Had to take the '79 Seville (350) in to pass emissions and the mechanic claims to have set the timing back to 10 degrees advanced, as he said it was at 20. OK. It passed here in CA. Only, now, for the first time since I've owned it, it has trouble on hills, and today I even had to downshift. Took a hill at 30 which I could have breezed over at 70 easy before, and I get the inefficiecy orange idiot light way too much. Is setting the distrib at 15 degrees a smart option? It also runs a smidge rough at idle now too. I don't want to keep it like this.
Hmmm. No one answered your earlier posts, so I'll give you a generic
answer that's good for all engines.
I'm not too familiar with the later model advance mechanisms.
Cadillac kept changing how they functioned due to tightening
emission standards and introduction of newer electronic controls.
Having said that, the best thing you can do (if it IS possible) is to
convert this to a purely mechanical system with an adjustable vacuum
advance connected straight to manifold vacuum, and a spring/weight kit
for the distributor centrifugal advance.
Is this possible? I don't know how the 79 system is set up since
I would have to look at a service manual for that year.
You'll have ask at a local speed shop, or find a fellow 79 owner
who has a service manual to read how the factory advance
system is set up.
Look at one of my previous posts for the proper curve setup.
That will give you the most power and fuel economy, emissions aside.
If you don't want to do that, then the answer you seek is this:
Advance the timing as far as you can go without introducing ping
under acceleration and load at higher rpm's.
The performance, fuel economy, and idle quality will all improve.
There is no danger (except to higher emissions) in doing this
AS LONG AS the engine does not ping under load.
Advanced timing also has the side benefit of reducing engine cabin
temperature since more of the fuel is burned inside the cylinder and
less is burned inside the exhaust manifold.
Good Luck!
One other thing the mechanic had seen the need for, and did, was cleaning the port from the EGR valve, into the throttle body. I wouldn't consider that this would cause poor performance somehow now, so I've been considering the timing adjustment he did. He had done an emissions pre-test, and claimed that the exhaust emissions looked good at the tailpipe before doing the 2 things I mention, and passing it. It just seems to me that if the timing is set at spec, then advancing another 5 or 10 degrees is just dealing with remedying a symptom of another problem. As I've said, the performance has never been this poor on hills, and the 'less-efficiency' indicator on the dash has always looked better. I don't recall setting timing at the distributor since I've had the car, now for 6 years. So, I'll sleep on it, and look at my Haynes book a bit. Then I suppose just advance the timing. Unless there could be another consideration first. Thanks for the thoughts thus far. Much appreciated.
The timing is spec 10% BTDC, as he adjusted it to. That's why it seems makeshift to me to advance it again, probably back to 20 (advanced). I can take it back to the same guy, but it really wasn't a tune-up job, and so he'll charge to further the solution. However, I do most mechanical work on my vehicles, so I'm looking for something to really click here, as a real solution. There's another shop I like better nearby, though they are not smog-certified. Had they been, I would have gone there. I may wind up doing that. However, I'm needing to see if I can lick this efficiency / performance problem economically. First choice : do it myself. Thanks for the perspective. It's all good for me.
Small block Chevy's want 10-12 degrees advance. This is BASE timing. That means the measurement is taken with the vacuum advance disconnected. Then, you rev the engine and you should have 32-36 degrees advance, full in, by 2500 RPM. Your vacuum advance rides on top of that. You want to run as much timing as possible, without having any lugging or pinging, on the fuel you typically run. If your motor is stock, it is very low compression, and you can get away with a lot more timing than most.
How do you adjust your advance, beyond base? Take a look at my website, I have a write up on this. In short, you need to open your distributor and play with the advance springs until you get the right amount. And the only way to do this, is through trial and error.
Also, if you're going to go down this road (it's really very easy) invest in, or borrow, someone's advance timing light. A basic timing light really isn't very helpful, unless you have a degreed balancer.
Also, these days, a lot of mechanics don't know the first thing about setting timing. It's becoming a lost art.
The '79 seville has ESS (electronic spark selection) that advances and retards the timing based on input fron the EGR solenoid, fuel economy switch (the one that turns the orange and green fuel economy meter on and off), and the coolant temperature switch.
It is possible your ESS system is not operating properly. You might consider disconnecting the unit and adjusting the timing higher, until it performs better. Most well tuned Olds V8s like about 13-15 degrees at idle and a total of about 36 degrees at 3500 RPM. Make sure the initial setting is performed with the vacuum advance disconnected and plugged.
I know that many people want to keep their cars original, but I prefer to keep mine running well, which often means eliminating the "high-tech-for-1979" stuff.
I would detach the ESS from the distributor (it is the unit above your master cylinder) and tune the car for best performance.
