Gee's 68 Mustang chat

[VitesseEFI]

When reading the wideband, don’t forget that mis-fires/partial fires put O2 into the exhaust and skew the readings lean. 

This makes it possible for a car that’s actually pig-rich at idle to the point it’s misfiring, to show up as lean. Especially if it’s also got a big cam. Ignition related misfires can have the same effect.

Sounds like it’s pretty rich everywhere right now.

Good luck with tuning. Wideband does help a lot!

[Gee]

On 17/11/2025 at 00:41, VitesseEFI said:

When reading the wideband, don’t forget that mis-fires/partial fires put O2 into the exhaust and skew the readings lean. 

This makes it possible for a car that’s actually pig-rich at idle to the point it’s misfiring, to show up as lean. Especially if it’s also got a big cam. Ignition related misfires can have the same effect.

Sounds like it’s pretty rich everywhere right now.

Good luck with tuning. Wideband does help a lot!

Thanks. I assumed the value is a bit iffy at idle, especially cold as it is borderline useless jumping around and quite lumpy. I have no idea what cam is in it so can't say if that is having an impact but the idle is the one area that has been tuned.

My auto sparky tuned the idle when swapping the dizzy for me and had a bit of trouble. I took it in as the idle was quite high, confirmed on my multimeter. The adjusted it and set the timing but said they couldn't get it to idle low, they said due to the cam. This was done old school, I assume, where you adjust the throttle screw down and then adjust the mixture so in theory the idle will be the leanest that can maintain an idle.

It is quite rich, and the dyno confirmed that too, but it does not foul plugs so should not be too hard (hopefully) to lean out a few points even for a novice.

[felixx]

Loving this project, keep the updates coming

[Gee]

On 16/06/2026 at 10:40, felixx said:

Loving this project, keep the updates coming

Thanks mate.