Well, my bad luck continues. My 94 ZF6 vette with 82,000 miles on it is starting to run rough.

It was running like a dream, and I don't recall doing anything extremely stupid, just driving it like it should be, and now there is a lower exhaust note, as if something is 'choking' my exhaust, and there is some vibration coming from the engine. No codes/dummy lights. If I push in the clutch, there is no change in vibration, so that's not a problem. I notice if I turn on the A/C, the vibration gets worse. If I am cruising, the vibration/exhaust choking is not noticeable, but if I step on it it sounds like a motorboat.

I know I had a small exhaust leak pre-cat, could it just be that, maybe it got bigger? Could that cause the vibration though?

Obviously I need to take it in to a mechanic, just wondering if you can offer some advice on where to start looking...

 

Just describe it best you can and let him drive it. If he's any good he'll find it.

 

OK... I was hoping I could mess around with it a little, check some usualy culprits but I guess off to the mechanic's I go...

 

mine sounded like that when it broke a rocker arm.

 

That's exactly what i'm hoping is not the problem.

What did you end up doing? Rebuild, replace, upgrade? What did it cost you?

 

the pushrods were fine, it just broke one rocker arm. at that time i just replaced the one. later i upgraded to 1.6 full rollers

 

OK... so one last question: I have a garage, and a lot of tools. (various wrenches/ratchets/specialty tools). The most I usually do on cars is alternator/master cylinder/water pump replacements. Batteries, lights, audio, fluid flushes and fills, filters, blah blah blah... I've never had the guts to open up an engine and have look-see, and try to rebuild one.

Is this something I should start to seriously consider with my vette? I plan on 'driving it like I stole it' and frequenting the race track with it, so am I in for a world of hurt at the mechanics if I don't start learning to rebuild this stuff myself?

 

If you plan on working on the car you should get the gm service manual. it will help you find and fix problems. if it a rocker, pull the valve covers and it will be easy to see.

 

Don't be afraid. There are very few things that I won't work on because I know that I could mess it up and it's worth it to me to pay someone else to do it right. The top end of the motor is pretty easy to work on. The hardest part is remembering what you took off to get to things. Some people use a camera, I usually just use a checklist. The manual pretty much covers everything, but if I'm winging it without the manual, I'll draw a little picture just to remind me where something goes or the order and just make a list of what I did during disassemby and use that when putting things back together. Put bolts back in the holes when you remove a part, use masking tape to number wires or label something, etc. Don't just start tearing into stuff without having a good idea what the problem is. If I am unsure about the cause of something, I will take it to the mechanic to diagnose. Then when I know what it is, I will do the work.
For instance, my F-150 was running rough and cutting out while driving. I knew there could be several things that I knew of that could be causing it and I figured there were probably a few more that I didn't know about. The mechanic found that the problem was a leaking intake gasket that was dripping down into one of the spark plug pits. It would have taken me forever to find this as it couldn't be seen without quite a bit of disassembly. They wanted 3 or $400 to fix it. I took it home and spent $50 on the gasket and $30 or so for antifreeze, oil, and plugs. Sure, it took a few hours of my time. There was some swearing and beer consumption. But it wasn't that difficult and was a heck of a lot cheaper. Really the only way to get confident about this kind of stuff is just start doing it. If you get stuck, make a few phone calls or come on here and describe your problem. Get a Haynes or Helms book to help guide you and you'll be set. Ultimately you have to make the decision whether you want to pay someone else to do the job or tackle it yourself. I prefer to tackle most jobs myself.
When I did my first clutch replacement, I needed a lot of support from my brother to get me through it. Since then, I've done several engine swaps, several clutches, many brake jobs, leaf springs, starters, intake gaskets, carburetors, timing chains and belts, water pumps, radiators, motor mounts, traction bars, swapped a rearend, u-joints, interiors, steering boxes, shocks, transmissions, etc. and even built my own motor from the bare block up, all with a 100% success rate. You already have the tools, all you need is the knowledge and there is only one way to get that. Just do it. I've saved thousands of dollars over the years.

 

When my opti-spark was going bad, it exhibited similar symptoms to what you are describing. The exhaust note sounded very flat and surprising louder, but very flat. After connecting it to a scan tool, I found out that the bad optispark was retarding the timing a great deal. Like -10 degrees at idle and -35 degrees with some throttle. I replaced the opti and it runs great. That may be your problem. Do you have a scan tool?

 

Not throwing any codes? The SES light isn't on.

And I have an OBDII scanner, but my 94 lacks the port to plug it into.

Is it worth trying to read the codes, if the SES light isn't on? Could there be anything in there to be read?

 

Yup, your '94 is OBDI....

yes, you could have History error codes stored, and the SES light does not have to be on.
Easy to pull yourself:
http://www.troublecodes.net/GM/

 

Well sunuva... there is no 'B' terminal to jump the 'A' to. That link says I need a scanner then? It looks like my OBDII scanner will fit, should I try it? Any other way I can pull the codes myself?

 

no problem, sounds like your '94 has the 16 pin OBDII style connector, but rest assured, you have an OBDI system. Follow the instructions from previous URL.

In this case, short Pin#4 to Pin#12 :

 

When my optispark was bad and was retarding the timing, it wasn't throwing any codes. They only way I knew that it was the opti was by reading the timing as the car was running. It was negative -10 to -35 degrees timing.

 

Thanks, I'll see if there are any history codes to read... I wonder what will happen if I put my scantron on it...? (It's raining, and my poor car is outside, so I'm not gonna read the codes now..) I doubt there are any anyways.

I think I'll bring it to a local guy who is a corvette specialist, let him diagnose the problem, and if it's expensive I think i'll start to teach myself how to do engine rebuilds...

 

Well I took a closer look tonight, and I don't see any arcs from the wires, so that's not a problem.

But the bad news is the sound is definitely coming from the passenger side of the engine, sounds like a 'woop woop woop woop' almost like a bunch of bullfrogs. Too bad my mechanics are busy for two weeks, guess I'll drive my beater car for a while until I can figure it out.

82,000 miles, and I have no idea when the last tune up was done. Guess I may as well change the sparkplugs for the hell of it, or at least pull one and see what the condition is...

 

Get a paperclip and scan for codes first thing. Check that exhaust leak is second thing, but unlikely to cause an enigne vibration. It actually sounds like the harmonic balancer on the crank pulley might be coming apart, but then I don't see how that would affect the exhaust tone.
Bullfrogs in the motor is new to me and I can not find a diagnostic procedure for that in my FSM. About the only thing I can thing off for that would be a loose spark plug letting compression get past it, or the exhaust leak. Possible right side cat breaking up inside and causing exhaust restriction? Just a few simple/easy things to check. Good luck with it.

PS--I was thinking you had a 95 with true dual exhaust. If the 94 has the precats, y pipe and then main cat I would bet $$$ to donuts the precat has come apart inside and pieces are getting pushed back into the main cat, causing the exhaust note change. Not so sure about if that would cause a vibration though, but possilbe I suppose.

 

I have a 93 with the OBD1...Autozone scans mine for free...

 

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