MyE28.com

I've had this problem ever since I installed megasquirt 2 on my 1988 535i. It never did it beforehand on stock engine management which leads me to believe its an issue with my tune or MS2 install. When warm the motor idles nicely right around 900-950 RPM but has a slight miss that you can hear and feel. Also when cruising and lightly on the gas (low load/low rpm and highrpm) it misses even worse and backfires, not as bad at low RPM but worse at high RPM. When accelerating or holding the gas pedal at any point past this one spot it runs very nice and very well. Problem has been present before and after turbo setup. Attached is my MSQ and a datalog before the turbo setup. No improvement has been made on this issue.

Setup:
MSD Blaster 2 Coil (Also tried stock Bosch coil no improvement)
BAV Auto Plug Wires (Came with the car)
New Stock Dizzy Cap and Rotor
ZGR5A NGK Plugs at .027
M30B35 60-2 Trigger Wheel and VR sensor
M30B35 Auto Variable TPS
AEM UEGO Wideband 30-4110

Turbo Setup:
Top Mount T3 Manifold
Holset H1C Rebuilt

https://drive.google.com/open?id=0B-cWb ... 0NpeU9sczA <<<MSQ
https://drive.google.com/open?id=0B-cWb ... E5YV2NPSmM <<<DATALOG

It may be your vr sensor signal needs to be tuned. There are two small pots inside the ms unit that can be tuned to get a more stable vr pulse. You may be able to see it happen if you can watch the flickering led on ms,. Get it to stumble, and watch to see if led flickers out momentarily. I had to tune the pots on mine. Look in mega manual for "tuning the vr signal " iirc
good luck

I will take a look at this. I haven't messed with them yet theyre just fully counter clockwise for now or whatever the build manual suggested. It makes sense that this would play into this problem.. Luckily I havent had to deal with the high rpm cutout alot of people experience with the 60-2 trigger wheel.

Thanks guys. I'm gonna mess around with it tonight. I'll let you guys know what happens.

So I messed around with the VR pots on the main board while the motor was running and monitoring the tooth logger and composite logger. I tried turning each pot individually and together numerous times and no change happened to the logger. It seems like I have a pretty good tooth log though, there are no missing lines and each line is where its suppose to be etc... Maybe a fueling issue of some sort? I've replaced the entire ignition system to no avail.

Was this issue present with the old cap & rotor? I went thru the same scenario with new stuff & turned out the new (purchased from dealer) cap was defective. I spent at least a month chasing that one.

Yes it was present with the old cap and rotor only AFTER the ms2 conversion. With the stock ECU it ran fine. Maybe its just in the tune. More fuel less timing at low load low rpm?

ReidCWagner wrote:Yes it was present with the old cap and rotor only AFTER the ms2 conversion. With the stock ECU it ran fine. Maybe its just in the tune. More fuel less timing at low load low rpm?

What are your settings currently? It's possible your map has a island or sudden jump in the timing map/ The fuel map should also be smooth...

https://drive.google.com/open?id=0B-cWb ... nptblpKWVk
https://drive.google.com/open?id=0B-cWb ... 3hQLWlYUlU

Fuel maps ^^

https://drive.google.com/open?id=0B-cWb ... l9qbkNVck0
https://drive.google.com/open?id=0B-cWb ... 1VwUVJrSFk

Timing Maps ^^

Typically the issue is under light throttle input. Right around 55-65 kpa and gets worse with rpm. Idle vacuum is right around 43-45kpa. If you plant your foot to the floor the issue goes away.

It seems to me your ve map is quite poor as you don't have the large hump near max toque (4000 rpm). How did you arrive at that map? I'm nto saying that is the root cause of your problem, but it could be contributing.

I just let VE Analyze Live tune it to the AFR targets so maybe this is my issue. I did notice it running lean in the problem area and bumped the fuel up a bit manually which seemed to help but im at around 14.7 AFR in these conditions and don't understand why it would need to be richer than that. Also do you have any maps of your setup so I can see the hump you're talking about at peak torque? The timing map was used from another member on here with an m30b34 turbo setup very similar to mine.

Here is mine in terms of general shape. With autotune, it tends to make the map less smooth so sometimes you have to go back through and and smooth out the cells.



My recent AFR targets


I run 91 octane on m30b34. Still had been working into the timing map and was probably a bit rich in the 80-100kpa region but my tuning got stalled again lately.

Could I get a shot of the timing and fuel table numbers just so I can get an idea of whats going on?

Sure,

This was where I was at when I left off tuning, 91 octane but haven't tried it on 89. Should be safe as I was going for a conservative map. Just make sure your base toothed wheel settings are set to ~88* falling edge. Some use 84 or 86, I am not. That's why I am hesitant to use other people's maps as thy don't always mention what base ignition settings they are using...





Generally you want the least ignition advance where the ve table has the largest hump, and then some can be added as the ve table drops off again. I haven't messed with this too much but had planned too...

How are you running 25' advanced at idle? I see a lot of timing maps running a lot of advance right around idle rpm and kpa. Do you have it set up to use idle rpm advance timing? I run 15'-16' advance at idle where its the smoothest. I run 89' trigger angle with falling edge and verified with a timing light.
I'm still kinda new to tuning but am trying to learn the most I can about it so I can do it all myself.

ReidCWagner wrote:How are you running 25' advanced at idle? I see a lot of timing maps running a lot of advance right around idle rpm and kpa. Do you have it set up to use idle rpm advance timing? I run 15'-16' advance at idle where its the smoothest. I run 89' trigger angle with falling edge and verified with a timing light.
I'm still kinda new to tuning but am trying to learn the most I can about it so I can do it all myself.

My idle advance is set at 16* controlled by the idle advance setting.