Volvo penta 5.0gxi 3869255

[Jrato14]

Hello,
I have a new long block but ran into issues last year. The boat was cruising at 3k on both engines when it suddenly reduced speed to about 1500 rpm’s. I went I. Checked the engine and it was backfiring we shut it down and I checked the oil which was low. I put more oil in and refired but the issue continued. It sounds great at low speed starts right up but will not go above those rpm’s. I changed the oil and filter. I hooked up my Rinda TechMate as recommended by people on this site. I have code 81 5volt reference voltage fault. Any ideas would be greatly appreciated

 

[Jrato14]

Hello,
I have a new long block but ran into issues last year. The boat was cruising at 3k on both engines when it suddenly reduced speed to about 1500 rpm’s. I went I. Checked the engine and it was backfiring we shut it down and I checked the oil which was low. I put more oil in and refired but the issue continued. It sounds great at low speed starts right up but will not go above those rpm’s. I changed the oil and filter. I hooked up my Rinda TechMate as recommended by people on this site. I have code 81 5volt reference voltage fault. Any ideas would be greatly appreciated

The code will also not clear

 

[Horigan]

I don't know this particular engine, but it could be a protective low oil pressure or high coolant temperature indication that's faulty that makes the engine run in limp mode, or whatever the term is for that engine. Usually the system has dedicated switches separate from the sensors that drive the gauges.

 

[Jrato14]

So how would I clear that

 

[Jrato14]

Maybe I should replace the oil sensor seems very easy

 

[dubs283]

The 5 volt reference is in regard to the voltage provided by the ecm to various sensors on the engine that provide data for the ecm to monitor engine health. Coolant temp, oil press, map, tps, iac, etc... Most likely you have an issue with one of the sensors, an issue with the harness wiring between the ecm and a sensor, or an issue with the ecm itself.

If the techmate has the ability to read live data you can start there by observing the live data (engine running) and verifying all the sensors are providing correct data. If one or more of the sensors is not providing accurate data you should look there first. A simple test is to unplug each sensor one at a time and observe a change in data provided and hopefully a fault associated with that sensor.

Possible (wag) issue could be a faulty sensor, faulty wiring in the harness between one or more sensor(s) - the sensor wiring includes 5 volt power/reference, sensor data (from sensor to ecm), and ground, or an issue with the ecm itself

I have no experience with the techmate tool so I do not know its capabilities/limitations as compared to the full diacom program

 

[alldodge]

Finding code 81 is 5V reference low on the Crankshaft Position Sensor (CKP). Suggest measure the 5V reference with turn the key on and engine off
See if it's actually 5V and not less than 5. Doing it this way will not set another code

Disconnect the CKP and see if 5V reference comes back up.

 

[Scott Danforth]

Maybe I should replace the oil sensor seems very easy

do some troubleshooting prior to firing the parts cannon

 

[dubs283]

Good info post #7, dodge

Would add that crank pos sensor also provides engine rpm data to the ecm. If possible on data items verify rpm number/signal is correct. A visual inspection of sensor/ecm harness connections and an ohms test between sensor connection and the ecm/ground will tell you if there is an issue with the harness wiring

Seeing as there may be an oil leak the cps does mount to the bottom of the timing cover, could also be a possibility of loose/broken/misaligned cps bracket/mount install, loose missing o ring/seal, etc

And yes, we do insist on proper troubleshooting over simply replacing parts on a hunch

 

[Jrato14]

Thank you so much. I am I ri the boat is out of the water. I was just trying to figure out if this is likely something major or minor and whether it should go to the mechanic or wait to troubleshoot after launch. Putting in and out of the water is obviously costly but seems necessary

 

[alldodge]

The CKP is down next to the crankshaft on the timing cover (item 7) part# 3858979

LINK

 

[Jrato14]

The CKP is down next to the crankshaft on the timing cover (item 7) part# 3858979

LINK

It has to be running to test this right? I have to wait it’s still getting cold at night up here

 

[ESGWheel]

It has to be running to test this right?

No, reread post #7

 

[Jrato14]

Got it thank you I will update on sat. Thanks all

 

[Fun Times]

If you haven't seen this past thread yet, it might help give you good reference points to follow,

Volvo Penta 5.7 GXi-C cranks but won't fire

Good morning ... I'm hoping to receive input on this issue from the more experienced personnel within the Forum. Thank you to all in advance. I've read so many posts on various forums that simply ended without conclusion, one thing I will commit to is closing the loop on whatever the solution...

forums.iboats.com

 

[Jrato14]

Thanks fun times. Definitely a useful post. I have some different issues.. my engine runs fine up to 2000 then will not go any higher and starts backfiring. Oil pressure is slightly lower than the other engine at some times not consistently especially as the engine warms up. View attachment IMG_1481.jpeg

 

[Bondo]

my engine runs fine up to 2000 then will not go any higher and starts backfiring

Ayuh,...... Have you changed the fuel filter, 'n examined the contents of the old one, for anything but clean fresh gasoline,..??
The backfiring, says it's going lean,.....

 

[Jrato14]

Hi,
I did change the filter and didn’t see any signs of water or contamination

 

[Jrato14]

Could IAC play a role. Last year they were back ordered so the marina put on an aftermarket

 

[Lou C]

I know from checking a crank position sender on another engine (Jeep 4.0 six) there is a way you can check for power and ground at the connector with the engine off but ignition on, and if you have a scanner that can read live data you can see the actual signal that the sensor is sending to the ECM as it reads the notches in the flywheel or harmonic balancer depending on where it's located. My experience with these is that when they start to fail it affects low speed and idle most notably, and it may run OK till the engine warms up, then at idle and low speed the rpm will drop and as the engine gets hotter it may just shut off and not restart. When the engine cools it will often restart as if nothing happened but this will repeat till you replace it. In my case I got a code when the engine finally refused to start (P0320).

The symptom you are reporting doesn't really line up with this, but it might be different on the GM marine engines than it is on the Jeep 4.0 six.
PS
looking at the prices Volvo charges for those sensors I'm glad my boat still has a simple carb/points distributor engine!
Even the Chrysler OEM crank sensor was cheaper than what Volvo is charging there.