Hello all, Just got my 95 Zf6 out from hibernation. Any how I recalled a problem I had last year coming back from Carlisle and a few other times. It seems if I run hard, for an extended period of time she developes a sort of high (4800+) miss that almost shuts the engine down. Only after an extended period of hard running. My only mods are a Hypertech PTM, LT4 knock module and an open air cleaner with a K&N. Any thoughts? At first I thought Opti, But now I'm thinking maybe a weak fuel pump. I don't want to just start changing parts. If the Opti was bad wouldn't it do this all the time? Any help is appreciatted. Thanks in advance.

A high-RPM miss is a signature problem of the opti. Not so much the opti itself, but the cap/rotor.

How is the idle? Is it rock steady?

How many miles? As an aside, what condition is the fuel in?

Was the car driven at all over the winter? I know for a fact that Mid-Atlantic winters are not show stoppers...

I would start with a basic - replace the fuel filter...

Final question - how many miles?

Thanks for the quick reply! To answer your questions: 56K mi idles like silk. 93 octane Shell and fuel stabilized. She was run about 15 to 20 mins a month during the winter. This started last summer. I am rarely in my Vette for more than a couple of hours. This problem only occurs on long trips at the worst times (Last time I had an RTS Neon coming after me , It was embarrasssing) Took it out yesterday and went from cruising to 150+ for about 2 hours, not a hiccup (Thank GOD, my passenger had just purchased a new Muskrat GT. Wanted to see the how the Corvette stacked up. He was impressed!) I'm thinking fuel pump because it's easier and cheaper! Thanks again! :thumbleft: :thumbright:

pump? eh... I am not so convinced. I would love to see a fuel pressure gauge put on the car. Pumps die a little differently than that.

I would do a filter, which is needed, I suspect, and monitor.

Checking my maintenance records she had a new filter about 750 miles ago. (last summer). Also no codes are set. I do have a fuel pressure gauge that I will try later. If the Opti proper dies it would just shut down right? Do you think I could get away with just a cap rotor and wires? Also who makes the best AFPR for the LT1. I have a holley on my L98 and I love it.
Thanks again.

Hi! I'm not so much of a car guru but I have a '96 with an extremely similar problem. No codes for me either, but ended up having some naked wires on front right 0-2 sensor - along with needing a replacement ignition module - be careful here - you might end up with new complete assembly. As I'm told, there's been a bulletin and a part design change in relation to water damage issues with old part design. When I went to get replacement module - found this out - no one had a module that looked like mine - then I found out why. One parts place ended up giving me warranty anyway on my complete unit and was so kind to give replacement of idential unit as he still had 1. Also I've changed my fuel filter too. That did seem to help also. in addition, now I have a iight set P0100 - circuit on MAF, possible vacuum leak - but can't find any problem and sensor for that is good. Any of you guys have a suggestion for what that might be? Let me know how it all comes out, maybe I'll know what to look for in the future with mine!

Thanks for the reply Blondie. Is the ignition module part of the Opti? If not where is it located? My Brother in law(who is a mechanic) weighed in with "You need a new Opti" Oh well. Anyone try the MSD unit yet? Anyone know where I can find a step by step process to replace an Opti? One that includes the correct profanity would be great.
Thanks again to all, Tom

The ICM is part of the coil. It's behind it.

However, there is a lot more that could cause this than a bad opti.

When was the last tune up? What plugs did you get? If you are running AC Delco Platinums, you are screwed... they suck. There are these little platinum pucks bonded to the ground strap that fall/burn off. The gap then grows from .050 to .065. Junk.

Get NGK Platinum or Iridium.

I really hate it when "experts" start blaming the opti at every turn. 1995-1997 LT1s had a vented opti. It had postive flow through ventilation. As such, much of the moisture related failures were ended. And most of those failures were caused by carbon tracing on the cap/rotor.

Finally, without a wondering idle, I don't think it's even the cap/rotor.

The symptoms of a bad opti:

1. Codes. This means the electronics are failing.

2. wondering idle. This means that the cap/rotor are not effectively passing the voltage, the computer senses the misfire and tries to adjust timing. It's a no-win situation.

3. high rpm miss. This is the same as #2... but without the wondering RPM. It just misses.

Check the coil wire. Make sure it's a) not chaffed and b) that it's connected to the opti and the coil completely. Check the coil wire terminal ends for burns and such as caused by arcing.

Thanks Bogus, Yup brand new Delco platinums, same time as the fuel filter. That sounds like it could be it. Never noticed a problem until I put all the new stuff on it! Some how didn't make the conection until you guys made me think about it. NGK huh? any idea on the number? I'll probably have to order them. If I'm doing this again I'm doing wires too, any suggestions? What about the "puck" possibly bounceing around in my combustion chamber? Platinum is not magnetic, If I remember correctly. Talk about dumb huh, the car was running fine, I just needed a reason to play with it. Thought I was safe with stock AC Delco parts. Bummer. Thanks again for the responses.
Tom

I don't remember the NGK number, but you can get them at Advance Auto.

I would also check the fitment of the wire to the plug. Are they original wires?? I wonder if when you removed them for the new plugs, that something was damaged? Did you use dielectric grease on the wires?

also, the puck is so small, it blows out or up... not sure which.

Yup again, the wires are original. I was thinking Granetelli's from Mid America. I did use the dielectric grease.
Thanks again, I'll let you know how it turns out.

Check MSD or Taylor. I have heard/had good luck with both.

Copy that, I've had good luck with Taylors on my L98 also. Thanks for the replies!

Well I bought the NGK's and also aset of Delco wires, cap and rotor about $250 in US dollars. Ouch. Oh well. We'll see if this helps.

Ok, Finished it all last weekend. Starts alot easier, Like click-Vooom. The seals on the shaft were all hardened up and the Opti case was 1/2 full of Mobile One. Cleaned every thing with CRC electronics parks cleaner, replaced all the vac lines, plugs(NGK Ir's) wires(Delco) cap,rotor(Delco) What a PITA! Oh well runs good now. Time to look for some LT headers! Maybe Melrose? Thanks again for the replies.

I am glad you found it! Oil in the opti is a real problem.

I will sound a slight bell of alarm... be cautious with the CRC inside the Opti. It could get into the bearing and cause bad things to happen. It's one thing to wipe down with, but another to soak with.

Hello Bogus, I did not soak it with CRC, just gave it a spray. That stuff evaporates so fast I don't think it got into the bearing. It was definitly well lubed when I opened it up! I find it hard to believe it ran as good as it did. I do plan on pulling it down again this winter and doing some mods so I will probably replace the whole thing with MSD. Should go alot quicker and easier now that I understand how it comes apart. Took 3 8-10 hour days. I also stopped to clean and repaint everything which made it alot more work. Looks good though! :thumbright:
Thanks again.