Spark Knock

[designit]

ahh, thanks toms.. That makes sense I guess... Hot pre-fire on a wrong plug?

Gap maybe? -- just weird he had it running fine for a couple days... very well could be plugs?

But wouldn't a prefire "be" a misfire in terms of timing? -- which the computer would pick up and post a code?... He ain't getting any codes either?...

 

[toms89]

ahh, thanks toms.. That makes sense I guess... Hot pre-fire on a wrong plug?

Gap maybe? -- just weird he had it running fine for a couple days... very well could be plugs?

But wouldn't a prefire "be" a misfire in terms of timing? -- which the computer would pick up and post a code?... He ain't getting any codes either?...

I consider misfire - no spark condition intermittent in nature.

Too large a gap would cause misfire but no spark knock. Too small a gap and it would just be less efficient combustion.

I grouped detonation and pre-ignition together which is technically not correct. Pre-ignition cannot be caused by too much timing advance. That would be detonation. While lean fuel and hot spots can cause pre-ignition. I know the difference between the two but I still tend to group them together..

The knock sensors are tuned to a specific frequency. They may or may not pick up all forms of spark knock.

http://www.streetrodstuff.com/Articles/Engine/Detonation/

 

[designit]

I consider misfire - no spark condition intermittent in nature.

Too large a gap would cause misfire but no spark knock. Too small a gap and it would just be less efficient combustion.

I grouped detonation and pre-ignition together which is technically not correct. Pre-ignition cannot be caused by too much timing advance. That would be detonation. While lean fuel and hot spots can cause pre-ignition. I know the difference between the two but I still tend to group them together..

The knock sensors are tuned to a specific frequency. They may or may not pick up all forms of spark knock.

http://www.streetrodstuff.com/Articles/Engine/Detonation/

Well holy 14deg BTDC burning combustion chambers batman... See there, that's why we come.

Good link, read a little but I got a headach from the basketball game!... Read later though... Great techie garb..

 

[NewbieVet]

Well holy 14deg BTDC burning combustion chambers batman... See there, that's why we come.

Good link, read a little but I got a headach from the basketball game!... Read later though... Great techie garb..

what he said ^^^

 

[00 Expy Police]

ok i changed out the plugs to double platunims (autolite),also changed out the idle control valve cause it popped a code,,road test and after 30 mins it still sparked knocked so back to drawing board,i was told to unplug the vacum from EGR valve and plug end of hose,cleared computer and this morning all the way to work and back 110 mile trip ran perfect check eng light decided to pop on 1 mile from house so im going to put it back on scanner in lil bit to see what code is,,im going to guess cause it ran smooth that the egr is plugged like Just4fun said above

 

[toms89]

I having trouble following what you did. If you disconnected the vacuum from the egr valve it cannot work which in effect would be the same as if it were clogged. Maybe I just misunderstood what you did.

The egr recycles exhaust gas back to the intake for emissions purposes. This is supposed to reduce combustion temps because the recycled exhaust will not burn. This has the effect of reducing spark knock which I am sure why Just4Fun mentioned it.

On the chance that the knocking returns I would suspect the 02 sensor(s) as it sound like it runs fine when you reset the computer. As the computer adjust for o2 readings while in closed loop mode it may be leaning out the fuel to much.

 

[00 Expy Police]

I having trouble following what you did. If you disconnected the vacuum from the egr valve it cannot work which in effect would be the same as if it were clogged. Maybe I just misunderstood what you did.

The egr recycles exhaust gas back to the intake for emissions purposes. This is supposed to reduce combustion temps because the recycled exhaust will not burn. This has the effect of reducing spark knock which I am sure why Just4Fun mentioned it.

On the chance that the knocking returns I would suspect the 02 sensor(s) as it sound like it runs fine when you reset the computer. As the computer adjust for o2 readings while in closed loop mode it may be leaning out the fuel to much.

I dont know for sure what it does by disconecting the vac hose but i do know it runs smooth,after sitting for for a while i connected the vac hose back to EGR and right away it spark knocked,while it was running i disconected it and drove away fine so im on my wat to get it scanned for code,,,,but what are chances of the code being the EGR valve cause it was unpluged?

 

[00 Expy Police]

i give up,i put new egr valve in it and still spark knock,,,any thoughts?????

 

[designit]

I'll just toss this out for now... I'm beating a dead horse into dust but try a full bottle of seafoam through the brake booster hose... Then stick another bottle in it & let it sit for about 45 mins...



Did you build the motor from the ground up?.. or was it sitting around for a couple years & you have a dead mouse in one of your holes that created a carbon layer 1" thick causing crazy compression? (I'm joking of course with that but geez... Any history on the motor?

 

[00 Expy Police]

i bought the motor minus the intake manifold,oil pal,timing cover,when we got home i dug into to it deeper and all looked good,under valve covers looks nice and clean,lookied down intake runners and looked clean,front timing set looked clean,even took a few rod and main caps off and bearings were perfect,everything else came off old motor that cam with the truck,other than the guy told me it ran perfect when came out i dont know much about it