tjvette

I have a 94 vert (auto) with 73K miles. I recently noticed a miss during idle while in drive. Over the last month the miss has become more frequent and occurs throughout the RPM range. I started by changing all the plugs, wires and cleaning the injectors. The problem continued to get worse. The car now misses constantly and bogs down while letting off the gas at 50mph+ and then accelerating. There are no DTCs.
I connected my PC using Datamaster and all the sensors look within range (O2, Map, Maf, temp, etc) The one problem I see while scanning is that as soon as I accelerate (at any speed and even in neutral), the computer activates a spark retard - and most times I also get some knock counts indicated in Datamaster.

I am suspecting the Optispark although it was changed about 40K miles ago (at the dealership) after my water pump started leaking. I was wondering if anyone on the forum has seen similar symptoms and how it was resolved.

Cherry6speed

I can relate to your problem. I recently went through the same thing. A couple things come to mind. First, It definately sounds ignition related.have you looked into your coil module? Also, try looking at your engine at night (with the lights out) and look at the individual plugs. My problem eventualy showed up as a new plug wire arcing to the block. I saw the blue spark at night and corrected the problem only, after replacing most of the ignition components . Sometimes it's something simple, like the coil wire going into the opti for example. That is a great place to come loose where you can't see it. The knock counts could account for some horsepower loss but not a miss, a few knock counts are normal. Twong or one of the tuner pros can help you sort that out later. Let's not jump into the opti just yet. I am leaning towards the above. Let us know what you find

tjvette

Thanks for your response. I did have a look at the wires at night to try and see arcing but did not see any. I haven't touched the ignition module or coil. I am going to have a closer look in that area as well as the wire between the opti and the coil this weekend. The car is not really driveable at this stage so I will be at this until it is fixed. I will post any findings. Thanks again

lt4red

I've seen clogged cats cause this kind of engine trouble.

DougSilver

I had similar rough idle/miss problems. The problems largely went away after I replaced the coil.

REDC4CORVETTE

I went through the factory coil one jegs and now I have an MSD.
The coil was arching to the block .You could only see it at night real dark out.At first I was not sure if that was it because it was a blue color.Replaced with MSD and good since then.
I did have a problem with knock counts after I installed my roller rockers.
I changed the computer knock moduel to an LT4 and it was lots less.

tjvette

Just wanted to let everyone know what I found. I checked around the coil and ignition module for and exposed wiring or shorts. I couldn't seen any issues with the wiring at all. There were also no signs of arcing on any of the plug wires or the coil to optispark wire. I decided to take a closer look at the Optispark. I removed the Optispark (after draining the coolant, removing the water pump, and hub pulley, etc.) and when I rotate the splined shaft on the Optispark it makes a strange noise. When I rotate the shaft, it sometimes catches on something on the inside (my guess is the rotor is catching).

I decided to go ahead and replace the Optispark with a new one. I just finished getting everything back together after a long weekend of leaning in the front of the engine. The good news is that the problem is now completely gone - no more missing, no spark retard and no knocks. The car has no hesitation and runs perfectly. The idle is smooth as silk.

I plan to take the old Optispark apart to see what is wrong inside. I will post an update when I find out.