135 optimax rough idle - voltage issue???

[DHott]

2007 135 Optimax - 1B508381

Hey guys, I’ve posted on here before about my rough idle that no one, including me, can seem to solve. Long story short, I blew my original 2005 135 opti about a year and half ago and ever since getting the new power head put on its idled like crap. Runs great at anything above about 1000 rpm. I’ve tested and/or replaced all the common and less common things that cause a rough idle so I’m now looking into possible voltage issues. I noticed with my old powerhead, the analog voltage gauge would show a little over 12.5 volts with key on and 13.5-14 volts while running. My current powerhead shows like 10 with key on and 12 while running. It’s the same gauge so I find that odd. Where does this gauge receive its signal? Also at the battery and alternator when tested with a multimeter show 12.7 when not running and over 14 while running. I just looked at the report that the last shop i took it to ran showing all stored faults. The snapshots of all the faults with the old powerhead show voltage between 13.8 and 14.3. Since replaced, the snapshots of faults show voltage at 12.6-12.7. Seems to me that the ecm isn’t getting all the volts that the batter/alternator is putting out. How could this be? Anyone ever heard of this? Thanks and sorry for the long post!

[JOE54]

analog what does digital volt meter show at batt when engine /boat is underway

[SilverFox579]

analog what does digital volt meter show at batt when engine /boat is underway

^^^^This^^^^

[DHott]

13.8-14.3 volts at the battery when running but there’s only 12.6-12.7 at the back of the gauge and that’s also what the ecm says it’s getting on the fault printouts as well

[SilverFox579]

If you have 13.8 - 14.3vdc at the battery when running your charging system is fine. Post a copy of your printouts so we can see the fault history and codes.

[DHott]

Yes it seems my battery and charging system are fine. I’m asking if it’s possible that the ecm isn’t getting all those volts. It seems that even though the system is producing the correct volts, the ecm is only getting about 12.6 volts while running, causing weak spark and misfires. Possibly a bad connection somewhere or a bad relay?

[leonreno]

Definitely check all the connections, loose or corroded connections or wires can cause these problems. Usually a ground but could be anything. Check the harness connections, disconnect and check the them. If they have small pins, Don recommends using an razor blade to gently spread the pins apart for better connection.

[JOE54]

clear all faults with G3 hooked up to engine run on lake and report back voltage readings from test equipment , yes its possible , if G3 determines voltage is low you very well could have wiring problem

[EuropeanAM]

How about posting a copy of those printouts? Also provide hours at which Powerhead was installed.

[lpugh]

Master power relay could cause this as well as intermittent stalling. Voltage drop test across pin 30 and 87 on relay with motor running, very gently tap on the relay with something light like handle of small screwdriver while watching the DVOM, should never see more than .5 volts lower the better
I think they will be a Red and Red with white stripe wires, 12 gauge I think.
Be sure all connectors are clean and tight to the power point hook up as well as the ground cable to the block.
Don't pass judgment by just feeling and looking, remove them for inspection or at least voltage drop test them.

[DHott]

Is the master power relay the same as the trim relays?

[EuropeanAM]

It's the Main Power Relay... and though it's the same part number, the MPR is separate from trim relays.

[DHott]

Can someone tell me if pcm 885557007 ser no 42820762 is compatible with powerhead 1B508381?

[EuropeanAM]

It does not cross-reference.

[DHott]

Thank you. The pcm is from my old 135 powerhead and is being used on the 150. After looking at parts diagrams, the motors aren’t the exact same like I was lead to believe. For example, the old 135 had the dual coil drivers where as my 150 does not have drivers. I would think electrical differences like this would cause the motor not to run properly, am I right?

[EuropeanAM]

Yes and can even cause damage.

[DHott]

Thank you Don. I’m going to order the correct ecm but before I do, a certified shop installed the powerhead and assured me the ecm would work although I was always skeptical. After going back to them several times saying it wasn’t running right they did nothing but say it’s probably a fuel issue and if I ever find out what it is then bring it back and theyll fix it. Do I have any chance of getting a free ecm out of them since they caused possible damage on my new powerhead or is that a lost cause? The shop was aqua marine in Henderson Nevada. Seems like there could be legal ramifications for knowingly installing incorrect parts that may cause damage

[JOE54]

my take is that if you replace PCM and engine runs correctly discussion is in order with the installer of incorrect PCM , PCMs are wiring harness specific and must remain that way

[leonreno]

Was anything else taken off the 135 and used on the 150?

[EuropeanAM]

Can't answer your legal questions- that's outside my field of expertise and something you should really talk with an attorney about.

That being said- ANY change to the Horsepower or Emissions Footprint of the engine is illegal. The fines for a dealer or repair center that does it are pretty steep...

One very simple item that changed on these engines was the temp sensors. We've had both plastic AND brass sensors- they required different calibrations (significant differences).