92-94 Optispark Repair
By Rick Frohnert



You can make the LT1 '92-'94 Optispark setup more reliable than a '95-'96, even with the early distributor configuration. Buy a $12 '96 GM Vette distributor vacuum harness assy. Buy a $4 clear plastic fuel filter. Buy a $3 tube of premium black Permatex RTV, because it withstands the highest temps. Reserve a long day to fiddle around. Here's how it all goes together:

1a) Disassemble and clean the inner and outer cap & rotor assembly with a mild soap like Murphy's, Ivory or equivalent and thoroughly clean off all carbon, soap and dirt residue. Early style top caps must be drilled in a specific spot and at a specific angle to provide venting and a piece of vinyl hose will need glued in the hole. You will have to examine a later style outer cap to see where to drill the hole. It is at 6 o'clock pointing toward the driver's side tire. Use masking tape on drill bit to prevent drilling the small molded spark shield inside. Sorry, I can't describe better. I elected to buy a new early distributor and also a late distributor cap kit. I removed the early upper cap and replaced it with the late upper cap. This was expensive but ideal. You need an odd E5 female Torx socket to remove & install cap.

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1b) Buy a new later '95-'96 style cap and rotor assembly. The outer cap that the spark plug wires plug into was revised to provide a vacuum system connector. It WILL fit the earlier distributors perfectly. Problem is, the lower cap assy is different on the early and late distributors and can't be purchased separately. I heard the Pep Boys early cap kit provides the proper early lower cap with a later style upper cap that has a plug in the vacuum hole. That would be ideal.

2) Use a liberal bead of Permatex to seal the lower cap section to the aluminum base, top cap to the lower cap and thoroughly cover the stupid "shrinking" white foam seal around the wiring harness area of the distributor. You may prefer to use a hobby paintbrush to cover seams better.

3) The fuel filter hangs under the dashboard with the inlet end open to the air. The outlet end goes to a piece of vacuum line and feeds thru the firewall or grommet near the upper door hinge into the engine compartment. This hose must feed to one of the three vent holes in the distributor base assy closest to the driver's side by gluing in a piece of thinwall 1/8" vinyl emissions control hose in with the silicone sealer. Form the hose so it routes away from the crankshaft dampener toward the driver's front tire and looping upward with a fairly tight but not kinked radius of about 3". Plug the remaining two holes with the sealer.

This vinyl hose in the distributor base must be routed up the front of the motor between the serpentine belt tensioner and alternator bracket. You will likely need to see a '95 or '96 Vette to see how they squeezed it in there without pinching or wearing a hole in it. It is a real snaked route. You can split rubber vacuum hose and cover the vinyl hose with it to prevent collapsing when you restrain it using plastic tie wraps . It follows the edge of the aluminum accessory bracket all the way up to the intake. This 1/8" vinyl hose in the base gets routed across the top of the motor toward the battery. I drilled aluminum bracket to access door hinge area from battery. You can convert to rubber vacuum hose if you wish and route it through the grommet in the upper driver's door hinge into the dashboard area. You're done with hose #1.

3) Now hose #2. Take the vent hoses from the '96 GM Corvette OEM Vacuum Harness kit and use the one with the two in-line gizmos in it. One in-line device is a one way valve and the other is a flow restrictor. The accompanying bare hose in the GM kit is not used. Remove the plastic cover off the driver's side of the engine intake manifold. You will see a nice vacuum source going to the EGR valve. Install a tee and plumb the modified early cap or stock later distributor cap hole to the intake vacuum source using the '96 hose with the 2 in-line gizmos. Make sure it's installed with the gizmo's near the intake. This hose is routed from the intake down the accessory bracket following the same path. Hose length is critical.

Conclusion: Low humidity air is sucked from under the dash and fed into the distributor aluminum base assy, out of the cap thru the one way valve and restrictor into the intake. This should be bulletproof, far better than the '95-'96 setup that has similarly poor sealing and draws moist air from the air intake assy. You should be able to submerge your ignition now. GOOD LUCK.

'95-'96 cars can benefit from Permatex bead sealing of all distributor cap seals too. Also, moving the vacuum fresh air source from the gray "L" fitting in the Air Intake hose to the cars interior dash area with the fuel filter method as described above will prevent intake hose humidity or rain infiltration from condensing in the distributor cap. This could be a real concern on RAM air modified cars that draw air from a license plate snorkel/scoop or from the positive pressure radiator shroud area.

Optispark repair kit C400 from pep boys is a Borg Warner product that is listed for 92-96's. This kit probably will work fine on 95's or 96's but it needs a little help to fit the early units.

It costs $153 dollars so if you aren't sure you can do this I suggest not trying because you may ruin one of the pieces. The kit gives you a vented cap and rotor, which are ok as is. The inside cover is what is different. The ECM plug is on the new part , but the old unit has the plug already molded and attached to the base. It goes in a notch in the old cover.

This is a source of leaks so the change in design is for the better. It is tempting to use the old inside cover but it may have carbon tracks due to its close proximity to the rotor and may not work when you are done. Carefully cut the plug snout off of the new cover flush with the outside diameter, using a Dremel tool or a small hobby saw. Saw a notch in the new cover working a little at a time until you are satisfied with the fit. Leave a little room for some epoxy. I used Aeropoxy, but JB weld would work fine.

Next you will notice the flange in the center will not clear the photo receptor on the base. Remove a small section of the flange until it just clears. Now clean everything as good as possible and put the unit together. Put a very small amount of Vaseline on JUST the portion of the cap seal directly above the ECM plug so the epoxy won't stick to it. Leave the screws a little loose until the epoxy sets, then tighten them to compress the seal.

What you now have is a hybrid unit that should be better than the original and you can hook up a vacuum vent if you really want to. The new cap has a vacuum fitting but no provisions for flow through so I elected to leave it open as it is on the bottom so nothing can get in. Hooking a direct vacuum didn't seem like a good idea to me but that is up to you.