1999 Exec – Fuel issues- M11 engine

[Dean Bennett]

This has been a long battle that now has come to a head. I don’t know if this is two issues or one. For a long time, there would be intermittent ‘bouncing’ of the fuel pressure. Bouncing down. The first owner installed a fast-response, electronic fuel pressure gauge you could see while driving. The pressure would bounce down to zero or almost zero. You would not feel this in the engine unless they got bad, then, there would be some bucking. The 2nd (previous) owner – Removed the old Racor pre-filter/purge system, changed all the filters multiple times, run bio-cyde and complete tanks of fuel thru it a few times and replaced the Racor with a new Racor 760R30. Still, it showed up occasionally? Most times it was only noticed during deceleration. Usually, accelerating would make it stop. All of this time, all of the fuel lines were dry (that we can see). Note: The very-small filter that Is actually inside the fuel pump has not been changed. Who knew there was one in there – On the list to change it.

 

 My last trip to the beauty shop, it died hard. Let it sit for 5-minutes and it would run for 60-90 seconds.

So, for the last few days, I’ve been moving some clear hose around the fuel run looking for bubbles or???

 

After blowing out the fuel-line to the tank and bypassing the Draco it idles nicely. I had not looked at the filter on the Draco as it was changed less that 500 miles ago. I should have looked there first. You can see from the photos there is granular, black, hard material filling the inspection bowl and the filter. Now I know why it will not run with the Draco on.

 

I’m trying to find any excuse not to deduce this is decomposing fuel lines that need replaced? I looked around the tank with my bore scope (see pictures). The tank sides look new. But, I see some tell-tale signs of a small amount of algae on the bottom (not a lot) and, what looks like black granules in there. But, it is really hard to tell looking thru diesel! My best rookie guess, the return fuel line is decomposing also?

 

Note: The coach spent the first 21-years in south (humid) Texas then moved to dry-Vegas area for the last 4 years.

 

Any thoughts from the seasoned pros for the back granules?

 

On the bucking - If it is not related to above, I hear from some old-time M11 mechanics that there is a plug on the top of the M11 pump where a mechanical Tach could be attached. That plug has an o-ring that is notorious for being bad and causing air in the fuel and bucking? For the life of me, I don’t see a plug (see photos)? Nor do I know if this is real?

 

Help.… Dean

 

 

 

Edited April 3, 2024 by Dean Bennett
Mark where pressure sender connects

[Ivan K]

You don't say where the fuel pressure gauge is hooked up but here is how manual pump test is done on ISM, presumably same. Since your pressure drop is intermittent, possibly RPM related, I would look at the shutoff solenoid voltage stability. No idea what the trash in your picture is, you could be right. Assume it isn't even a little magnetic, like rust. 

[Benjamin]

The gunk in the plastic bowl looks like classic bio diesel gone bad.  Some of the parts in the metal filter look like they sure could be from a fuel hose.  Are there any unnaturally rounded smooth chunks, or bits with a grid from the woven hose reinforcement?  Those would be the smoking gun that's it's hose material.  The plastic bowl stuff looks like it would be softer dried varnish like stuff, from bio diesel. 

[timaz996]

10 minutes ago, Benjamin said:

The gunk in the plastic bowl looks like classic bio diesel gone bad.  Some of the parts in the metal filter look like they sure could be from a fuel hose.  Are there any unnaturally rounded smooth chunks, or bits with a grid from the woven hose reinforcement?  Those would be the smoking gun that's it's hose material.  The plastic bowl stuff looks like it would be softer dried varnish like stuff, from bio diesel. 

I am no pro but those chunks in the filter. Don’t look like a hose to me. Speaking of bio diesel. I have a son-in-law that drives a fuel truck in Arizona and he said there are no separate tanks in the ground for bio diesel. Sometimes they haul biodiesel sometimes they haul regular ultra low sulfur diesel and it all goes in the same tank. So when you buy diesel, I doubt you’ll ever know what you’re getting.  No matter what this stuff is, it gives me another reason that I am happy I put in the FASS on my motorhome. I have the dreaded caps pump and lost it in 2019 and shortly after I put in the FASS set up.

Edited April 3, 2024 by timaz996

[Ivan K]

Looking closer at your last picture, you already have a hose on the test port so that must be for your gauge. That port is past shutoff valve so that makes it even more of a suspect. These arent expensive. The little filter you mentioned is past in front of the test port. If the regulator failed, you would have to open up the pump...

Edited April 3, 2024 by Ivan K
Corrected filter location

[Dean Bennett]

36 minutes ago, Ivan K said:

You don't say where the fuel pressure gauge is hooked up but here is how manual pump test is done on ISM, presumably same. Since your pressure drop is intermittent, possibly RPM related, I would look at the shutoff solenoid voltage stability. No idea what the trash in your picture is, you could be right. Assume it isn't even a little magnetic, like rust. 

I updated the Pump photo to indicate where the pressure is taken off. It mostly runs steady at about 150 PSI. Good for an M11. I just checked, the material in the filter is not magnetic at all. It is hard and granular but, if you rub it between your fingers, it will fracture and break up. Not RPM related. There is no solenoid in the fuel circuit? At least my M11 manual does not show anything and I don't see anything? 

[Ivan K]

This is where the solenoid is and where to check the voltage. Behind the marked hose in your updated pic.

Edited April 3, 2024 by Ivan K

[Dean Bennett]

12 minutes ago, Ivan K said:

This is where the solenoid is and where to check the voltage. Behind the marked hose in your updated pic.

I see it - Thanks! What am I looking for on the voltage? Would an intermittent voltage to it cause the pressure to bounce down? Thanks....

[Ivan K]

Should see stable full voltage with IGN ON. The solenoid could be allowing the internal disk valve to close and you would see the drop in pressure.

I have corrected previous note, the little filter on top of pump is in FRONT of the solenoid valve.

Edited April 3, 2024 by Ivan K

[Dean Bennett]

Ivan, it is starting to feel like I'll be whole-sale replacing all of the fuel lines and filters first. If that does not fix the intermittent pressure bouncing, this solenoid looks like another great place to check. I'll probably need some sort of voltage recording device as it can go 500-1000 miles between it happening. It is just curious that accelerating usually makes the pressure bouncing (down) stop? 

Anyone with a great recommendation on fuel line, please chime in. The local hose shop is recommending: FLEXTRAL GRIP LOC J3 

At least, that is what they sell. 

[Ivan K]

Because you mentioned accelerating cures it, I thought of voltage variation or vibrations. I would at least make sure the connection is solid. The pump filter is a good idea too.