Engine Idle Question

[Paul Bryant]

3: Air -This makes me suspect IACV stepper motor as the key culprit. A control: swap on a known good Throttle Body assembly, my money is on this fixing the problem with the low idle..

Note;
We swapped the entire throttle body assembly, Injectors, TPS, Stepper motor.

 

[Claviger]

Oh ok, didn’t that part sorry.

I’d suggest a dry/wet compression test or leak down test just to rule that out, because the next item is the wiring harness and that ain’t no fun!

 

[Claviger]

Forgot to ask, have you tried loading the stock map and tors map, unmodified, to verify it’s not the base tune file the custom tune was written on?

 

[Claviger]

To answer the reset adaptation question.

With the stock setup and tune, the computer is looking for a set frequency of events for the narrow band o2 sensor to cross back and forth across stoichiometric. If it lingers too long on one side, the ECU adapts by adding fuel or removing, represented as a trim value. This small adjustment can compensate for wear and age of items, it’s intended purpose. The adaptation algorithm is only active in the RPM/TPS ranges of the AFR target table that are 14.xx (forget exact value at the moment), which are also the only places the bike runs in closed loop mode, everywhere else it totally ignores the narrow band O2 and runs in open loop mode using the trim amount developed by the closed loop adaptation.

By resetting it, you’re falling back to the base values in the table + the modification variables (baro, IAT, ECT). Then the software runs through the setting of the idle control circuit. They’re tied together, the reset and idle adjustment, because a trim reset will throw off the idle if not adjusted since it leads to a change in idle AFR.

When disabling the O2 sensor, the bike will never adjust the trim, it has no feedback, so there’s no narrow band O2 sensor value for it to adjust against. The rocket idles much smoother at 13-13.5 than at 14.7, one of the main reasons I firmly believe all rockets should have the O2 sensor turned off.

When going with a disabled O2 sensor and custom tune, it’s good practice to reset the adaptation to ensure it’s at zero, because it ensures that you don’t do all your tuning with a trim value and then later that trim value is changed or reset to zero, which would then significantly modify the fueling into the motor with no changes in the tables.

This is why some canned tunes are far off when perfect on one bike but run like ass on another, the trim values were different.

Hope that makes sense....

 

[Claviger]

Further, the “12 minute tune” is simply a way to force the rocket to make that adaptation and adjust the trims.

As you could posit, the 12 minute tune does absolutely nothing on a bike with the O2 sensor disabled.

 

[Paul Bryant]

I have PCV&AT so this has a wide band O2 sensor.

Thoughts:

The stepper motor is cycling, we know this as we have checked.
The ECU is functioning properly as we swapped for another one with the same results.
So the stepper motor is doing what it is told by the ECU which gets its parameters from the various sensors.
The Fan is kicking in at the appropriate temps so the Engine Temp sensor is O.K.
The MAP sensor is fine, swapped it.
The Barometric sensor is fine, swapped it.
The TPS, Stepper motor and injectors are fine, swapped complete Throttle body assembly.

So what other inputs are giving the ECU inputs that it tells the stepper motor to set idle at a lower than required setting ?

We haven't checked compression ratios, but the bike runs like a scolded Cat when out on the Road, (I know Engines, so know what a bike feels like with one jug down) also we can force it to idle where we want so if compression was down this wouldn't happen.

It comes down to some input giving the ECU false information, which then in turn directs other functions such as the Steeper motor with false info.

 

[sleeves]

Forgot to ask, have you tried loading the stock map and tors map, unmodified, to verify it’s not the base tune file the custom tune was written on?

When we swapped the ECU we left the stock map in the ECU we fitted a base 20050 map, unchecked the 02 of course as its removed. Made no difference to idle, even left the secondary controls on and the spare fuel injection system still had them fitted.

 

[sleeves]

Sleeves,
So look at injection pulse width between the two bikes, they’re nearly identical. Fueling is being controlled properly, so let’s move to the next three factors. The AFR sensor be ****ed, if the injector pulse with is the same, the fueling is the same, and the problem lies in the air supply.

1: Compression - test it, I had a feeling it was this upon initially reading the original post. If a hole is down on compression you’ll definitely see it on a wide band.

2: Ignition - if you’ve new plugs with good gap and all three coils are good move on.

3: Air - Don’t stress the not reaching 1100 RPM, but it should at least idle in the 850-900 range without issue. This makes me suspect IACV stepper motor as the key culprit. A control: swap on a known good Throttle Body assembly, my money is on this fixing the problem with the low idle.

The 99% value... you’ve a sensor backwards . The main TPS and secondary TPS are physically interchangeable, however they work inverse internally. At max voltage the MTPS is read by the ECU as 100% but at max voltage the STPS is read as 0%. It appears that you’ve got a MTPS sensor installed on the STPS location.

I do not think that has anything to do with the idle low issue however.

Side Note: At the very low RPM he’s idling at you’ll start to get some strange effects because of the low air velocity and very long times for each of the 4 cycles of running. 640 is not far above the lower limit before it’ll stall out (around 550-570 in my experience).

Thanks all done on 1,2&3 and we may have the 2 TPS's plugged in wrong way, I plugged them in and may have messed that up, we'll check tomorrow on that.

Not worried about fueling as this seems to be not too bad, but the low revs are the issue (agree re low speeds), concerns me we can jack the idle up by adjusting the ISM nut but once we do a TPS and ISM reset back to square one. Of note are the different manifold pressures on the bikes indicating my throttles are further open and lowering the pressure we need to try and emulate this and the only way to do it seems to be forcing the ISM adjustment. On the injection system this nut is the only one that works directly on the throttle disc main shaft

 

[sleeves]

To answer the reset adaptation question.

With the stock setup and tune, the computer is looking for a set frequency of events for the narrow band o2 sensor to cross back and forth across stoichiometric. If it lingers too long on one side, the ECU adapts by adding fuel or removing, represented as a trim value. This small adjustment can compensate for wear and age of items, it’s intended purpose. The adaptation algorithm is only active in the RPM/TPS ranges of the AFR target table that are 14.xx (forget exact value at the moment), which are also the only places the bike runs in closed loop mode, everywhere else it totally ignores the narrow band O2 and runs in open loop mode using the trim amount developed by the closed loop adaptation.

By resetting it, you’re falling back to the base values in the table + the modification variables (baro, IAT, ECT). Then the software runs through the setting of the idle control circuit. They’re tied together, the reset and idle adjustment, because a trim reset will throw off the idle if not adjusted since it leads to a change in idle AFR.

When disabling the O2 sensor, the bike will never adjust the trim, it has no feedback, so there’s no narrow band O2 sensor value for it to adjust against. The rocket idles much smoother at 13-13.5 than at 14.7, one of the main reasons I firmly believe all rockets should have the O2 sensor turned off.

When going with a disabled O2 sensor and custom tune, it’s good practice to reset the adaptation to ensure it’s at zero, because it ensures that you don’t do all your tuning with a trim value and then later that trim value is changed or reset to zero, which would then significantly modify the fueling into the motor with no changes in the tables.

This is why some canned tunes are far off when perfect on one bike but run like ass on another, the trim values were different.

Hope that makes sense....

Thanks just wanted confirmation on this. I was hoping it re-ranged the ISM position also as part of this to allow idle adjustments up and down in case the adjuster arm got too far towards one end of its adjustment and was locking up at the end of its stroke. Obviously not, the adaption reset is just the baro, air temp and engine temp to baseline.

My bike is running a solid 13.5 in the above image as we were monitoring the PCV at same time

 

[sleeves]

Oh ok, didn’t that part sorry.

I’d suggest a dry/wet compression test or leak down test just to rule that out, because the next item is the wiring harness and that ain’t no fun!

Think the comp test is not far off here...