MikeNice

Hey guys, I have a 94 Z28 M6 that recently had the timing chain break. When it went the car just died, I thought it was the Opti. So I went ahead and swapped out the Opti, only to find the timing chain was the culprit. Regardless, I put in a new timing set, plugs, wires, opti, and seals. I go and start the car, and it is running horribly. Before anyone asks, yes, timing was set correctly, cam sprocket at 6 oclock and crank and 12 oclock. It sounds very lumpy at idle, idles a bit lower, and sounds a good bit louder. When i go to drive, it hesitates, bucks a bit, and backfires a tad. Its like it doesnt want to go anywhere. I have checked all connections, wires, plugs, etc. Could this be a symptom of bent valves, or ignition-related? It has to be one or the other. Anyone, please lead me in the right direction, easiest solutions first, thank you so much in advance, I need my DD back!

Injuneer

Are you sure you indexed the Opti splined drive shaft correctly. Its possible to assemble it with the splines aligned incorrectly.

MikeNice

How is that possible? Its splined on each side, there is only one way it can go in, without JAMMING it on...

Injuneer

I'm going to give you the benefit of being here for 10 years, and reading most of the posts that have ever been made on the LT1 Tech forum.... it is very possible to assemble it incorrectly. I'd estimate up to 10% of the unvented Opti installations manage to do it. I know I've posted many times to people who swore up and down they did it the right way, only to find they managed to do it incorrectly.... I'd guess a couple dozen times.

MikeNice

I trust your experience and will listen very carefully. If it went on very smoothly is it still possible, or only forced on? Mine slid right on...Other than taking off, is there any way to check? And what are the possiblities that bent valves are causing my problems, in all seriousness.

MikeNice

Just wanted to say, also, thanks for your time helping me with this, you seem to know your stuff.

Projectz28

It is possible to assemble and install the opti out of time. Yes it is splined but I cant tell you home many guys here have done it. its possible. You could check by taking off the cap and bar the engine over to tdc#1, then pull the valve cover to make sure your at #1 tdc with the valves. This will not tell you if the chain was installed off by a tooth but it will tell you if the opti was installed off time.

If the timing chain broke it is also very possible to have bent a valve. If it broke and left a valve wide open the piston may come up and hit the valve before the engine stopped turning. Very possible. easiest way to test is to run a quick compression test. if one is bent you will know very quickly.

MikeNice

Yes but would a bent valve/valves due to a chain breaking cause the car to run SO bad as mine is now as to be completely undriveable? How much would the opti being off one tooth really affect it? Enough to cause this? Ways to check these things?

Projectz28

yes, yes, and yes.

You should be able to check the opti being off by a spline with a timing light. Sounds like its not in your case. I am willing to bet you got it in right. ifit went in very smooth and no force then it probably went in right.

If valves are bent it will run like crapola. No compression or very low compression in 1 or more cylinders.

Tell me this. Cut the ignition by pulling the opti wire. crank it over with a good battery. does it crank over smooth or does it speed up/slow down while cranking? should be smooth cause all cylinders have compression.

MikeNice

Im not so great at telling these things, but it does not seem too smooth. Kinda like duhduhduhduh,pause,duhduhduh, but i may be explaining completely wrong sorry lol

87bandit

I installed an unvented opti incorrectly before, it can happen

MikeNice

How EXACTLY do i check timing on these cars with a light? I have an inductive pickup timing light. Just not sure on the LT1.

Guest47904

You can't check the timing with a light as there is nowhere to reference since the unit has no timing mark.

Before you go lowering the water, check the bridge to see if it goes up and down. By that I mean, double check the wiring order. You could have a crossed pair of plug wires. If that gets you no where.

There are 2 things you want to do. Confirm the valves are in good shape by using a leak down tester. Although I doubt this is the case since you would either have a glowing exhaust manifold due to hot gases escaping a bad exhaust valve. Or, back firing through the intake due to a bad intake valve.

Run a cylinder of choice up to TDC and confirm the rotor is facing the direction of that same cylinders contact point in the distributor cap once the cap is removed. BTW, I recommend the opti be installed this way to avoid indexing it wrong from the start.

I'll wager money either there are 2 crossed wires or the opti is indexed wrong. I haven't figured out how peeps manage it but I, like Fred, have seen way too many do it.

SS RRR

Yep... either opti is off or a crossed wire. The backfiring tells the story...

MikeNice

Well, definitely not a crossed wire, as I went on shoebox's site and followed the picture of the firing order on there and its dead on. Does anybody have a link to somewhere else just to double check?

But with the opti, I know you feel that is the issue, but it went on with no force. How can I be more sure that is the issue before I delve any further?Do I have to remove everything the same I had to to replace the opti, as I do to remove the cap?

Thanks for the input guys, any more?