engine and drivetrain starting engine on MS3x after sitting for a few years

[///mChris]

I had the same concern. The engineer in me screamed out for a camshaft based sensor.

It turns out that the cam sensor doesn't have to be accurate at all. The timing all comes from the crank. The problem is that you have 2 crank rotations for every 1 cam rotation. This is why wasted spark is so simple. It just sparks both on compression and exhaust. The crank timing gear has 36 teeth. It can very accurately know where the crankshaft is. The cam sensor has only one tooth. The sole job is to tell the computer if the cranks sensor is on the compression stroke or exhaust stroke.

Steve (77e21) was the one to point this out to me. You can acutally read his response to my same question in the archive. I learned he was right.

He went to a cam based sensor because he was having problems with his 320i dizzy. The stock 320i dizzy has a VR sensor. VR sensors are analog sine wave and sensitive to noise. Hall sensors put out digital square waves and aren't sensitive to noise.

I did have to fix the advance in the distributor as did Steve.

If I had to do it again, I'd use a 2002 distributor with fixed advance and an optical sensor. Cheap, easy and works well. Also keep in mind once you cut a hole in your timing cover, you have to deal with sealing it from leaking oil...

My cam timing is fed by a distributor I built. I used a 320i dizzy and modified it to use a hall sensor from a jetta.

I followed the standard startup. without fuel and spark, check timing, apply fuel and spark. It backfires alot which makes me think there is unburned fuel.

I cleaned the sparkplugs last night. I'll try again.

I don't know how accurate that is going to be... I'm doing mine via the camshaft.

http://77e21.info/mscop.htm

[rover1]

I agree it sounds like an ignition issue.

I've tried going to wasted spark and semi-sequential to rule out the cam sensor.

To get an idea of what I've done to double check the timing...

I put the engine to TDC compression on #1. Verified it by full overlap on the cam for cylinder 4, a notch on the cam pointing up, keyway on crankshaft pointing up, front bolts on cam gear alligned.

The crank pulley was set by Tom at 02again (Thanks tom!). The keyway locks the configuration on it. The sensor reads tooth #1 at 80 degrees BTDC, which is standard for EDIS. I then set the cam sensor to tell if #1 is at compression TDC or exhaust TDC by rotating the distributor to align it.

http://www.msextra.com/doc/ms3/trigger-wheel.html#dualmiss

[Dave_Ganzer]

It's not clear... Did you check the timing while cranking with a timing light?

DaveG

[bmwmalcolm]

Chris, My son (builder and installer of 10 MS systems + diagnose Many others) says to post your MSQ file and a data log of the start attempt and he will look at it. Also suggested a timing light on No. 1 cylinder as others have suggested.