Re: 97 Z-28 Back Fire, sputter, stall
92-94 opticraps were unvented. That's where most of the water issues came from. Being as his is a 97, I'd go for the coil pack first too. In 95 they updated and went with a vacuum/vent set up. I had the same issue as soljavet01 on my 93. I found a ton of info in my research and was able to modify my opti to set it up with a vent and vacuum. I still have about three of them in a box. If you do it right, most of your troubles disappear. When I had mine, there weren't any real alternatives. Now, you can buy a real nice after market set up with a replaceable distributor cap and rotor. I'd definitely invest my money in one of those if I still had my Z. They're expensive though.
Here's a great write up for the mod. I have all the pictures to go with the mod if anyone needs them. Good luck.
"The Opti-spark is the distributor that is installed on all late model Corvette LT1's and LT4's.
The concept of the Opti-spark was a great idea. It allowed for very accurate control of the spark to each plug. The cap and rotor were pretty basic in design, however the heart of the Opti-spark was the LED/disc setup. There were 2 LED's that controlled the spark and timing of the engine. Additionally, it was mounted to the CAM which greatly assisted in giving an accurate position of TDC/BDC.
The problem however was just that. The location of the Optispark. It allowed road dirt, grime and water to attack the Optispark. Because of its location, it had to be mounted behind the water pump and the balancer making removal very time consuming. Dealers can charge upwards of $1200 to simple change a distributor. Additionally, water pumps as we know fail. When they go, more times than not the pump starts with a small leak. Because the water pump is located directly above the Opti-spark, guess what? Another source of damage. This is by far the worst. Water from the road MIGHT dry out. Antifreeze won't, and will instantly damage it!
Finally, from 1992 - 1994 the Opti-spark was what is known in the gear head world as "unvented". The reason it is called this is because it does not have the vacuum hoses connected like the newer 1995+ LT1/LT4 engines have. What the vacuum hoses do, is they pull the moisture out of the Opti-spark.
What a lot of people don't realize is the unvented Opti-sparks are actually vented!! Yes, they have 3 weep holes at the base of the Opti-spark to allow moisture to escape. Well, all this does is pull moisture back in. Put cold water on a hot Opti-spark, it's going to suck the water in! This is the BIGGEST problem with the design.
Before you go out and buy a brand new 1995+ Opti-spark, be forewarned. You CANNOT bolt a 1995+ Opti-spark up to a 1992-1994 LT1. The CAM is different. You could change the CAM, timing cover, CAM gear, etc but this gets expensive, and is very labor intensive.
So, what is the solution?
You can do 1 of 2 things :
1. Change the Opti-spark out and be up and running again. However you risk damaging it again. There have been people who have had to replace a brand new Opti-spark because they got them wet.
2. Change the Opti-spark out with a modified unit.
The conversion process is simple!
Buy a older style Opti-spark (the one you're supposed to buy), and simply change the cap! Of course you will need to do a few additional things.
Here is a listing of parts you will need before you begin :
GM Parts :
Optispark for 1992-1994 LT1's PN - 10457702
Cap and Rotor kit PN - 10457735 or
1995+ Distr. rebuild kit (Pep Boys or NAPA)
1996 Vacuum Hose Kit PN - 12556174 or
1995 Vacuum Hose Kit PN - 12555323
Inverse Torx Bit - E4, deep well!!
water pump gaskets
Vacuum T or a brass T that will screw into the manifold
Long Breaker bar, or torque wrench
Brass fitting for the base of the Opti-spark.
3/16" Drill Bit (slightly bigger than the hole your drilling out)
Remove your cap from your new Opti-spark. Remove the rotor from the Opti-spark. This is a torx T15 I believe. Carefully remove the rotor, and the metal disc. Do NOT remove the slotted one! It's spot welded on for a reason. Only the disc directly behind the rotor should be removed.
Remove the middle spacer. This is the center portion of the Optispark body.
Set aside everything, but the back plate. BE careful when handling this. Try not to get any grease, dirt or anything on the disc. You will notice 3 holes on the base. Fill the center one, and the one closest to the long pointed portion of the base in with JB Weld or something similar. I drilled out the remaining hole. Try not to get the metal shavings in or on the Opti-spark. Next I tapped in a brass fitting. Do not use the center hole for this, as it won't clear the balancer hub. I use a straight brass fitting from a local parts house. Vacuum the metal shavings from the previous step. MAKE sure it's clean before you put it back together. Reassembly is the same. MAKE SURE you don't forget to put the metal disc back in place. If you leave it out, the gap for the rotor and cap will be WAY off. The rotor and disc are keyed, but still make sure you put them in correctly.
Remove the old RTV Sealant, and put some new RTV on the cap at the electrical connection. Put it back together with the newer style cap. Lightly blow into one of the hose connections while closing off the other. You should hear no hissing.
Installing the unit.
First disconnect your battery.
Drain your coolant. Be sure to open the bleed screws. This will help it drain much quicker.
Remove the rubber intake bellow.
Remove the upper radiator hoses.
Disconnect the bottom radiator hose from the water pump.
Remove the coil wire, and the electrical connections from the Optispark and water pump.
Pull the belt tensioner out of the way, and loosen the accessory belt.
Remove the water pump. There are 6 bolts holding it in place. Additional coolant will dump out when you remove the drivers side lower bolt. Clean the old gasket material and set the water pump aside for now. You MIGHT need to remove the coil, but I didn't need to. Check the weep hole on the water pump to make sure it's not damp.
This is the fun part. Remove the 3 bolts from the balancer. To pull off the balancer us 2 pry bars or 2 long screw drivers. Place them on each side of the balancer between the Distributor and balancer. Carefully wiggle the balancer off. ( Take your time it will come off.) MAKE SURE you make a note of the position of the balancer in relation to the hub. Both the hub and balancer should be marked, but not keyed.
Remove the remaining plug wires. If they are old, you may want to replace them. Now is the time to do it!
Remove the 3 bolts that hold the Opti-spark in place. Pull it straight out. There is a shaft that connects the Opti-spark to the Cam gear. This may or may not come out with the Opti-spark.
At this point, you should look at the old Opti-spark and make a mark of where the notch (spline) is. This will assist you later.
This would be a good time to put some gasket sealant on one side of the gaskets, and place them on the water pump so they can dry. This will make reinstalling the water pump much easier.
With the old Opti-spark to compare, rotate the shaft on the new one until they match up.
I found it easier to insert the shaft on the cam shaft, and then sliding the Opti-spark on top of it.
If there is any gap on any of the 3 mounting screws, you probably haven't lined the Opti-spark up correctly with the spline on the shaft. It should slide all the way on with no gaps on any of the mounting areas. Tighten the bolts, but do not over tighten.
Run your vacuum lines. The clip goes on the alternator bracket. MAKE SURE the hoses are going to clear the belt.
The hose that has the filter and regulator is the vacuum supply.
Poke a hole in the rubber bellow (on the top) and push the L into it.
Put a T or something similar on the drivers side intake manifold, and hook the vacuum hose up.
Reconnect the plug wires.
Reinstall the 3 bolts on the balancer. Tighten the bolts to 60 Ft-lbs. Make sure you line it up properly (see step above where you removed it)
Put gasket sealant on the remaining gasket material, and reinstall the water pump. Tighten to 30 Ft-lbs.
Reinstall the belt. It is much easier to do it now before you do the next step!
Reconnect all the hoses, the coil wire and the other misc. electrical connections (temp sensor, Opti-spark connector, etc).
Lightly tighten the bleed screws.
Refill the cooling system until it is full. Place a rag around the bleed screws, and bleed off the excess air. Don't let any coolant get on your new Optispark!
Check and recheck everything.
Fire it up.
If everything looks good, your done!
You should also pull the hose out of the bellow, and check for vacuum. If it gets clogged, or a hose gets pinched, it will cause the cap to cave in, and burn up the rotor."
'69 SS396 X66 L34 08D M21 BS
Z23 711 U17 72 B
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