Can a new alternator cause rough idling when cold?

[gettinthere]

Changed out the alt a few weeks ago. Same size and config as previous one, small frame, P type with ARS 5 regulator.

1985 Perkins 4.154-200 and the glow plugs were never hooked up.

After the alt swap, engine starts fine but runs rougher than normal and wants to stall. Air temps 40 to 60. I can goose the throttle to prevent stalling. Then it has a cycle of about 1 minute where the idle is up and smooth; followed by a drop in idle, rough idling and maybe stalling. This cycle repeats for about 10 minutes until warm and then all is normal. No noticable change in smoke, light amount of white at start that goes away. How fast depends on air temp. In the 40s the white will linger, in the 60s it goes away fairly quick. That has always been the same.

Cant connect the new alternator to this problem. But an interesting coincidence if not.

 

[kloudie1]

Yes it can do that if the batteries are asking for a top off charge right at first.. YA might have to adjust the "start delay" and "soft ramp" stages of the alternator ..
Check (with a calibrated tachometer) that your idle speed is correct.. That could also be a problem.

 

[gettinthere]

Doubtful. This never happened before when batteries were significantly lower SOC than recently. I have a delay programmed in.

Also, when rough idle kicks in, the victron says my amp flow drops to about 40. When the idle smooths out and RPMs come up a few hundred, on their own, the amps jump to about 60.

Thanks

 

[Ralph Johnstone]

When the idle smooths out and RPMs come up a few hundred, on their own, the amps jump to about 60.

Thanks

My bet says the operation of the alternator is unrelated to the engine labouring due to the engine increasing RPM on its own followed by the amps coming up.

A quick way to eliminate the alternator from the equation is to temporarily increase the Start Delay to about five minutes and see if the problem rears its head during the delay. If it is unrelated, it's back to the drawing board.

 

[Stu Jackson]

Good idea, Ralph. An easier way, without reprogramming the regulator, is to start the engine and then just turn the key off.

 

[Maine Sail]

Doubtful. This never happened before when batteries were significantly lower SOC than recently. I have a delay programmed in.

Also, when rough idle kicks in, the victron says my amp flow drops to about 40. When the idle smooths out and RPMs come up a few hundred, on their own, the amps jump to about 60.

Thanks

Pull the regulator fuse in the red power feed wire and fire up the motor....

 

[gettinthere]

Of course RC had the best answer! Pulled the fuse and started the engine. No alternator on line. Still had the stalling issue. Needed to eliminate that coincidence. Done.

Time to investigate further. Looked at the fuel hose feeding the secondary fuel filter. The end looked slightly frayed so I pulled it and cut back to good hose. I have a secondary fuel pump to prime the system and ran that. It ran and ran and ran before finally spilling a bit of fuel out of the bleed screw... My problem was low level of fuel in the fuel filter. Restarted the engine and it idled smoothly.

For now, the issue is fixed but I'm not so sure the real problem is solved. I dont know why the fuel filter would be low. I will be monitoring closely

 

[kloudie1]

Good that ya found it... AND it was a "cheap and easy"

 

[Ralph Johnstone]

My problem was low level of fuel in the fuel filter.

And if the filter had a low level of fuel ............................... what was in the rest of the filter ?
Locate the air leak and your problems should be over.

 

[Stu Jackson]

Of course RC had the best answer! Pulled the fuse and started the engine. No alternator on line. .......................The end looked slightly frayed so I pulled it and cut back to good hose. ...........................Restarted the engine and it idled smoothly..................... I dont know why the fuel filter would be low.

Any of the ideas presented would have eliminated the alternator as a culprit.

Frayed end? Seems to me that would the the PERFECT candidate for air getting into the system and THE reason for air in the filter. Don't you?

Seems like you fixed the issue.

 

[gettinthere]

Stu
I agree. RCs method was just easier than others.

I hope the frayed end fixes the issue...we shall see.

 

[gettinthere]

Started another thread on the engine forum. Fuel system still has issues. Thats all for this thread.
Thnx