Printable Version | Subscribe | Add to Favourites
New Topic New Poll New Reply
Author: Subject: Megaquirt variable AFR
zammobhoy

posted on 15/7/18 at 02:10 PM Reply With Quote
Megaquirt variable AFR

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.

View User's Profile E-Mail User View All Posts By User U2U Member
MikeRJ

posted on 15/7/18 at 03:58 PM Reply With Quote
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.)?
View User's Profile View All Posts By User U2U Member
40inches

posted on 15/7/18 at 06:20 PM Reply With Quote
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]

View User's Profile View All Posts By User U2U Member
wombat258

posted on 16/7/18 at 10:16 AM Reply With Quote
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.
View User's Profile View All Posts By User U2U Member
zammobhoy

posted on 16/7/18 at 10:45 AM Reply With Quote
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

View User's Profile E-Mail User View All Posts By User U2U Member
SPYDER

posted on 16/7/18 at 10:53 AM Reply With Quote
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]

View User's Profile Visit User's Homepage View All Posts By User U2U Member
chris

posted on 16/7/18 at 11:42 AM Reply With Quote
I found having a weak mixture at tickover causes wot you are experiencing
View User's Profile E-Mail User View All Posts By User U2U Member

New Topic New Poll New Reply


go to top






Website design and SEO by Studio Montage

All content 2001-16 LocostBuilders. Reproduction prohibited
Opinions expressed in public posts are those of the author and do not necessarily represent
the views of other users or any member of the LocostBuilders team.
Running XMB 1.8 Partagium [ 2002 XMB Group] on Apache under CentOS Linux
Founded, built and operated by ChrisW.