M30B35 Base timing setup and vacuum question.

Hello again!

Back with, yet another question about my M30B35 that I'm trying to get running on megasquirt MS3PRO PNP.

I'm struggling to get it to idle properly and I'm relying, yet again, on your experience on this particular engine so I have a bunch of questions. I really hope I can get some answers to.

I'm learning that it likes to run rich, or at least what I consider to be rich, around 12.8/9 AFR besides that, I see that the idle gets smoother at pretty advanced ignition timing, well above 20 degrees, close to 25. Does this seem right?

I adjusted the base ignition timing by setting fixed advance to 10 degrees, then using a timing light wich I dialed to 10 degrees and adjusted the #tooth setting until the timing marks aligned. Basically, I followed the procedure described in the installation manual, so that should be ok.

If anyone has an idea of what I'm doing wrong, please share your taughts, I'm really new in this, and I'm learning along the way..

Thank you!

Also, I forgot to ask.

My idle fuel load is about 40-42 kpa, is this normal for the M30B35?

Sometimes, it rises to 45-47 kpa and it gets very lumpy and hunting, then it drops down again, but it doesn't go under 40.

Anyone have a clue on what's going on?

If you dial 10 degrees advance on the light the engine will be firing 10 degrees after the timing mark it lights up. Are you sure your real ignition timing isn't closer to 15 degrees? What is the timing mark supposed to be?

It's pretty common for engines to be happier around 0.85-0.9 lambda at idle, especially if idle air has been reduced.

I'm setting fixed advance on the megasquirt at 10 degrees so, if I keep the timing light at 0, I will be able to see the TDC mark 10 degrees to the left of the cover mark, but if I dial 10 degrees on the timing light, the TDC marks should align. This makes perfect sense for me. Please correct me if I'm wrong.

The thing that I'm not sure about, is that the TDC mark is, perfectly, at TDC or another degree of rotation. I know that, BMW are kinda sketchy about timing their engines sometimes. I can't explain the high idle advance, any other way. But, on the other hand, I'm no expert, that's why I'm asking for your help.

Got my answer.

I read the BMW service manual and the mark on the balancer is at TDC.

Does it make sense to have such high ignition advance at idle, 22-23°?

It does if the throttle is very closed. If you want to run less timing, just adjust the throttle stop to open it a bit more.

I'm running a closed loop idle configuration, shouldn't the IAC Valve take care of the ammount of air entering the manifold at idle? Sorry if this a noob question, I'd like to understand better.

Another thing that doesn't, quite, make sense to me is, why I need to be so rich in order to have a smooth idle 0.85 to 0.90 lambda. I do understand that the injectors are wired in batch fire configuration, but I expected nothing this richer. I guessed it would idle a little richer than stoichiometric, but this is, in my opinion, a lot richer...

Thank you!

ok, what's happening with the IAC? Can you control that to set a target position? Or does the Closed Loop Idle control let you set a target ignition timing?

I taught that the IAC compensates for the closed throttle valve. But, I tried opening the throttle valve a little more, as you guys suggested and, now, I can run 17° of ignition advance with no problem.

I'm left with the fact that it still likes to run fat at idle 0.85 - 0.90 lambda. Leaner, it starts to wonder and run rough.

I'm comming back with my vacuum related question.

Is 40-42 Kpa MAP, a good idle vacuum reading for a bone stock M30B35? And how come, sometimes, it drops to 45-47? I don't know on what it depends, it's got a mind of it's own.

I checked for leaks, there aren't any, I pluged in a vacuum gauge and the needle sits at the very bottom of the Green zone, close to 17-18 InHG.

If you're seeing 40-42kpa on the MAP sensor, that's roughly 60kpa worth of vacuum. Remember that the MAP is an absolute scale, where atmospheric pressure at sea level is around 100kpa and total vacuum is 0kpa. That will change a bit depending on where you're located in relation to sea level, but it should be in that ballpark unless you live at a really high elevation. But you're at 40-42, which corelates well to the 17-18InHG. To me, that seems like a fairly normal amount of vacuum for that engine.

I can't speak to the amount of fuel it's wanting at idle though. My personal car like to idle a bit rich, but it's happy around .95 lambda. I don't know if I've ever seen an engine that likes to idle 10-15% rich, though, my experience is probably a bit more limited than most of the other guys on this forum.

Thanks for your reply!

40-42 kpa, may be, fairly right, but, why does it, sometimes jump to 45-47, or even closer to 50. This makes it so difficult to tune the idle. It's like chasing a constantly moving target.

What affects the idle vacuum, where should I look for issues?

Oil and block temperature and changes in frictional resistance, electrical loads, air conditioning, air temperature/density changes will all effect the manifold pressure required to maintain target idle speed.

What are the cells set at for MAP? Realistically, those first few cells should be really similar in VE numbers since you’re at idle. So, if your cell breaks are at like, 40,45, and 50, you shouldn’t see more than a few percent VE change at the same RPM. Also, you don’t need to be perfect within 1%. If it’s within 2-3%, you can let closed loop fueling handle the slight error. Personally, I’d get it idling decently, fill out the rest of the map in steady state, then circle back to idle. You’ll have a better idea of the general shape of the fuel table, and you’ll probably find that a rough estimate based on the rest of the map’s shape will get you pretty close.

Thank you all for the answer, I'll try to figure, everything out, now, I'm wondering if the IAT sensor reads the correct temperature, because, I'm having trouble getting a constant AFR as temperature varies, no matter what I do with the air density correction table.

I'll keep you updated.