confusing mixture and timing adjustments

mack6820 · 05-04-2008, 06:10 AM

Good morning. Ive been reading and searching for a while and Ive seen so many opinions that now Im really confused. So here we go:
83sc, 3.0L, CIS. No cat.
Im trying to get the most out of it. It starts pinging at 3-4000 RPM. I richened it a little, the pinging got better but its still there. Now it surges in idle.
Heres my question:

1. Exactly where should by timing be setup with the vacuum retard disconnected?

2. Should I disconnect the 02 sensor? What will benifit from this?

3. What should my mixture be set at?

Thanks in advance? Im going to a DE in a couple weeks and I want to get this thing set up just right.

psalt · 05-04-2008, 07:32 AM

1. The timing is set with both vacuum lines disconnected and plugged. Factory spec is 5 BTDC @ 950 rpm, but also check the high speed advance, 25 BTDC. If your engine is pinging at the factory spec with premium fuel, something else is wrong, either the engine is running hot, or you have an oil burning problem. If you are putting the car on a track, you need higher octane fuel or take out timing, or damage the engine.

2. The lambda system ignores the O2 sensor after 35% throttle, anyone who tells you disconnecting it will improve performance does not understand the system. Leaving it connected will give you better economy and lower emissions. The system has a delay to prevent idle fluctuation, but without an IAC, the idle is not rock steady. If your main concern is idle performance, consider a Buick.

3. Hook up a dwell meter to the lambda test port. Cold open loop dwell should be around 58 on the 4 cylinder scale. When the engines goes closed loop at 15C, the needle should fluctuate between 40-55 dwell. Most engines run best with the mixture set a little rich around 30-40 dwell. This makes the WOT mixture richer, but the O2 sensor will pull back the part throttle cruise to stoich.

mack6820 · 05-04-2008, 11:21 AM

Ok. When I disconnected the vacuum lines, the RPM jumped to 1600. I set the timing as you said. At 5 BTDC at idle, and it was 30 at 6000RPM. Took it for a drive, no detonating but I lost alot of power. So I reconnected the vacuum lines and set the timing with the lines connected. Got my power back. Went next door to a Dyno and ran 170HP. Not real good but they were having a charity run and wouldnt allow me to make any adjustments. So I brought my embarrassed a$$ back home.

ianc · 05-04-2008, 11:39 AM

Mack,

You set it correctly with the hoses disconnected and plugged, but after you do this, the idle will jump up as you noticed. It's important that you set the idle back down to spec before setting the timing, otherwise your setting will be off since the engine is already getting some advance at 1600 RPM.

You may have done this, but your descrip is not clear, so just wanted to throw it out there...

ianc

mack6820 · 05-04-2008, 11:49 AM

mack6820 · 05-04-2008, 11:52 AM

Ok, let me give that a try. Keep ya posted.

mack6820 · 05-04-2008, 12:07 PM

Ok. I pulled and plugged the lines. checked the timing and it was at 10 BTDC at 950 RPM. Not off by much so I set it at 5 BTDC. It doesnt seem to have as much power as before but I guess its better to be safe that to chance on blowing a piston.

ianc · 05-04-2008, 12:16 PM

Sounds like you were 5 deg advanced then. That will make it ping...

ianc

psalt · 05-04-2008, 12:23 PM

Sounds like your distributor is working correctly. When you set the timing to 5 BTDC, then reconnect the vacuum retard, it gets pulled back to ATDC. If you set the timing to 5 BTDC with the vacuum line connected, you have advanced the timing 5 degrees. Yes, you will make more power, but if it is pinging, you need higher octane fuel, epecially if you drive it on a track. These cars were retarded to 21 +/- 3 BTDC to run on 87 spec fuel, while the engine will continue to make power out into the mid to high 30's BTDC if you have the octane.

The engine was rated at 172 hp, 161 at the wheels seems low to you ? What's up with the 7.3 AFR ?

mack6820 · 05-04-2008, 12:27 PM

7.3 AFR? Not sure what that it. Is that the air/fuel? What should it be?
When I got to the dyno and shut the car off. It cooled for a bit, then didnt want to start. I bumped up the idle and it was surging so I leaned it out to stop surging. Then we hooked it up to the Dyno.

It wasnt pinging at the 10 BTDC. Could I keep it at 10 for more power?

psalt · 05-04-2008, 12:47 PM

It wasnt pinging at the 10 BTDC. Could I keep it at 10 for more power?

Depends on the engine, temperature and fuel. On the road where you spend 85% below 30% load, usually OK if the temp is low and you have good premium fuel. On the track where you can hold the throttle down, and the cooling is marginal, bad idea unless you use race gas.
Getting the hot breather out of the intake air is usually worth a few octane points (1 RON/12C). Oil in the cylinder really increases knock, if the engine is worn, burns oil or has oily plugs, forget about advancing the timing.

AFR =air fuel ratio, it should be around 13:1 under load for a dyno test. 7.3 would be so pig rich it probably wouldn't run, it must be an error

mack6820 · 05-04-2008, 01:06 PM

wow!Im gonna have my AFR checked tomorrow then. I dont have an O2 meter yet. I know I had to lean it out some to keep it running after it cooled down a little. Im gonna keep it at 5 degrees then. I dont wanna blow the engine at the track. Even though it would be a great chance for a 3.6!
Thanks for your help guys!