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7 MPH

Shaners

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Shaners Senior Enthusiast

Shaners

Posted
Posted

I had the truck parked in the garage tonight, and I revved the engine (I mean I really revved it).  I didn't bounce it off the rev limiter, but I saw at least 5200 RPM (maybe higher) and I noticed my speedometer raised up to about 7 mph and then dropped back down to zero.

 

I wonder why it would do that...  Hmm...  ???

Guest Friz

Guest Friz

Posted
Posted

You're asking for trouble revving an unloaded engine that high.

It was probably vibration or just the truck saying, "Oh, Sh#&!!" when you revved it up that high.

Shaners Senior Enthusiast

Shaners

Posted
  • Author
Posted
You're asking for trouble revving an unloaded engine that high.

It was probably vibration or just the truck saying, "Oh, Sh#&!!" when you revved it up that high.

Yea I know that Friz, but it quit knocking after I did that... !!!

 

I could hear the motor rapping pretty loud when I backed into the garage, so I took it up to about 2000 RPM and then brought it back down.  Still knocking...

 

So I spiked the throttle really quick and the knocking quit!!!  Needless to say I will be seeing the dealer about this knock.  It seems to be a rod knock to me or maybe a main bearing.  It is deep in the block at the rear of the motor.  I'm not a happy camper right now...  :angry:

Guest Friz

Guest Friz

Posted
Posted

That knocking is definitely not a good thing. :crazy:

Z71GUY Enthusiast

Z71GUY

Posted
Posted

I have a 99 GMC Safari for a work van & it does the same thing.  I'm not going to try it with my truck, but I assume its just some kind of vibration..??

 

 

Eric

CityTruck Enthusiast

CityTruck

Posted
Posted

All of them do that.  I think (since the gauge is electronic) you just generate a small charge in the system by reving in Neutral (or Park) and the needle will move up a bit.  It's normal.  My 95 did it too.

vortec4800 Enthusiast

vortec4800

Posted
Posted

Yeah I noticed the same thing a while back, I don't know why it does this, but if you bounce it off the rev limiter it beeps at you - I imagine because of the oil pressure.

 

If you don't hold it there for long, you can't really hurt the engine if you rev it high. Just make sure you don't keep it too close to the limiter and make sure the oil pressure doesn't get too high...

 

About the speedo gague, I think it's just vibrations and such making a signal and sending it through, something like citytruck said... Though I'm not positive, and I suppose it doesn't really matter, the gagues are very accurate under normal driving conditions - and if you can't tell you're not moving while in park revving the engine there are other things you should be looking into :crazy:

vortec4800 Enthusiast

vortec4800

Posted
Posted

Oh and the reason it may help with the knocking is when you rev the engine high the computer has to adjust all the timings and such very quickly, then when it goes back to normal the timings are 'reset' to where they should be, possibly fixing the knock temporarily. Gets things flowing well, the knocking is probably just from bad air/fuel/timing programming in the computer.

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