Anyone care to enlighten me?

[ZeroLux]

Question: how does a vacuum advance on a distributor work, what does it do, and what kind of side effects would you see if it were to stop working?

The reason I ask is because the problems I've seen with my car almost seems like a timing issue at higher rpm's under load. With that said, what are the chances my dist isn't advancing as it should and making the spark timing not match up with the fuel? Or am I thinking this whole system wrong? Sorry, I'm no good when it comes to dist's and whatnot.

Zero

[russiankid]

It advances the timing depending on the amount of vacuum it receives. I had mine disconnected for a week or so without any problems. I believe it works at higher RPM's than on lower.

[AC439]

......a vacuum advance on a distributor work......stop working?.....what are the chances my dist isn't advancing as it should and making the spark timing not match up with the fuel? Or am I thinking this whole system wrong? Sorry, I'm no good when it comes to dist's and whatnot. Zero

My suggestion to your "What's not" is to never buy the vacuum advance from rockauto if you would need one !!!

[ZeroLux]

My suggestion to your "What's not" is to never buy the vacuum advance from rockauto if you would need one !!!

HAH yeah I caught that post today. I had been thinking about this problem for a while now though. Thanks for the tip though.

Zero

Question to you though, It looks like one of the vac posts on your old advance is broken leading me to believe you've run into trouble with this part before- how did your engine respond when it wasn't getting proper vacuum? Did you have problems with highway driving or higher sustained rpm ranges under load?

[Hauntd ca3]

vac advance is the load dependent part of the advance system.
centrifugal advance is the rev dependent side of the advance system
vac advance is used more at lower revs and small throttle openings

[cygnus x-1]

vac advance is the load dependent part of the advance system.
centrifugal advance is the rev dependent side of the advance system
vac advance is used more at lower revs and small throttle openings


Correct. The optimum ignition timing varies because the time it takes for combustion to occur varies based on several factors, one of which is the density of charge in the cylinder (not air/fuel ratio, but the total amount of both). At low loads the mixture in the cylinder is sparse (less dense) because airflow is throttled by the throttle plates and therefore not much fuel is injected. As the throttle is opened farther the air/fuel density increases. Dense mixtures burn faster, so combustion can't start as soon as it could with a less dense mixture.

Vacuum is inversely proportional to engine load and mixture density. High vacuum means low load and low mixture density, and combustion needs to start sooner. So more vacuum means more timing advance.

At WOT (wide open throttle) vacuum is essentially zero, so the amount of vacuum advance will also be zero. If you're vacuum advance stopped working, your fuel mileage would probably suffer and the engine wouldn't feel as responsive at low loads. At WOT it wouldn't make any difference at all.

Vacuum advance has no relation whatsoever to RPM. Mechanical (or centrifugal) advance is what changes with RPM. The idea is that for a given mixture it takes a certain amount of time for that mixture to burn. But as the engine RPM increases there is less time for combustion to take place, so it has to start sooner. Mechanical advance therefore increases as RPM increases. If this were to fail, engine performance would get worse as RPM increases. A total failure of the mechanical advance would be unusual though.


C|

[AC439]

HAH yeah I caught that post today. I had been thinking about this problem for a while now though. Thanks for the tip though.

Zero

Question to you though, It looks like one of the vac posts on your old advance is broken leading me to believe you've run into trouble with this part before- how did your engine respond when it wasn't getting proper vacuum? Did you have problems with highway driving or higher sustained rpm ranges under load?

Yes, one of the connections is broken (I broke it when I was leaking on the engine few years ago and I glue it back). The reason I need to replace it this time is because of the leak through the diaphram inside. The glued part does not leak. I have been running the car without vacuum adv for some time and I advanced the overall timing a little bit to compensate until I can get a new vacuum adv. I also found without a vacuum advance and only running with centrifugal advance, the car lacks torque at low speed and the gas mileage suffers. After I compensate the lack of vacuum advance by advancing timing a little bit, the car drives OK with reasonable gas mileage (about 29-20 mpg mix city/hwy). No engine ping or knocking observed.

[ZeroLux]

Nice thanks for that information, it will help a lot. I think my two next biggest issues are the secondaries being open below 5k cutting out my bottom end torque a bit and possibly the vac adv not working as it should giving a bit of the same problem. Though when I think about it, that would lead me more towards having a vac leak somewhere but damned if I can find it. I did some tinkering with the car earlier this week and got some MASSIVE improvements out of it so I am feeling a lot better about this car again. I'm sure if I keep plugging away at it I'll have it figured out eventually. I'm gonna go a bit further with things soon and replace some basic items that could use a refresh since I swear the engine looks mostly stock. When I replaced the O2 sensors last year they looked like they had never been out of the car before and were OE type so either the old owner never changed them or went to Honda for the part every time which I highly doubt because I'm starting to think his former mechanic was a bit of a nut with some of the randomness I've seen so far.

Oh, my primary rad fan runs full-time if the ignition is at ACC or the car is running, so I did some checking and below the battery box it looks as if someone MacGuyvered the wires for it away from the relay in the fusebox and rigged it direct to the switch on the bottom of the rad, which it would seem is bad since it's always on. I'll have to take a closer look at that later on and see if I can put it back to the way it was and hopefully figure out why it was bypassed in the first place. I already checked both relays and they seemed to be ok so I'm a bit confused as to why this was done.

Zero

[Oldblueaccord]

Pinch off the vacuum lines to the distributor and see if that helps you out. Wire tie the 2ndaries closed for the time being and plug the vacuum line and see if it drives differant.

A car with that many miles on it has some engine wear that can cause it tnot to run very well.

Have you keep track of your oil use in the last 3k miles?


wp

[ZeroLux]

Yep and it's used plenty!:D

Hard to tell where it was coming from with some of the other problems I had at the time but I did occasionally burn a bit of oil while driving, mainly when the valve rattle happened. It would consume no more than a quart in a month though and if I took it easy on her probably not even half a quart. Since I readjusted a few things it seems to be doing better and I have not heard the rattling much since. No smoke out the back either.

I'll keep an eye on it and see if anything changes. With it being cold outside it's hard to tell if what is coming out of the exhaust in the morning is from the temp difference or a little bit of smoke that burned off from accumulated oil overnight. Even if it is from oil, it's not very much and only lasts less than a minute at best.

Zero

[Oldblueaccord]

Try to get a number that is in Miles driven. So if I say, my Accord wagon burns 1 quart every 500 miles. Thats something we can go by a little better.


wp

[ZeroLux]

Will do. I had planned on doing more to her in the morning so I guess I'll toss an oil change into the plans and record the mileage for a while and see what happens. I know I have a slight oil leak around the pan on the back side but it's not very severe and only causes a light thin coating on the lower part most of the time. I get spots on the driveway occasionally but not enough that I'd worry about, I've driven other cars with oil problems before (an old 87 Camry comes to mind) where it felt like it was impossible to keep oil in it. Amazingly the last time I saw the car four years ago (and after I had driven it for many years before then), she still ran perfectly fine with approaching 300k on the odo.

Zero

[cygnus x-1]

I think my two next biggest issues are the secondaries being open below 5k cutting out my bottom end torque a bit and possibly the vac adv not working as it should giving a bit of the same problem. Though when I think about it, that would lead me more towards having a vac leak somewhere but damned if I can find it.

Check the vac advance diaphragm itself. I once checked all the advance diaphrams on the several 3gs at the local junkyard, and almost every one leaked. As long as it's not a huge leak the advance will work, but it's still a vac leak.




Oh, my primary rad fan runs full-time if the ignition is at ACC or the car is running, so I did some checking and below the battery box it looks as if someone MacGuyvered the wires for it away from the relay in the fusebox and rigged it direct to the switch on the bottom of the rad, which it would seem is bad since it's always on.

Zero


Hmm. That switch is not designed to handle the full current of the fan, which is why there is a relay. I'm betting it's fried and stuck closed.

C|

[Dr_Snooz]

The distributors on these cars are showing their age in a lot of cases. The advance mechanisms get dry and don't work as well as they might. You might try a Lazy Man's rebuild (http://www.3geez.com/forum/showthread.php?t=66468&highlight=lazy). It's cheap and will make things work a lot better in any case.

Also, there's an extensive troubleshooting section for the ignition timing in the manual. You'd be well served going through it carefully. It will narrow down the problem if there is one.

[ZeroLux]

Thanks for the info Dr. I had thought about the possibility of the dist being a piece of the problem but admittedly I know diddly about dizzy's. One things I DO know is they are not cheap. I took a look at the how-to, and though I'm not 100% on taking such a vital and pricey object apart I might give it a shot as a last ditch effort.

One thing I would LIKE to know though, since I am fairly new again to the world of older engines is how much I can attempt to advance the timing by adjusting the pivot bracket holding it in place. I get the main idea around why and how it works, but the specifics of doing so aren't very clear to me. I am assuming this is done with the engine running, correct? If so, what changes should I be listening for while adjusting it to know if I've gone too far?

Being that almost every other minor detail under the hood has been out of adjustment I am not ruling out a small timing issue with the firing coming off the dist. I have thought about giving it a very slight twist counter-clock towards the firewall to advance it a little bit to see if anything changes for the better and if not, having marked the original position with a scribe ahead of time to put it back to where it was and calling it a day.

Suggestions?

Zero

[AC439]

Working on the "Lazy man's" rebuilt wasn't too bad. I didn't realize the problem with my dist and the vac advance until I saw that thread and started working on it. Of course, it opened a can of worms for me to fix. But before you take the dist off the car, mark the current location. I used a little nail and a small hammer to tap two marks, one on the dist side and one on the engine side so I can realign them if I mess up. The original grease inside my dist was dry and sticky. I ended up cleaning everything and reapplied new grease. It works like a charm. Afterwards, I figured out my vacuum advance was broken too. As you know, I have a mess with rockauto with the new part and have just put it on with new vacuum hoses. I have not driven it yet but will post result in my original thread.
-AC

[cygnus x-1]

One thing I would LIKE to know though, since I am fairly new again to the world of older engines is how much I can attempt to advance the timing by adjusting the pivot bracket holding it in place. I get the main idea around why and how it works, but the specifics of doing so aren't very clear to me. I am assuming this is done with the engine running, correct? If so, what changes should I be listening for while adjusting it to know if I've gone too far?

Zero


The only difference you will likely see right away is the idle speed will probably go up as you advance the distributor. As for going too far, you won't be able to tell at idle since there is very little load on the engine. The only symptom you'll get is pinging under load. The only way to really know what's going on is to check it with a timing light. But if you don't have a light you should be able to put it in the middle of the adjustment range and it will be pretty close to where it should be.

C|

[Dr_Snooz]

I second the timing light. Get one if you can at all swing it. I've had to completely retard mine to get it right. I had it too far advanced and it was pinging like a son-of-a-gun but I couldn't hear it until I went through tunnels.

[ZeroLux]

Sorry to dig up an old thread, but I did some poking around under the hood today.

More questions, as usual. I checked my vac advance and as I suspected it does not hold vacuum. Toyed with it for about 30 mins, removed it from the dist, noted how it functioned inside the distributor. The arm inside is pulling the lever in the dist under vac, right... so if I wasn't holding vac on that advance and that part wasnt moving, what would the effect be after periods of long driving? The reason I ask is because I am still getting chatter if I drive "too far" at any given time and I am trying to determine if the whole dist needs some help or if those symptoms could all be to blame on the vac issue on top.

What gets me is that I can floor it not too long after the car has been cold started and it will take off, but if I drive like a reasonable human being about 5-10 miles at regular city speeds it degrades after a while.

From what I read I am trying to get a mental picture of how the system operates and why only sometimes I get the problem from the engine. Would a leaky vac adv cause this, or do I have a deeper problem yet to be found?

How much play should be in the shaft where the rotor button is? I can twist mine slightly by hand and wasn't sure if that was indicative of a problem or not.

Should I dive in this weekend and check the mech side of the dist while I am at it?

Zero

[cygnus x-1]

A leaky diaphragm would obviously cause a vacuum leak, and may not provide as much advance as it should at low and medium throttle. Not having enough advance would make the engine less likely to ping, so I don't think this is your problem. Check the mechanical advance to see if it's sticking.

C|

[ZeroLux]

Yeah I was figuring when I replace the advance I'd just wind up taking the whole dist out and giving it the rebuild listed in the guide here. It looks original so chances are the old grease is now more like glue. Did anyone ever find a place to get the springs for the mechanical side anywhere? Also what grease would be recommended for those parts, since I think that write-up before said white grease was only used where the ignitor goes.

Zero

[1987AccordLx-i]

hmm... so having timing too far advanced causes pinging ey? dam i knew mine was too advanced... and the secondary intake runner topic.. my secondaries arent opening.. would that be the solenoid?