cleaner. You should see a bunch of black juice come out. You will be able to feel when the valve starts to move freely if you move it back and forth.

I took it out for a test drive after I put the old part back in and it burned quite a bit oil (lots of blue smoke) that it didn't do just a few months ago. Is it possible that the oil consumption is related to this PCV problem? On a related subject, what kind of compression tester do you guys use? The one I have doesn't reach down the spark plug hole, so I need to get a new one.

If the PCV is bad it will dump oil right into the intake manifold.

My compression tester has a length of rubber hose on it that I can screw right into the spark plug hole.