Loss of spark / revs

[nakedninja900]

Matt
Im not running an IAT sensor at the moment as I'm only running spark.should I (can I)cswitch it off?
I've tried calculated but it didnt make any difference.
It seems a bit odd that negative number that it goes into is always the same as my trigger offset number.
On MS3 I see that "cranking advance" is adjustable , but I don't recall seeing that on the Microsquirt?

[Matt Cramer]

You should definitely zero out your IAT timing retard if you don't have an IAT sensor.

IIRC, the "trigger rise" setting defaults to a particular tooth with the wheel decoder when cranking, and I can't recall which tooth off the top of my head, but it would be tied to the offset number.

[nakedninja900]

Just a quick update that might help some people , I thought that I might have some fouled plugs as someone else on the forum had a similar problem and that cured it so I fitted new plugs but there was only a very slight improvement, I then noticed that I was running 20deg advance in the sub 700rpm which got me thinking am I overloading the ECU ? Perhaps it's too much for it to get sync and then try to reach 20deg straight away so I lowered it to 2 deg at 700rpm and then 18deg at 1000 rpm so it should have an easy time starting and then quickly ramp up at idle speed. I also switched to calculated trigger and hey presto she fires up on the button hot or cold
I'm chuffed to bits , now I just need to sort the high rpm cut out and I'm there.
Thanks guys for the help and advise much appreciated.

[24c]

..Perhaps it's too much for it to get sync and then try to reach 20deg straight away so I lowered it to 2 deg at 700rpm and then 18deg at 1000 rpm so it should have an easy time starting and then quickly ramp up at idle speed. I also switched to calculated trigger and hey presto she fires up on the button hot or cold ...

Just dropping in on the forum, and saw your comments. I too found that reducing the advance boosted the "starter button" performance, and just thought it was the mistimed (over advanced ignition) combustion event hitting the piston, that was fighting against the cranking rotation, and slowing the crankshaft down. Retarding the ignition like you did will reduce kick back, and probably increases the life of the starter drivetrain on a motorcycle, but never tried calculated trigger though.

PS. This affects non EFI stuff too, as I was driving an old flat twin engined car some months back to a classic car event, which had a manual advance and retard mechanism linked to the choke (cold start) & distributor mounting, and this exhibited the same slowness to fire, hot or cold. It turned out the old boy that owned the car had set the engine up with too much advance, so once I retarded the distributor some more, it fired up straight away, but strangely it was still way too advanced at high speed. So I disconnected the choke mechanism, and ran with a manual advance retard mechanism as I went down the road, which worked a treat and was like going back in time, listening to the engine and tweaking the timing. Now if it was Microsquirted, I'd have missed all that!

The subsequent over advance was due to the bob weights being so knackered & sloppy in the distributor, so the engine was running 50 deg of advance versus 20 degrees originally. Always the simple things

[nakedninja900]

Well I've been on the dyno for 3 hours in total and we've got some lovely graphs, gained 10hp between 5&8 thousand RPM,
I was however getting the occasional kickback when starting ,especially in this cold weather. I seemed to still be losing synch now and again while cranking so I played around with the pulse tolerance and ended up with 100% cranking ,85% after start and 20% running and this seems to be spot on now. I noticed that cranking pulse can be set at a value of more than 100% what effect does this have ? Is there a recommended maximum setting for this?
Cheers.

[grippo]

You can't go above 255% but greater than 100% tolerance is more than 1 missing tooth, so if you need more than 100% how can the ecu distinguish the real missing tooth from the tooth that is requiring more than 100% ? That said, I have heard of people using 150 or even 200 to get started. If it works, there's not much I know to say, but you only want to use this much to get it to fire, so only for cranking.

[mfro]

I've found that estimating the right advance for the ease of starting and smooth, clean idle isn't easy, especially with low rotational mass and hot cams on a small capacity, high compression motorbike engine (single cylinder, in my case). Of course you could always gear to OEM specs, but what if there are none for a tuned engine?

Common sense tells you you'll need low advance to make sure you'll move top cylinder pressure behind TDC under all circumstances but actually it showed up that it's basically the combustion quality at low rpm on tuned small capacity engines that determines advance needs (tuned engines have a tendency for bad combustion quality at low rpm due to large intake cross sections resulting in bad mixture quality at low airspeeds).

I started with 12° of idle advance which let my engine run, but also caused the exhaust glow from front to end in seconds at idle after start (exhaust gas still burning when exhaust valve opens due to hot cam timing). Hot cams make the practical "advance window" very tight at idle.

Ended up with a compromise (which works pretty well, actually): measured exhaust manifold temperature with a cheap infrared thermometer and adjusted advance to the lowest temperature where I still had stable idle. Turned out that was also a good settings to ease starting behaviour.

Determining the right advance at higher rpms is even more difficult as it's always a delicate compromise between good power and engine longevity. The closer you move top cylinder pressure towards TDC, the more power you'll get, but you'll also increase stress to your engine because this will also increase cylinder pressure before TDC due to near-constant duration of combustion. Better stay on the safe side ;)

[nakedninja900]

Spent another hour on the dyno yesterday and we have the final advance curve nailed, however I still can't get her to rev to the redline (12000) I'm only getting to 9250 ,the confusing thing is that I'm not losing synch but its as if all four coils are just being switched off. The rev counter also goes berserk but synch remains on 3 ! I've tried the resistor on the VR sensor wiring but that made it worse ,I thought it may be too short a dwell time so I changed it from 2ms to 2,5 but the value never changes on a running motor it always stays stuck on 2ms even changed the duration but no change?
Any ideas?
Thanks guys.

[mfro]

What does the triggers +/- display in TunerStudio say?

[nakedninja900]

mfro
thats a good question ,I forgot to datalog the last dyno session
I'm in the process of getting her ready for the road and I will then log a run on the road, i just need to get the mobile software and bluetooth adapter sorted out.