Hi Folks,

I've built a Westfield kit car with a 1800cc Blacktop Zetec and Megasquirt EFI. Car runs well even though I've mapped it myself using the autotune feature in TunerStudio. The issue I have is that the AFR is variable at idle, the car doesn't stall but the difference in in running is clear and the AFR can wander from 13 - 16 without anything obviously changing during a drive. Anybody experienced this or have any ideas what could be causing it. I have noticed a difference when the cooling fan cuts in so I was thinking Voltage Compensation?

Any help appreciated.

Cheers,

Paul.

If you record a log during idle while this is happening, can you see the injector pulse width changing and do you see any of the input parameters changing (e.g. TPS, MAF/MAP, CLT, IAT, system voltage etc.)?

Try using autotune with the car idling for about 20 mins. Worked for me
You will need to drop the lower threshold to around 500rpm.

[Edited on 15-7-18 by 40inches]

I second that you should log with TunerStudio to see what is happening to cause the AFR swings. Also make sure that your VE numbers around idle are the same, so that the ECU is not chasing wildly different VE values with small RPM and MAP changes.

Thanks for the replies guys,

I'll take some logs when I get a chance. Inputs seem pretty stable but I suppose I'll need to log over an extended period and do some closer analysis.

Cheers,

Paul

Hi Paul. Widebands aren't always accurate at tickover. It could be running weaker than the reading suggests. Try commanding for a lower AFR and see if it settles down. My 3SGE engine is best at 12.5 at tickover. It may, or may not, actually be 12.5 but who cares? Give the engine what it likes. This all supposes that you are running "closed loop" at idle. If you are not then you would need to increase the idle bins in the VE table to richen up the AFR.
As already suggested, the VE numbers around the tickover bin should be the same. Many people arrange a square of four bins, all the same, with your tickover spot sitting right in the middle. You could try a similar arrangement in your ignition table.

[Edited on 16/7/18 by SPYDER]

I found having a weak mixture at tickover causes wot you are experiencing