ZZ4 with MSD distributor and 6AL box
And yes I've read all the papers (Lars) sticky's etc. many many times.
Here is what I had when I put my ZZ4 in and at the same time I installed the MSD components.
10*BDC initial and 36* mechanical all in at 3000 RPM. That ran fine for years. I just put that curve back in and off idle is good but WOT is not.

My clutch went out almost two years ago and after I replaced it I've had this ping problem for some reason. I did not remove the distributor when I worked on the clutch so I'm not sure why I've got this presistant ping now.

After the clutch change the ping would be during off idle cruise by just giving it a little gas around 2000 to 2500RPM. WOT was fine. I tried to get rid of the ping by retarding the timing 2* at a time. When I got to 4* BDC the off idle ping was gone but WOT would ping.
Since then I've tried different curves and I can get the ping out of off idle/part throttle acceleration or WOT but not both. This is driving me crazy and wanted to know if there is anything I'm missing.

BTW I have a B26 vac can but have not been using it because it seems to make everything worse. According to Lar's vac can spec the B26 is starting vac @ 5 - 7 inches and 8* distributor advance @ 11 - 13 inches. Not sure why this can shouldn't work perfectly. Yes I tested it and the diaphragm is good and doesn't leak. Idle manifold vac is 21 inches. I do have a B1 can if needed.

This is driving me crazy and wanted to know if there is anything I'm missing. Any timing guru's in the Northern Virginia area, I'm in Warrenton and will buy the beer if you can help me get rid of this problem.

 

Ping can happen from several things- Too much ignition advance, too lean fuel mixture, carbon build-up in the combustion chambers or the engine is running hot due to cooling issues.

You may need to look at all these other areas to determine the root cause-
Timing is just part of the equation.

 

Thanks
Engine runs at a constant 190* temp. I'm actually a little rich on my mixture. I don't think carbon is my problem as my plugs look good (a little on the dark side as my rich mixture indicates.
I guess I'll go get some fuel additive to help clean my valves and combustion chambers to see it it is carbon. Can't hurt. Heading out to get some Seafoam now.

Keep'em coming.....

 

I'd check the timing at 4000, see if it keeps advancing passed 36*@3000.... At 5000 it may be 40*...who knows... Lots of times those curve kits needs limiters put in them or stops welded on the shaft.

Leave the vacuum advance off for now as it will make it worse at cruise by a long way.

 

ajrothm - Thanks
The MSD distributor has a changeable stop bushing stud. The re-curve kit comes with a bunch of different diameter stop bushing to limit full mechanical advance along with different weight springs to speed up or slow down how fast the mechanical advance comes all in.

I haven't been running vacuum advance for a while as like I said it seems to make things worse. Without vac advance my engine doesn't run any hotter but I'm sure my gas mileage is down a bit but I don't drive my car for gas mileage.

I just poured a whole can of Seafoam in my tank and filled up. I'll see what that does.

 

seafoam is best used by pouring directly down carb with high idle.
the amount and density of white smoke will tell you how much carbon build up there is.
beest to almost kill the engine with the amount of sf you pour in then turn off engine and let sit. then start and race rpm.
do it in the open and up wind.

 

I'm going to try that next but I'm going to wait until all the neighbors are at work next week. LOL.
I found one video where they pulled off the brake booster vacuum line and poured it down through that. Since I don't have power brakes I'll just either pour it down the carb or take my vacuum source line for the headlights/wiper door and use that like they did in the video. Either way I think will be effective. In the mean time I put 3/4 of a can in my tank and will run that down to E and see if that makes a difference.

 

Check to make sure your timing marks haven't moved. Make sure they coincide with #1 TDC.

 

I guess we will have to wait and hear back from you and see if you adding stuff in your fuel tank helped.

I know this may not be a common practice. But when I get cars that have an issue like this. I always check the fuel quality. This is because I work on a lot of fuel injected cars and the fuel quality can really screw things up...so...regardless if it is fuel injected or carburated...I pay close attention toe fuel quality or possible water in the gas tank. If it appears to be bad by me checking the alcohol level in it. I remove the hose from the fuel line that comes from the fuel tank that goes on the fuel pump and add my own hose going into my racing gas container with fuel in it.... and I have good ethanol free fuel in it and run it and see what it does. I also have other fuel containers with gas with ethanol in it...but I also test to see what the percentage of ethanol is in that fuel.

If all that was done was a clutch...and it ran perfectly fine prior to that. The I am not buying into carbon on the top of piston that is creating hot spots...but crazier things have happened.

DUB

 

Thanks Dub. I do use 93 octane as the ZZ4 is 10.5:1 compression but the only problem is it's 10% ethanol and there isn't anywhere close to get 91 or 93 octane without ethanol close to me. I can get 100% pure 87 octane but that's it. I too think this may be related to fuel quality but wanted to go through some other stuff before I invest in a case of octane boost.
I'll keep ya posted.

 

I don't know if this can happen on a corvette, but on some cars, if you pull the trans and don't support the engine, the distributor will pick up the slack and support the engine from the firewall. Did you damage or bend the distributor?

 

I know it has been some time...and I am sure the fuel in the tank has been used up and fresh fuel in it and your problem still being there.

I agree to check other options out BEFORE you go out and buy octane booster.

'Google' ....'ethanol testing tool' and see what comes up. This tool allows you to check the percentage of alcohol in the fuel you use....or verify the ethanol free fuel is what it is. The tool is really inexpensive. The reason I am saying this is a friend was working on a high end German car and was having a fit trying to figure out why it was not running right. he used this tool and found that the fuel in the fuel tnak was 20% ethanol.

Check out this video.

this video is REAL...If testing true ethanol free fuel...it will not cloud up and separates darn near instantly. When it has ethanol in it...well..watch this video and see for yourself. Not saying this is your problem..just may be worth knowing about.




But I feel that he has checked the cap and operation of his distributor....or at least I hope so. I know I remove the cap when I do transmission removals ...but I also support the engine via a plate I use a support stand to keep the engine from falling all teh way back.

DUB

 

The problem seems to have occurred right after the clutch was repaired. The only two things I can think of is bad gas or a damaged distributor. I would hope the OP ran a tank or two through before starting to chase the problem. My motto is if it worked before you "fixed" it you probably broke it.

Thinking out loud... If I set timing on #1 and checked timing on #6 shouldn't the timing be the same using the same timing marks? The dist would only have traveled 180 degrees (half a revolution) and this may show if the dist is damaged?

Probably should know how long the car sat during the clutch replacement.

 

I pulled the engine and trans together when I replaced my clutch. I was well aware of the distributor hitting the firewall when removing and installing. I even took the cap off to lower the height of the distributor to keep it from contacting the firewall during maintenance. I think my distributor is OK.
Thanks for everyone's help. I've got a full tank of gas with some Seafoam in it and a full week of work to empty it and see what that does.
Right now my timing is 10*initial and 36 all in at 3000RPM. I'm still not running the vac can yet as I want to get the mechanical timing right and go from there.

 

Interesting - I'll give that a try and see if this works. Never thought of that.


About 8 months but I did put fuel stabilizer in the tank while it sat and I only had about a 1/4 tank at that time. I've put about 12,000 miles on it since so many tanks of gas.

 

Any chance it sounds like this ?


Sounds like engine ping, but in fact it is gear rattle after I changed to a Aluminum light flywheel & Twin disc clutch. This happens because the twin disc doesn't have any dampeners (springs) in the clutch discs and normally the heavy steel flywheel also dampens the noise.

Dose the new clutch have dampeners in the disc. ?

 

I haven't listened to your video as I'm at work but I will.

Interesting I installed an aluminum flywheel when I installed my new clutch. My clutch is not a twin disc setup and has the dampener springs. Things that make you go Hummmmm........................

 

When I used the Alum flywheel and a single disc you could still hear the gear rattle but nothing like the twin disc. Open up the console area and place a stethoscope on the transmission. See if this is the noise you are hearing.

Since I have a MSD Programmable ignition system (make your own timing curves) I was able to very quickly determine this is not engine ping noise.

The noise is usually RPM based and the more throttle during the RPM range and loader the noise.

 

You do realize the GM Performance Parts Catalog from 2014 listing the ZZ4 shows total mechanical advance as 32 degrees with an initial of 10 degrees?

 

Thanks and yes. I've been playing around with a bunch of different curves. My ZZ4 is a 2000 model. Not sure if anything is different for 2000 to 2014. That curve is also for the HEI distributor that comes with the engine. I'm running an MSD system.