How to tune Idle Modded 502 MPI w/MEFI-3 Mefiburn VIDEO inside
 

How to tune Idle Modded 502 MPI w/MEFI-3 Mefi burn?

I have 2 502 MPIs with JE pistons, ported/shortened runner intake, ported heads, etc...

COMP CAMS
16HR00004
HR-236/359-2S-14 IG

The engines required advancing the throttle to start. I noticed the IAC was near 100 percent at idle to achieve 733 RPM target. I opened thee secondary throttle until the IAC is at 10/100. Now it starts better. Anything I can do to make it idle smoother. I am looking for a strategy to systemically improve the idle quality as best I can. I have a LM-2 I will get on there soon.

VIDEO

Engines visable at 1:36

Couple of observations. Make sure your DLC line is isolated as best as you can from extraneous electrical noise. This can interfere with the data stream. Your data was jumping around a bit. Disconnect ScannerPro via the double arrow 'button' and then reconnect using the same button. It may take several attempts for the data to be smooth. I never start with Scanner Pro connected. I let the engine start and stablize then connect.

Merc spark stabilization and AFR are the best things I've seen that can tame a cam and make idle quality better. Too rich it will surge and sound like a top fuel car, too lean it will stutter and get crispy.

I will get the AFR soon. What is "Merc spark stabilization"?

Depending on the ignition system you have some employ spark stabilization. Basically in the idle regime the module with run the advance to stabilize the idle, and if you were to scan the spark advance it would be all over the map. You might see 8 deg one second and then up to 18, then 12, then 14 then 6 etc. Basically whatever is required to smooth out the idle.

Ok I go a LM-2 AFR

here is the warm up


Here it it warm. It seems to be 12.3 afr at 1000-1100 but at idle of 733 rpm the afr leans out to 14.0 aft. What should be my target idle afr???


THanks!!

I like 13.5 to 13.8 warm at idle. The MAP will shift a bit when put in gear IN the water as the prop puts a load on the motor. This usually leans it out too. Let us see your BPW / RPM / MAP table and we'd be able to offer a little more guidance. The scanned BPW was hovering around 1.95-2.0x, so I would make the values about 2.15 or so. That's a big shoot from the hip suggestion not having seen the table. Bottom line is it's a small change in 2 to 4 cells to get the idle AFR to where you want it.