squarehead

I have been thinking about this solution as well for my car. I have now the second optispark in about 30,000 miles and I know the previous owner had opti trouble too. I have used aftermarket opti sparks and they are not well sealed but it was clear to me that the venting with vacuum was only causing a negative pressure on the opti housing and if any liquid contaminant got near the leak it could not help going into the housing. I had a post a few weeks ago about this and asked if any one with a OEM opti could check if the darn things really seal any way. I never heard any reply.

What type opti are you using?

squarehead

I just read shoebox last post where he measured the vacuum on his opti. If I read correctly he was reading 10 inches at the air feed to the opti and 16 inches at the intake manifold so there is a leak in the opti (or lines) reducing the vacuum by 6 inches.

On my aftermarket opti (summit) I could get no vacuum reading on the opti inlet line so 100% of the vacuum that the intake manifold was creating was being lost through (in my case) the bearing for the distributor drive shaft.

divineprime

Now he might be leaking a little bit since this test was during runtime. However one of those orifice checkvalves is supposed to reduce flow. If that flow drop is around 6hg then he's got absolutely no problem and it serves as a proper working model. Our condition of zero is obvious, there is no vacuum at all at the inlet line, tee or no tee. As shoe said though the factory service manual listed 10hg, which is what he saw.

squarehead

What brand of optispark are you working with?

divineprime

Mine appears to be OEM with 105k.

squarehead

Thanks for the info. I suspect that the less expensive optisparks do not have some sort of air seal at the drive input shaft. That would make an OEM unit well worth the money.

My first opti spark failure was repaired by a local shop using a Summit opti spark and about two years later it failed again. This time I fixed it my self trying to be sure the part was properly installed. Unfortunately I also used a Summit unit (to avoid shipping delay for an OEM unit from Ohio).

After I replaced the optispark and got the car running again I looked carefully at the old (summit) unit I had removed. There was oily residue on the metal chopper wheel and spots of some sort of liquid inside the distributor cap. The oily stuff appeared to have come from the drive shaft. That was when I thought to check the seal of the vacuum leads and discovered no vacuum at the line going to the optispark. I checked the vacuum line from the engine (after the filter and orifice) and had good vacuum so I knew I had a big leak in the optispark.

To see if I could find the leak I set a low (2 psi) amount of pressure on my compressor and ran it to the intake line then I took mechanics stethiscope and put an open hose on it and listened around the optispark body. In the gap between the cam cover and the optispark I could hear a lot of air near the drive shaft of the distributor. I did not hear any air from else where on the optispark.

Since then I have been driving the car with the vacuum line plugged. The two hoses the the optispark are covered with a filter cloth to prevent anything from going into them.

I have thought that an improvement would be to install a DC voltage pump to flow a small amount of air to the optispark so the ozone would be purged and any liquid at the drive shaft would be moved AWAY rather than toward the optispark internals.

squarehead

PS

I know this air pump idea is a bandaid to having used a less than oem part in my repair but at this point I sure would like to extend the time before it craps out again!!!

divineprime

Thank you for posting all of your info, I hope others will too. As I said mine is OEM and leaks like a sieve, but since it is 105k I suspect it had been leaking for longer than 5k. It probably would begin to leak slowly and gradually over time get worse until finally complete leak. This is not certain until a new OEM unit is tested by a reputable member. It may be that from the factory the OEM's leak, but I highly doubt it at the same time.

Not sure it should be considered a bandaid if you really put a good system in, or if a good aftermarket hits the market. Proving the concept was the first step, and now vacuum readings on various setups. I am not entirely sure if there is not an automotive air pump that would do the job more appropriately. lol, fish air pump is a dead ringer for contraption however there are high performance pumps if you want to spend more than 20 bucks.
That is a good point though a new distrib would cost me a couple hund, but in a pinch I got mine vented for under 20 bucks. Completely confident that the unit will last for plenty of hours until I decide what else might be available for air pumps.

divineprime

Moreoever tapping into the vacuum system to vent the darn thing is a bandaid. It wasn't originally designed to do this. If GM had a choice they would have gone with an air pump, but it was more economical to simply tap off an existing system. This had unintended consequences that can be avoided with a pump style vent.

divineprime

I found a robotic application of an air pump that would work for a reasonable price. This pump allows you to use the vacuum inlet(16hg) or the vent outlet(32psi) to move air. It already uses 12 volts so there is no need for an inverter. https://www.sparkfun.com/products/10398

shoebox

I'm pretty sure GM had a choice, LOL. They picked a way that works pretty well for the most part and with little to no complexity. While it is nice when it lasts a long time, a distributor is a wear and tear item.

If they had gone another route, I can see people exclaiming about DTC Whatever-fish pump malfunction.

Anyone can come up with a one-off solution to something, but corporate engineering solutions have to tick hundreds of check-off boxes to be viable. It does not mean it was engineered wrong. The beauty of it is that if you don't like it, you can make your own solution. My car is happy the way it is.

divineprime

Well exactly! you would need a DTC, which would be great BTW. This would cost additional money on top of the electric motors, so no they did not have a choice really. The wear on these distribs is now beyond mechanical though. Mine is fine mechancially, but now I gotta toss it because it leaks vacuum. I'd rather not since it can be done better for cheaper.

shoebox

I wonder how the MSD tests seal-wise?

squarehead

Before I bought my Z28 I spoke with the only friend I knew who had one (a sweet 97 anniversary edition) and I asked him about his ownership experience Opti-spark came out of his mouth within a few words. He liked the car but warned about the trouble/cost he had experienced with the opti spark. I bought my 95 and now I know what he means. Don't get me wrong it is not a deal breaker but it has been a bit of trouble. I read Corvette Magazine just for fun and they always warn people about the troubles associated with LT1 C4 models.

The guy who sold me the car gave be a box of spares and other parts he had collected and there was a MSD optispark in the box which he had removed but not thrown away (I tossed it, in hind site foolishly), so he must have had to work on the optispark as well.

I see on post in this forum and in fact within this thread that people have not had trouble with their optisparks and wonder why any one would want to change the factory set up. I beg to differ. My car has had to be towed three times in three years, twice due to the optispark.

I have old Volvos that I take care of and in 20 years of messing with them I have only had a couple break downs requiring towing.

When I was doing the research to figure out why my car was not running this latest opti break down I was looking to see if there was one brand of opti that had a great reliability record. Post after post I would read some one assert that Brand X was great but within a few posts some one would chime in with a contrary experience on the very same brand.

I guess what I am saying is that the optispark does seem to have a dubious reliability reputation and thus it deserves attention and if possible, improvement.

squarehead

PS

Devine, thanks for the link to the little pump. this looks just like the ticket! I had been thinking of a fish tank battery backup pump, this looks better.