Mercruiser 4.5l low vacuum, WOT 4350 and higher fuel consumption

[nola mike]

It does but too much imo. Vacuum is not shown directly. Vacuum is a difference between barometric pressure and manifold pressure. At WOT they both read nearly the same as you would expect but it's very low at 3000rpm when throttle demand is at 58.2% but arbitratted throttle position only 21.4.%. Got a feeling that engine is unable to create enough vacuum and PCM closing throttle to keep RPM steady.

Oh, gotcha. Looks like everybody was thinking that was relative/gauge value. Not sure what "arbitrated" TPS means? Is it drive by wire system? Also, looks like these values are at steady state conditions rather than WOT (otherwise demand should be 100% the whole time)? In other words, if you have it floored, does the TPS and demand both = 100% through the rpm range? When you hooked up a manual gauge, is that 13" steady? Lastly, your timing is (I think, LOL) going the wrong way. 29' at 3k, 19' at 4300.

Maybe I missed it but thus far i haven't noticed 12.9inHg in any of the screenshots...Saw 17.2 under Manifold pressure at idle of 6.22 RPM?

See his reply to me...those numbers are absolute manifold pressure.

 

[damo79]

Oh, gotcha. Looks like everybody was thinking that was relative/gauge value. Not sure what "arbitrated" TPS means? Is it drive by wire system? Also, looks like these values are at steady state conditions rather than WOT (otherwise demand should be 100% the whole time)? In other words, if you have it floored, does the TPS and demand both = 100% through the rpm range? When you hooked up a manual gauge, is that 13" steady? Lastly, your timing is (I think, LOL) going the wrong way. 29' at 3k, 19' at 4300.


See his reply to me...those numbers are absolute manifold pressure.

 

[damo79]

Called arbitrated because that's probably average of two throttle sensors (TPS1 and 2 counts) but it general its percentage of throttle opening. It is drive by wire. I thought what whatever value of demand is should be achieved. Looks like engine is struggling to breath and PCM is doing everything to keep desired rpm. Spark advance it's going right way up to 3000rpm and then PCM delays it for some reason. My initial thought was timing chain - either slipped or came so lose or hang valves.

 

[damo79]

Maybe I missed it but thus far i haven't noticed 12.9inHg in any of the screenshots...Saw 17.2 under Manifold pressure at idle of 6.22 RPM?
Maybe the new TMAP sensor changed the readings and hadn't really noticed it yet?

Yes, you can run with the vacuum line disconnected for a bit to test as that ought to raise the fuel pressure up roughly 5 psi on the pressure gauge and look for fuel leakages.

Looks like the boat is new to you?

Engine serial number sometimes helps when possible on your end.

New boat to me that's correct. See serial number on attached picture

 

[nola mike]

Called arbitrated because that's probably average of two throttle sensors (TPS1 and 2 counts) but it general its percentage of throttle opening. It is drive by wire. I thought what whatever value of demand is should be achieved. Looks like engine is struggling to breath and PCM is doing everything to keep desired rpm. Spark advance it's going right way up to 3000rpm and then PCM delays it for some reason. My initial thought was timing chain - either slipped or came so lose or hang valves.

Why do you think it's struggling to breathe? If the throttle isn't opening all the way And the timing is retarded, that seems like something the PCM is doing on purpose. I'd like to see a graph of demand vs throttle opening at WOT throughout the rpm range. I didn't see any knock sensor data on there...

 

[damo79]

Why do you think it's struggling to breathe? If the throttle isn't opening all the way And the timing is retarded, that seems like something the PCM is doing on purpose. I'd like to see a graph of demand vs throttle opening at WOT throughout the rpm range. I didn't see any knock sensor data on there...

Because of low vacuum on idle. If its low on idle and its probably wrong throughout the rpm range. PCM control's throttle and timing. I will try to get graphs next time on water. There are no knock sensors on that engine.
Found something interesting but that general info for ecm555. Injection time can double for example for 3000rpm if vacuum is very low. See attached screen. That's what's happening in my case at 4000rpm there's nearly no vacuum so PCM uses correct multiplier and it burns 50% more than it should

 

[jimmbo]

Low vacuum, as well as an Inverted Vacuum curve, I would be inclined to think the Sensor that monitors it defective.
In Post #24 you said the Boat-motor was new to you, so you haven't got the repair History of it. I assume this below the WOT range of this motor, rpm you posted is how it has been running since you got it. What boat is this in/on, and what pitch are the Props you have tried on it?

 

[damo79]

Low vacuum, as well as an Inverted Vacuum curve, I would be inclined to think the Sensor that monitors it defective.
In Post #24 you said the Boat-motor was new to you, so you haven't got the repair History of it. I assume this below the WOT range of this motor, rpm you posted is how it has been running since you got it. What boat is this in/on, and what pitch are the Props you have tried on it?

MAP sensor is new and compared redings in Diacom with gauge connected to intake manifold. It works well. Its on Bayliner VR5. Bought it with 14.25x21 and now 14.5x19 is installed. With this setup it should rev to 5000-5200.

 

[Scott Danforth]

The VR5 with the 250hp came with a 19p prop

 

[damo79]

I know that's why changed ot

 

[jimmbo]

However since you don't know the Service-Repair History, what is the Gear Ratio of the Outdrive currently on the Hull?

What is the Manifold Vacuum at Idle, and at WOT, read from an actual Vacuum Gauge?

I know on my 5.7 it is 18" at Idle, and 4.5" at WOT with the 500cfm 2bbl, and with the 650cfm 4bbl, it was 1.5".