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ping at part throttle and miss at idle

4K views 19 replies 6 participants last post by  RABIDDAWG 
#1 ·
ok I had this issue since last year before putting the car away for winter.
I changed coil, installed new distributor (I think i blew the module when i started car with battery buddy hooked up by mistake).
but old one was fine.
took out and hooked up vacum gauge.
needle fluctuates between 17" and 19".
normal is a steady 18".
I readjusted the idle mixture but still has same fluctuations and part throttle ping.
all the cylinders are firing. (all about same temp)
I have MSD 6 AL box and could that be whats causing the issue?
 
#3 ·
Did you re-check the timing after you put in the new distributor? It could be too much advance at too low an rpm. Put a timing light on it. Check it at idle then increase in 500rpm increments until it doesn't advance anymore. That will tell you what your timing curve is. Report back here and someone will be able to help.:p
 
#4 ·
Exactly. Just sounds like too much advance. Too much timing down low will cause what can be interpreted as a miss as well. As you increase timing, once you pass the sweet spot, the engine will start running rough.
 
#11 ·
ignition was checked
advance all in at 3000 rpm
(same as before the problem started)
no vacum advance btw.
no noticeable vacum leaks using carb cleaner around perimeter of intake and carb base.
 
#12 ·
I think 3000rpm is too low for a street driven car. You need to find what the total timing is at 3000rpm and at idle.
I am referring to mechanical advance not vacuum.
Lets say ou have the static timing set at 8* on the dampner, and total is 36* at 3000 rpm. That means you have 28* in the distributor centrifical advance which is controlled by the weights and springs. You really need to check at what rpm the advance starts and when it reaches full advance.
I think your problem lies therein.
Just tryin' to help.:)
 
#13 ·
Hell lock out the dist and put in your total timing in and forget about it..:cool:....

Have you looked at what the carb is doing..?? Meaning are the boosters dribbling/running over../?? floats set correctly..?? Carb my need to have the air bleeds played with and or the metering blocks... My guess is at put throttle it sound like you have the boosters dribbling which will cause for a pinnging or rough sound driving...
 
#15 · (Edited)
drained all the fuel and put in some fresh 110 octane leaded race gas.
I ran car till it started raining and didnt notice a difference.
i only drove it for about 4 miles( not enough to get all the old fuel out of the fuel lines)
I did a exhaust temp check on each header and drivers side is averaging about 370 degrees and the passenger side is averaging about 227 degrees?
maybe the drivers side of the carb has some crap in it??????
all plugs are sooty black carbon .
 
#16 ·
maybe this is a good time/excuse for some billet metering blocks with adjustable air bleeds????
 
#17 ·
im thinking maybe a blockage in one of the heads (ie coollant flow).
or a steam pocket?
it is a 400 block after all.
 
#18 ·
mystery solved!
gasket between 1&3 intake ports was leaking.
actually torn
 
#19 ·
well that fixed the sooty plugs but still got a ping?
did a compression check

185 to 195 in all cylinders except 3&5 which reads 30 psi and 50 psi.
damn head gasket time!
 
#20 ·
well got the motor reassemled and still had the pinging issue but the miss at idle and sooty plugs are no longer a problem. decided to do a compression test instead of leakdown test and 3&5 were rearing 50 psi!
removed heads and its the head gasket!
check out the head gasket between 3 and 5


there is a bit of a crater im hoping the machine shop can fix it!
 
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