tachometer ?'s

[RLT III]

my motor was idling at 800 the fuel pump was about to crap after i replaced it i just cranked it and it sounded the same as before but was reading 1800 and giving it some fuel it seemed to fluctuate any ideas

 

[Silvertip]

Re: tachometer ?'s

Let's break this up a bit so we can make some sense out of this collection of words. It would also be helpful to know what engine you are working on!

1) My motor was idling at 800. [800 is a little high but close enough]
2) The fuel pump was about to crap. [Sorry to hear that but how did you determine that?]
3) I replaced the fuel pump. [Great]
4) I started the engine and it sounded the same as before but now was reading 1800. [You obviously did something wrong. Binding throttle linkage, air leak, or lots of other things]
5) Giving it some fuel it seemed to fluctuate. [That's what a tach does. More gas, more rpm. Or did you mean the engine itself seemed to speed up and slow down on its own? Big difference. The tach only tells you what the engine is doing. There is no connection between the pump and the tach. If the pump is causing the engine to speed up and slow down on its own, then the pump or what you did wrong is the problem -- not the tach.]

So what exactly is the problem?

 

[RLT III]

Re: tachometer ?'s

#1 that's what it idled at when i got it
#2 at wot the engine died and then could only get 2000 rpm took apart pump and diaphragm was shot
#3 thanks
#4 did not touch linkage and followed instructions on pump replacement (complete rebuild)
#5 higher rpm at a steady rpm the gauge bounced(not maintaining constant reading) the engine did not speed up or slow down it was steady just gauge

The problem seems to be the gauge is not staying steady at a fixed rpm( which it did previously

I hope that explains things better

 

[Silvertip]

Re: tachometer ?'s

Tachometers can vary if the pulses to the "S" terminal on the tach change which they can only do when engine rpm changes. If there is loose connection on the ground, +12 volts, or "S" terminal the needle could bounce around. A loose connection at the engine or the plug on the control box (if that's where the connection is made) is also a possibility.

 

[RLT III]

Re: tachometer ?'s

well re-cleaned ground that bolts on with pump and seems to have stopped bouncing HUH poor ground i guess but taking it out tomorrow so will let you know

Thanks for the help as always