Relationship between Timing and Vacuum
Thread Starter
Drifting
Joined: Nov 2001
Posts: 1,783
Likes: 2
From: Latham NY
Relationship between Timing and Vacuum
My vacuum increases as I change the timing from the base of 6deg to 12 deg (EST connector disconnected). Engine idle stays the same between 590-630 in park, engine temp 185-195. Does this mean that is is running more efficiently at 12deg? :confused:
Timing (BTC) Vac (measured from brake booster)
12--------------19
10--------------18.5
8---------------18
6---------------17.5
[Modified by Bluevette85, 10:35 PM 4/24/2002]
Timing (BTC) Vac (measured from brake booster)
12--------------19
10--------------18.5
8---------------18
6---------------17.5
[Modified by Bluevette85, 10:35 PM 4/24/2002]
Pro
Joined: Oct 2001
Posts: 525
Likes: 0
From: Newport MI
Re: Relationship between Timing and Vacuum (Bluevette85)
My vacuum increases as I change the timing from the base of 6deg to 12 deg (EST connector disconnected). Engine idle stays the same between 5900-6300 in park, engine temp 185-195. Does this mean that is is running more efficiently at 12deg? :confused:
Timing (BTC) Vac (measured from brake booster)
12--------------19
10--------------18.5
8---------------18
6---------------17.5
Timing (BTC) Vac (measured from brake booster)
12--------------19
10--------------18.5
8---------------18
6---------------17.5
Actually you should find the RPM go up a little as timing advances, more efficient @ 12 deg... probably not I think it may ping there, 8 sounds Ok, check it out.(under load)
Wait a minute IDLE @ 6K on an 85 (L98) I hope you are off by a factor of 10 buddy, otherwise that L98 ain't long for this world
[Modified by Shark ssn591, 9:45 PM 4/24/2002]
Safety Car
Joined: Dec 2000
Posts: 3,767
Likes: 5
From: Jacksonville Fl
Re: Relationship between Timing and Vacuum (Bluevette85)
Yes, it is running more efficiently. I'm not sure the official detroit reason to back off timing at idle but it does keep combustion temp down for lower emmissions and less chance of overheating. High idle timing also causes hard starting and hard to control idle speed.
The ECM is programmed to increase timing at above idle by quite a bit so as to have the engine run like it has plenty of initial timing, but still lets the idle speed be low and controllable.
The ECM is programmed to increase timing at above idle by quite a bit so as to have the engine run like it has plenty of initial timing, but still lets the idle speed be low and controllable.
Thread Starter
Drifting
Joined: Nov 2001
Posts: 1,783
Likes: 2
From: Latham NY
Re: Relationship between Timing and Vacuum (BBA)
The ECM is programmed to increase timing at above idle by quite a bit so as to have the engine run like it has plenty of initial timing, but still lets the idle speed be low and controllable.
[Modified by Bluevette85, 10:37 PM 4/24/2002]
