My 1992 LT1 has a slight misfire and stumble, it has 155k miles on it. I know the Opti was changed a few years ago by a Chevy dealer.

I just have a bad feeling it's about to go... any thoughts?

Incidently on the stumble concern I have replaced the plugs, fuel filter and cleaned the throttle body as well as ran Sea Foam through the engine. I have an intermitant check engine light that comes on during highway speeds and goes off on it's own (I think thisis the EGR valve)

 

yes. that means the high voltage side is in trouble.

Did you check the coil wire? What about pulling the codes?

There is that cool doc on how to pull codes over at www.c4guru.com.

C4 Guru - Reading CCM Codes

The code could be the EGR, but it could also be 16 or 36, which leads to the optical side of the opti.

 

I will see if there are any code tomorrow, Thanks Bogus

If the Opti is going can I put a later model one in it (one thats vented) and if so what am I looking at for mods if any and what is the aprox cost

 

To upgrade the opti to the 95/96 unit you'll need:
95/96 opti
95 front timing cover
95/96 opti vaccum harness
95/96 opti wire harness
Different camshaft, or somehow change the dowel pin in your current cam (95/96 dowel is longer).

 

I know nothing other than what I've read here and there (and that ain't much) but MSD has a vented Opti replacement however the link below only references 93-94 LT1s:

http://www.sdpc2000.com/catalog/4405...istributor.htm

 

While you're in there, you might as well install a new waterpump. You can get a new, OEM, GM pump from Chris May @ Superior Chevrolet for around $160, or you could opt for a Meziere electric WP.

I went with the former option, but many have been happy with the Meziere...

 

I have had 3 opti symptoms. The first time it was the opti and change it. Another time it was the coil wire shorting to the water pump area on top of the opti. And the last time was a loose plug wire. Of course it was left front, tough to see and find. Ran like a bad opti, with a stumble, just a little different.

Check for any arking in the dark and listen for any ticking, it may not be a lifter. Best of luck.

 

Solve the fault that's causing the intermittant SES light first, and there's a good chance this problem will go away.

When does this slight stumble appear? Idle, off-idle, cruise, acceleration, WOT?

If the stumble never occurs at WOT, it's probably not ignition-related, and there's a reasonable chance it's EGR-related, although there are many other possibilities.

A high-voltage-side (distributor cap/rotor) fault in an Opti should not directly trigger a code.

An optical-side-fault in an Opti should trigger a code -- Code 16 for a low-resolution sensor fault, Code 36 for a high-res sensor fault.

The ECM should be able to run the engine well enough (not optimally, but no stumble) with a high-res fault. The high-res signals are used to calculate camshaft velocity and acceleration, which the ECM uses to fine-tune spark timing. A fault with (or the absence of) a high-res signal should not impair the ECM's ability to run the engine reasonably well.

The engine should die completely with a low-res signal fault. The low-res sensor signal provides camshaft position information to the ECM. The ECM is programmed to not try to run the engine if it does not have reliable camshaft position data.

Good luck with it. Keep us posted on how you're doing with this.

Be well,

SJW

 

IMHO, it's just not worth the hassle and expense to bolt a Second-Generation, actively-vented OEM Opti onto an engine that is set up for a First-Generation, passively-vented Opti. A far better choice is the DynaSpark, which is a true bolt-on swap for the Opti, and is a better quality piece than either of the OEM Optis.

Be well,

SJW

 

There are also kits available for venting earlier opti sparks.