Problems with high idle rpm on subaru with CNG

[h2.subaru]

Hello guys,

We are working on a project in the Netherlands at a automotive rechearch center to convert a Subaru Impreza STI prodrive MY07 to run on hydrogen for our graduation. When we are finished the Subaru is able to run on petrol and on hydrogen. We are able to switch control from the original ECU to the Motec ECU. We are running a M800 ECU.

Before running it on hydrogen we started with CNG to get the motec under controle. We now have the problem that the engine keeps running 2000 rpm at idle. We tried lots of things, but can't find the problem. The TP reads 0% on idle, so it looks like that can't be the problem. Idle Aim is set to 1000 rpm. The position translation of TPD to TP is set lineair. We have tried to change the position translation at 0% TPD to different TP settings like 0%; 1%; 2%, But this doesn't effect our problem. Cam position is set to zero degrees and keeps running close to that. Changing the inlet cam positions also doesn't effect the problem.

The basis we used is a mapping of a CNG running subaru from stohl racing. So most of the basis sensor settings should be correct. When we are able to test again we will start logging data and try to find the problem

Has anybody ever had the same problem of heard of it? What are things for us to look for? How can we solve it?
We hope somebody can help us out.

Many thanks in forward,


Henri van Beuningen
Ernst Vossers

Working for "Applied Research Laboratory-Automotive Arnhem"

[stevieturbo]

Im sure you know more about these things than me...


But although the TPS says 0%, have you confirmed it is actually shut ?

If so, have you tried spraying something like easystart around, to see if there are any external air leaks ?

Could the gas itself be allowing too much air into the system causing the high idle ?



What effect does ign timing have ?

[h2.subaru]

But although the TPS says 0%, have you confirmed it is actually shut ?

If so, have you tried spraying something like easystart around, to see if there are any external air leaks ?

Could the gas itself be allowing too much air into the system causing the high idle ?

The problem is we are really close to our deadline [5 working days] and now spending time on reporting. So we haven't took the time to remove the intercooler, but that will be one of the options when we continue.

External air leaks can't be the problem in our opion, because the engine runs fine on petrol. Idle is nice around 800 rpm. If there was an airleak there also had to be problems on petrol.

Thanks for your reply

[Martin]

Its getting air,....thats why its idling high.

Its either 1.leaking into the Inlet manifold, or 2.Your butterfly is letting it through

to find out which one it is, take the IC of and choke the throttle by hand. If it dies immediately then the Butterfly is letting the air through. If this is the case have a look at Adjust>functions>Idle Control>Min Output. (also check Max output)

This limits the Throttle position when its in idle control


I hope you find it...
M

[RossB]

It sounds like the TP low setting might be wrong. If TP low is set with the throttle in its rest position it will never close down to the idle position. Follow these instructions:
Setting the High and Low for TP & TP2
When setting the high & low TP (on the Adjust menu, select Sensor Setup > Throttle Position Hi/Lo) values for the two pots on the Throttle Body (TP and TP2), the throttle must not move while setting the Lo value on each pot, and similarly for the Hi value. This is to ensure that both pots read the same - otherwise a diagnostic error may occur.
It is recommended that one or both of the Auxiliary output wires that control the DBW motor are disconnected whenever calibration is being carried out.
Using a feeler gauge of approx. 0.5 mm, (you may need to use a smaller one than this) press on the butterfly until it clamps the feeler gauge and then set the Lo position for TP and TP2. Then move the butterfly to full throttle, i.e. 90 degrees. Ensure not to close the throttle butterfly to its physical stop, or open the butterfly past the fully open position. This will upset the control and cause the servo to draw excessive current.

If this does not fix the problem you will need to look for other air leaks in the intake system.

[mhd]

It has happen with my 2006 sti and the problem was the setting of the low tp was too much 1.5
check and re set again

[MarkMc]

With the DBW idle control you can ask for negative throttle positions in the normal position and minimum position. This may be a quick way of working out if it is a throttle position setting problem.

[mrsaturn7085]

I'm having this same problem - manifold is sealed up tight, no air leaks...

How much success has everyone had using the 0.5 mm shim? I followed the white paper to the letter, and my throttle is most certainly open too far at 0% TP (cannot attain lower than 2000-2200 RPM). The shim I made was almost exactly 0.5 mm measured with calipers, and I made it extremely narrow so it wouldn't effectively become 'thicker' by resting on the curved throttle body wall.

I am hesitant to use negative values in the normal/minimum position tables as I do not want to force the throttle motors beyond a 'fully closed' physical position and overheat/damage them.

Should I just re-calibrate with the throttle resting on the closed position (and make ALL my minimum TP values > 0)?

May or may not be related - cam positions are a little off after a re-flash until the integral winds up. After 30 sec or so, they appear to be hitting the target value within a degree or two. Engine runs rough until then, but high idle problem persists regardless.