Trying to help a friend - Page 2 - ZR-1 Net Registry Forums

bdw18_123 · 10-22-2013

I'm thinking Opti as well. I used to have a '93 6-speed LT1 Corvette and I had a very similar issue. Back then, I also initially ruled out the opti as a cause of the failure because I too had replaced the opti a few thousand miles ago at the time.

The Optispark units in the '92 to '94 LT1 Corvettes have such a high failure rate because they do not have an active venting system to remove the buildup of moisture which leads to corrosion and eventual failure of the unit. In the '95 and '96 LT1 Corvettes, GM changed the design of the optispark unit and added the active venting system.

The aftermarket opti that I had purchased went bad because I sealed up the seams with RTV and the corrosive gasses (and condensed moisture too, I'm sure) stayed in and took out the optical portion. But even if you don't do the RTV thing that I did, the opti will sit have a very high chance of failing if the active vent system mod is not done. That opti I bought came with a warranty, so I was able to get it replaced for free. I also purchased the '95-'96 style of opti cap with the hose nipple for the vent hose so I wouldn't have to glue in one like is described in the Corvette Fever article I used (see CF thread linked to below).

Here is a link to a thread where I described my problem in detail and what I did that ended up fixing the "cranks, but doesn't start" problem:

http://forums.corvetteforum.com/c4-t...ral-times.html

pcolt94's post in the middle of the above CF thread is a really good one for understanding the role that the ICM and coil play in the sparking system, which helps to narrow down the source of problems with the spark system in the Corvette LT1 engine.

I just edited my last post today in my old thread I linked to above because I never posted the update I promised in that last post.

Schrade · 10-22-2013

If it started up after cooling off, I'm guessing NOT opti-spark.

Opti laser (or whatever the 'light' reader mechanism is), gets fouled by dirt, and occasionally coolant. I don't think a cool-off will allow a fouled opti to read better.

Lotta' snappics here:
http://forums.corvetteforum.com/c4-t...rs-needed.html
(thread I got CF mods to merge with another CF'er, with identical problem...

Did VATS problem get addressed by GM prior to '95?

Sudden shut-off (was he at speed?) seems HIGHLY likely a hot ignition module, which would NOT allow a code to set.

Does he have SES light???????

10-22-2013	#11
bdw18_123 Join Date: Apr 2009 Location: Prather, CA Posts: 809	Re: Trying to help a friend I'm thinking Opti as well. I used to have a '93 6-speed LT1 Corvette and I had a very similar issue. Back then, I also initially ruled out the opti as a cause of the failure because I too had replaced the opti a few thousand miles ago at the time. The Optispark units in the '92 to '94 LT1 Corvettes have such a high failure rate because they do not have an active venting system to remove the buildup of moisture which leads to corrosion and eventual failure of the unit. In the '95 and '96 LT1 Corvettes, GM changed the design of the optispark unit and added the active venting system. The aftermarket opti that I had purchased went bad because I sealed up the seams with RTV and the corrosive gasses (and condensed moisture too, I'm sure) stayed in and took out the optical portion. But even if you don't do the RTV thing that I did, the opti will sit have a very high chance of failing if the active vent system mod is not done. That opti I bought came with a warranty, so I was able to get it replaced for free. I also purchased the '95-'96 style of opti cap with the hose nipple for the vent hose so I wouldn't have to glue in one like is described in the Corvette Fever article I used (see CF thread linked to below). Here is a link to a thread where I described my problem in detail and what I did that ended up fixing the "cranks, but doesn't start" problem: http://forums.corvetteforum.com/c4-t...ral-times.html pcolt94's post in the middle of the above CF thread is a really good one for understanding the role that the ICM and coil play in the sparking system, which helps to narrow down the source of problems with the spark system in the Corvette LT1 engine. I just edited my last post today in my old thread I linked to above because I never posted the update I promised in that last post. __________________ [IMG]http://i13.photobucket.com/albums/a292/bdw18_123/_zr1netforumsigphoto.jpg[/IMG][B] 1990 Corvette ZR-1 [/B][I] White/Flame Red, #2299, mostly stock, 144K miles.[/I] -Cams timed to the '93-'95 405HP LT5 stock timing. -IAT sensor relocated to below front bumper. -Haibeck hoops installed in airduct. -OBX cat-back exhaust. [COLOR=DarkRed][B](SOLD - December 2012 [/B][/COLOR][COLOR=DarkRed][B]:hello:)[/B][/COLOR] 1993 Corvette Coupe Black/Black, 6-speed (SOLD - October 2009 :hello:) Last edited by bdw18_123; 10-22-2013 at 09:18 PM.

10-22-2013	#12
Schrade Join Date: Dec 2012 Location: NC Posts: 1,786	Re: Trying to help a friend If it started up after cooling off, I'm guessing NOT opti-spark. Opti laser (or whatever the 'light' reader mechanism is), gets fouled by dirt, and occasionally coolant. I don't think a cool-off will allow a fouled opti to read better. Lotta' snappics here: http://forums.corvetteforum.com/c4-t...rs-needed.html (thread I got CF mods to merge with another CF'er, with identical problem... Did VATS problem get addressed by GM prior to '95? Sudden shut-off (was he at speed?) seems HIGHLY likely a hot ignition module, which would NOT allow a code to set. Does he have SES light??????? __________________ I'm getting my snappics / threads removed blindly as fast as I can, to get in compliance with copyright / license TOS on the boards here (lots of FSM pages and other copyright / license violations on my part; sorry guys). And thanks to all the guys who didn't whine when I posted those FSM copyrighted / licensed stuff in my threads... ( :thumbsup: [b]and to think I complied with a mod's request to delete a pic of him in a Challenge Car in NCM Museum, so he wouldn't get in hot water)[/b] Thanks to several guys here for sending parts FREE; BearlyFlying, WeGone, Geezer, GoldCylon, and more there, TonyD, mike100, fletchusmc... 1990 #2794; 4L60e Stage V by RPM Transmission, TCI Dedicated TCM, OBX Stainless, Power Effects 3" [IMG]https://lh5.googleusercontent.com/-GHpfzty7DVU/UQn-0Ru2xAI/AAAAAAAAA14/08mz1p4QLD4/s445/Screenshot-5.png[/IMG] Last edited by Schrade; 10-22-2013 at 10:30 PM.