Spark advance.

[Chero77]

The following was a response to a question on the first gen camaro board. The original poster's engine was pinging with an MSD distribuitor. He got the following anwser.

"[Vaccum advance] cannister is on wrong port, NEVER use ported vacuum unless you have an EGR valve. Early performance engines don't have EGR valves.

Vacuum advance is only supplement for idle and cruise modes (helps stabilize idle against converter, gives better mid-range fuel economy), should never be used as an added top end timing provider.

EGR engines need the added ported source top end timing advance to build heat in the combustion chamber to properly burn the added recirculated gasses from the EGR system."

I disconnected EGR from my engine a few months back and it runs better without it and doesn't ping (on 89 octane, knocks a little on 87). However, I would like to optimise the spark curve for 87 octane.

To establish a baseline I am going to check my total advance at 1000, 2000, and 3000 rpms using ported vaccum and will compare those numbers to the total advance I get using manifold vaccum.

However, it would be interesting to have some baseline numbers from a pre-EGR engine, so if anyone has a TSM for a pre-EGR AMC engine could you post the total timing advance at 1000, 2000, and 3000 rpms.

The '77 TSM has spark advance curves for each engine used by AMC, so I am assuming that earlier TSM's probably have this info also.

Thanks,
Dave

[ December 16, 2001: Message edited by: Dave _S ]

[Gladi8r]

I have a 72 TSM that shows distributor advance from 500 to 2000 RPM ranges. Not sure if that is what you are looking for but I would be more than glad to send a pic of the TSM page showing this.

[Gladi8r]

You got mail :D

[Gladi8r]

Hey Dave, your email came back undeliverable. If you want to send me your new email address, I will resend the info.

[reddog]

Dave,

What happened with your engine knock??? Enquiring (nosey) minds what to know.

Kerry

[Chero77]

<BLOCKQUOTE>quote:</font><HR>Originally posted by reddog:
Dave,

What happened with your engine knock??? Enquiring (nosey) minds what to know.

Kerry<HR></BLOCKQUOTE>

That's an FSJ mystery. Did I say I got this truck in Roswel? Anyway, I took the truck to a third mechanic to get one last opinion before shelling out for a rebuild (or just parking it for a while), and as the guy was reving the engine and saying "I don't know what that is, but it sounds bad," the noise stopped. Drove around town for a week, no noise. Ran it down to San Diego to help my parents get a Christmas tree, no noise. I am putting it down to a stuck lifter or other oiling problem. As for the two mechanics who said "rod-knock," either their incompetent, or their cracker jack mechanics who can diagnose any computer control problem, but rod-knock is something they have only read about in textbooks.

[Chero77]

Surprise! I went out to do some tests on my rig and discovered that my spark cto is not working. It supplies manifold vaccum all the time, hot or cold. Port 1 never closes and port 2 never opens. Its probably been running on manifold vaccum for years.

[Chero77]

I did a test run on ported vaccum and there is very little difference (with engine hot) between running the vaccum advance on manifold or ported vaccum. The only thing I noticed is that idle is about 100-150 rpm higher with manifold vaccum. About a month or so back I noticed that the engine was idling somewhat higher and just attributed it to colder weather or the usual FSJ quirks. That must have been when the cto went out. Since its easy to get to so, may as well put in a new one.