EFI, Crower intake, idle problem

[Hocky]

This is what I got:
Chevrolet 547cui BB
Crower stacked intake with 8 x 2.9" throttle plates. Modifed to EFI and split the axles.
Autronic SM4 EFI
Autronic R500 CDI ignition (8 coils, wastefire)


My problem:
Have made some test starts and tried to get a stable idle. When leaning out the fuel to get to a nice 14.7AFR a get cylinders "sneesing" up thru the intake. I know this is because some cylinders is going too lean :(
I have made some adjustments to the throttle plates trying to get them all in sync. Have also tried to get them synced with a Uni sync tool.

I know the intake is not 100% in the axles and the plates maybe not all seal 100% but very very close.
I have can not use the idle screws at all and the plates are as closed as they can be. If I open the throttle with the idle screw I get to high idle. Some throttle plates vibrate (opens a little) sometimes and I have a feel that its maybe a plate thats a little to sealed and the cylinder is making the plate open by vacum.

I know that I must make new axle bearing and maybe replace the throttle plates and axles but not now.

Any advice?
Drill a small hole in the throttle plate?
How to get all plates to seal better?

Getting frustrated :machine:

Pictures here,
http://www.hocky.se

[camcojb]

As far as the A/F I have never seen an IR EFI setup that was happy idling anywhere near 14.7:1 A/F. Mine wanted to be 12.8-13.2 at idle and was very happy there. It could be 14.7:1 or leaner at cruise areas, but not idle. One thing I learned a long time ago is give the engine what it wants, don't get hung up on the numbers. If it idles better at a richer A/F that what I do.


As far as the idle speed, it's obviously pulling air from somewhere. If you can richen the idle and live with the butterflies closed for now that'd be my suggestion, at least until you can re-do the shafts, etc.

Jody

[Hocky]

As far as the A/F I have never seen an IR EFI setup that was happy idling anywhere near 14.7:1 A/F. Mine wanted to be 12.8-13.2 at idle and was very happy there. It could be 14.7:1 or leaner at cruise areas, but not idle. One thing I learned a long time ago is give the engine what it wants, don't get hung up on the numbers. If it idles better at a richer A/F that what I do.

As far as the idle speed, it's obviously pulling air from somewhere. If you can richen the idle and live with the butterflies closed for now that'd be my suggestion, at least until you can re-do the shafts, etc.
Jody

I noticed that its ideling fine at ~12.5AFR but I can smell it too. I have not made big investements in a one of the best EFIs on the market to live with it ;)

I do believe that even if I get the shafts ok it will not be 100%. When I open the throttle with the idle screw its to unsensitive.
Im considering creating a adjustable pass thru channel bypassing the throttle plate (like on some production cars).

[Hocky]

Autronic uses timing to handle the idle. It uses a table with the RPM on the x scale and user configurable y (TPS, MAP, LOAD...).

Now the engine is ideling 900rpm at 10degrees of timing and I do believe that this is rather low.

I can also make adjustments to each cylinder on the timing or fuel. This is also done in a table with RPM on the x scale and user configurable y (TPS, MAP, LOAD...)
I have tried to put some more fuel (at low TPS) to the cylinders going lean and this is helping some.
When trying to add/reduce timeing on these cylinders I get no effect that I noticed.

[TD509EFI]

Hocky,

I think you're right about the idle timing. Doug Flynn at Holley has mentioned that many BBC with a healthy cam like to have around 20 - 25 degrees of timing at idle. It's also mentioned in the Holley tuning manual. Might try advancing the timing and playing with the A?F ratio at the same time. More advance might clean up the exhaust odour.

As Jody mentioned, give it what it likes.

John

[Hocky]

Hocky,
I think you're right about the idle timing. Doug Flynn at Holley has mentioned that many BBC with a healthy cam like to have around 20 - 25 degrees of timing at idle. It's also mentioned in the Holley tuning manual. Might try advancing the timing and playing with the A?F ratio at the same time. More advance might clean up the exhaust odour.

As Jody mentioned, give it what it likes.
John

I have now recalibrated the throttle plates and got an idle of 900-1000rpm with the throttle a little open. Changed the timeing to 20 degrees and this was making alot of difference. I now can have a idle AFR of ~14 without the irritating sneesing up thru the intake ;)

Getting there...

[kmcanally]

The initial timing on such an engine should be a minimum of 25. I would run as much initial lead as you can until it strains the starter.

[Hocky]

I have now found what I think have made the adjustments more difficult than it should. The intake gaskets was leaking from underneat on all cylinders except one. Air and oil has been sucked this way, alot on a couple cylinders as it looks https://static1.pt-content.com/images/pt/2006/05/frown1-1.gif

Hopefully fixing this will getting things even better!