changed timing to 10 degrees got a question

[walkersimpson]

so i changed my timing to 10 degrees without the vacuum advance unplugged and when i plug it back it the timing shows 20 degrees is this right or have i done something completly wrong i know when you set timing to 5degrees it says that it jumps to 13 so it seems wright but im just curious let me know what you guys think just curious

[Gottolovem]

You say without it unplugged and then you plugged it back in?

[dlb]

yes, that sounds correct, walkersimpson. manifold vac advances the timing about 8* at idle so 10* to 20* is about right.

[durecell]

im curious, advancing the timing to 10* or so and then applying vac to the advance changes it even more. is that hard on the car to advance it that much? what is the max you can advance it without it pinging? is this depended on the engine?

[Petros]

the idea is to get the highest peak pressure in the combustion chamber, at the optimum point in the cycle, without getting per-ignision or ping. The more advance you can run without ping, the more efficient the fuel burn. Too late in the cycle and the energy goes out the exhaust, possibly doing heat damage to the exhaust valves and exhaust system, too early you get pre-ignision that sends shock waves though the combustion chamber that can damage the piston or head gasket.

the speed of the fuel burn varies with the density of the fuel/air mixture charge. low throttle settings yield low density charge and the fuel burn is slower, so the spark can be advanced to get the optimum peak pressure occurring at the right time in the combustion cycle.

The mechanical advance advances the spark so peak pressures occurs at right place in the cycle just based on the piston moving faster, the vacuum advance moves the ignition point based on the slower combustion speed.

to optimize efficiency the spark has to be advanced based on engine speed, and based on throttle position. the mechanical advance is just a straight line advance based on RPM, the vacuum advance moves it based on manifold pressure, which is directly related to throttle potion. So when you accelerate hard (full throttle) the manifold pressure is high (low vacuum) and there is no vac advance, but there is mechanical advance only. when you get to cruising speed and you back off on the throttle the Mansfield pressure is low (high vacuum), than the vac advance moves the spark to improve fuel efficiency. The two times when vacuum is high is at idle and at part throttle cruise conditions.

It was discovered back in the dark ages of automobile development that at the peak efficiency setttings also results in slightly higher NOx and CO output, so if the peak pressures were lowered it would lower NOx and CO output. The easy thing to do was to have a factory setting that was below optimum. this has harmed economy of course, and personally I am not so sure it actually reduces total emissions. if you have to burn 10 more fuel to travel the same distance, even if your parts per million are lower, I can not see out your total emissions (in parts per mile) would be lower.

On several of my first cars, "BS" cars (before smog), the spart timing was set at 16 to 22 degrees advance BTDC, the Tercel factory setting is only 5 deg, which not only results in poor efficiency, but also risk head damage to the exhaust valves (I have seen it, the valve can even melt and break off and cause very severe engine damage). Setting it at 10 degree will not harm a thing, improve efficiency and even save the exhaust valves from heat damage. If you set it further advance you could improve efficiency even more, but you may have to switch to high octane premium fuel to prevent ping.

So for best efficiency you always want to run the most advance you can without getting ping. Modern EFI engines reduce emissions with careful computer controls on both spark and mixture through the EFI system, we are not so lucky with these old carburated engines. so we have to experiment to get the best efficiency.

[dlb]

there's no danger in advancing the timing as far as you can without pinging. just keep going until you hear pinging and then back off until you don't hear it anymore. each model of engine is different, and each individual engine will vary a bit too due to mods (higher compression will increase likelihood of pinging), carbon buildup, and a functional EGR, among other things.

the big thing is that you don't want to drive with pinging happening long term. a small amount while nailing your timing down won't damage anything though.

[durecell]

so from what im reading if I plug my idle vacuum advance and set it to 10 then when I plug it back in it will be slightly higher and be ok. sounds good thanks a lot. ill try messing with it. ive check all my emissions stuff and all functions per fsm. my gas mileage varies from 26 to 30 depending on my foot and weather conditions. lately it is so cold that I have to warm it up longer and it messes with my mileage but I was looking for another way to help it and I think that this might help the economy of the car. thanks guys!

[dlb]

i started tracking the mileage of every tank of gas in both my and my wife's car this last spring and i have bee quite surprised at how much of a role ambient temperature plays in fuel economy. time spent idling, longer times warming the engine up to operating temp, the expansion and contraction of air and fuel...lots of things add up. in my 4wd corolla wagon, i average 13-14 km/L (32-33 mpg) in the summer and 11-12 km/L (26-28 mpg) in the winter doing about 50/50 city/hwy. so i would think that at 26-30 mpg in the current WA temps, your car is running pretty well. not bad after sitting for 10 years.

[durecell]

that is true dlb. the engine is in pretty good shape leaks a little oil around the oil pan. think that's my next project. I hate leaks. it was leaking oil out of the head gasket, believe it or not, so I pulled the head and did the petros method on a new gasket and cleaned her up good. all is well now. other then minor things she is a good car. lots of rust but I cleaned most of it up. a little body work. next summer I will get it painted. the benefit of knowing that this car was mechanically taken care of helps. has had regular oil changes every 2500 miles since it was new. my mother made sure of that. even if my father protested. I continued that when I got the car. I love this little car and don't care how much money I put into it to keep it alive. just hope I never get in an accident with it. anyway thanks again for all the helpful information. you all are very smart . I see you are from BC. my mother was born and raised in Edmonton so I spent a lot of time in Canada when I was younger. it amazes me how many members are in the pacific northwest.

[Petros]

it would be pretty rare for an oil pan gasket to develop a leak. more likely is it is running down the block from higher up and running around the oil pan gasket, making it look like it is coming from the oil pan. The most common places for it to leak is the front and rear main seal, the cam seal, the valve cover gasket (the most common) including the half moon plug at the back of the valve cover, the distributor o-ring, the fuel pump gasket and the oil pressure sender. Check all of these places first before you try and fix the oil pan gasket,chances are it is from one of these places, most of which are a much easier repair..

[durecell]

I replace the camshaft seal when I had the head off. never thought about the front main seal didn't look like it was leaking but I didn't pull off the lower sprocket to see. its hard to get off and wasn't obvious that the front main was leaking. the rear main looked good when I had the tranny out. replace the distributor o ring. also the valve cover is super dry all around I made sure of that being that it is the more likely culprit. ill take a look closer at the front main. thanks petros