Diesel Engine "Surging" or "loping"

sandybeach · Aug 6, 2016

My diesel engine has developed a problem with "surging" or "loping." The engine speed changes dramatically repeatedly below 2200 RPM It will jump from 800 to 1500 down to 1200 up to 1800 and so on. Sometimes it will drop below idle speed and shut off the engine.

This speeding up-slowing down is constant. The only way to stop the cycle is bring engine speed up to operating RPM=2200. Even then the speed varies a little bit, in the 2000-2200 range.

This started the last time I used it (2 days ago). Engine has less than 100 hours.

Ideas of why - and how to fix it?

TORQUIN · Aug 8, 2016

First, I think trash or dirt in fuel system. But, if that's all clean, how old is it? I wonder if it's governor springs getting weak, but the governor springs are extended a little at 2200 RPM so they have more even tension there and hold the RPM better. Yes, I read the engine has less than 100 hours, but I don't know if that means new or rebuilt, and if rebuilt, that doesn't necessarily mean the governor was rebuilt.

Chris

Tx Jim · Aug 8, 2016

How long since fuel filter was changed? Have you checked for good fuel flow from tank to inj pump? Is fuel tank venting?

DLTTrekkers · Aug 9, 2016

Make and model will help a lot !

DLTTrekkers · Aug 9, 2016

Mereringvalve sticky deu to dirty fuel

sandybeach · Aug 20, 2016

Nothing like surgery to take you off-line at the tractor and the internet

(Original question was about engine surging on a Branson 3510H (year=2010). Engine rebuilt and injector pump replaced 200 hours ago (under warranty)

I changed the fuel filter - it didn't have a lot of crud. Also changed air filter, since it was quite dirty.

After changing the fuel filter I primed the system - or thought I did. I opened each nut (flared pipe), one at a time.I cranked it until bubbles stopped, and tightened the nut. The difference in how the engine ran was insignificant.

Ignoring Einstein's advice, I tried the same thing again hoping for a different outcome.

The next time I opened each nut more - one at a time - and cranked. I got a feeble spray squirting out if each fuel line. I was expecting a flow of diesel.

QUESTION: is this the right way to bleed it?

When I started the engine, it started easily (all things considered). It runs without surging. Too soon to celebrate! Moving throttle handle 1/2" either "faster" or "slower" made the speed move instantly to 500 or 2100. Not slowly, instantly: before I could count "one thousand-one" either way (faster or slower), the speed flips between minimum and maximum.

Sorry Einstein, but I did it again. Now it runs mostly smoothly (very slow and small fluctuations) but has very little power.

By the way, I'm sure the dealer drained the fuel: the fuel gauge has been wrong all the time, ever since.

I idled it several minutes and then ran it at 2100 for several minutes. It runs runs smoothly, but it has "no" power. At 2100 lifting the bucket slowly almost kills the engine.
I backed the tractor up a small incline and ... it kills the engine.

Since bleeding makes a difference - but not enough difference, I assume that there is some blockage or remaining air bubbles.

What should i try next?

Tx Jim · Aug 20, 2016

Engine attaining 2100 rpm's but lacking full power indicates engine possibly isn't firing on all 3 cylinders. I agree with you I think fuel system still has air in it somewhere from tank to injectors. Is tank venting?

sandybeach · Aug 20, 2016

Tx Jim said:
Engine attaining 2100 rpm's but lacking full power indicates engine possibly isn't firing on all 3 cylinders. I agree with you I think fuel system still has air in it somewhere from tank to injectors. Is tank venting?

Hmmmm. To vent it, for purposes of diagnosis, I could just remove the cap on the filler. I'll get back to you.

Dealer said look for a bleed screw on the fuel bowl assembly. Bleed there before bleeding at the injectors.

Also: a good fuel additive. I asked "Sea Foam?" She (yes she) said it's as good as any and can't hurt.

Because of our cool, damp climate (Washington coast). there might be algae on the inside of the tank when the inner surface of the tank is exposed to cool, damp air when the tank isn't topped off (which is 99% of the time). Clumps of algae could block the the fuel line opening. Sea Foam might break up the clumps so they can clog my fuel filter instead.

Last resort, drain tank. Sounds weird, but she gets paid to service tractors. I pay for the privilege of driving one. I'll bet on her solutions.

Come to think of it, I pay for the privilege of paying for one. :thumbsup:

sandybeach · Aug 21, 2016

Engine surges frequently.

I bled the air out at the bleeder screws on the fuel filter assembly - good flow of fuel coming out at the screws, so fuel flow into the fuel filter and out to the injector pump is good. But fuel flow out to the injectors seems weak - it sprays instead of flows. I'm probably wrong, but I thought the spraying should be at the injectors inside the head, not at the nut at the end of the fuel line that delivers fuel to the injectors.

Sometimes I can get the engine to idle for several minutes at 650 RPM and at 2100 RPM, and most speeds in between. However, RPMs still sometimes go up up and down without my help.

The throttle lever and cable seem to work fine when the engine is off: full throw on the lever and full movement where the cable connects to the throttle (which I assume is inside the injector pump). But when the engine is running, a tiny movement of the throttle lever - less than a half inch either up or down - can cause big movement in RPMs.

Worse, it has low power at any RPMs. At 2100-2500 raising the bucket drops the RPMs rapidly - as in kills the engine - if I don't give it more throttle (to keep from stalling). Same for driving up a very slight incline - it wants to stall unless I futz with the throttle lever.

I'm already planing for the worst case: R & R the $600 injector pump. That project looks nasty. There's fuel lines (running from the pump to the injectors) sitting behind other stuff. Who designed that?

Any ideas here?