Ford Lehman sp135 automatically goes to idle from 2k rpm

[paulga]

yesterday we traveled 18 hours with no issues. today's trip started from 6am, we fueled up before noon, cruised at 2k rpm same as yesterday. temp, pressure, voltage have been within normal range. around 5pm the engine suddenly rolled back its rpm to idle. we returned the throttle and gear to neutral then throttled up, the rpm climbed again. soon after cruising at 2k, it throttled to idle again. since then we maintain the rpm near 1900 and still monitoring.

has any one with FL observed similar issue?

 

[RT Firefly]

Greetings,
Mr. p. Might be your fuel line(s) have delaminated and collapsing (internally) under draw (vacuum). Had that happen twice.

 

[paulga]

could you attach a picture? I don't have the knowledge to follow. do you refer to the fuel line to each injector? and where is draw?

we never touched the fuel lines. there was no issue yesterday.

 

[kchace]

If it cruises fine at a lower rpm then the chances are high it’s simply a clogged fuel filter.

 

[CharlieO.]

Very probable fuel restriction. Fuel line, filter or a valve(check or hand).

 

[paulga]

If it cruises fine at a lower rpm then the chances are high it’s simply a clogged fuel filter.

Racor filters most likely? I would want to change all fuel filters including the fuel filter on the engine. But we have only one spare racor filter onboard.

Does continuing on lower rpm ruin the engine? In that case we should find a channel to change the fuel filter asap

 

[RT Firefly]

Greetings,
Mr. p. Sorry no pictures. Boat's gone. What I suggest may or may not be the problem but it is one possibility. What does the fuel in the Racor bowl look like? Dirty/cloudy/water layer?



Rubber fuel line would be most likely used from the tank to the lift pump and/or then to the Racor filters. Onward from the Racor would most likely be metal.


Suction from the fuel lift pump might collapse a compromised rubber feed hose. When you throttle down to idle, hose is allowed to un-collapse and fill Racor(s) when you throttle up again, fuel in the Racor is used up and engine slows down.

 

[Flatswing]

Do you have mechanical (cable) or hydraulic throttles? If hydraulic, is the system full of oil and correctly pressurized?

 

[TJM]

I would guess fuel restriction somewhere. Check both fuel filters. You can visually see the condition of the Racors but the spin on cartridges filters are tough to evaluate. Do you know the Micron size of the filters? They might be 2, 10 or 30 Micron. 30 Micron has the largest holes. Sometimes too fine a filter will restrict flow after a while.
Your fuel delivery system has two parts. Suction from the tank and then pressure to the injectors. A hole/ leak in the suction side will draw in air bubbles causing this kind of issue. Are you Racor bowls full of fuel to the top?

 

[paulga]

Do you have mechanical (cable) or hydraulic throttles? If hydraulic, is the system full of oil and correctly pressurized?

Hydrolic.
Is the oil is low, does it cut off the throttle?

 

[paulga]

I would guess fuel restriction somewhere. Check both fuel filters. You can visually see the condition of the Racors but the spin on cartridges filters are tough to evaluate. Do you know the Micron size of the filters? They might be 2, 10 or 30 Micron. 30 Micron has the largest holes. Sometimes too fine a filter will restrict flow after a while.
Your fuel delivery system has two parts. Suction from the tank and then pressure to the injectors. A hole/ leak in the suction side will draw in air bubbles causing this kind of issue. Are you Racor bowls full of fuel to the top?

We just changed both 30 micron racor filters this morning. Now the engine stopped. as soon as rpm goes up to 1800.

 

[TJM]

Did you check the dual e cav spin on filters on the side of the engine? Typically they are right above the oil heat exchanger tube on the same side of the engine as the injector pump.
Does your engine have an electric fuel pump? Have you ever bleed the fuel lines of air?
The spin on filter assembly and injector pump have bleed screws to allow air out of the lines.

 

[paulga]

Did you check the dual e cav spin on filters on the side of the engine? Typically they are right above the oil heat exchanger tube on the same side of the engine as the injector pump.
Does your engine have an electric fuel pump? Have you ever bleed the fuel lines of air?
The spin on filter assembly and injector pump have bleed screws to allow air out of the lines.

engine runs smooth at low rpm. does not sound like air problem. we did use racor refill pump to top up the racors when changing the filters. engine will throttle back or stop when cranked up to 1800.

we are stuck at Cape May. any diesel expert near here?

 

[Bmarler]

Can you see the throttle image on the injector pump move by itself? Or, with the engine off, advance the throttle lever fully. Then go to the engine and see if you can easily move the lever on the injection pump.
Just trying to see if it’s a control problem or fuel restriction problem.

 

[Bmarler]

engine runs smooth at low rpm. does not sound like air problem. we did use racor refill pump to top up the racors when changing the filters. engine will throttle back or stop when cranked up to 1800.

we are stuck at Cape May. any diesel expert near here?

You say racors. Usually, the racor is used as a primary filter before the lift pump. A filter after the lift pump might be a spin on, or draw stud type. This is the secondary filter. Usually a finer media than the racor primary.
Of course someone may have installed a custom setup, we have no way to ascertain without pictures.
If you changed both the primary and secondary filters, the next thing old be the rubber hoses, followed by the lift pump.
If the lift pump isn’t working, you can temporarily install an electric in series to get you home.

 

[RT Firefly]

Greetings,
Mr. p. Rubber fuel hose is cheap (in the greater scheme of things).

 

[paulga]

You say racors. Usually, the racor is used as a primary filter before the lift pump. A filter after the lift pump might be a spin on, or draw stud type. This is the secondary filter. Usually a finer media than the racor primary.
Of course someone may have installed a custom setup, we have no way to ascertain without pictures.
If you changed both the primary and secondary filters, the next thing old be the rubber hoses, followed by the lift pump.
If the lift pump isn’t working, you can temporarily install an electric in series to get you home.

Here is the starboard side of the engine. I guess the lift pump is at the far end (toward the bow).

There are "2306" written on the econdary fuel filters, so they are only 4 months old. Waiting for the mechanic to reply

 

[TJM]

It appears as though there are hand written markings on the secondary fuel filters. It says 6-23, Which implies June of 2023. Fuel quality is very important as well as the sequencing of filter micron sizes. Those filters could get clogged up very fast, within a few hours if they are 2 micron size and you had some bad fuel. The particles would go right thru your 30 Micron Racor and clog up the paper pleated spin on. A Racor element can be changed in minutes with no tools and no mess in bad seas.
FYI, 10 Micron filter size is .0004 of an inch. Paper is .003" thick.
Have you checked the spin on filters?

 

[Larry M]

Your lift pump is behind your oil cooler (circled in green). Trace the fuel line from the duel filters back.

Edit: The second picture is from another SP135 but show the lift pump.

 

[paulga]

Spin is in normal range. Both racor filters are changed this morning

 

[TJM]

You are missing something. Your Racor set up is nice, dual filters are useful. Currently the valve is turned so the fuel is flowing thru filter #1 ONLY. When and if that element gets clogged you can switch to filter #2 by rotating that silver valve in the center clockwise 90°.

Those pressure gages are NO good for low flow engines like the FL135. They will always show in the green. Plus unless they were modified they DO NOT FIT the Racor 500 series. The thread in the center is too long and bottoms out before sealing the top. I have had extensive conversations with Racor on this. I have the FL 120's.

There are 2 other spin on cartridge filters after your Racor. Have you checked them?

 

[paulga]

Can you see the throttle image on the injector pump move by itself? Or, with the engine off, advance the throttle lever fully. Then go to the engine and see if you can easily move the lever on the injection pump.
Just trying to see if it’s a control problem or fuel restriction problem.

Just tested the lever, it moves freely without a lot of resistance

 

[paulga]

How do you check the spin on filters?
We have two spare spin on available

 

[paulga]

Thanks for the photo I was able to locate the lift pump lever

 

[TJM]

The lift pump is a manual diaphragm pump that is used to bleed to fuel lines after a filter change. You loosen the bleed screw on the top of the dual canister housing and pump the lift pump lever 20-30 times or until fuel comes out of the bleed screws that you just loosened.
What are the micron sizes of the new filters? 2,10 or 30 microns? Are you by yourself? I wish we could have met for a few hours to pass on some knowledge.

 

[paulga]

Racor filters 30 micron , the same as that was installed last time
2nd fuel filters are Baldwin BF825, I cannot see micron on the filter.

We are taking a slip at Utschs marina at Cape May, anyone close by?

 

[RT Firefly]

Greetings,
Mr. p. "...it moves freely without a lot of resistance." There should be some resistance. Try "bumping" the motor and check resistance again. Need only be for 1/2 second or so. IF the lift pump arm (can't see it, it's internal) is on top of it's driving cam it won't pump by the external priming lever. Really poor explanation. Perhaps someone can describe better.

 

[paulga]

This is bleeding procedure from the sp135 manual. it seems to align with desc from @TJM
I saw a lever on the lift pump, not a plunger, so sp135 is considered natural not turbo, correct?

The lift pump is a manual diaphragm pump that is used to bleed to fuel lines after a filter change. You loosen the bleed screw on the top of the dual canister housing and pump the lift pump lever 20-30 times or until fuel comes out of the bleed screws that you just loosened.
What are the micron sizes of the new filters? 2,10 or 30 microns? Are you by yourself? I wish we could have met for a few hours to pass on some knowledge.

 

[paulga]

A mechanic changed the spin on filters, the engine has been running well. We just arrived at Jersey City.

The mechanic found water in the bowl of one spin on filter. Could rain water get into the tank through the fuel fill cap?

 

[TJM]

That is awesome news. Thanks for presenting how it was solved. Sometimes we get lucky and have the right answer.

Yes, Rain water may enter the tanks from the diesel fill cap. This must be addressed. Water is heavier than diesel fuel and will settle on the bottom of the tank(s). Our tanks are iron and will rust if not resolved.
I am confused as to why the Racor did not catch the water and be very easily seen thru the clear bowl.