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Date:         06 Sep 95 13:25:00 PDT
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         BOWMANR%em.EDW@mhs.elan.af.mil (Mr.Roger Bowman)
Subject:      Running FI engine empty- long reply

--PartBoundary Wed Sep 6 14:33:22 8214

========================================================================= Date: Sender: Vanagon Mailing List <vanagon@vanagon.com> From: Subject:

Form: Memo Text: (85 lines follow) On Thu, 31 Aug 1995, Harvey Chao wrote: > Running out of gas in a fuel injected engine, gas or diesel is > a real "NO-NO".

I've heard this before. Could someone please explain if this is in fact=20 true, and if so, why and what could be damaged? (Besides one's ego,=20 slogging down to road in the rain on foot with a gas can...).

Tobin _______________________________________________________________ well:

Both diesel and FI use fairly specialized fuel pumps to move all that fuel = =0D around. Diesels, in particular, are very specialized; these pumps time a = =0D VERY specific amount of fuel at a VERY specific time (relative to piston =0D position....5=BABTDC, for example) under HIGH pressure (350 PSI? maybe more= ) =0D directly into the combustion chamber. These pumps are precision parts, ver= y =0D expensive.....and they are lubricated by the fuel traveling through them. = =0D Diesel fuel is somewhat more lubricative then gasoline, and this scheme =0D works our pretty well.....until you run out of lube oil (fuel). At this =0D point, all those precision parts under high stress start scraping against = =0D each other, and well....I can't continue.

Gasoline FI is very different. In a gasoline engine (with VERY few =0D exceptions, and no production examples I know of...) the fuel pumps puts =0D about 30-50 PSI (depending of pulsed or continuous FI) on the fuel, which i= s =0D metered by injectors located int he intake manifold....lower pressures, les= s =0D precision of timing.....less stress on fuel pump, cheaper fuel pumps (I kno= w =0D FI pumps are expensive....but diesel pumps are more so. Gasoline pumps are= =0D what...$100? Diesel pumps are probably $500, rebuilt, with a $100 core =0D charge....hope yours is rebuildable, by the time you get into this arena, = =0D the rebuilders know what to look for, and track the pumps through thte =0D system, and back charge....)

Gasoline is a much poorer lubricant, so I can;t believe that the fuel in =0D gasoline FI is doing very much lubrication, the pump must be designed so =0D that it is "self" lubricated, or just doesn't need it. So I do not think = =0D that running out of gas would cause the pump to fail as a result of losing = =0D the lubricant.

Gasoline, however, being a fluid, is probably a good conductor of =0D heat.....and that is where the presence (or absence) of fuel in the pump =0D could be a problem. With all ($100) worth of precision parts whirring =0D around, they must get pretty warm, warm enough to damage the wearing =0D surfaces due to friction without the cooling influences of the fuel flowing= =0D through on a fairly regular basis.

FI systems have an interlock, tying the ignition signal to the FI pump. =0D Running out of gas means the engine stops, no ignition signal.....and the = =0D pump stops after a few seconds, not enough in my opinion to damage the pump= . =0D Of course, if you are coasting down hill, in gear, and run out of fuel, th= e =0D engine will continue to produce spark, the pump will continue to =0D run.....that is a problem. Don't do that. It would be Very Bad for your = =0D fuel pump.

Diesels, on the other hand, I would never run out of fuel for any reason. = =0D Pumps are expensive, and without some means to replace the fuel up to the = =0D pump (Some Mercedes Diesels have a little hand pump to transfer fuel up to = =0D the injection pump in such a case) It occasionally will completely drain th= e =0D battery trying to repressurize the system after running out of =0D fuel....again, not good.

Bottom line: for gasoline, don't make a habit of it. If you are running = =0D close to the edge, feel for the edge with your right foot, and as soon as i= t =0D becomes clear that ALL the fuel is gone (as much as a couple of mile after = =0D the first stumblings of fuel deprivation) push in the clutch, turn off the = =0D ignition, find neutral, and coast the rest of the way downhill into the gas= =0D station that you have been praying for (!) I don't believe any harm would = =0D result.

For Diesel, don't do it if you can possibly avoid it. ever. Harm (expensiv= e =0D harm) could result.

Bear in mind the idiot principle; surely the designer would have accounted = =0D for this condition (our of fuel) to present itself sometime during the =0D equipments lifecycle. One would like to think it can happen...once or =0D twice...and no harm would come of it. Don't, however, push your luck.

bowmanr%em@mhs.elan.af.mil Live Smart. Think for yourself. Transform the future. 90 Westie Synchro...FI, run out of gas on purpose 1 time.

bowmanr%em@mhs.elan.af.mil Live Smart. Think for yourself. Transform the future. Use Proportional Font: true Previous From: BOWMANR @ EM (Mr. Roger Bowman) Previous To: vanagon@SC-NGM1 {MHS:vanagon@lenti.med.umn.edu} Original to: vanagon@SC-NGM1 (Multiple recipients oflist){MHS:vanagon@lenti= .med.umn.edu} Attachment Count: 0

--PartBoundary Wed Sep 6 14:33:22 8214

========================================================================= Date: Sender: Vanagon Mailing List <vanagon@vanagon.com> From: Subject:

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--PartBoundary Wed Sep 6 14:33:22 8214--


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