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Old 06-03-2017, 12:55 PM   #1
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Ford Lehman engines

I have twin 2715E 120 hp engines. Both seem to operate about the same and have about the same hours (less than 4,000) on them. However, one engine easily cranks up to 2500 rpms under power and the other one only goes up to about 1900 rpms. Both racor filter containers have been rebuilt and all fuel filters changed. This made no difference. It could be linkage in the cables but I don't think so. It seems that one engine just plateaus at the 1900 rpm range. Has anyone else had this problem?
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Old 06-03-2017, 01:09 PM   #2
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There are two basic reasons why this is happening:

1. The 1,900 rpm engine is severely overpropped and you are putting stress on the engine if you don't correct it.

2. The 1,900 rpm engine for some reason doesn't put out full power. First check the wot rpm in neutral. It should hit 2,700 rpm or so. If it is down near 1,900 then it probably is an easily fixed linkage problem.

But if it revs to 2,700 rpm then the most likely cause is a a fuel restriction.

David
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Old 06-03-2017, 01:23 PM   #3
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Begin by calibrating your tachometers. Buy a Handheld Digital Laser Photo Tachometer at Amazon for $15-20.

Next measure rpm's at WOT with no load. Then with load.

If more than 10% difference then you have linkage problem, fuel restriction, or air leak as Marchand mentioned. If you have eliminated all of those potential issues, it might be time to send the injectors out for testing.
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Old 06-03-2017, 01:40 PM   #4
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Thank you gentlemen. I don't think the tachometer is the problem as the other engine can easily be heard revving up while the one just sounds as if it reaches a point and just doesn't go further. The linkage could still be a problem but I don't think that is the case. The props are identical on both engines and the one easily reaches the 2500 rpm so I don't think it could be a prop problem. Both props are in good shape. I agree it could be a fuel problem or and injector problem but I would sure hate to take the injector unit off if that were not the problem. I am appreciative of your feedback.
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Old 06-03-2017, 01:51 PM   #5
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Just humor me and do a wot test in neutral. That will definitively rule in or out the linkage not opening the throttle to wot.

As SoWhat indicated, it could be an air leak into the fuel system, but that usually shuts the engine down or causes severe surging, not just topping out at low rpm.

Diesel engines need air, fuel, and compression to make power. It could be an air restriction like a very plugged foam air filter, but also unlikely. It could be an exhaust restriction which also limits air so check the mixer for carbon/scale fouling.

But the overwhealming reason that an otherwise healthy engine doesn't make full power is a throttle link problem, followed by a fuel restriction. Bad injectors would be far down on my list and would have to be cutting out one or more cylinders to cause a 500 rpm drop at wot under load. You can crack each injector pipe at the injector at idle and see if the engine rpm drops a bit. Dropping is good, not dropping indicates that the cylinder isn't firing.

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Old 06-03-2017, 02:10 PM   #6
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Do as David has suggested and when you crack the injectors, make sure you have a suitable rag to catch the fuel. Do cylinder number 6 first, it is the most likely to be damaged. Any smoke?
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Old 06-03-2017, 02:21 PM   #7
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Thanks again gentlemen. I will try the rpm's again without a load on them. If they only go up to 2100 or so that is one problem but if they can get up to 2500 or more then, as you said, it has to be one of the problems mentioned. Also I can try disabling the linkage and see what happens when I manually increase the throttle. You both sound as if you are far more attuned to these engines than am I. Thanks again.
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Old 06-03-2017, 02:34 PM   #8
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Also, I am sure it is not air as I have experienced that in the past and there was always a lot of surging before the engine shut down. This engine sounds very smooth. Both engines are about the same with smoke. Just a little white or light greyish smoke when starting and very little smoke underway. I am wondering about the exhaust though. Perhaps there could be buildup that is causing problems. I assume if this is the case though that the engine will not get high rpms in neutral either.
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Old 06-03-2017, 03:33 PM   #9
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Quote:
Originally Posted by BoOliver View Post
I am wondering about the exhaust though. Perhaps there could be buildup that is causing problems. I assume if this is the case though that the engine will not get high rpms in neutral either.
Probably not. An engine should be able to rev up to rated rpms in neutral even with a partially plugged exhaust.

But you don't know yet whether it will or won't. This is all just speculation without some tests to tell you where to go with this troubleshooting.

David
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Old 06-03-2017, 04:40 PM   #10
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Any time you have issues with Lehman's, contact American Diesel in Kilmarnock, VA. The founder of the company, recently deceased, was the daddy of the marinized Lehman and knew the engine inside and out better than anyone. I understand his son, who now runs the company, is almost as knowledgeable.
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Old 06-04-2017, 07:25 AM   #11
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I would still check the tachometers for accuracy. If you don't do that you are shooting blind.
You need data.
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Old 06-04-2017, 08:02 PM   #12
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First thing to check is tach accuracy, then throttle linkage/cable/lever mechanism. One of those items is more likely to be the problem than engine. Only if all those check out first would I dig into engine bits.

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