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Author Topic: The mystery deepens -- fuel delivery question.  (Read 8990 times)

Offline DrivingMissLazy

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Re: The mystery deepens -- fuel delivery question.
« Reply #15 on: August 09, 2007, 01:21:18 PM »
Sean, I used a regular air nozzle with a rubber tip to blow back thru the line to the tank. It really takes very little pressure.

Needless to say I think, due to your knowledge, but be sure to have a fuel cap off when you do this so that someone can hear the air bubbles in the tank and to keep from over pressurizing the tank.
Richard
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming:  WOO HOO, what a ride

Offline Frank @ TX

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Re: The mystery deepens -- fuel delivery question.
« Reply #16 on: August 09, 2007, 01:43:39 PM »
Hi Sean,
The filter can be pushed around a little thru the fill cap.
I don't push it around much , the filter end cap has a depression in the top for the spring to set in so I never had a need to readjust it.
Run it at fast idle, if air is getting in you'll see it.
Remenber there is a drain valve at the bottom to be used when changing the filter, if it is not tight air will enter that way.
BUT still you should see the bubbles at fast idle.

The folks that say back pressure the fuel line with air may not know that MOST often there is a check valve in the fuel line put there by the manufacturer.  If that check valve is in good shape no air can go back to the tank.

Let us know when you run it at fast idle.
Frank

Offline HB of CJ

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Re: The mystery deepens -- fuel delivery question.
« Reply #17 on: August 09, 2007, 01:57:01 PM »
Do you have rubber fuel lines anywhere in your coach?  If soosss, how old are they, and are they of the proper diameter to pass enough fuel when the fuel heats up?  Sometimes the insides of rubber lines swell up, thus restricting the fuel.  Kinda like my arteries. :) :)

Offline gumpy

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Re: The mystery deepens -- fuel delivery question.
« Reply #18 on: August 09, 2007, 04:19:15 PM »

The folks that say back pressure the fuel line with air may not know that MOST often there is a check valve in the fuel line put there by the manufacturer.  If that check valve is in good shape no air can go back to the tank.

Not always in the supply line. MCI put them in the return line. Not sure what Neoplan did, but if there's a check valve in the supply line, that's the first place I'd look for a blockage.

Craig Shepard
Located in Minnesquito

http://bus.gumpydog.com - "Some Assembly Required"

Offline Sean

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Mystery Solved!
« Reply #19 on: August 15, 2007, 08:18:35 PM »
And the answer is (drum roll, please):

Kidney stones.

No, seriously -- debris in the fuel return system, at the restrictor orifice.  They showed me the debris -- it was smaller than a kidney stone.  You could hardly see it.

We took the coach in to Stewart & Stevenson in Albuquerque this morning, at the recommendation of Virgil Cooley over at PEDCO.

When they tested the fuel pressure, it was around 60PSI at idle, and it should be closer to 25 PSI.  So that told them right away where to look.  When they pulled the restrictor, they found the debris clogging it.  And they were confident that this was the sole reason for both the low power and overheating complaints.

And the good news for us -- they didn't even give us a bill.  They called PEDCO when they found the trouble, and PEDCO immediately agreed to take care of it.  There's no guarantee, of course, that this happened during the in-frame (although the debris was too large to make it through the fuel filters, so it is more likely it got in there while things were open).  And this, after all, is one reason we drove 400+ miles to PEDCO when we needed an in-frame -- we trust them, and know they stand behind their work.

I have not confirmed this yet, but I suspect the return restriction is also the reason our Kysor fuel pressure switch was cutting out the starter prematurely.  I still haven't found a replacement switch, so tomorrow I will put the original one back in and see if it's working now.

We had good power coming out of Albuquerque today, and we pulled a couple of good grades without overheating, at much higher speeds and in a higher gear than we were able to a few days ago.  So my fingers are crossed that our problems are behind us.

That said, the Davco Fuel Pro emptied out again on today's drive, and the coach, subjectively, feels a bit "sluggish" (although definitely not the level of problem we were having in Santa Fe).  So the jury is still out on the Fuel Pro issue.  I'll put more fuel in it tomorrow and we will monitor the performance moving forward.

-Sean
http://OurOdyssey.BlogSpot.com
Full-timing in a 1985 Neoplan Spaceliner since 2004.
Our blog: http://OurOdyssey.BlogSpot.com

maria-n-skip

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Re: The mystery deepens -- fuel delivery question.
« Reply #20 on: August 15, 2007, 08:25:19 PM »

 Sean,

  I swear by the time you get everything that can go wrong, figured out, and fixed
 you will have a well earned    PHD in busology


   Skip

Offline gumpy

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Re: Mystery Solved!
« Reply #21 on: August 16, 2007, 06:25:17 AM »
And the answer is (drum roll, please):

... at the restrictor orifice. 

So, what's a restrictor orifice, and where is it located?

Any photos of such?
Craig Shepard
Located in Minnesquito

http://bus.gumpydog.com - "Some Assembly Required"

Dallas

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Re: Mystery Solved!
« Reply #22 on: August 16, 2007, 06:53:54 AM »
And the answer is (drum roll, please):

... at the restrictor orifice. 

So, what's a restrictor orifice, and where is it located?

Any photos of such?

Craig,
The restrictor orifice sits on the return side of the fuel system and allows pressure to build up in the fuel rail. It's usually found on the head where the fuel return line is.
Basically it's a bushing that screws into the head with a small, (.080?) hole in it and the return fuel line connects to it.

There are a number of different sized orifices that may be used, depending on the application.

Offline Chris 85 RTS

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Re: The mystery deepens -- fuel delivery question.
« Reply #23 on: August 16, 2007, 07:20:26 AM »
Can anyone explain the logic behind this clogged return causing overheating?  I have been fighting overheating and have never heard of this before.   Is there a plugged port to check fuel pressure?
1985 GMC RTS II 40x96 6V92TA MUI V731 IFS

Offline Sean

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Re: The mystery deepens -- fuel delivery question.
« Reply #24 on: August 16, 2007, 07:45:46 AM »
Can anyone explain the logic behind this clogged return causing overheating?  ...   Is there a plugged port to check fuel pressure?

Chris,

Two ways:  First, and this is the lions share, any engine that is having trouble making power will have to "work" harder to achieve any result at the wheels.  More work means more heat, so engines with power trouble will generally heat up more.

Second, the injectors themselves are cooled by fuel.  The extra fuel flowing past the injectors and returning to the tank carries away this heat.  I find that my fuel return temperature is generally in the 120-130° range.  By further restricting the flow rate, less fuel flow is available to carry away this heat.

You can check your fuel pressure at the secondary.  There should be an "extra" port on the secondary mount.  Often, there is a tee on this port, with a pressure switch or sender on one side, and a plug on the other for priming.  Connect your gauge to this priming port.

-Sean
http://OurOdyssey.BlogSpot.com
Full-timing in a 1985 Neoplan Spaceliner since 2004.
Our blog: http://OurOdyssey.BlogSpot.com

Offline H3Jim

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Re: The mystery deepens -- fuel delivery question.
« Reply #25 on: August 16, 2007, 07:49:12 AM »
Any idea on what is / was causing your fuel pro issues?
Jim Stewart
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Offline Sean

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Re: The mystery deepens -- fuel delivery question.
« Reply #26 on: August 16, 2007, 09:31:28 AM »
Any idea on what is / was causing your fuel pro issues?

Jim,

The service manager at S&S felt that the restrictor blockage was 100% of my problem, and that the Fuel Pro is not implicated.  When I asked him about the level dropping, he felt that it was normal, and I should not worry about it without other symptoms such as low power.  I'm not sure I agree, so we are monitoring the situation moving forward.  I just filled the bowl back up to the top of the filter, and we'll see how far down it goes in today's driving.  The filter is brand new, so normal level right now should be at the very bottom of the media.

-Sean
http://OurOdyssey.BlogSpot.com
Full-timing in a 1985 Neoplan Spaceliner since 2004.
Our blog: http://OurOdyssey.BlogSpot.com

Offline Len Silva

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Re: The mystery deepens -- fuel delivery question.
« Reply #27 on: August 16, 2007, 09:44:44 AM »
It seems to me that you were very fortunate that the trash all ended up at the restrictor and not in the injectors, unless it originated south of the injectors during assembly.

Len

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Offline Hobie

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Re: The mystery deepens -- fuel delivery question.
« Reply #28 on: August 17, 2007, 08:15:45 PM »
I sure learned something here.  Many thanks Sean for the detailed answer. 

I had no idea and would never think to look at a return line.  The strange part was you would think you would notice more 'pedal' resulting in higher fuel flow.  I'm sure that if it was obvious Sean would have immediately noted that, so it holds that it must mean a very slight increase in accelerator pressure to compensate for the lack of power resulted in the higher temp.  Glad its fixed Sean.

And a big thanks to Louise for the source books and travel guides.  Everyday thing for you guys but huge for the rest of us.