Hello all. I am hoping someone here can give me some insight. 1994 Corvette. Engine had extensive work done on it about 20 years ago. Since then, I have probably put 7000 miles on it. It has always ran great. One day I tried to start it up, and it would not fire at all. Long story short, it was in the garage for the last 2 years, with nothing done to it. I have finally had the time to get around to looking into it, and here is a list of what I have done so far. Removed all old fuel. Replaced the fuel sending unit, fuel pump, fuel filter, fuel pressure regulator. Replaced all spark plugs. Replaced water pump and opti spark (which was converted to the vented 95 and up style). Replaced PCV, TPS, Idle Air Control sensor, ICM. Replaced the old MSD 6AL with a new MSD Digital 6AL. Car was converted to a standard Blaster coil, and I replaced the coil with a new one. Car started hard, and would not idle. If I keep it at 1000 rpm or more, it will run, but not super smooth. Removed water pump, re checked the opti spark to be sure my pin position was correct, and double checked my routing on the plugs for the correct firing order. Opti went on flush with the block the first go around, but I removed it anyway to double check the position. Re installed those items. Same issues. Car starts hard, and I have to give it gas immediately to get it to run. Sometimes while it is turning over, I get what I would describe as a reverse backfire which almost sounds like it is coming out of the intake. Fuel pressure at the rails is correct, and I did remove the injectors and tested them. They seem to be spraying ok, but I have not had them professionally checked. It is almost like it is out of time, but from my understanding with the opti spark it can't be out of time if it is installed correctly. I am not getting any codes from the OBD on the speedometer. I am 99.9% sure that the opti is in the proper position, but with the way it is running I am at a loss and think that might be the issue. I can remove and replace the opti in about an hour and a half now...lol...but before I do that again, I wanted to get some insight from those more knowlegable than me. About the only thing intake wise I didn't change is the MAF, but the engine isn't throwing any codes. Thank you in advance for any suggestions.

 

Something amis here , when you said you converted optispark from 94 to 95 unit .
This means you would have switched camshafts and timing cover because the 94 is a spline drive and 95 and later is pin drive .
Or did you change over to a vented distributor cap?
Don't toss your old optispark as they are still good many a time.
In answer to your first question . Many time the ignition
control unit can go bad and is easily tested

 

Yes, the cam was changed. If you happen to have any old issues of Corvette Fever laying around, it was on the cover of the 3/02 issue, with a write up in the magazine. It has a Crane cam (part number 104227), 6" SRP connecting rods (which had to be machined to clear the cam) and JE racing pistons, on a Cola forged flywheel. Engine was bored out to what equated to 391 ci. 30# injectors with the fuel pressure set at 43#. Heads were also given the stage III treatment from CNC Heads. Chris and his crew at the Corvette Clinic in Sanford did all of the work back then. I do still have the old opti spark, which looks almost identical to the one that Jegs sells with the tan color front. I replaced it with a unit from Summit. I thought about the MSD opti, but after reading several bad reviews, I was hesitant to drop $500 + on it. I was thinking about the ECM as well, but I don't know how to test that. Fastchips in Texas did all of the reprogramming on the original ECM, but a quick google search shows that he has since retired. If there was something wrong with the ECM, how would I get a new one programmed to the same specs as the old one? With all of that being said, while I read that the opti can only go on one way, is there any chance that it is not correct? It seems to me the pin on the cam can fit into anyone of those notches in the clover. I lined it up with the one that has the "extra" notch in it. Thanks a bunch for the reply!

 

I wouldn't be in a hurry to condem the ECM just yet. In 94 GM went to a programmable ECM compared to the programble chip unit of 93 ,which was susceptible to solder joint failures .The 94 ECM was more reliable as well .
Try to get some fault codes to give you some direction . At this point you could have fuel or ignition problems that could cause hard starting
.

 

I will try to keep it running long enough to see if it will throw a code...that would certainly save a bunch of trial and error. Thank again!

 

It seems to me you had a fuel problem causing you to replace the fuel pump, the pressure regulator, and the fuel filter. What about the injectors themselves?
I had a similar problem last August and had to replace all including the injectors. Then when I replaced all the injectors I went with the 40 pound injectors which was wrong. Final fix was all injectors in the 20 pound class. Been fine since!