knocking before it shifts gears

[Kahuna]

Ok I got a knock which occurs right at the shift points, if you hold the car in first or second and let the engine tachs up say 3k, hold it there steadie you get a knocking noise, it does this in every gear, once it changes gear the noise goes away untill it tachs up again, you don't hear the noise when reving up the engine, only before the shift points, I think it's a rod bearing bad but not sure, it's been a long time since I hear a rod knocking.

[FANTA-Z]

It has been known that the pcm will pick up false knock in between shifts. My car use to do it as well.

[Kahuna]

pcmforless did the tune, and I have changed to the LT4 module, it's not misfireing or loseing power, it just a high rpm knock at shift points, is it possible to be coming from the valve train, which is a little noisey, but I checked one side and they were all tight, and I do have 129k and spraying 150 shot. I think I will give Rob (mr23) a visit.

[Gatorhead]

Does it do it in neutral whe you bring the RPM'S up?Could you clarify whether or not it is a knock that you hear, or one you see on a programmer?

[jmdespres]

or maybe the gas

[jmdespres]

bc mine spare z28 does it only with "low gas oct"

[ncz28ragtop]

Originally Posted by Kahuna

Ok I got a knock which occurs right at the shift points, if you hold the car in first or second and let the engine tachs up say 3k, hold it there steadie you get a knocking noise, it does this in every gear, once it changes gear the noise goes away untill it tachs up again, you don't hear the noise when reving up the engine, only before the shift points, I think it's a rod bearing bad but not sure, it's been a long time since I hear a rod knocking.

man thats flyin for just the mods u have, or did u live one off?

[Kahuna]

only time it makes the noise is before shifting, not at idle or throttle up in idle, yes I did forget the last mod, a little laughing gas, which is great, and also a 58mm TB but have not run at track yet, trying to figure this noise out first, have a short block that going to the shop within a week or two to become a 383.

[Gatorhead]

Well a rod knock generally knocks no matter when or where you are at in the rpm range. Sometimes only at a higher rpm, but if you are not hearing it neutral with it revving its not likely what you are hearing, I still wouldn't rule it out, beacsue I have seen it where they have only knocked under load.It sounds like one or two things to me, and its very hard to try and determine something like this online without hearing it As you stated it "if you hold the car in first or second and let the engine tachs up say 3k", 3k is not very high at all With that shot of nitrous I am beginning to wonder if maybe its detonation, but some lil demon on my shoulder says its coming from the tranny~!

[thesoundandthefury]

Could possibly be a broken tranny mount that is causing the crossover to knock against the floorboard when the transmission "jerks" during a shift.

*EDIT* Can you pinpoint the general location of where the noise is coming from?

[01Z]

What you are describing is what I had with a 3.8 ford engine except it began at 2200 rpm and continued until shifting. I thought it was an intake sound as it was reminiscent of a performance rap rather than a knock. It turned out I had bought a car treated with motor honey. The bearing knock was masked by the super thick oil.

One thing I learned about listening for a low end knock was that it can be heard just as you start the engine. There's a slight moment of rattle as the engine comes to life.

[Gatorhead]

Could possibly be a broken tranny mount that is causing the crossover to knock against the floorboard when the transmission "jerks" during a shift.

Yeah thats what I was thinking, that or a bad solenoid, that is if in fact it is from the tranny.

[dkishton1486]

The higher oct in gas the less knocking you get

[Kahuna]

there's a little man inside my engine using one of the push rods to beat on the crankshaft, oh well, that's what I get for spraying 150 shot, off to shop I go for my 383.
thanks guys..