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Discussion Starter #1
Hey all. I hope someone can help. This is only my second posting. I have a 1996 Impala SS, stock LT1 internals with 143K. I have a CAI with a new K&N filter, Edelbrock headers and Flowmaster exhaust and 3yr old (as of now) AC Delco Platnium sparkplugs. It ran great. Last summer as a precaustion I replaced the Optispark II (with new Summit Racing), waterpump (w/new GM), sparkplug wires (new GM), and hoses (Goodyear Hi-Miler). After that if I revved it hard just once (3500rpm +) it would start to lose power and not be able to rev and slowly decrease until I was having trouble revving past 1500rpm, unless it sat for about and hour or so. I replaced the ignition coil and ignition control module and it fix the problem.
Then late this winter it started to stumble alittle off idle, in gear, from a dead stop when the engine was warmed to normal operating temp. It would stumble then clear it's throat and drive normally. Then at highway speeds if I floored it, it would stumble so badly at about 4000rpm (75mph) that i have to let off the gas. There was no codes and the engine light only came on for about 10min on my way to my mechanic. The fuel vapour vent switch was clogged (from my overfilling the gas tank all the time). So it was replaced and code fixed, but the problem persisted. The throttle body was brush cleaned and sprayed and MAF sprayed, no diff. Now it is starting to soft stumble starting at about 3600rpm at highway speeds when I floored it. Please help !!
 

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Discussion Starter #3
I used a new Summit Racing Opti
 

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That is more than likely your problem. I have seen NON GM opti sparks fail within hours or days even. Something in the opti aftermarket scene is not copied well enough and fails. Does exactly what you mentioned, but usually it was the MSD version that messed up in that exactly same fashion as yours.
 

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Frig man. I replace something as a precaution and it is the replacement part that fails on me. Is there a way I can check it without replacing it ? It is not something I did myself, but at garage. And today my new rotors arrived and 2 of them had rust on it. Now I have to contact the dealer and get them shiped back and refunded. One of my rotors is warped and this is not something I want to wait for a replacement.
 

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Go back to the shop and have them put your car on a "scope" have them run the car and see which cylinder is showing misfire, have them turn off your car and restart it, now you should see a different cylinder misfire. Have them do this a few times and it should come up a diff cyliner each time...... thats a pretty tell tale sign of a bad opti and easy enough that they should not charge you to check in this way.
 

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Discussion Starter #7
Thanks Man.
 

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I am fortunate enough to work with an "old timer" who believes in older technology for whatever reasons. While I have tools like our Mastertech and such, the "scope" shows me most vital things as far as running of the engine (350-LT1) if used properly its very handy and easy to use and interpret. And we have 2 Scopes, one is new looking even though built in the 70's the other is identical and looks like it was dropped off a truck (because it was) and still works, we got that one from another shop since they thought just by looking at it that it was toast......still works like new:)
 

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Well I went back to the performance shop and all they said they could do was tell me to drive it until there is a check engine light so they could look at the code. Otherewise they would have to check everything they suspect is causing the problem. I think that they may be good at power but not problem solving. They rely on the plug-in code reader. My engine is getting worse. When I gun it hard at any gear, when it reaches about 3500rpm there is an electrically sparking sound and have realized that it only happens before the engine is properly warmed up. I am not a mechanic but have seen enough 'Rides', 'Overhaulin', 'American Hotrod', and 'Wrecks to Riches' episodes to recognize that sound and know it is bad.
I am seriously considering changing the Optispark even without a definitive answer just to be sure even if it costs me $300. The shop thinks it might be that one of the injectors is at fault and is compensating by enriching the fuel - air mixture when cold but not when hot.
 

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I think you need to step away from that shop. If they rely on a code reader to diagnose a car, they are suffering from lack of will or knowledge. These cars on NOT hard to figure out, they are packer with old but proven technology. I can almost assure you its not an injector problem simply because the injectors in these cars have rarely given any problems even with high miles.....and that statement comes from personally seeing more than 6000 of these cars in this shop.
 

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Discussion Starter #12
I was driving through traffic today and noticed the hotter the engine/engine bay got, the less I could rev before it starts to soft stumble.
 

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How much fuel has been in your tank when this problem shows up?

1) If happening below 1/2 tank on hot days your fuel pump may be getting ready to go out. It may be getting hot and not providing sufficent flow. Electric in the tank fuel pumps really should be kept covered in gasoline which helps take away the heat that the electric pump build up while running.
If happening this way a good test would be to keep the fuel level above 1/2 tank and see how the car behaves. (Personal experience with the van I own.)

2) Check your fuel lines from the tank forward and see if any are near the exhaust system. If they are running closely beside some of the exhaust you may want to make a heat shield for the lines to keep them from trying to vapor lock on you.
 

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Discussion Starter #14
This problem happens at all levels from full to empty. I know what you mean about the fuel pump. On empty and through traffic in 90F weather it was going crazy. Now I always keep at least a 1/4 tank until I can swap the pump for a Racetronix model another poster mentioned. The George Bates Automotive member is pretty sure it is the Summit racing Optispark I installed and I am beginning to believe him. This problem didn't happen until after I had the factory Optispark changed out as a mileage precaution (143k) along with other parts (water pump, sparkplug wireset,...). On Monday night after work I floored it on the highway twice to make sure and it had no trouble going to redline when the engine wasn't at normal operating temp. After it warmed up is when the problems appear. The fuel lines looked okay when it was on the lift last week for brakes.
 

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Sounds like all other possible causes have now been ruled out.

Time to replace the Opti-Spark unit. I agree that G.B.A. seems to know about them units. I personally have not worked on one of them, nor have I seen one yet.

I have also heard that they are not fun to change because of their location as well, so watch out for your knuckls there.
 

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rely on a code reader to diagnose a car, they are suffering from lack of will or knowledge.

I use code scanners, but I also understand the fundimentals of engine operation. They can be very helpfull tool for the most part. But with my old Impala I have a joke that the kids today could not work on it for they would not know where to hook up the code reader, and with out that they are lost. LOL.
 

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I use code scanners, but I also understand the fundimentals of engine operation. They can be very helpfull tool for the most part. But with my old Impala I have a joke that the kids today could not work on it for they would not know where to hook up the code reader, and with out that they are lost. LOL.

Im not knocking anyone for using a code checker, we all have to use something at some point. I simply say if there limited to only using one to diagnose, find another shop. And yeah, most people these days would lift the hood and look at the aircleaner (on your 77 for example) and probably ask "where's the fuel rail" :)
 

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G.B.A.,

I hate to rehash an old thread, but how do you feel about MSD Opti-spark caps?

Thanks,

indychevyman
 

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I am not a fan of them. I have seen people use them and work.....But I also remember the time when I did several for people who just had to have the new msd stuff and then having to replace them with a GM opti less than a week later. The "rivet" on top of the contact on the rotor would actually eat thru the cap causing it to fail. Good idea from msd but bad/poor execution.
 

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Dude I think tht mite b wrong with my 96, I rebuilt the engine n I went with aftearket optispark. It stumbles at 40mph and at 60mph. It sucks.
 
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