Author Topic: Engine stalls when blipping throttle  (Read 9342 times)

Offline Tcal

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Engine stalls when blipping throttle
« on: November 01, 2007, 02:25:40 pm »
So i got that cold start setup right, so it´s time to move to next "problem"..

When iat is about 10-20 degrees, that stalling doesn´t usually happen.
But when iat rises, engine stalls after blipping throttle or if i use steady rpm at 2000 like 5 secs and then release throttle..
Sometimes revs drop down to 500 and then it recovers to idle...

I´m thinkin that could this be cured by activating that Idle PID.
I did try to search some instructions to how use it, but i didn´t find any good info what those values really mean.

I know that this could be caused by other wrong setup too.
Im just thinking that it´s coming from that IAC setup..

And i noticed that if i start warm engine and idle should be 950rpm, revs might be at 1100, but if i blip throttle a bit revs drop down to 950.
IAC DC is at warm idle 54-55
In IDLE ref table i have 55 in warm value.
When revs are at that 1100 rpm, and i put 54 to that warm value then revs drop to normal too..

For example if i have IAC dc at 58 at 4degrees clt should that 4degree value in that table too be at 58, or should it be a bit higher than that 58?


« Last Edit: November 01, 2007, 02:29:08 pm by Tcal »

Offline rob@vems.co.uk

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Re: Engine stalls when blipping throttle
« Reply #1 on: November 01, 2007, 10:59:28 pm »
PID tuning is a hugely complex thing to explain, its probably best to google pid tuning.
Theres a good wikipedia page: http://en.wikipedia.org/wiki/PID_controller

Offline Sprocket

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Re: Engine stalls when blipping throttle
« Reply #2 on: November 02, 2007, 12:49:54 am »
Threshold for activating IAC looks rather small.

Set the advance change max advance to 5, advance change max retard to 5 and set threshold for activating IAC to 4. What this does is alow the PID to alter the advance plus minus 5 degrees, but when the change reaches plus minus 4 degrees it activates the iac to add remove air bringing the advance back into the middle of these settings and hopefully to what you set in the ignition map.

PID settings not to bad, but id be looking at more I. 40 for P is not too bad, i havent yet worked out how to determine this value, normally when talking about temperature controllers this value is a is in percent, of the input range (temp sensor min max)Anayway, I found 60 in my set up to be about right

Try an I value of 20 and a D value of 10 and see how you get on, you could try a P value of 60, but try the 40 first. Make a note of your setings you have now, so at least you can go back to your original config if changes dont work. You could remove D altogether for now and introduce it later only if the idle seams to hunt?

IAC dead band looks a little small to what im using, i think i use the default of 25. Integral increase and decrease I have set to 20 and 140 respectively. Integral dead band is 25. Again, they work on my set up, may or may not work on yours.

Not sure what you would set the stepper speed / PWM frequency to with a PWM valve, but as its set to zero and the PWM valve enabled, whats the frequency??? zero??, again not sure on this as i run the stepper.

One other thing is I have Asymetric PID enabled but dont really know how this affects the idle, i enabled it and didnt notice much difference.

Some other things to consider, on the low KPa low RPM sites in your ignition map put a larger value so when the RPM drops below idle, the igniton gives the engine a little more energy.

If you have the lcd, watch the EGC value when you lift off the throttle, if it stays at 00 below about 2000rpm, the fuel cut may be set too low. If it goes way high or low, the VE table needs altering, as i found that the large EGC values takes longer to recover.

The PID refference table is the amount of DC required to give the correct amount of airfor idle at different CLT temps, the colder the engine the more the DC. The 71 degree value is the base value that the IAC will try and maintain when the engine is idling correctly when the engine is warm. The actual value will change with idle control, but if its miles away from the base value, these settings need to be revewed.All the other values for the cooler CLT values, this would be the DC required to maintain the idle speed at that temp so if its 55 at 71c it will be higher at -40c

Bliping the throttle stalling is down to acceleration enrichments, i suffer this, yet the driving is pretty good, I have had a hard time to get the AE anywhere near right in my set up, its nearly there, but blipping the throttle is still dodgey. I have some work still to do here.

Remember to record the settings you have now so you can at least go back to where you were originaly if anything i suggested about doesnt work for you.

Hope some of this helps a little, as some of this sounds very familiar to what i experienced.
« Last Edit: November 02, 2007, 12:54:45 am by Sprocket »

Offline Tcal

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Re: Engine stalls when blipping throttle
« Reply #3 on: November 02, 2007, 12:13:17 pm »
I did some research at work last night about that pid.
I´ll try first with it disabled..

I did found good instructions to set that P value.
I have to use mdi command to find correct IAC DC values. ( Idle advance control disabled)
First, higher 200-400 rpm value above desired idle and then that desired idle.
There i have just have to count how many steps is between.
There´s the P value...


Offline Tcal

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Re: Engine stalls when blipping throttle
« Reply #4 on: November 02, 2007, 06:25:30 pm »
Hmm. more questions coming...

That IAC valve in oem setup:
When throttle is opened above idle threshold, ecu drives that valve to fully closed state, so it is powered all the time..
When unpowered or in faulty condition that valve is resting against brass bolt which is setted in factory so that engine idles at 1300-1400 rpm if connector is removed.

When tps is above idle threshold, iac valve is unpowered in vems, correct?
Maybe i should set that bolt so that the valve is closed when unpowered or tps is above idle threshold.
As now some air flows through that valve when it shouldn´t.!!

Maybe i should try to put less advance  (now approx 18) and more fuel to idle, kpa is near 35 at idle. Or should i try to set that idle kpa as low as possible?

I looked at firmware 1.0.73  (I´m still running on .53) that there is a new option:           
Iac follows tps when not idle
Does this mean that when tps is at 100%, that iac is opened 100% too?

Here´s an picture of it to help,  brass bolt is missing from that



« Last Edit: November 02, 2007, 07:39:22 pm by Tcal »