LT-1 no spark (optispark)

Hi guys, 

So I'm not really a GM guy, and pretty much have zero experience working on anything they've made since they went to fuel injection... lol, but hopefully someone can help. I have a LT1 powered (93 Corvette according to the ECU) 34 Ford, and it has no spark at the plugs. I've done all the multi-meter tests (battery voltage at both sides of the coil, and a 1-4v AC signal, along with a good ground, all tested at the ICM connector.) and everything checks out good. I even swapped the coil and ICM, as they're easiest to get to. Still no spark at the plugs. I then had the bright idea just to pull the coil wire off the optispark and check for spark there.. and it DOES have spark from the coil, going into the optispark unit, but not out to the plugs. That's got to mean the rotor/cap assembly is messed up somehow, and it needs a new optispark unit, right? There's nothing that I can be missing is there? This reallly isn't a job I want to do more than once. To say clearance is tight is an understatement! Thanks!!!

Sorry dude, looks like you will have to at least remove the radiator and cooling fan.  Optispark resides under the water pump, which has to be removed to replace it.  

Yeah you need a new opti, don't cheap out if possible

Patrick said:

Yeah you need a new opti, don't cheap out if possible

+1

I would also replace the water pump if you don't know how old it is.

In reply to Patrick :

Yeah, I'll be going genuine GM if thats still possible. Then maybe MSD if not. 

If you are serious about this engine and car a 24x conversion may be in your future.  It solves most the gen2 SBC downsides.

The key words here are "water pump."  Water pumps leak, and on that LT1, they leak into the dizzy cap.  There is also basic humidity, but pretty much every one of those ironically named Optispark things will get this problem.  Google is full of the stories . . .

Replace the water pump while you're at it.

You can get cap and rotor kits for it that aren't expensive.  That way you're keeping it GM.  The optical trigger in those things is bulletproof.  I have never heard of one dying ever.  The cap and rotor are, well, a cap and rotor.  They go bad.  I have also had a rotor crack and go cockeyed and not send spark.

Before you put the new water pump in, JB weld or epoxy a little stub of stainless brake line in the weep hole on the bottom.  That weep hole is the reason Optis get their internet reputation.  It drips on it and kills it.  Once you have that little stub of tubing, you can connect a rubber hose to it and drain any coolant drips out the bottom instead of on the dizzy.

If you don't currently have one, make sure to get the later vented optispark which pulls a slight vacuum on things to keep them dry.

Also, when installing the optispark, make sure it seats all the way on the timing cover by hand.  If there is space between the ears and the bolt bosses, it's not right.  If you use the bolts to draw it on, you risk pressing the shaft which pushes the rotor into the cap and you can bust things the moment you hit the starter.

How many miles?  GM used a pretty good timing chain, but if it's north of 150k it doesn't hurt to go the extra step and do a new chain.  I did a cloyes single roller... I don't think a double roller fits under the stock cover.  The front end of an LT1 is definitely one of those "while you're in there" kind of front ends.

If you're doing the work yourself, parts are pretty cheap, and going the extra mile is only a few more Hamiltons

In reply to Curtis73 (Forum Supporter) :

I thing the 93 was not vented if still original. 
Im still living with a slight miss at idle on the 94 I did get plugs,(with both of my vehicles not trustworthy, I haven had time to put in) but "read" a lot of info that decent quality opti parts are hard to come by these days. Definitely not MSD, anymore (for opti)

Thats inter web talk. Not sure what truth is!

Your diagnosis and fix suggestions are spot on, from what I know (you da man!)

just unsure of good quality parts source!

Update since I've had some time to work on it... replaced the Opti with a new AcDelco unit, and now I have spark... but it still won't start. It went back together smoothly with me lining up the spline drive to the distributor (all done by hand) I'm about out of ideas. It loses injector pulse (verified with a noid light) after 2-3 pulses. Everything I read seems to point back to the Opti being the cause of such failure... and I really don't want to do this again. Please help me with further diag!