Pinging @ 1/2 throttle

[landyacht67]

I've had this problem for a while, but I haven't invested any real time into it, so before I go hunting I thought I'd get some suggestions.
Car info: 5000lb 67 town & country wagon
440 with mild cam (dont have specs handy)
9.1:1 compression
750 cfm carter afb (not edlebrock)
Points distributor converted to pertronics module
dual exhaust, with shorty headers
I run 94 octane premium fuel
The car runs at @180 degrees
the car idles beautifully, and flies under full throttle, but pings like crazy at 1/2 throttle. The problem seems to have gotten worse (but not much) over the last 6 mos. The car didn't have this problem last year though. disconnecting the vac advance made no difference. changing to a richer metering rod for the primaries also made no difference. Changing brands of fuel makes no difference. The problem appears in all 3 gears, and doesn't seem to really change with rpm. I forget the exact timing but I believe it totalled 34 degrees, and @ 8 at idle. (now here is where it really makes no sense) The problem does seem to go away a little when I turn on my heater bypass (for air conditioning) and the car runs a little hotter (@195 degrees)
the problem is still there though, just not as bad.

any suggestions?

Julian

[Rust collector]

Does your egr work(and do you have it at all?)

[landyacht67]

The headers delete the egr

[Rust collector]

oops! brain doesnt turn at specified speed today...

[pishta]

Can the Pertronix kit be for a small block? If you run a hall effect in the wrong direction (by design, there is a leading edge trigger and a falling edge trigger type) you may end up with a screwy advance. Check MP E-distributor installation instructions about phasing a hall effect trigger. Does the Pertronix even use a hall effect or is it a diode (optical)? That, you have an extremely lean situation at part throttle (very thick rod, or very thin primary jets), or you got a bugger in a cylinder.

[djswwg]

is it possible you might have carbon buildup in there? another thing you can try is a colder heat range spark plug. it sounds like your timing figures are OK...................djs

[landyacht67]

I dont know if the pertronix is for a big or small block, (I ordered for a big block but that means nothing these days). I may look at the spark plug heat range as I've never really checked it. I suspect this problem may have started not long after my last plug change, but I cant remember for sure.

Either way I'll have to wait to check it as my tranny took a dump on the weekend (lost 3rd then 2nd and just limped off the freeway in 1st)

I'll update when I get it driving again.



Julian