We all know there is a special procedure you need to set the timing on 3.0 EST ignition systems, by jumping into base timing mode, and then set the base timing to either 1 BTDC, 1 ATDC, or 2 ATDC depending on SN. This all makes since, but what I don't understand is how setting the base timing more retarded is supposed to equate to a more advanced run timing. From service manual #26, and also #46:
• If initial timing is 1° BTDC: 12° BTDC, plus or minus 2°. At 2400-2800 rpm maximum
(total) advance is obtained and should be 23° BTDC (plus or minus 2°).
• If initial timing is 1° ATDC: 14° BTDC, plus or minus 2°. At 2400-2800 rpm maximum
(total) advance is obtained and should be 25° BTDC (plus or minus 2°).
• If initial timing is 2° ATDC: 15° BTDC, plus or minus 2°. At 2400-2800 rpm maximum
(total) advance is obtained and should be 26° BTDC (plus or minus 2°).
They all use the same EST module, so how is less advance in base timing supposed to create more advance in actual run timing? The advance curves show the same conundrum as above.
The newer engines are speced to 2 ATDC, which is presumably for less advanced timing in the newer higher compression 3.0s to avoid blowing out head gaskets, but the above (and the advance curves) seem to indicate a the actual run timing should be more advanced than the older 3.0s speced to 1 BTDC in base?
Are these advance curves in error? What should the actual run timing curve be for a 3.0 with a 2 ATDC spec? My testing on two different 3.0s that setting the base timing to 2 ATDC will not give you the at idle advance or full advance shown in the published advance curve (you end up closer to 24 BTDC at full advance).
Thanks for the insight.
• If initial timing is 1° BTDC: 12° BTDC, plus or minus 2°. At 2400-2800 rpm maximum
(total) advance is obtained and should be 23° BTDC (plus or minus 2°).
• If initial timing is 1° ATDC: 14° BTDC, plus or minus 2°. At 2400-2800 rpm maximum
(total) advance is obtained and should be 25° BTDC (plus or minus 2°).
• If initial timing is 2° ATDC: 15° BTDC, plus or minus 2°. At 2400-2800 rpm maximum
(total) advance is obtained and should be 26° BTDC (plus or minus 2°).
They all use the same EST module, so how is less advance in base timing supposed to create more advance in actual run timing? The advance curves show the same conundrum as above.
The newer engines are speced to 2 ATDC, which is presumably for less advanced timing in the newer higher compression 3.0s to avoid blowing out head gaskets, but the above (and the advance curves) seem to indicate a the actual run timing should be more advanced than the older 3.0s speced to 1 BTDC in base?
Are these advance curves in error? What should the actual run timing curve be for a 3.0 with a 2 ATDC spec? My testing on two different 3.0s that setting the base timing to 2 ATDC will not give you the at idle advance or full advance shown in the published advance curve (you end up closer to 24 BTDC at full advance).
Thanks for the insight.
