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Author Topic: What is this? And could it restrict fuel? Photo included.  (Read 831 times)
Scott Bennett
Scott & Heather MCI-9
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« on: August 15, 2012, 08:20:57 AM »

Bus is still not getting enough fuel. Wondering if this is a regulator?? 6v92.turbo




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Scott & Heather
1984 MCI9 6V92-turbo with 9 inch roof raise & conversion in progress.
http://www.scottmichaelbennett.com/p/our-bus.html
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luvrbus
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« Reply #1 on: August 15, 2012, 08:43:59 AM »

That is a fuel pressure sender has nothing to do flow

good luck
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Scott Crosby
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« Reply #2 on: August 15, 2012, 09:55:15 AM »

Are you sucking air through a bad seal on the fuel filter?  I had that problem and changed the filters with new gaskets.  I thought it was a fuel issue and instead it was sucking air.
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OneLapper
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« Reply #3 on: August 15, 2012, 10:24:28 AM »

I fought with a low power issue for a year when I first bought my bus. It was fine cruising and on short hills, but fall flat on its nose in the hills.  I eventually found a blockage in 90 degree fuel fitting on top of the tank/pickup tube when I installed a new fuel line.  After removing it, the engine had new found power.  Solved the problem completely. 
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OneLapper
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bevans6
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« Reply #4 on: August 15, 2012, 10:27:16 AM »

Have you measured the fuel pressure at idle and governed speed?  Reason I ask is that handy dandy little fuel pressure tester port just behind the fuel pressure switch...   Grin  Anyway, the other thing I wondered is have you checked to make sure there is a fuel restrictor in the return line.  That would cause low pressure as well.  My thinking is that the fuel system on the DD is capable of flowing far in excess of the actual fuel used since the fuel is used to cool the injectors.  If you truly have low flow, your injectors will be starting to have issues.  Pressure, on the other hand is created by the restrictor.  The pump creates the volume of flow, the restriction in the system creates the back pressure that builds the pressure.  Both have to be right, but if you have the correct pressure (60 - 70 psi at governed speed comes to mind) by definition of the design of the system, you also have sufficient flow.  On my 8V71 (MCI setup) the restrictor is built into the fitting screwed into the head that the return line bolts to.  If you didn't know it was the restrictor, you might replace it with a standard fitting.

Edit - I had another thought.  There is no regulator on the fuel system - just the restrictor orifice.  So - if you were to read the pressure at the test port, you would be reading the "going in" fuel pressure, before any of the injectors etc.  You could then install a fitting such that you could read the fuel pressure next to the restrictor fitting, where ever that is located in your system.  There are several ports for the "in" and "out" fuel rails on each cylinder head, you would just attach your pressure gauge to an unused "out" port on the cylinder head next to your restrictor fitting.  I think they are 1/4" npt threaded ports.  I hope this makes sense...

Brian

« Last Edit: August 15, 2012, 12:01:52 PM by bevans6 » Logged

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Scott Bennett
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« Reply #5 on: August 15, 2012, 08:58:49 PM »

Thanks Cliff. Wasn't sure. Why does it have a pressure sensor? What does it do? I have no gauge at the dash so is it for another use? 

Scott, already replaced the filter gaskets. If I had a leak I would guess I would lose prime. Don't have that issue.

Onelapper, interesting. I blew the lines out with compressed air, but just maybe I still have an issue. Will check this.

Brian, I didn't know that was a fuel pressure test port. I always used it to prime. The restrictor orifice wouldn't have just stopped working all of the sudden? Right? The only thing I've done to the coach that might affect this is I rebuilt the throttle assembly shutoff lever for fuel shutoff. The one operated
By the skinner valve. I took that throttle plate off and unseized the washer that was jamming the lever. Could I have put this back together wrong?!?


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Scott & Heather
1984 MCI9 6V92-turbo with 9 inch roof raise & conversion in progress.
http://www.scottmichaelbennett.com/p/our-bus.html
˙ǝɯoɔlǝʍ suoıʇɐuop ˙snq ʍǝu ɐ pǝǝu ʎlqɐqoɹd ll,ǝʍ 'sıɥʇ pɐǝɹ uɐɔ noʎ ɟı
thomasinnv
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« Reply #6 on: August 15, 2012, 09:25:13 PM »

The fuel pressure switch is part of the emergency override system. If you have the engine shut down due to one of the safety switches you can hold the start button to keep the engine running. The fuel pressure switch disengages the starter when there is pressure at the switch to keep from "grinding" the teeth off the starter or flywheel.
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« Reply #7 on: August 15, 2012, 09:25:38 PM »

Scott people use that port some times as a test port but it is for priming DD sold a priming pump to hook there, the pressure switch is part of the override system remove a plug from the base of the secondary filter if you have 50 lbs they run good.

The fuel pump has a pressure relief valve it could be bad or the fork on the fuel pump drive could be rounded not letting the pump develop enough pressure  

Could be a lot of things trial and error buddy start in one area and stop jumping around and you will find it, the check valve could be half plugged or a line collapsing on the suction side number of things could cause your problem it's not a rocket science keep digging you will find it

good luck .
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Scott Bennett
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« Reply #8 on: August 16, 2012, 09:30:02 PM »

Thanks guys! Still digging cliff. Car just blew a brake line so switching my attention to that. I have been busier this summer than Ive been my entire life. So trying to sort this out slowly. Already replaced the only rubber section of the fuel line with a new $55 Jose custom crimped. That didn't solve issue. No load rpm is just fine. No smoking At all and a nice sweet sounding turbo whine suggests turbo is ok. Going to test fuel pressure and crAck the line at the 90 degree bend at the tank too to eliminate blockage. Looked for the check valve but didn't find it. I'll have to look harder. I'll keep digging. Slowly


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Scott & Heather
1984 MCI9 6V92-turbo with 9 inch roof raise & conversion in progress.
http://www.scottmichaelbennett.com/p/our-bus.html
˙ǝɯoɔlǝʍ suoıʇɐuop ˙snq ʍǝu ɐ pǝǝu ʎlqɐqoɹd ll,ǝʍ 'sıɥʇ pɐǝɹ uɐɔ noʎ ɟı
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