68 CdV 472 "pinging" under light throttle when really warm

[Steve W]

If you've followed any of my posts, you know that I had my mechanic add a pertronix unit to get rid of the points...as well as doing a lot of other work... and that took care of ALMOST all my issues.

I say ALMOST because when the car gets really warmed up...like a hot day and stop and go traffic on one of our overly congested "freeways"...the engine will "ping" or "knock" at light throttle. If I push harder on the throttle it pings less usually, then I have to listen very carefully and jockey the throttle to continue...I find myself "driving by rattle". When it cools down again...no problems, runs like a top! Its only when the temp gauge reaches about 1/2 way or more that the pinging begins.

Normally my car's temp gauge hovers between just over 1/4 and just under 1/2, but on a very warm day with heavy traffic and maybe some long hills, the needle will pass 1/2 way...and thats where the pinging comes in.

Any ideas?

[R Schroeder]

Sounds to me like its running a little to hot.
Bad water pump, clogged up radiator, water passages in the engine block, thermostat , carbon on the pistons ?
The fact that you said if you stepped on it hard ,and the pinging was less tells me the vacuum advance is retarding the spark correctly.
An engine that runs hot ,will cause pinging.
Just my 2 cents. I'm sure you will get more answers .
Roy

[Gene Beaird]

Make sure the manifold heat control valve ('flapper' valve that's between the passenger side exhaust manifold and the exhaust pipe) isn't rusted shut.  If it is, it'll route all the exhaust from the passenger side over to the driver's side, _really_ warming up the intake manifold. 

Other than that, you may want to back the timing out a degree, or two to see if that doesn't help. 

[cadillacmike68]

Half way up on the temp gauge is fully warmed up, aka "hot engine".  Have a radiator shop point one of those fancy thermo gauges on your radiator to get a reading of the temp across the top. It shouldn't be more than 220F

You might be running too lean though, 472s need a lot of fuel in the mixture.

I have a similar problem with the temp in FL, the car's radiator and fan cannot keep up in congestion. I'm going to have to put an auxiliary electric fan in front of  the condenser to keep it cool. I really don't want to do this, but I don't want to burn bearings in my overhauled engine either. I'm sure that'll cost me points if i ever enter it in a judged event again.

Backing the timing can also help. Today's fuel's octane is not what it used to be...

[Eric DeVirgilis CLC# 8621]

Are you using any fuel additives? These higher compression motors often need a big octane boost above and beyond what most of today's "super" fuels offer.

[Dave Shepherd]

The timing can change slightly when installing the Pertronix, I assume both the base timing and advance have been checked?

[TJ Hopland]

Im not sure if its a problem with the points style but with the HEI's I have seen the replacement vacuum advance units have more than twice the amount of advance in them than the originals did.  The 'performance' replacements usually have a an option for a little stop mechanism to limit their travel.

[cadillactim]

I don't the guage being a half means it's running hot. My 67 will go up to half on a hot day in stop and go traffic, and my friend's 68 will do the same. Normally our guages read a little above the first 1/4 notch.

I would check base timing and the heat riser for sticking closed.

Tim

[cadillacmike68]

Tim, I didn't mean overheated hot, just hot engine as opposed to a warm engine. There is a big difference between the 3.

["Cadillac Kid" Greg Surfas 15364]

Steve,
It has all been mentioned before but  Fuel grade (no less than 93 octane), Initial timing, Vacuum advance, Mechanical advance in distributor (if the Pertronics was not installed correctly if may inhibit the mechanical advance mechanism), and then timing chain condition in that order is what I would check if this were mine.
Greg Surfas

[Glen]

This is what I posted in a similar thread: 

  I had pinging at light throttle on my 68 ELDO for a long time.  I chased that many times.  I then got a digital timing light and checked the vacuum advance.  It was going to 22 degrees advance. The max for a 68 engine is 12 degrees.  The curve was correct up to 12 degrees so I added a stop on the vacuum advance to prevent it from going passed 12 degrees.  The car ran great after that. 

The problem is getting the correct vacuum advance, most of the parts houses sell a generic one that goes to 22 degrees

HTH

[cadillacmike68]

Try a Crane Cams adjustable vacuum advance. They make one for GM HEI.

[R Schroeder]

T.J.
I can only post as to what is in my 78 - 425.
The 78 manual lists 5 different distributors in it. 4 are for the 425. One is for the Seville.
Mine is the second one down. It has the most advance of all of them.
The fourth one down is for a 425 in California, in a Eldorado, which has very little advance.
I think my emissions card on the radiator cover says 26 degrees at 1450 rpms.
I guess my point here is , you should have all the info for your particular car., and to the distributor that your running with in that car.
I cant say what is correct for this car. This is just info for you.
Roy

Click on the JPG to make bigger.

[Scot Minesinger]

vacuum hoses, same post as before

[Steve W]

Climbed under the car today and I noticed that while the mainfold heat valve moves pretty freely...but the end of the spring is NOT connected to anything. So it just sort of stays wherever I leave it.There is a thing that looks like a nail connected to the  manifold..I am assuming that is where the spring should attach?

But...I live in Los Angeles, do I really need this thing to close?

And...what is the orientation of the lever when it is supposed to be fully open??? I would just like to try and wire the thing open, but which way is open???

Thanks for all the replies!