We have replaced the right side head gasket in my son's 94 LT1 Z28. This is beyond anythign we have done before, but we are researching and trying to learn as we go. The car runs, but not well. I've posted two other threads recently about other aspects of this project:
1. https://www.camaroz28.com/forums/sho...d.php?t=772396 - About a pit found in a cylinder wall
2. https://www.camaroz28.com/forums/sho...d.php?t=774042 - About oil not flowing up through the push rods as fast as I thought it should.

When the head gasket blew, cylinder 2 blew a small piece of the metal ring out, allowing coolant to enter the cylinder and resulting in a good deal of white smoke out the exhaust. Machine shop checked and resurfaced the head. We cleaned up the block, installed a new gasket and bolts, adjusted valve lash, and put everything back together. Also did two oil changes to be safe and flush anything that got in out, and flushed and replaced coolant.

We took it around the block once after replacing the head gasket. Some stuttering and misfires... generally runs rough. My son says it was starting to run rough some time before the head gasket went so I don't know if this is all from before or after the gasket failure.

I built an interface/cable and ran FreeScan to see what it would tell me. Left O2 sensor stayed consistently low (mostly under 0.3v), even with left BLM at 160 and left integrator getting up to 200. Right O2 sensor was doing what I beleive to be normal... bouncing up and down with integrator reacting and staying mostly in the 120's and 130's. Right BLM was also at 160. Eventually I think the PCM gave up on the left side and took it out of closed loop mode. The engine actually seemed to run a little better in open loop mode. Replaced the left O2 sensor, but no change.

At idle MAP is about 0.45 with outside air pressure at 1.00. I've read that it should be about 1/3 of outside air pressure so is this a little high?

I tried pulling injector wires to see if I could narrow things down to a particular cylinder. There was no noticable difference when I pulled the #2 and the #7 injector wires. I tried swapping injectors (#2 with #4 and #7 with #5) and the problem did not move. Listening to the #2 and #7 injectors with a long screwdriver to the ear I can hear them clicking so it seems that they are getting a signal. I pulled the plug on #2 and it looks like it is getting a good spark. I haven't checked #7 yet. I think 7 & 2 are next to each other in the firing order... so is it maybe something in the Opti? Maybe a dirty area in a sensor?

One other thing... but I am not sure how to describe this. There is a shaking feeling... almost feels like someone is kicking the engine. I can't really hear it, but I can feel it when sitting in the car or by putting my hand on the engine. When idling it happens at varying intervals... maybe from something like 2 or 3 times a second to every one or two seconds. If I pull the wire from injector #2 it stops. Pulling #7 does not affect it.

Sorry if this is all over the place. I've tried to include what I think might be relavent. Any suggestions as to what might be wrong or what to look at next are appreciated. You guys were very helpful in my other posts... thanks.

 

First thing to check would be the plug wires for cracks/burns and double check that all the plug wires are on the correct cylinders.

 

On the issue with oil to the pushrods.....it could be that your priming tool is not sealing the oil lifter galley well. I bought the one that was recommended on this board and it did not fit correctly. I have a picture I took where it shows the plug for the lifter valley .250" too low. My Dad machined me some new snap ring grooves .250" higher and it fits much better now. I'll try to dig up that picture later.

I didn't pay attention....did you try to prime it with the starter(engine fully assembled?) or a drill and priming tool?

If you did it with the starter....ditto what Shoebox said....takes a couple of mins to see pressure start to rise.

 

second that... (i would ohm out the wires too)


how many miles on the car? (i would also pull the opti cap and replace if not the whole thing)

Check the MAF sensor to make sure its working right (you will need a scanner for that (or just unplug it to see if there is any change)

 

The car has about 140k miles on it.

At idle FreeScan reports air flow around 9.5 give or take 0.4 (I am not sure what units FreeScan is reporting this in). During an easy acceleration up to 2k RPM it got up in the high 20's, and somewhere in the data I captured it got as high as 40.

Sorry if I wasn't clear... the two threads I referenced were just for background info... the oil is flowing ok now. I did not use a priming tool.

Plugs and wires were changed earlier this year. I've checked that the wires go to the correct cylinders a couple of times. I will check them cracks/burns and ohm them out.

After that I guess I will take a look at the Opti... not sure how to check it except to pull the cap off and do a visual inspection of opti and cap for corrosion, etc.

Thanks for all the replies. I really appreciate the information.

 

If FreeScan is showing "9.5" at idle, its reporting in grams/second. Maybe a shade on the high side, but it depends on the idle speed.

Here's some help with interpreting the scan data:

http://www.injuneer.com/ScanMast.html

 

the opti is a funny thing simple in theory but if not working correctly can cause a host of problems since it controls the fuel and timing you can be chasing your tail if you are not 100% sure its in good working order .... with over 100k on it i would change it....
over the years i have had problems with my lt1 with sputtering cutting out at high rpm miss fire, rough running and in most cases when i replaced the opti all problems gone.....

 

here is an example of my opti i just pulled out last month after a month of trying to figure out what was going on


http://www.youtube.com/watch?v=SfxnQXKeh3s

 

Finally got around to pulling the opti and I think the problem is in the cap. Inside the cap there is a trail between the points for the #7 and #2 cylinders... which just happen to be the two cylinders that I identified as problems by pulling the injector wires. This trail is somewhat conductive (I measure about 50k ohms resistance between the two points) and I would bet it is causing the problem. I wonder if this was even the cause of the head gasket to blow at the #2 cylinder by causing it to sometimes fire early with #7.

Otherwise the opti does not look too bad except for some very fine grained powdered rust sprinkled about the inside and some rusted screws. The question now is should I replace the whole opti or just the cap and rotor? Is the rust I see enough to cause problems later? I am leaning towards replacing the whole thing just to be safe, even though it can be a bit more expensive. Also has anyone had experience with after-market or re-manufactured optis?

Here are some pics:













Thanks

 

The aftermarkets and rebuilts are disasters. The MSD is similar in performance to the AC Delco but has its own quirks.... making it questionable whether it is worth the high premium over the AC Delco. The Dynaspark billet unit seems to be very good, but now you are looking at $600.

The back 1/2 of the Opti has the optical cam positions sensor that can and does fail, and the bearing, which wears and causes erratic timing. I'd replace the entire unit on a 16 year old car, with the AC Delco unit.

There's a Corvette website that has an article on venting the unvented 93/94 Opti. Try and find the link, because the vent will reduce the corrosion, by pulling the ozone out.

 

You will definitely want to replace the whole unit and not just the cap.

 

Looking at Summit Racing I see two different versions of the Optispark (the car is a 94):
- Optispark I (10457702) for 93 & 94 $480
- Optispark II (1104032) for 94 through 97 for $380

Of course, I would like to take the less expensive route, but I am not certain which one will work in this car. When I plug the VIN in to GM Parts Giant it shows a part number ending in 457702... which leads me to beleive I need the more expensive Optispark I.

Questions:
- What is the difference between the two Optispark versions?
- Can I use the less expensive Optispark II?
- Pointers to places where I can get it for a good price are welcome

Thanks!

Troy

 

Looking for the site the Injuneer mentioned led me to some answers to my own questions.

The two opti versions are not interchangeable. The newer one is the vented one, I need the older unvented one. The car can be converted to use the newer vented model but it requires a new front timing cover, camshaft timing gear, additional vacuum lines, and different wiring harness.

The info was found at http://www.nookandtranny.com/Info_LT1.html.

 

You figures it out..... 93/94 unvented = Optispark I.

Price seems high. Did you check the sources Shoebox mentions on his site?

http://shbox.com/1/4th_gen_tech2.html#Dal_and_Jason

 

think you can also get the unvented optispark and use the msd cap and rotor kit which is vented..

loctite the rotor screws when you swap opti's no matter what opti you use..

heres the corvettefever article.
http://www.corvettefever.com/howto/16758/index.html