Megasquirt e36 M50B20TU/M50B25 w/ ITBs idle surge...help?

[bmbelo]

Hi there! My name is Bruno and I'm writing from Portugal....hope I'm posting in the right section...

Some time ago I assembled a MS-II V3 unit to get into an M50B20TU engine with M3's ITBs. All went well, apart fom the tach out circuit which I couldn't get to work, untill we killed pistons 1 and 6 due to temp. lean conditions in high loads - this turned out to be a poorly welded fp relay which cut fuel at certain points due to car vibration. We didn't notice at the time since the ms unit remained online and synced. Since we couldn't find pistons for this engine, we went for a M50B25 non-vanos block, which worked perfectly, apart from the issue described in the subject. It's kind of a "beneton" car really...M3 itbs, m50b20 vanos head and m50b25 block but my concern is really to get it idling properly. There's no idle valve...we're using the throttle stops to feed some air and regulate idling using a tb vacuometer to get'em synced. Now the issue:

1: starts normally and idles normally while under ASE and WUE.

2: as soon as wue goes away (about 60ºc) it starts surging madly.

I tried everything...installed a vacuum "damper" (small canister to stabilize the signal - I'm running percent baro), got the idle bins richer/leaner at closer and further apart rpms, gave it lower timing and higher timing and the result is always the same....it has no vacuum leaks (tested).

Any help would be greatly appreciated. Please find my .msq attached along with some logs in different conditions. There's also a vid and a pic of the setup. You'll just need to rename logs.pdf to logs.rar and extract, msq.pdf to msq.msq and video.pdf to video.mp4. Dunno if this is allowed but...just working with what I've got

MS specs are as follows:

MS-II V3
2.0.1d
COP ws
VANOS JS0-IAC1A
Tach Out JS3-IAC2B

Thanks for your time, regards from Portugal.

Bruno Belo

[Jimmer411]

I have ITBs in my 86 MR2 with MS2 and had similar issues at first. You want to make sure at idle that your staying in the same cell or make sure that the 2 cells are the same.

I isolated the 4 cells around my idle and set them to to the same amount of advance. From there I increased and decreased my fuel map till it was stable. You may need extra rpm cells around idle to stabilize it as well. it's surging because your jumping between 2 or more cells that have different fuel and timing settings. Increasing fuel and advance increase idle rpm.

It's mostly trial and error but I found my 4age idled smoother a bit richer.

[bmbelo]

Hi there, thanks for your prompt reply. I also have a 4AGE but in an AE86..carbed at first, fuel injected now with MS-II also. Regarding the beemer, I could swear I'd tried about anything....I might have the first 2 RPM settings a bit too spaced (600 and 1300 rpm). Might need a bit more "resolution" at idling... I have idle timing advance function instead of the table for timing. helped a bit. Strange is the engine idles perfectly while cold and under WUE. anyway...

Thanks for your input, will let you know tomorrow how it goes!

Regards from Portugal, Bruno Belo

[bmbelo]

Got it.

wb feedback and PID were ruining idle for me. all sorted.

thanks