Idle problems after bigger cams on a 3SGE

[Wolf_Tm250]

Hi All !

I put bigger cams on a friend ST202, and I know it would happen, idle is steady only if I set it to 1500/1600 rpm.

Lift at TDC is:

intake 1.0mm - exhaust 0.8mm

Is there any other possibility to have a better/lower idle without going for an aftermarket ecu ?
Reduce a bit the overlap, for example turn the intake lift at TDC to 0.8mm ?
Increasing fuel pressure ?
Any other idea ?

Thank you !

[fivebob]

About the only thing you can do is to reduce overlap, either advance the exhaust cam, retard the intake cam, or both. As this problem is most likely caused by reversion (exhaust gas flowing back into the cylinder) I'd try advancing the exhaust cam first.

It might also be caused by changes in the ignition timing that the ECU makes, but the only way to fix that is with an aftermarket ECU.

Anything you do to fix this is likely to lose you a bit of power at the top end.

[Wolf_Tm250]

As this problem is most likely caused by reversion (exhaust gas flowing back into the cylinder) I'd try advancing the exhaust cam first.

Sure.... I was only afraid by the small number at TDC of the exhaust cam... I'll try to decrease it from 0.8 to 0.6mm....

Thank you, fivebob... bye

[RedMist]

What's the duration?
Are you running standard injectors, fuel pressure?

You may find that the ECU is being fooled by intake reversion and thinks at idle it's actually under load, hence over fueling.

If you have altered the fuel pressure or injector sizing, again this may be the cause of over fueling at low RPM.

I drive my 4age with 304 degree cams via a Link. It runs the first three rows Alpla N and all additional rows Speed Density. Makes for a very nice idle at around 800.

[Wolf_Tm250]

What's the duration?
Are you running standard injectors, fuel pressure?

You may find that the ECU is being fooled by intake reversion and thinks at idle it's actually under load, hence over fueling.

If you have altered the fuel pressure or injector sizing, again this may be the cause of over fueling at low RPM.

I drive my 4age with 304 degree cams via a Link. It runs the first three rows Alpla N and all additional rows Speed Density. Makes for a very nice idle at around 800.

264 degrees, std injectors and std fuel pressure...
as I told, I know that the ECU would be a must to have a good and fine idle...

but he ( my friend ) as just bought that ST202, so is actually out of money , and he asked me if it was possible to make it more stable...

Bye !