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Author Topic:   BRP tachometer 250 RPM less than real

holmaldo posted 08-07-2006 03:37 AM ET (US)
My BRP tachometer in my Evinrude E-TEC 90 2005 shows as much as 250 RPM less than real, according to my dealer who has tested my boat with his digital tachometer.
Background is my earlier reported problems with too low RPM (4850) at WOT, correct RPM is then 5100. Solving that problem is another discussion.
The dealer says the difference is within margins for such an analogue type. Is he right?
My measurements:
a) At idling it shows precisely 500 RPM, I put it in gear and RPM rises slowly to showing 650-700. Both numbers are nearly exactly the numbers from the manual.
b) Tachometer shows less after som minutes. Idling RPM remains the same, but the difference increases with higher RPM and I have found it to be about 150 RPM at WOT, measured several times under same conditions:
Cold engine WOT: showing 5000 RPM, GPS speed 32,9 MPH
Warm engine WOT: showing 4850 RPM, GPS speed same, 32,9 MPH
Then my conclusion is that the tachometer shows 100 RPM too low when cold, rising to the dealer-measured 250 RPM when warm.
Anyone with similar experiences? Should I ask for a new tachometer according to the warranty?
Buckda posted 08-07-2006 01:08 PM ET (US)
I think that instrument variation is more common than most people think.
For instance, I think there are many times when a Police officer pulls someone over and says "I clocked you at 80 MPH on Laser."
There is only one response to this comment. That is "REALLY?"
The unspoken point is that more often than not, the driver is thinking honestly to him/herself that they were either doing less than or more than that...i.e. the speedometer was not accurately reflecting the speed of the vehicle as measured by an accurate, calibrated instrument, the Police Officer's laser.
The point is that an instrument does not need to be exactly accurate, so long as it is repeatable and the end-user (you) understands what the instrument is telling them.
My EMM says that each of my motors has hit 5,600 rpm. I can't think of a single time that I looked down and saw the tach at 5,600 RPM.
Finally, do you think it is possible that your engine is more efficient when warm, and that is the reason that your tach readings and speed readings are different?
Sal DiMercurio posted 08-07-2006 01:47 PM ET (US)
Your not going to get exactly the same speed over the top of the water, while turning 5000 rpms vs 4850 rpms.
At 4850 you have to be going slower.
Is your tach set on #6 [ thats where it needs to be ] in the back?
Sal
BOB KEMMLER JR posted 08-07-2006 01:51 PM ET (US)
You could hook up 10 different tachs and you'd probably have 10 different readings.I think a few hundred rpms either way at max WOT won't hurt anything,so just go off the tach you have and you'll be fine.
ratherwhalering posted 08-09-2006 01:30 AM ET (US)
I had this exact problem when I first installed my E-TEC 90, with a Faria tachometer. I excahnged it for a brand new BRP systems check tachometer. My dealer's computer confirms it is spot on. I recall you installed an older OMC systems matched tachometer. Try changing to a new BRP tachometer.
holmaldo posted 08-09-2006 02:30 AM ET (US)
Thank you so far.
Ratherwhalering, the tachometer is a new BRP one, delivered with the motor last year.
SalDiMercurio, the speed is not slower when showing 4850 RPM compared to showing 5000 RPM. Measured by GPS several times, data reproduceable.
seahorse posted 08-09-2006 08:03 AM ET (US)
holmaldo,
The only real accurate way to check the tach is to compare it to the rpms on a laptop or PDA using the Evinrude diagnostic software.
Ask your dealer tech to go for a ride with you and take the laptop along.

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Author	Topic: BRP tachometer 250 RPM less than real
holmaldo	posted 08-07-2006 03:37 AM ET (US) My BRP tachometer in my Evinrude E-TEC 90 2005 shows as much as 250 RPM less than real, according to my dealer who has tested my boat with his digital tachometer. Background is my earlier reported problems with too low RPM (4850) at WOT, correct RPM is then 5100. Solving that problem is another discussion. The dealer says the difference is within margins for such an analogue type. Is he right? My measurements: a) At idling it shows precisely 500 RPM, I put it in gear and RPM rises slowly to showing 650-700. Both numbers are nearly exactly the numbers from the manual. b) Tachometer shows less after som minutes. Idling RPM remains the same, but the difference increases with higher RPM and I have found it to be about 150 RPM at WOT, measured several times under same conditions: Cold engine WOT: showing 5000 RPM, GPS speed 32,9 MPH Warm engine WOT: showing 4850 RPM, GPS speed same, 32,9 MPH Then my conclusion is that the tachometer shows 100 RPM too low when cold, rising to the dealer-measured 250 RPM when warm. Anyone with similar experiences? Should I ask for a new tachometer according to the warranty?
Buckda	posted 08-07-2006 01:08 PM ET (US) I think that instrument variation is more common than most people think. For instance, I think there are many times when a Police officer pulls someone over and says "I clocked you at 80 MPH on Laser." There is only one response to this comment. That is "REALLY?" The unspoken point is that more often than not, the driver is thinking honestly to him/herself that they were either doing less than or more than that...i.e. the speedometer was not accurately reflecting the speed of the vehicle as measured by an accurate, calibrated instrument, the Police Officer's laser. The point is that an instrument does not need to be exactly accurate, so long as it is repeatable and the end-user (you) understands what the instrument is telling them. My EMM says that each of my motors has hit 5,600 rpm. I can't think of a single time that I looked down and saw the tach at 5,600 RPM. Finally, do you think it is possible that your engine is more efficient when warm, and that is the reason that your tach readings and speed readings are different?
Sal DiMercurio	posted 08-07-2006 01:47 PM ET (US) Your not going to get exactly the same speed over the top of the water, while turning 5000 rpms vs 4850 rpms. At 4850 you have to be going slower. Is your tach set on #6 [ thats where it needs to be ] in the back? Sal
BOB KEMMLER JR	posted 08-07-2006 01:51 PM ET (US) You could hook up 10 different tachs and you'd probably have 10 different readings.I think a few hundred rpms either way at max WOT won't hurt anything,so just go off the tach you have and you'll be fine.
ratherwhalering	posted 08-09-2006 01:30 AM ET (US) I had this exact problem when I first installed my E-TEC 90, with a Faria tachometer. I excahnged it for a brand new BRP systems check tachometer. My dealer's computer confirms it is spot on. I recall you installed an older OMC systems matched tachometer. Try changing to a new BRP tachometer.
holmaldo	posted 08-09-2006 02:30 AM ET (US) Thank you so far. Ratherwhalering, the tachometer is a new BRP one, delivered with the motor last year. SalDiMercurio, the speed is not slower when showing 4850 RPM compared to showing 5000 RPM. Measured by GPS several times, data reproduceable.
seahorse	posted 08-09-2006 08:03 AM ET (US) holmaldo, The only real accurate way to check the tach is to compare it to the rpms on a laptop or PDA using the Evinrude diagnostic software. Ask your dealer tech to go for a ride with you and take the laptop along.