5.0 Volvo Penta GXI rough idle and knocking

[alldodge]

Didn't ask me but
The ALT when disconnected from a battery it spikes and can blow the regulator of the ALT. Many battery switches are make before break contacts. If the switch is make before break then it can be switched while motor is running. Could install a ACR and never have to move the switch again unless needed to combine to get motor started

 

[kdiddle]

Thanks alldodge . I've thought about installing an ACR, just haven't gotten around to it. Makes sense about the alternator spike - guess I'll just play it safe and shutdown before switching batteries for now...thanks for the response!

 

[muc]

Didn't ask me but
The ALT when disconnected from a battery it spikes and can blow the regulator of the ALT. Many battery switches are make before break contacts. If the switch is make before break then it can be switched while motor is running. Could install a ACR and never have to move the switch again unless needed to combine to get motor started

Great answer.
Only thing I can add; another component that is at risk. That high $$$$ ECM don't like them voltage spikes. ALT = couple hundred $. ECM = couple thousand $ and up.

 

[dschnacky]

I hate to awaken the thread with bad news but...

We only had it out the one time basically idling in gear. Tried to take it out again and it kept stalling every time I tried to throttle at all. To the point that I couldn’t get it to idle sitting still.

Since then, I’ve had a marine mechanic give up on it.

He replaced the fuel pump assembly, ran it off an outboard tank, and attempted to read codes off the engine. Nothing.

I have it back home until I can get a VP certified shop to look at it (in 3 weeks). So I’m to figure it out.

Now the issue is as follows:
I can get it to start and idle on the trailer with garden hose connected. Even get it into fwd and reverse. Every other time it seems that it stalls out when moving throttle.

New issue too (or newly found), idling wonderfully and going to trim up or down also causes a stall out.

I put a jumper on the fuel relay to eliminate the pump losing power and it stalled the same way.

I’m not sure what to check at this point. I’m going back to basics for now tomorrow and checking battery terminals, battery on/off switch, etc.

Thank you in advance for your help.

 

[alldodge]

New issue too (or newly found), idling wonderfully and going to trim up or down also causes a stall out.

This is a voltage issue, power is dropping and the ECM is turning off

Place a voltmeter on the main engine breaker and watch the level

 

[dschnacky]

alldodge i appreciate the info. Where is the main engine breaker located? Forgive me but I checked the diagrams online and have a seloc manual on the way.

also on my alternator, I noticed the one wire plug going to the L terminal was unplugged. I believe it has been unplugged the whole time, can’t imagine it just happened.

 

[alldodge]

Breaker should be I think a 40 amp, and its on the motor

The terminal being off the ALT will keep it from charging the bat and cause a low power issue. Check the voltage at the ALT of Battery with it running and it should be 14.5V

 

[dschnacky]

alldodge I will try to locate that. No chance it's in the fuse/relay box? I see in one diagram it should be mounted by where the wiring harness is attached to the top of the engine but it's not there.

Also, on the alternator, the plug that is disconnected goes to this L terminal from the photo attached. (This is a new non-marine alt that I have to send back but same thing)

When I'm able to get the engine running, the alternator is putting out 14.3 volts so it seems to be good.

 

[Lou C]

If stalls or loses power when you hit the trim button then that's a voltage issue, the trim pump is pulling enough amps to draw down the system voltage. I had a similar problem with my boat years ago with the standard junk battery cables that some boat makers install. You should go through all your basic connections and replace any battery cables that look questionable. ie, the common feed from the battery switch to the starter solenoid, and also on the same terminal the wiring that feeds back to the alternator (large gauge wire might be orange in color). Then, find the battery grounds and make sure those cables are in good shape, no green corrosion traveling up the cable and the connections are clean and tight. They will be on the bell housing on each side behind the exhaust hoses. Also and important: if you have wing nuts holding the battery terminals on the battery, get rid of them! They get loose and cause exactly this kind of problem. Either use locking nuts or, better yet, bolt on marine quality battery clamps to the terminals and then use those on the big battery posts just like in a vehicle. I did this years ago, and have not had low voltage problems in a very long time.

Finally, make sure your trim system wiring is not corroded.

I'm thinking you may have a low voltage to your ECM issue.
Every time I read of these somewhat mysterious problems, I am glad I have one of these each on my stone age 1960s tech engine:

 

[alldodge]

Also, on the alternator, the plug that is disconnected goes to this L terminal from the photo attached.

The L terminal is where the sense and excite leads attach to power the ALT. Without it connected the ALT does not produce

 

[dschnacky]

alldodge so safe to say that if I’m getting 14+ volts output from the alternator, this plug must be plugged in properly?

 

[alldodge]

Yes

 

[dschnacky]

alldodge good deal. I’ve verified that the alternator is wired up appropriately and that’s it’s putting out proper voltage to charge the battery.

now about this circuit breaker. There is a 40 amp “fuse” as the manual calls it within the relay/fuse box. I’ve traced the harness and verified again that this is the main engine circuit breaker. Now how do I test this? There’s continuity when I test side to side but I have no idea when it trips if it does. There’s a little black reset button on it.

 

[alldodge]

Looks like you have a fuse instead of a breaker. Since the motor is running and ALT is charging, it all sounds like its working

 

[dschnacky]

alldodge thats the crazy part. I’ve had it running and idling etc, now I can’t even get it to start. Seems like it’s back to square one... it’ll crank and crank. I’ve verified that high pressure fuel side is 55 psi while cranking so should have fuel.

I wonder if the coil could be bad now... just put new plugs, cap and rotor in, new battery. like I said I’ve had it running fine. But not anymore.

 

[alldodge]

Oh yes you had the issue of it dying and now it won't start. Fuel pressure is good, but unless the ECM seeings the spark plugs firing the ECM will not turn them on.

Need to scan the motor to see if the crank position sensor is working

Hey muc this one has had all kinds of issues, have any thoughts?

 

[dschnacky]

alldodge i don’t have a scan tool but I have a new CPS arriving today or tomorrow. Will pray and replace. Also I have a manual coming tomorrow so I’ll be able to troubleshoot more effectively moving forward

 

[muc]

Would need a serial number to offer anything other then general advice. There have been many 5.0GXi engines and there can be big differences between them. Volvo doesn’t use year to differentiate between them.

General things i see. That white box between the two fuses is a circuit breaker. Seloc is one way to gain an understanding of how system works, but very poor to use for troubleshooting. Volvo manual is much better. Parts swapping is usually a a bad method for troubleshooting, especially if the parts your using come from anybody other then Volvo. Swapping out with aftermarket parts has a better chance of making things worse.

 

[dschnacky]

I installed the new CPS and had no affect. Still cannot get it started. I pulled a plug to see if I was getting spark. No spark to be found.

 

[dschnacky]

muc thanks for your input. I’ll attach a photo of the engine serial.