knock at cruise

[turboaddict2]

I'm still getting this knock at cruising speed in 4th gear(OD and lockup of course). It only happens in this gear. It happens when i ease into the gas pedal from partial throttle to half throttle then i have to let off. I know it ain't the EGR because I checked the diaphram and motor stumbled so it must be working. It's probably false knock somewhere. Anyone ever have a problem like this?

 

[turboaddict2]

anyone?

 

[MARINES185]

at what boost does it start to knock at? accelerating in 4th
gear while the torque converter is locked is a serious load
on the engine. mine will knock with less than 10lbs of boost
under these conditions. if its only doing this under thoughs
conditions i really wouldn't worry about it.

 

[Red Regal T]

Try installing a powerplate. Lowered my incidence of this kind of knock.

 

[turboaddict2]

Got on it today on the highway in 4th gear and actually floored it. No knock, alchy spraying too so thats a good thing. I guess partial throttle knock at 4 th gear is normal because you are not in PE mode correct?

 

[bruce]

Originally posted by turboaddict2
Got on it today on the highway in 4th gear and actually floored it. No knock, alchy spraying too so thats a good thing. I guess partial throttle knock at 4 th gear is normal because you are not in PE mode correct?

No, there should be no knock at any time.
A dgree or two at WOT is acceptable to some, but for every degree the ecm pulls out is darn near twice as much as what's happening.

Generally it's due to tipin leaness which can be anything from the wrong FP, vacuum leak, marginal gas to a slight chip misque.

 

[DynamicGN]

I have the same problem. I don't know what it could be, I have the powerplate installed and that helps alot with false knock at WOT. However, in 4th gear it knocks sometimes when i am crusing from part throttle to half throttle. It's weird cause if i floor it, it wont knock. When it knocks at cruising, I can actually feel the car not responding as it should. Sorta like a hesitation.

 

[turboaddict2]

Dynamic, did you ever get to fix the problem? Let me know if you did.

 

[turbosam6]

I wouldn't see any way possible a power plate could fix "false knock", DynamicGN. False knock is from noise that isn't actual knock, but sounds like it. For example, loose convertor bolts, exhaust hitting stuff, etc. If you put in a power plate and it reduced knock, then it was actual knock, not false knock.

 

[DynamicGN]

Oh Wow then the power plate helped out a whole lot. It eliminated a good 80% of my knock then. I still havent fixed the knock at cruise problem yet. The car is in Miami getting a new powermaster installed then its going to Cal Hartline's place for the alcohol kit. I will ask him about the knock problem to see if he notices anything. Let me know if you fix it too.

 

[John at J&S]

More than likely, it's piston slap. Lightly loaded engines are often noisier than at WOT.

 

[DynamicGN]

What exactly is piston slap?

 

[DynamicGN]

Sorry for all the questions, i dont know much about this, but does the scanmaster pick up "false knock" or is it just something that you hear. Cause I dont hear anything but i can feel a hesitation and the car being extremly sluggish sometimes.

 

[John at J&S]

Kind of a crude definition, but the way I see it, the pistons are free to "flop around" in the bore.

Our knock controllers don't turn on until the vacuum drops below 5 inches. This eliminates a lot of phantom knock.

Don't know if the GM ECU has that provision, but it shouldn't be hard to incorporate.

 

[DynamicGN]

Thats weird the engine was rebuilt last yearwith JE pistons, Champion heads, nd comp cam 206/206. Nw that you brought up the ECU i should get that checked out. Thanks alot.

 

[John at J&S]

Knock sensors are trying to detect inaudible knock, and at the same time, ignore engine noise that we can hear. Tough job.

If it shows up on the Scanmaster, the ECU has most likely heard about it, too.

 

[750H.P.V6]

Piston Noise

Guys,

I agree with John about what is going on. It's not uncommon to see false knock indications at cruise or light throttle especially in a motor that has been rebuilt with forged pistons.

The reason for this is that there is more piston skirt to cylinder wall clearance with a forged piston than with the stock pistons. A stock piston can be run as tight as .0015" clearance where as it's not uncommon to run upwards of .0045"clearance on a forged piston in a turbocharged application.

To give you an extreme example on my combo I run .006" clearance on the pistons and a solid roller cam. In this application the knock sensor can't differentiate between real knock and engine noise. I had no option but disconnect the knock sensor. I DO NOT recommend you do this!! I'm just illustrating my point.

As a test to make sure what you're seeing is indeed false knock and not from a real source go ahead and pick up some high octane gas (Av gas, race gas etc.) and see if the problem goes away. If it's false knock the problem will still be there.

Not really all that much that can be done if it's false knock except possibly having your chip guy (whoever that is) play with the knock attack rate in your chip to lessen the sensitivity of the knock sensor.

I hope this makes sense.

Neal

 

[gnXfan]

Originally posted by turboaddict2
I'm still getting this knock at cruising speed in 4th gear(OD and lockup of course). It only happens in this gear. It happens when i ease into the gas pedal from partial throttle to half throttle then i have to let off. I know it ain't the EGR because I checked the diaphram and motor stumbled so it must be working. It's probably false knock somewhere. Anyone ever have a problem like this?

Turboaddict - I see your sig lists MM boost command. Are you running still running that? If not set correctly - it doesn't lower boost depending on gear (ie, it can boost to x pounds in 1,2,3 and 4th!) That was my problemo.

 

[GN HEAD]

I had the exact same problem, with the cruise set and the car would start up a hill and it would knock like crazy. I stumbled on to the problem when I put a new cam in the car.... the EGR ports in the heads were completely pluged up. I cleaned them out and I did not expect it to fix anything, but the part throttle knock was completely gone. Someone here on the board said that it was probably because the the pluged ports were keeping heat in the head, and not circulating the exhaust gasses, thus making it more prone to knock.......I couldn't make complete sence of it, but all I know is it fixed my problem....hope this helps.