Engine "idle" runaway

[greenamex2]

Hi all

Well my make shift engine kill switch came in handy today!!!!

Finally got the engine started (long list of issues, still haven't fixed the dead injector). As per the attached log the first start went fine but the second (when I was recording some footage) I got extreme RPM runaway and the artificially low rev limiter had to step in.

The engine is Drive By Wire, 3L V6 on ITB''s.

Any idea what I have done wrong? My theory is related to the engine idle system not being entered because the idle maximum throttle open is too high...but I am new to M1 ECU's...my old Pectel T6 was a much simpler beast!

Any tips welcome.

For your amusement...a short clip of the engine starting - https://youtube.com/shorts/9Rj3Z59njbk

[Sean]

Firstly I need to preface my remarks with the disclaimer, I'm no M1 scholar, just a M800 guy trying to learn a bit.

At 177.7 seconds roughly, where the idle starts to rise rapidly, it seems to me that the ecu is adding timing at exactly the ramp rate (30 deg/sec) specified for when it exits idle state. I see the limiter has grabbed it

I don't know why the idle aim is at about 1500 rpm, I can't see enough compensations (but it is nearly midnight ) that would add 600 rpm or so. Seems like the idle speed got away from the aim a bit and the ecu decided to switch from idle to normal mode.

I think the idle speed increase seems normal for the timing increase.

Cheers, Sean

[greenamex2]

Hi Sean

Like you I am coming from a different ECU, a 90's Pectel T6, and am trying to learn all this new fangled technology!

Good spot on the idle ramp up...another lesson learnt!
the point

I guess it is dropping out of idle and ramping up timing because of hitting the following rule in the help -
Engine Speed is below Idle Aim + Idle Activate Engine Speed Margin

At the point ignition starts ramping up idle aim (177.1s) is around 1464RPM and the speed margin is 500RPM, making 1964RPM, obviously less than the actual rpm of around 1981RPM.

Kind of makes sense. Learning all the time.

I guess the short answer is the engine doesn't need 15% throttle to start and idle!

[Sean]

As a comparison, the engine I have most years of experience with, a 6.7 litre v8 @ 760 hp with biggish ITBs, idles at 1.3% throttle (with 0% being fully shut).

Do we think the idle aim is 1464 rpm because the ecu is applying compensations that we can't see on top of the target rpm that's in the table? The idle aim before it starts is 1050, which seems right, 900 plus 150 initial post start comp.

[greenamex2]

As a comparison, the engine I have most years of experience with, a 6.7 litre v8 @ 760 hp with biggish ITBs, idles at 1.3% throttle (with 0% being fully shut).

Do we think the idle aim is 1464 rpm because the ecu is applying compensations that we can't see on top of the target rpm that's in the table? The idle aim before it starts is 1050, which seems right, 900 plus 150 initial post start comp.

Interesting...I have gone from a full race 1.6L 4A-GE (beyond Formula Atlantic...which isn't hard) to a fast road VQ30 (3L V6). Guess I am having difficulty adjusting from something that ticked over at 2000RPM and was mapped to 10,000RPM.

Part of the high idle aim was due to some idiot left the air con stuff enabled, despite not having air con yet! Sooner I actually get exhaust manifolds and silencers fitted the better. Think my neighbours will appreciate it as well!

[David Ferguson]

Questions/Comments looking at your package:

-- Are your injectors really located above your throttle plates? You have Fuel Injector Primary Location set to Before Throttle Airbox Referenced?

-- I think the reason your Idle Aim is initially 1550 RPM is because, Idle Aim Main (900) + Engine Post Start Idle Aim Compensation (150) + Idle Aim Ramp Down (500) = 1550. Can you verify that the "Idle State" is not Enabled (this is what causes the Idle Aim Ramp Down to be added. This is not in the log, you will need to look at it in M1 Tune after a start.

-- I suspect your Idle Mass Flow Feed Forward values are too high. But for an initial startup, I would just change "Idle Actuator Throttle Aim Maximum" to get the system to work. Try lowering this to 10%. This is just for initial startup, then you can figure out what it really needs to be. With ITB's it may be that you need 5-7%. And the Feed Forward values will be 30 - 70% of that to control the idle.

-- From the log I see that you have a Fuel Output Diagnostic of "Combined Open Fault". Might want to double check wiring, or injector characterization, but I have a similar issue with one engine and everything seems fine and it doesn't affect the running.

-- Is your throttle bodies calibrated so that fully closed is 0% Throttle Servo Position? I am surprised you need the "Engine Crank Idle Mass Flow" to be 100%. Again, this is often only 50% or coolant dependent, and more open on colder starts.

-- Since you don't have a tuned efficiency table, you might want to start with a value closer to 50-60% instead of 100% efficiency. That may be why you find you need more throttle to get it to start.

[greenamex2]

Many thanks for assisting David -

Questions/Comments looking at your package:

-- Are your injectors really located above your throttle plates? You have Fuel Injector Primary Location set to Before Throttle Airbox Referenced? They aren't but as per CTN0036 I have set it to before the throttle "Set Fuel Injector Primary Location and Fuel Injector Secondary Location to Before Throttle
Airbox Referenced. Use this setting even if the injectors are positioned after the throttles.."

-- I think the reason your Idle Aim is initially 1550 RPM is because, Idle Aim Main (900) + Engine Post Start Idle Aim Compensation (150) + Idle Aim Ramp Down (500) = 1550. Can you verify that the "Idle State" is not Enabled (this is what causes the Idle Aim Ramp Down to be added. This is not in the log, you will need to look at it in M1 Tune after a start. I'll add this to the logging

-- I suspect your Idle Mass Flow Feed Forward values are too high. But for an initial startup, I would just change "Idle Actuator Throttle Aim Maximum" to get the system to work. Try lowering this to 10%. This is just for initial startup, then you can figure out what it really needs to be. With ITB's it may be that you need 5-7%. And the Feed Forward values will be 30 - 70% of that to control the idle. Thanks, will do.

-- From the log I see that you have a Fuel Output Diagnostic of "Combined Open Fault". Might want to double check wiring, or injector characterization, but I have a similar issue with one engine and everything seems fine and it doesn't affect the running. Yeah, know about that. One of the injectors has a burnt out coil, waiting for a replacement from Vivid...didn't realise the ECU had spotted it as well, clever!

-- Is your throttle bodies calibrated so that fully closed is 0% Throttle Servo Position? I am surprised you need the "Engine Crank Idle Mass Flow" to be 100%. Again, this is often only 50% or coolant dependent, and more open on colder starts. Yes it is calibrated to 0% fully closed. Just left this one at default, will try dropping it next test

-- Since you don't have a tuned efficiency table, you might want to start with a value closer to 50-60% instead of 100% efficiency. That may be why you find you need more throttle to get it to start. This is set to 100% as per CTN0036 "Turn off all Engine Efficiency table axes and set the remaining site to 100%. This table will not be adjusted."

Massive thanks for your assistance, learning all the time!