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Old 07-03-2010, 03:14 PM
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LT1 Z/28 no spark

i just traded my yamaha for a 1995 Z/28 with a LT1 not got it home yet but guys saies no spark? an i've not messed with any of these systems yet! an would like some ideas of what i should check before i go buying a bunch of parts!

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Old 07-03-2010, 04:19 PM
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Check the Optispark distributor, it is a known problem point/weakness on the LT1. Rather expensive to fix also.
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Old 07-03-2010, 06:07 PM
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Expensive, indeed. My nephew spent something like $350 for a cap & rotor, wires and plugs for his- that's not labor included, JUST parts. Good parts, though.

It's hard to see/feel but if you detect any coolant leakage from the water pump, it will go right down onto the Optispark distributor- this will eventually kill it. There's a seal that's supposed to keep water out, but over time it deteriorates.

Getting to the O/S is a chore, too.
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Old 07-04-2010, 06:17 AM
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oh i know not going be easy to change, just i hear some dist. some it ecm, some it's crank sensor, guess just get a factroy repair manual like i did with my 1984 cadillac coupe,
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Old 07-04-2010, 03:22 PM
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Quote:
Originally Posted by rachet ralph
oh i know not going be easy to change, just i hear some dist. some it ecm, some it's crank sensor, guess just get a factroy repair manual like i did with my 1984 cadillac coupe,
Start by retrieving the stored codes, if there are any.
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Old 07-05-2010, 12:18 AM
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'95 should have a vented opti... they don't fail unless something else is wrong.

No spark... I'd check the coil, coil signal, ecm...
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Old 07-05-2010, 05:30 AM
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Everybody seems to hate the Optispark

The "opti" means optical, meaning its an optical trigger. That part of it is dead-nuts reliable, impressively accurate, and will probably outlast you, your children, and your grandchildren. The "spark" part is a rotor and cap style distributor which is no better or no worse than any cap and rotor, although its semi-sealed and positively vented style does help it live a lot longer.

Mine finally gave up the ghost at 127k. The rotor broke. You can get aftermarket cap/rotor combos from MSD and Accel if you like taking it up the tailpipe, or you can just call Dal Slabaugh at the dealer in Akron, OH and he'll send you a brand new complete one for about $180.

I personally think the O/S is a great setup. Accurate, long-lived, needs no service except replacement when it goes bad. What gives the Opti such a bad name is due mostly to the fact that the water pump weep hole drips right on the unit. People complain about having to R&R the water pump to replace optisparks, but one opti usually outlasts two water pumps, so chances are the water pump needs to come off anyway to be replaced.

But, like silverback said - something is wrong. The coil is mounted on the front of the driver's side head and is pretty easy to test. Of course, check the fuses too .

I love the opti. Now - plug wires.... don't get me started
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Old 07-05-2010, 07:37 AM
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Opti's have a higher than normal failure rate and are real expensive to fix. Very poor design from GM. If the water pump leaks, you most likely will be fixing the opti as well.

They are very accurate when they work but so is any quality distributor. You haven't lived until you have replaced the plug wires on one.
There are troubleshooting guides on line you can follow. Please don't just start replacing stuff, it can get real expensive. You don't want to replace $300 worth of parts and find out you have a bad ground or a broken feed.
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Old 07-05-2010, 08:11 AM
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The "vents" are drain holes at the bottom of the unit, they are too small and often get plugged early on. They are often enlarged at rebuild time to offer a bit of better drainage.



Later units have a vacuum harness assembly to circulate air through the Optispark distributor, the idea being this will evaporate the condensation. The problem is, the seal goes bad between the cap and body-either by being installed wrong or just old age- and this allows more wet IN than the vacuum can evaporate OUT.

If (when, more like it) the vacuum harness fails for one reason or another, even this meager help for the situation is lost.


An Optispark WILL fail, no IF to it. And the most often found outside cause is infiltration of water/coolant into the unit.
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Old 07-06-2010, 11:53 AM
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You can go to a site called EFIConnection. They have a 24x reluctor wheel kit that allows the use of LS1 CNP(coil near plug) ignition. It totally rids you of the Optispark ignition.

http://www.eficonnection.com/eficonnection/24x.aspx

peace
Hog
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Old 07-06-2010, 08:10 PM
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That LSx conversion is expensive, but those who have done it say they are very glad they did.

The 95 doesn't have a crank position sensor so that is not the issue (and it only sends a mis-fire code anyway). The opti does have a higher than normal fail rate, but is also dead on accurate cam postition signal sender. Easy check for opti to see if it is dead- Pull #1 spark plug wire off plug, stick a plug in it and ground it out on something. Have someone turn the key and watch the spark. If dead there will be non. If working properly That plug should spark very rapidly. This is just a quick check. If the spark is weak I built a little test wire that contects to the coil and spark plug on the other side, same principle to test coil spark. They make test lights for this stuff, but I am too cheap for that.

Here is an actual process for diagnosing optisparks. Comes from website www.shbox.com . Great site for LT1 info.

Check to see if you have a signal from the PCM to the ICM on the white wire. While someone cranks it over, check the white wire to ground for 1-4 volts on the AC scale. If that's there, the problem is between the ICM and the coil.

2 of the wires go from the ICM to the coil. With key ON engine OFF, those 2 wires have 12 volts on them. Find them and be sure they have 12 volts with the key on. One of the other 2 wires left goes to ground. Find it and confirm it goes to ground. The last wire left is the one that carries the control signal. It will test out as I said on the AC scale when someone cranks it with 1 to 4 volts AC. Also measure the resistance of the wires on the opti harness.

If you are getting 1-4 VAC on the white wire it means your opti is sending pulses to the PCM which is sending signals to the ICM to fire. Then your problem is not the PCM or harness. It would be ahead of that which leaves the ICM, coil, and opti.

http://shbox.com/1/95_ign_system_schematic.jpg

Disconnect the ICM connector. Leave the coil connected. Turn key ON engine OFF. Check for dc voltage at harness terminal "A" to ground and and also "D" to ground. You should get 10v dc or more on both terminals.

If you get no voltage then its the coil or ignition fuse.

If you have good voltage, switch the meter to AC and connect the leads to terminal "B" and ground. Watch the metre while someone cranks the engine. You should see between 1 and 4 VAC. If you don't see the proper ac voltage the problem could be the optispark, the harness to the optispark, the PCM or any of the wiring in between.

Measure the resistance of your coil. If its around 5000 ohms or so its fine. Any higher than 7000 ohms means you should replace it. Measure the resistance of the opti harness and if it seems very high, replace it.

So then if your car passes all the above tests, its the opti.
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