Ignition Timing on the 3A-S (3A-SCV)

[deejay1272]

Last night I acquired a timing light from a friend and endeavored to find out if a timing concern could be responsible for my poor power and fuel economy woes. The FSM specs timing for the 3AC engine to be 5 degrees BTDC when the vacuum advance vacuum line is removed (and capped) and 13 degrees BTDC when it's connected again.

I have a 3A-S engine (also known as a 3A-SCV I'm told) and I discovered last night that my ignition occurs at about 3 degrees BTDC (without the vacuum advance line connected). First question is this: Since the 3A-S engine runs at much higher compression than the 3AC, will the suggested timing be different?

Second question: Could a ~2-3 degree difference in timing really be the cause of my low power and poor fuel economy?

[Petros]

Yes it could. The timing spec is an emission issue. The best power and economy comes from the most advance you can get WITHOUT pinging or detonation (at full throttle and on steep hills, espcially on hot days). I have mine are 12 deg BTDC, and I get more power and better economy. I have a high compression engine and I run premium fuel. I would suggest trying at least 10 deg, if you get a lot of knock or ping, switch to premium fuel.

Good luck.

[deejay1272]

So when you say that you've achieved good results with timing set to 10 degrees BTDC, is this with or without the vacuum advance connected?

(The FSM says that the timing should be set to 13 degrees BTDC when the vacuum advance is connected and 5 without).

[takza]

Yes it could. The timing spec is an emission issue. The best power and economy comes from the most advance you can get WITHOUT pinging or detonation (at full throttle and on steep hills, espcially on hot days). I have mine are 12 deg BTDC, and I get more power and better economy. I have a high compression engine and I run premium fuel. I would suggest trying at least 10 deg, if you get a lot of knock or ping, switch to premium fuel.

Good luck.

I just tested a pretty significant drop in mpg after resetting my ignit advance to slight ping in 5th gear from around 1200 to 1700 rpms...I had marked my previous ignit setting...next tank I put it back to where I had it and mpg went back up.

So maybe it's set to ping...then back it off some? I don't use vac advance...stock engine.

My pulley key is bunged up some...since the bolt was slightly loose the first time I did the tbelt....so using a timing light might not be accurate.

[deejay1272]

Petros - should I adjust my timing to 10 degrees BTDC with the vacuum advance disconnected or connected?

[Petros]

you always set the timing with the vac advance disconnected. 10 deg BTDC with vac line disconnected and idle at 800 rpm.