Question: Cranking - No Fuel...
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Posting Guru
Joined: Jul 2001
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From: Austin, TX USA
Question: Cranking - No Fuel...
Ok - question for y'all....
The fuel pump issues have been discussed widely - But I got a question for anyone who is more mechanical savvy than I...
Cranking without fuel is probably never a great idea - but it happens - maybe after repair or when someone runs out of fuel, etc....
Is it any harder (worse than usual) on these Bosch fuel pumps than any other vehicle? I realize that the closer tolerances and the very high pressure might make things a little more fragile in a "no fuel" situation...
This question came from a discussion that I was in (maybe beer was involved) a couple of days ago... Of course we had 4 different opinions... I would like to know the facts - if someone is more qualified then us "redneck mechanics"
Thanks in advance for any comments.....
The fuel pump issues have been discussed widely - But I got a question for anyone who is more mechanical savvy than I...
Cranking without fuel is probably never a great idea - but it happens - maybe after repair or when someone runs out of fuel, etc....
Is it any harder (worse than usual) on these Bosch fuel pumps than any other vehicle? I realize that the closer tolerances and the very high pressure might make things a little more fragile in a "no fuel" situation...
This question came from a discussion that I was in (maybe beer was involved) a couple of days ago... Of course we had 4 different opinions... I would like to know the facts - if someone is more qualified then us "redneck mechanics"
Thanks in advance for any comments.....
Fleet Owner
Joined: Mar 2012
Posts: 20,148
Likes: 15,923
From: Wisconsin
They need fuel to stay lubricated so it's a matter of how long are you cranking with no fuel before the damage is catastrophic. I believe the instant there is no fuel, damage is being done. It's just a matter of how much. That's my cheesehead opinion.
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Posting Guru
Joined: Jul 2001
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From: Austin, TX USA
Fixed fuel pump and about 3 weeks later it happened again.... Turns out is was a bad inertia switch.... but it got cranked a lot (starved for fuel) - would this kill the Bosch pump? - it didn't seem to greatly effect the v-10 pump...
Fleet Owner
Joined: Mar 2012
Posts: 20,148
Likes: 15,923
From: Wisconsin
I assumed we were talking about a 6.7 pump as that was the section it was posted. You should have clarified it was for a gasoline engine. I don't know crap about the V-10 as I didn't ever work on one or own one. My opinion is irrelevant on this matter, but would say that it certainly could have been a contributing factor in the premature failure of the pump. Once they get some time (mileage or gallons in this case) through them it doesn't take much to upset them. They are like an old carb...run perfect until you try and clean them up. Might as well buy a rebuild kit...
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Posting Guru
Joined: Jul 2001
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From: Austin, TX USA
I assumed we were talking about a 6.7 pump as that was the section it was posted. You should have clarified it was for a gasoline engine. I don't know crap about the V-10 as I didn't ever work on one or own one. My opinion is irrelevant on this matter, but would say that it certainly could have been a contributing factor in the premature failure of the pump. Once they get some time (mileage or gallons in this case) through them it doesn't take much to upset them. They are like an old carb...run perfect until you try and clean them up. Might as well buy a rebuild kit...
In other words - if I had cranked the 6.7 like I had to crank the v-10 in the past would the Bosch come to pieces ??
Sorry for confusion, again & thanks for reply....
Fleet Owner
Joined: Mar 2012
Posts: 20,148
Likes: 15,923
From: Wisconsin
Based on that, then I'd stick to my original response. Cranking without fuel briefly may not do any significant damage immediately, but it will cause damage as it is designed to be lubricated with fuel. If you remove lubrication from mechanical parts, they tend to fail quickly. The low pressure pump may fare better than the high pressure pump, but both are designed to be run with the diesel fuel to lubricate them. Cranking without fuel present is not something I would ever do intentionally.
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Posting Guru
Joined: Jul 2001
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From: Austin, TX USA
Based on that, then I'd stick to my original response. Cranking without fuel briefly may not do any significant damage immediately, but it will cause damage as it is designed to be lubricated with fuel. If you remove lubrication from mechanical parts, they tend to fail quickly. The low pressure pump may fare better than the high pressure pump, but both are designed to be run with the diesel fuel to lubricate them. Cranking without fuel present is not something I would ever do intentionally.
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Elder User
Joined: Aug 2007
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From: Saskatoon, SK, CA
Can't really compare the diesel fuel pumps with gas fuel pumps. Two completely different beasts. Gas fuel pumps can be cranked dry with minimal damage for some time. I wouldn't want to try that with a new diesel fuel pump - damage would likely start much sooner. Pressures and design are night and day between the two. Our diesel pumps create somewhere around 29,000 psi of pressure at the injection point, gas pumps are drastically lower because a spark is used for ignition, not pressure. Gas pumps can overheat and burn out if run dry long enough as most are located in the fuel tank and are cooled by the gasoline surrounding it. The diesel pumps are cooled by diesel going through it as already mentioned and if run dry damage would likely occur much sooner. With two different pumps in the diesel, the high pressure fuel pump is your biggest concern.
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Hotshot
Joined: Nov 2000
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From: Pflugerville, tx
they run when they are on, and have a pressure relief to limit 'overpumping'.
some computer systems also can ask the pump to run or not depending on the pressure sensor. My assumption is that a no pressure detection from the pressure sensor would have the computer turn off the pump after a timeout time to protect itself.
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Posting Guru
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From: Austin, TX USA
Can't really compare the diesel fuel pumps with gas fuel pumps. Two completely different beasts. Gas fuel pumps can be cranked dry with minimal damage for some time. I wouldn't want to try that with a new diesel fuel pump - damage would likely start much sooner. Pressures and design are night and day between the two. Our diesel pumps create somewhere around 29,000 psi of pressure at the injection point, gas pumps are drastically lower because a spark is used for ignition, not pressure. Gas pumps can overheat and burn out if run dry long enough as most are located in the fuel tank and are cooled by the gasoline surrounding it. The diesel pumps are cooled by diesel going through it as already mentioned and if run dry damage would likely occur much sooner. With two different pumps in the diesel, the high pressure fuel pump is your biggest concern.
Thanks for Replies...
I guess y'all got me to thinking - If the inertia switch went out on the 6.7 like it had in the 2001 truck - cranking would not be a problem as the fuel pump is not getting power and that is why it cranks - instead of starting - so the fuel pump is not spinning at all...
Man - I need a beer!
Hotshot
Joined: Nov 2000
Posts: 11,591
Likes: 14
From: Pflugerville, tx
Thanks for Replies...
I guess y'all got me to thinking - If the inertia switch went out on the 6.7 like it had in the 2001 truck - cranking would not be a problem as the fuel pump is not getting power and that is why it cranks - instead of starting - so the fuel pump is not spinning at all...
Man - I need a beer!
I guess y'all got me to thinking - If the inertia switch went out on the 6.7 like it had in the 2001 truck - cranking would not be a problem as the fuel pump is not getting power and that is why it cranks - instead of starting - so the fuel pump is not spinning at all...
Man - I need a beer!
sam
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Joined: May 2004
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From: Melbourne, Aus
The low pressure pump in the tank in both a gas engine and a diesel engine is cooled by fuel in the tank - and both will eventually overheat/fail if you crank it excessively without fuel.
The High Pressure fuel pump is driven by the camshaft on these motors, so it doesn't have a motor to overheat without fuel - but because the pistons in the pump are lubed by the fuel, it will no doubt quickly fail (and we know what happens then). I'm not sure if they have a sensor/program that will prevent the engine being cranked without fuel (they should!)
Either way, it should be common knowledge in all diesels not to crank without fuel - the fuel system needs to be bled in any diesel engine to prevent permanent damage.
The High Pressure fuel pump is driven by the camshaft on these motors, so it doesn't have a motor to overheat without fuel - but because the pistons in the pump are lubed by the fuel, it will no doubt quickly fail (and we know what happens then). I'm not sure if they have a sensor/program that will prevent the engine being cranked without fuel (they should!)
Either way, it should be common knowledge in all diesels not to crank without fuel - the fuel system needs to be bled in any diesel engine to prevent permanent damage.
Post Fiend
Joined: Mar 2013
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From: EC Iowa
Ok - question for y'all....
The fuel pump issues have been discussed widely - But I got a question for anyone who is more mechanical savvy than I...
Cranking without fuel is probably never a great idea - but it happens - maybe after repair or when someone runs out of fuel, etc....
Is it any harder (worse than usual) on these Bosch fuel pumps than any other vehicle? I realize that the closer tolerances and the very high pressure might make things a little more fragile in a "no fuel" situation...
This question came from a discussion that I was in (maybe beer was involved) a couple of days ago... Of course we had 4 different opinions... I would like to know the facts - if someone is more qualified then us "redneck mechanics"
Thanks in advance for any comments.....
The fuel pump issues have been discussed widely - But I got a question for anyone who is more mechanical savvy than I...
Cranking without fuel is probably never a great idea - but it happens - maybe after repair or when someone runs out of fuel, etc....
Is it any harder (worse than usual) on these Bosch fuel pumps than any other vehicle? I realize that the closer tolerances and the very high pressure might make things a little more fragile in a "no fuel" situation...
This question came from a discussion that I was in (maybe beer was involved) a couple of days ago... Of course we had 4 different opinions... I would like to know the facts - if someone is more qualified then us "redneck mechanics"
Thanks in advance for any comments.....
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