Tahoe 4.3 no Power 3400 max RPM

[ccdrrp]

Mercruiser 4.3 MPI
Serial # 2A046127

Engine won't exceed 3400 RPM and doesn't have enough power to get on plane without ballast on the bow.
Fuel Pressure holds and is 43 at 1800
Cap and rotor replaced ( suggested by many on other forums)
I replaced the output O2 sensors as the didn't seem to read on the diacom graph.
Lon term fuel trim is 4 or 5 left bank idel and 16 to 17 right bank idle but both seem to decrease with higher idle.
The throttle lever always says 0 but the throttle plate changes with the increase of throttle.
I will try and downlod the Diacom Recording if I can. Not sure if it attached it says failed couldn't be written to server?

Any help would appreciated

Rick

 

[ccdrrp]

Sorry I see I posted in the wrong forum!

 

[alldodge]

Moved to Merc section

The throttle lever always says 0 but the throttle plate changes with the increase of throttle.

Seeing Diacom is showing 0 but throttle plate is actually moving this is strange. Guessing the motor is DTS correct?

Attachments not working, we hope this can be fixed but not as yet

 

[ccdrrp]

Thank you alldodge!
I'm not sure what DTS is?

 

[alldodge]

Digital Throttle Shift
Basically drive by wire, so no throttle cables go from helm shifter to motor, it's only wires

 

[ccdrrp]

Sorry just looked it up I don't believe it is DTS it's a 2013 boat. It is cable operated but has a Throttle position sensor.

 

[alldodge]

Sorry just looked it up I don't believe it is DTS it's a 2013 boat. It is cable operated but has a Throttle position sensor.

With motor OFF and Key ON, use a voltmeter and measure the TPS to see if it goes from around 0.1V to 4.3 or so volts. Will see this when throttle is moved from idle to WOT in throttle only mode

 

[ccdrrp]

I will check that but would you think the Throttle blade position on Diacom would be the same as the throttle position sensor? It reads 0 at idle and 5.2 at full throttle.

 

[alldodge]

I will check that but would you think the Throttle blade position on Diacom would be the same as the throttle position sensor? It reads 0 at idle and 5.2 at full throttle.

I must be misunderstanding something. Your first post

The throttle lever always says 0 but the throttle plate changes with the increase of throttle.

So what is saying 0 ?

 

[ccdrrp]

The Diacom program shows 2 one is throttle blade position reads 2.8% at 1094 RPM and one is throttle lever position reads 0.0 at 1094. Tried to send a pic of the screen but it won’t let me do that either.

 

[alldodge]

The Diacom program shows 2 one is throttle blade position reads 2.8% at 1094 RPM and one is throttle lever position reads 0.0 at 1094. Tried to send a pic of the screen but it won’t let me do that either.

ok all good
and yes uploads not working

 

[ccdrrp]

Thanks for your input alldodge!
Any thoughts to why the right bank fuel trim is staying around 17 at idle? Also do you think it’s possibly in guardian mode? I see nothing to indicate it is or any readings that I would think are out far enough to cause the computer to put in guardian mode.
Thanks, Rick

 

[alldodge]

2A046127
Normally the 4.3 lags behind Mercs other motors so the control system will not be the latest. Your 4.3 uses the older HSV distributor and Gen 2 cool fuel. It does list the newer PCM 112 (8M0059350) for closed cooling.

I bring up the old and new because the older 4.3 used Batch firing of fuel injectors and the newer uses individual firing. There are no sensors on the fuel rail so only way for the PCM to know is if the injectors are individual. I'm getting long winded because I don't know if it can tell or now, maybe @muc can advise. It could be this is just a place holder in the software and it doesn't actually know.

The difference in fuel trim of each bank at idle could be from actual sensors readings but would need to see all readings from each bank at different RPMs. Looked for manuals and found parts and the Op and Maint one 8M0058192 and did not find diagnostic one.

When using Diacom as motor throttles up, watch percentage power and percentage guardian. Power should always be more then guardian. Watch difference between O2 sensors

 

[ccdrrp]

alldodge thanks for the information! I don’t see any place that shows percentage power or percentage guardian. It seems the Diacom doesn’t support everything on this style computer. I wish I could download so you could see the info I’m sure it would make more sense. The long term fuel trim on both banks go to 0 or close as they should when the throttle is increased and held there for awhile so If it would be a vacuum leak it must not be too bad but I can’t find any leaks. Also the Diacom doesn’t show short term fuel trim and the O2 sensors only read -12 or 21 and never anything else? On a car the readings fluctuate much more and do not only toggle from one extreme to the other.

Thanks Rick