piston slap under load and 0 boost

tazmixsc

Registered User
i run my sc and i get to 0-4 psi boost and the car hesitates and bucking i replaced the dis mod and i put new plugs wires plus i replaced the fuel pump and fuel filter,plus iwhen it is hot the car will not start after i shut it off can some one help me with this
 
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i accidently ran 87 octane once and had alot of pinging and chatter,no slapping sounds though,though i,d like to slap my fiance sometimes...sorry.......
 
thirdbird said:
what's "piston slap"?

Piston slap is the piston attempting to move perpendicular in the cylinder instead of up and down. I think most of the time it can be due to wear, or mismatched pistons or anything that allows the tolerance between the piston and the wall to become to great. If you actually DO have that condition, plugs and wires aren't going to do crap. I would imagine you'd have to do some internal work. What makes you assume its that?
 
If you have piston slap you may have a problems with rings. Do you have stock pistons? Thier tollerance is tight enough that if you're getting slap something is going to have to come apart to fix it.
 
Piston Slap

Piston Slap is an old term. Back in the '60's & '70's when Forged Pistons first became popular, the alloys used in the pistons were Much different. The Forged Pistons had to be run with a much greater piston to wall clearance than used today. This was due to the vastly different expansion rates of the alum. alloy used & the cast iron blocks. When these engines were initially stated up, the pistons would "slap" around in the bores. If I remember correctly, the 1968 TRW forged pistons in my BB, have a cyclinder to bore clearance of .004". Drag motors were run even looser than that!!!! That's why the old forged pistons had their own "sound".

Todays forged pistons can be run with much tighter piston to cyclinder tolerances, because the newer alloys better match the expansion rate of the cast iron blocks.

68COUGAR
 
Hesitation, pinging (slap, dance, torsional a-symmetrical movement, whatever you want to call it) sounds a LOT like a cam position sensor going bad. And no, a CPS will not cause ping, but is part of the cause-and effect; i.e. timing, unknown CP & limp mode, default timing, etc. If you romp on a car with a bad CPS, it will hesitate, then it'll run but will knock due to a lag in the timing. CPS's can be intermittent, or the detection range can be less than linear. May or may not throw a code too since the older OBD systems may have had longer latency times for errors to be recorded due to slow firmware.

Just my 2 cents, but I had the same problem & fixed it with the same solution as above... Pinging is one of the clues of... lean condition, excessive timing (either way), higher head temps, inadequate KI rating fuel. I mix 100LL avgas (about 2 gallons with a 16 gallon fillup) and yes the cats stink, but it runs reeeeaal nice.

M
 
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I would pull those bosch platinums and chuck them over a hill, get some motorcraft or ngk plugs. I have seen bosch plugs tap pistons several times.
Alan
 
I would think that you are blowing out the spark and hearing pinging. I too would check (not chuck) the plugs....then put a good set in. I would be willing to bet that your problem is not slap as you have indicated.

Chris
 
my last engine did this only under none boost at 2500-3500 rpms
I took it apart and found worn piston pins
and a bent rod guess my piston rod bent a little when it blew head gaskets this made it wear piston pin it clattered but not under boost or at idle .

infact it ran great

but yours sounds like timing check cam sensor and crank sensor
 
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