8.1 idling 10 rpm too high

[boatrboy]

I’m a newbie to the Diacom so take it easy on me….

My stbd motor has always idled 10 rpm higher than spec of 650 rpm. Using my new laptop set up I tried to diagnose this. I even changed the IAC valve with a spare new one I have onboard.

I checked the throttle cable and the reading of the throttle position sensor as this keep the port engine running higher and after a cable adjustment that motor runs perfect at 650 rpm.

The IAC “duty cycle” on the problem motor reads 0. But on the port motor it reads ~24%.

I saved a couple of files running and backed up all the data on both motors to have the files on my laptop.

I then did an IAC “test” and I increased the value and decreased the value on the test screen and no change at all to the idle.

Both motors run perfect. I just had the cool fuel upgrade with all new complete cool modules and all new injectors and I was hoping one of the injectors was contributing to this (wishful thinking) bit I guess not.

Any thoughts?

 

[Ericinmich]

10 rpm is small enough to be noise on the signal, wno cares.

 

[jmcdboater]

10 RPM??? 10 RPM??? With all due respect, you need to get a life, or a wife, or a girlfriend. You’ll forget all about the 10 rpm’s. What makes you think any of these gauges are that accurate to really be showing you a true, true, reading?

 

[Bill Curtis]

10 RPM is well withing the window for the gauge accuracy error and means nothing.

 

[boatrboy]

Tough crowd this am
Do any of you have experience with the Rinda Diacom software? Are you saying that software and the gages are both off? Same software when I tested both motors. If you’ve seen this before let me know.

I’ll repeat why I believe something is amis.

“The IAC “duty cycle” on the problem motor reads 0. But on the port motor it reads ~24%.

I saved a couple of files running and backed up all the data on both motors to have the files on my laptop.

I then did an IAC “test” and I increased the value and decreased the value on the test screen and no change at all to the idle.”

Maybe that doesn’t mean anything but since I’m new at looking at this software, I was hoping someone who does this a lot could chime in

As always - thanks for the feedback

 

[Fun Times]

Tough crowd this am
Do any of you have experience with the Rinda Diacom software? Are you saying that software and the gages are both off? Same software when I tested both motors. If you’ve seen this before let me know.

I’ll repeat why I believe something is amis.

“The IAC “duty cycle” on the problem motor reads 0. But on the port motor it reads ~24%.

I saved a couple of files running and backed up all the data on both motors to have the files on my laptop.

I then did an IAC “test” and I increased the value and decreased the value on the test screen and no change at all to the idle.”

Maybe that doesn’t mean anything but since I’m new at looking at this software, I was hoping someone who does this a lot could chime in

As always - thanks for the feedback

What is the exact engine temperature/s when hot and what percentage/s of the throttle position sensors?
Spark advance numbers.

When on the Diacom, Is one engine running between 643 - 648 rpm while the other is up to almost 660 rpm?'

Pull the flame arrestor's and see if there's a hole drilled into the throttle plates.
Throttle body have been cleaned? IAC mufflers are clean/new?

Engine serial numbers are?

 

[ttmott]

Tough crowd this am
Do any of you have experience with the Rinda Diacom software? Are you saying that software and the gages are both off? Same software when I tested both motors. If you’ve seen this before let me know.

I’ll repeat why I believe something is amis.

“The IAC “duty cycle” on the problem motor reads 0. But on the port motor it reads ~24%.

I saved a couple of files running and backed up all the data on both motors to have the files on my laptop.

I then did an IAC “test” and I increased the value and decreased the value on the test screen and no change at all to the idle.”

Maybe that doesn’t mean anything but since I’m new at looking at this software, I was hoping someone who does this a lot could chime in

As always - thanks for the feedback

You don't mention what the MAP is for both engines at idle.
The throttle body should be adjusted to zero open and then TPS set to the correct voltage.
I suspect (if the throttle body and TPS is correct) a vacuum leak as that will drive the IAC closed and, consequently, prevent the ECM from controlling the idle RPM. Start with replacing the PCV hose and valve.

 

[boatrboy]

I replaced the foam mid season last year and have a couple of hours on it this year so i will assume that's clean enough. It was doing this before I changed that.

Here is the port snapshot from yesterday if this helps

And here is the starboard

I did not try the IAC test on the good motor.

S/N's Port OW393606, Stb OW393610

... actually 20 rpm higher

 

[ttmott]

Take a look at the MAP between the two - a full PSI difference. And, the IAC on the higher pressure shows 0% open. Again, vacuum leak or the throttle body mis-adjusted or possibly the IAC stuck open.
Remember the IAC is the ECM (as shown in the data) commanded set point and does not represent the actual position.

 

[boatrboy]

Take a look at the MAP between the two - a full PSI difference. And, the IAC on the higher pressure shows 0% open. Again, vacuum leak or the throttle body mis-adjusted or possibly the IAC stuck open.
Remember the IAC is the ECM (as shown in the data) commanded set point and does not represent the actual position.

Ok I will look for a vacuum leak and pull the flame arresters - I did adjust the throttle cable to make sure it was pushing back all the way to idle but I did not open the arresters up yet. I have put three IAC valves in this side to see if that was the case so I am doubting that it is stuck, but I will pull it out again and study it.

 

[Jimmy Buoy]

Tough crowd this am
Do any of you have experience with the Rinda Diacom software? Are you saying that software and the gages are both off? Same software when I tested both motors. If you’ve seen this before let me know.

I’ll repeat why I believe something is amis.

“The IAC “duty cycle” on the problem motor reads 0. But on the port motor it reads ~24%.

I saved a couple of files running and backed up all the data on both motors to have the files on my laptop.

I then did an IAC “test” and I increased the value and decreased the value on the test screen and no change at all to the idle.”

Maybe that doesn’t mean anything but since I’m new at looking at this software, I was hoping someone who does this a lot could chime in

As always - thanks for the feedback

I've done the same IAC test using a Rinda. It would lower the RPMs with the down button to the point of stalling the motor, but it wouldn't increase the RPM past normal idle speeds. I replaced the dirty muffler but haven't done the test since then.

 

[boatrboy]

I've done the same IAC test using a Rinda. It would lower the RPMs with the down button to the point of stalling the motor, but it wouldn't increase the RPM past normal idle speeds. I replaced the dirty muffler but haven't done the test since then.

Thanks for the info - I will have to try the port motor and see if that test has any effect on that motor as I expect it will.

 

[km1125]

I'd be much more focused on the IAC reading "O" than I would the 10 or 20 RPM. If you've eliminated the vacuum leak as a possibility then check the throttle plate on the throttle body, It may not be closing as much as it should, either due to a cable issue, or it's possible someone messed with the stop and it's holding it open just a tad.

 

[aerobat77]

10 RPM??? 10 RPM??? With all due respect, you need to get a life, or a wife, or a girlfriend.

In an urgent situation when reading this difference next time he can also beat the meat behind the helm to relax

 

[boatrboy]

In an urgent situation when reading this difference next time he can also beat the meat behind the helm to relax

Really? That comment is not what I would expect to get on THIS site, especially after my many years of posting helpful suggestions on this site.

 

[aerobat77]

Really? That comment is not what I would expect to get on THIS site, especially after my many years of posting helpful suggestions on this site.

It was already answered that 10rpm,s are well within signal noise

so lets have some fun in further debating ;-)

 

[Ericinmich]

But after providing some more data I believe there is an issue. The iac has stepped down to zero and is likely still trying to step further closed as rpm is higher than target.

 

[boatrboy]

Take a look at the MAP between the two - a full PSI difference. And, the IAC on the higher pressure shows 0% open. Again, vacuum leak or the throttle body mis-adjusted or possibly the IAC stuck open.
Remember the IAC is the ECM (as shown in the data) commanded set point and does not represent the actual position.

TT - Does this data mean anything to you? I looked at the same data from my survey report and noticed the all zeros on the port motor both now and then, but the starboard motor shows 388 seconds with a MAP input hi fault... During my survey, 50 hours earlier, it was 265 seconds. I can't get to the boat until Friday to inspect anymore, but wanted to pick your brain on this.

Also - the fault codes show this only on this motor. Is the 620.12 hrs. the time when the fault occurred?

 

[ttmott]

TT - Does this data mean anything to you? I looked at the same data from my survey report and noticed the all zeros on the port motor both now and then, but the starboard motor shows 388 seconds with a MAP input hi fault... During my survey, 50 hours earlier, it was 265 seconds. I can't get to the boat until Friday to inspect anymore, but wanted to pick your brain on this.
View attachment 147270

Also - the fault codes show this only on this motor. Is the 620.12 hrs. the time when the fault occurred?
View attachment 147271

It appears the MAP sensor has exceeded it's expected output voltage range. Input voltage is 5 volts and it should output about 4.5 volts at 100 Kpa (14.7 PSIA atmospheric pressure). 14.91 PSIA (shown on your data) is 102.8 Kpa (4.62 volts) which is above atm and above an expected condition. So it appears in fact the MAP sensor is out of cal and may need replacement. I would take actual measurement of both the 5 volt ECM supply as well as the output voltage at atm.

 

[boatrboy]

It appears the MAP sensor has exceeded it's expected output voltage range. Input voltage is 5 volts and it should output about 4.5 volts at 100 Kpa (14.7 PSIA atmospheric pressure). 14.91 PSIA (shown on your data) is 102.8 Kpa (4.62 volts) which is above atm and above an expected condition. So it appears in fact the MAP sensor is out of cal and may need replacement. I would take actual measurement of both the 5 volt ECM supply as well as the output voltage at atm.

Are MAP sensors the same as the auto ones? I did see that NAPA has one for a fraction of the Mercruiser one, even lists it as a direct fit for my Mercruiser.
Also - do mean put some small wires in the back of the plug and a digital meter to check with the power on but not running?