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Old 19-01-2016, 00:51   #1
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Surging engine?

The last two times I have started my Ford Lehman 80HP diesel engine, it has surged up and down with the RPMs. Not bad but something new. Not liking surprises I figured I post the question here as I've always gotten good advice.

I'm guessing it's a fuel filter problem as the last voyage we were on was quite rollie and what ever was on the bottom of my tanks surly got stirred up.

I have a Racor filter in the line with a 20 micron filter in it that looks pretty good as well as two spin on filters on the engine.

Any suggestions?
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Old 19-01-2016, 01:48   #2
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Re: Surging engine?

Can you make your normal full RPM under way? I'd try changing filters as a first shot.
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Old 19-01-2016, 03:29   #3
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Re: Surging engine?

20 year diesel mechanic here, few options come to mind, abundance of water in fuel/water seperator or have you ran low,low on fuel lately to where it could have sucked air that can get trapped in fuel system for a long time unless cracking injector lines while running or rare but was tuff to figure out, your fuel filter housing can crack internally between in and out ports causing air bubbles in fuel system. Not familiar with that exact motor but they all work nearly the same way just look different.
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Old 19-01-2016, 03:34   #4
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Re: Surging engine?

Yes, no problem at high rpms. Only showing up at start up. After that, it seems fine. Figure to start with the obvious--fuel filters. Have three on the fuel line. Just change them all. See how it goes. Thanks.
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Old 19-01-2016, 04:56   #5
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Re: Surging engine?

My 2c: likely fuel filter issue or small vaccum leak.

What did you last work on before this problem started?
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Old 19-01-2016, 10:31   #6
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Re: Surging engine?

Drained the gunk out of the bottom of my Racor filter and went through a bunch of really bad sea conditions(Cape of Good Hope)for about a week.
I changed out all three fuel filters this afternoon and it seems much better. I'll clean my air filter tomorrow and check all the hoses going to the engine. At least it's much better. I'll start it again tomorrow when it's stone cold and see what happens.
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Old 20-01-2016, 09:56   #7
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Re: Surging engine?

Changed the air filters and all the hoses for any kind of leak. Found none. No water in the racor. No water in the other filters either.
Still surges slightly, about 70rpms, up and down till the engine is warm and then it evens out and runs fine.
The injector pumps oil is right where it is supposed to be and when I loosen the bleed screw with the engine off, some diesel comes(supposed to from what I was told).
still not sure why it's doing what it's doing.
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Old 20-01-2016, 09:58   #8
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Re: Surging engine?

It is often a fuel flow issue. I'd bet on that. Check the end of your pickup tube, replace all filters
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Old 20-01-2016, 11:09   #9
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Re: Surging engine?

I've already replaced all three filters. As for the fuel pickup tube, I have two tanks so unless both are blocked, it can't be it either. Puzzled.
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Old 20-01-2016, 12:05   #10
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Re: Surging engine?

I know nothing about Fords, but have had governors due what you describe on other Diesels, I believe it's called hunting. Had one do it for years, until I sold the tractor, goes away if you raise the RPM well above idle?
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Old 20-01-2016, 12:22   #11
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Re: Surging engine?

I've had the same experience with the Lehman 120 when it is first started. It goes away after a minute, so I put it down to the governor sticking a bit when cold.
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Old 20-01-2016, 12:45   #12
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Re: Surging engine?

I had a surging problem with a Perkins 4236 which was caused by the 28 year old lift pump getting "weak", swapped out the pump and the problem went away

Good luck
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Old 20-01-2016, 13:11   #13
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Re: Surging engine?

As a young fella I Skippered a LCM-8 with four 671Detroit diesels. All four engines hunted and smoked for about 90 seconds when started cold. At first I was concerned because the engines were brand new. I was told by an old hand that it was lube oil that had collected in the superchargers causing the smoke and the hunting was simply a trait of that engine and slightly increasing the RPM during warmup reduced it. Whenever it became more pronounced a fuel filter change would bring it back to acceptable range. I realize the 671 is a two stroke with common rail injection and very different but the response to fuel line restriction seems similar
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Old 20-01-2016, 17:47   #14
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Re: Surging engine?

The Detroits have fuel rail racks, under the valve covers I believe and let them get out of adjustment and they hunt, it's the rump, rump, rump that to me I love, makes them sound like they are drag motors or something.
I think though that Detroits are an animal all to themselves, nearly bullet proof and will run forever if cared for.


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