5v reference

[dray0151]

Question on the 5v reference sent to sensors and if a reading of 4.97-4.98v at key on engine off is good or should I be looking for a short?

This is on a 2004 F115TLRC. The Intake pressure sensor and the Throttle position sensor are the only two that have the 5v reference wire from the ECM.

I know Rodbolt has referenced the voltage check many times but I was unsure if the above values were okay?

[99yam40]

I would think they are close enough to 5V

[boscoe99]

4.75V ~ 5.25V is the range for the input voltage that is to be seen on the orange reference wire.

[dray0151]

Thanks, just continuing to try to determine if the intake pressure sensor is operating correctly as the readings on the YDS running even at 4000 rpm never get up as high as the actual atmospheric pressure we have discussed before. Your last remark on a previous thread said that it should start to reach the actual atmospheric pressure as the rpm increase but it stays well below that running in my tub. The last diagnostic I did the highest it reached was 18.66 and the atmospheric pressure was give or take 29. Would not being under "a load" in the lake effect that?

[fairdeal]

when the engine is off, the sensor is a barometer.

but once the engine is running, it is an "intake manifold vacuum gauge"

when the throttle plates are wide open, that "vacuum" may drop to near "zero"

> atmospheric pressure

of course you need to be running under load to get to WOT

[dray0151]

Fairwinds as boscoe would call you I understand at key on the sensor sets a starting point that equals the atmospheric pressure around you for the ECM to use to gauge the O2 and how to mix fuel for the rpm's etc. My understanding from Boscoe was that the engine running intake pressure should start to get closer to the actual atmospheric pressure as the rpm's rise to keep the fuel mixture correct for the rpm's, load and O2 present, not that the guage or sensor would go to zero. On my YDIS it shows running in a tub not load that it rises but will get nowhere near what the atmospheric pressure is even at some rpm's not WOT.

[boscoe99]

I think what fairdeal is suggesting is that you connect the motor to YDIS to monitor intake manifold pressure and then run the motor at wide open throttle while it is pushing the boat. Running the motor in a tub does not allow you to open the throttle fully.

With the throttle fully opened you may then see intake manifold pressure approaching normal atmospheric pressure. It won't reach it of course due to pressure losses within the intake system.

Throttle mostly closed, engine at idle RPM, air pressure is low.

Throttle wide open, engine at full RPM, air pressure is high.

Air pressure rises within the manifold as more air is allowed into the manifold as the throttle is opened. And vice versa.

Boscoe tries to avoid the use of the word "vacuum". Boscoe prefers "pressure".

[dray0151]

Thank you Boscoe. Dennis gets confused when to many different words, pressure-vacuum etc gets thrown around. I tend to loose track of my thoughts which seems to wonder anyway.

How do you keep a lot of water from getting in the engine when running a test in the lake if the upper cowling is off so the YDIS can be hooked up? Or does it not get much in it? It would seem if your moving at 4000 to 5500 rpm's and speed which I would get over 30mph, water would tend to splash all over the engine?

[boscoe99]

On a lake I don't think there would be any water that would splash on the motor. But some will take the trim switch blanking plate out and run the cables through there. The cowling can then be reinstalled.

[dray0151]

Thanks I'll look at that so I've learned several things today to put to use! Unfortunately now I need to go mow.

[pstephens46]

On a lake I don't think there would be any water that would splash on the motor. But some will take the trim switch blanking plate out and run the cables through there. The cowling can then be reinstalled.

You might get a little in engine pan when you come off of plane!