Hello,

The problem is that my engine RPM oscillates under load.
I've made a log of the engine turning stable at 900RPM. When I turn on headlights, interior fan or cooling fans, the AFR goes lean and the idle oscillates.
How can I solve this? Min Voltage is 12,4V. Tried different PID settings, but can never solve this issue.

Thanks for reading

 

The AFR going lean causing the idle to oscillate is the answer to your problem. Tune your idle region of your fuel map so that your AFRs are steady and then see what happens. If you do a search on this topic you will find that is the number one recommendation.

 

Hi,

Idle region, ignition and AFR is tuned properly I think. Check my files please.
No oscillation occurs when engine idles without any load.

AFR at 13,5, tried timing 10,12,14 and the VE table tuned stable in idle region.

When I turn the PWM back to open loop, the idle RPM only drops with load but there's no oscillation at load...

Thanks

 

I did look at your files. Your RPMs were from 650-1180 and your AFRs were from 12.5 to 15.1 all the while your TP% was at 0. So I would say that your idle region fuel is causing the oscillation when PID idle is running. Unplugging the IAC valve will have the same result as turning off PWM.

 

Hi,

Thanks for looking at my files. You're right.

AS you mentioned, the idle region fuel is causing the oscillation when PID idle is running, but why only when the load increases?

In the first and last seconds of the log file, the engine is running stable because it is running without any load. AFR numbers are good there.


Should it run more rich than AFR 13 in idle to prevent going lean under load?
What do you suggest?

Thanks Hector

 

Exactly, as long as your AFR is steady then so is your idle. You have to make it so that when load increases at idle it doesn't change your AFR so wildly.

If your engine likes 13 then try to not let it swing too much one way or the other. I don't think it needs to be that rich but most people report the engine idles better below stoich. I run 14.2 I think. I had your same issue and getting the fuel and ignition steady in idle regions greatly helped my idle under load conditions although I will admit it is still a work in progress.