Strange problem on 753

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scsindust

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I have a '93 753, and I keep having a reaccuring fuel problem. If the gauge goes to 3 bars, the machine sputters, and only runs when you pump the primer bulb. But it will only run for 5 minutes max. Today, it showed 5 bars, and it ran fine, until it hit 3 bars. Is there something in the tank that could have broken off, and not letting it get those last few gallons? Or do you guys think it is a weak fuel pump?
 

Tazza

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So this is ONLY when the fuel level hits 3 bars? or does it stay there even after you fill the tank?
The fuel level sender may have a problem, they use a vairable resister attached to a float that sits in the tank to get the level.
 

sterlclan

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So this is ONLY when the fuel level hits 3 bars? or does it stay there even after you fill the tank?
The fuel level sender may have a problem, they use a vairable resister attached to a float that sits in the tank to get the level.
sounds like a bad sender to me may be telling you there is fuel when there is none how many gallons do you put in from 3 bars to fill and how many does it hold?
 

StuZ

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sounds like a bad sender to me may be telling you there is fuel when there is none how many gallons do you put in from 3 bars to fill and how many does it hold?
Sounds like a suction hose to me. There is an 8 - 9" long suction hose with a screen inside your tank that might be falling off. Check your gauge, and hoses and primer, maybe even run it with a jerry can for awhile to make sure it not something else .
 

scsindust

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Sounds like a suction hose to me. There is an 8 - 9" long suction hose with a screen inside your tank that might be falling off. Check your gauge, and hoses and primer, maybe even run it with a jerry can for awhile to make sure it not something else .
I think the sender is right. It had one bar, and I put 7 gallons in it, and it went up to 5 bars. I used it for 2 hours, and it dropped down to 3 bars over that time. My thoughts were the suction hose, but I didn't know if this was a common problem like in older ford diesel trucks... the suction hose breaks off and doesn't suck anything below 1/4 tank. Anyway, if the fuel in the bobcat runs low, your can use the primer bulb to suck up more fuel, and it will run for a few minutes, then sputter and shut off. I was also contemplating a fuel pump problem too. But, if the suction hose is made of hard plastic, it could have cracked or split, which would make sense too. The machine has 4400 hours on it, so it could be anything, and I don't have the service records from the previous owner (I bought it with 4000 hours). Any thoughts?
 

StuZ

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I think the sender is right. It had one bar, and I put 7 gallons in it, and it went up to 5 bars. I used it for 2 hours, and it dropped down to 3 bars over that time. My thoughts were the suction hose, but I didn't know if this was a common problem like in older ford diesel trucks... the suction hose breaks off and doesn't suck anything below 1/4 tank. Anyway, if the fuel in the bobcat runs low, your can use the primer bulb to suck up more fuel, and it will run for a few minutes, then sputter and shut off. I was also contemplating a fuel pump problem too. But, if the suction hose is made of hard plastic, it could have cracked or split, which would make sense too. The machine has 4400 hours on it, so it could be anything, and I don't have the service records from the previous owner (I bought it with 4000 hours). Any thoughts?
I assume you have a BOSS monitor system ?? The 753 has a 14.0 gal tank, and uses on a medium load 1.5 gals. an hour to 1.9 gph. on a high, but not yet full load. By this, you should have used 3 gal. or more. Either way, I have never trusted any fuel gauge that much. When it dies, is the bulb collapsed or is it hard ?? The suction tube IS a problem in a 12 year old loader.
 

scsindust

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I assume you have a BOSS monitor system ?? The 753 has a 14.0 gal tank, and uses on a medium load 1.5 gals. an hour to 1.9 gph. on a high, but not yet full load. By this, you should have used 3 gal. or more. Either way, I have never trusted any fuel gauge that much. When it dies, is the bulb collapsed or is it hard ?? The suction tube IS a problem in a 12 year old loader.
That is what I assumed it was. I do have the BOSS system. The bulb is rather soft when it dies to answer your question. The bobcat is at my parents house right now, and I am supposed to be grading their back. I am planning on going down there on Tuesday to look into it more. Is the tank hard to get to? The manuals I bought don't give me many good illistrations to go off of. I am hoping I can get to it by lifting up the cab...
 

Tazza

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That is what I assumed it was. I do have the BOSS system. The bulb is rather soft when it dies to answer your question. The bobcat is at my parents house right now, and I am supposed to be grading their back. I am planning on going down there on Tuesday to look into it more. Is the tank hard to get to? The manuals I bought don't give me many good illistrations to go off of. I am hoping I can get to it by lifting up the cab...

I believe it is accessible by just lifting the cab. It may pay to remove the pickup and replace the hose that runs down inside the tank, it may have a crack in it causing it to suck air and still have fuel in the bottom. But this wouldn't explain why you can pump the primer bulb and get the machine running for about 5 mins, as it shouldn't be able to pick up any fuel if the hose was cracked........
Another way you could test for this, is to disconnect the fuel hose from the inlet to the lift pump, hold your finger on the end of the hose to stop the fuel just running out, and squeeze the bulb and see if you get any bubbles when you release your finger (do this for a while just to be sure), run the diesel out into a bucket so you can re-use it. If you have bubbles this will tell you that you have an air leak, and if your fuel is running without bubbles it could be your lift pump.
Good luck!
 

scsindust

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I believe it is accessible by just lifting the cab. It may pay to remove the pickup and replace the hose that runs down inside the tank, it may have a crack in it causing it to suck air and still have fuel in the bottom. But this wouldn't explain why you can pump the primer bulb and get the machine running for about 5 mins, as it shouldn't be able to pick up any fuel if the hose was cracked........
Another way you could test for this, is to disconnect the fuel hose from the inlet to the lift pump, hold your finger on the end of the hose to stop the fuel just running out, and squeeze the bulb and see if you get any bubbles when you release your finger (do this for a while just to be sure), run the diesel out into a bucket so you can re-use it. If you have bubbles this will tell you that you have an air leak, and if your fuel is running without bubbles it could be your lift pump.
Good luck!
Thanks! I was looking at it today, and the suction hose is solid, but missing the screen. Not a major problem, but something to fix. Anyway, I'll have to do what you said. I have a gut feeling it is a lift pump, but we'll see. I am really hoping it isn't the injector pump... it wouldn't make sense, but you never know... how long do injector pumps last in a Bobcat?
 

Tazza

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Thanks! I was looking at it today, and the suction hose is solid, but missing the screen. Not a major problem, but something to fix. Anyway, I'll have to do what you said. I have a gut feeling it is a lift pump, but we'll see. I am really hoping it isn't the injector pump... it wouldn't make sense, but you never know... how long do injector pumps last in a Bobcat?

I wouldn't worry too much about the missing screen on the suction pipe, as you will have a filter a little further down the line. Don't get me wrong, the more filtration you have the better but the pickup one isn't essential, but i would replace the hose if it has gone hard.
Injector pumps, this really depends on so very many variables. The major causes of injector pump failure would be water, crappy fuel and dirt/impurities in the fuel. If you use a bad fuel it doesn't have the lubrication that good fuel has, this is why you can't use kerosene as it is abrasive.
Really, a well maintained engine/pump should last well into ten thousand hours, but this depends on many factors.
With the problems you describe i would seriously doubt injector pump problems, if it doesn't blow smoke or hard to start i honestly would forget about pump problems. I would suspect an air leak or lift pump.
Let me know how you go
 

scsindust

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I wouldn't worry too much about the missing screen on the suction pipe, as you will have a filter a little further down the line. Don't get me wrong, the more filtration you have the better but the pickup one isn't essential, but i would replace the hose if it has gone hard.
Injector pumps, this really depends on so very many variables. The major causes of injector pump failure would be water, crappy fuel and dirt/impurities in the fuel. If you use a bad fuel it doesn't have the lubrication that good fuel has, this is why you can't use kerosene as it is abrasive.
Really, a well maintained engine/pump should last well into ten thousand hours, but this depends on many factors.
With the problems you describe i would seriously doubt injector pump problems, if it doesn't blow smoke or hard to start i honestly would forget about pump problems. I would suspect an air leak or lift pump.
Let me know how you go
THANKS!! I am assuming the suction hose is supposed to be soft??? If that is the case, someone took a hard plastic tube, cut it to length, and forced it on the fitting... Yea, the PO was an idiot. I'll let you know in the next few days. Thanks again for some direction.
 

Tazza

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THANKS!! I am assuming the suction hose is supposed to be soft??? If that is the case, someone took a hard plastic tube, cut it to length, and forced it on the fitting... Yea, the PO was an idiot. I'll let you know in the next few days. Thanks again for some direction.
I am not sure if it should be soft or not..... I attacked a 743 yesterday that i got a while back at auction to clean the fuel tank, its suction hose was soft rubber but this may be just for this loader. One thing you may check is the length, see if it looks like it will suck fuel up off the bottom of the tank, you never know the PO as you call him may have cut it too short?
*shrug* worth a thought.
 

scsindust

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I am not sure if it should be soft or not..... I attacked a 743 yesterday that i got a while back at auction to clean the fuel tank, its suction hose was soft rubber but this may be just for this loader. One thing you may check is the length, see if it looks like it will suck fuel up off the bottom of the tank, you never know the PO as you call him may have cut it too short?
*shrug* worth a thought.
Problem fixed!! I replaced teh suction hose and screen and fuel pump. The pump was shot. It had no suction power at all. I runs great now! Another question for you: I have to replace one of the hoses that operates the bucket, the last rubber hose before the tilt cylinder. How do you bleed these?
 

StuZ

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Problem fixed!! I replaced teh suction hose and screen and fuel pump. The pump was shot. It had no suction power at all. I runs great now! Another question for you: I have to replace one of the hoses that operates the bucket, the last rubber hose before the tilt cylinder. How do you bleed these?
Replace hose, refill system, run loader at idle while holding pedal for a few seconds after full stoke in each direction. Do this maybe 6 times.
 

Tazza

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Replace hose, refill system, run loader at idle while holding pedal for a few seconds after full stoke in each direction. Do this maybe 6 times.
Just as StuZ said, you just need to top up your hydraulic tank and operate it. It will self bleed, it may seem spongy for a little while, but after a few minutes it will be as good as new.
 
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had the same problem on my 763 i pulled the hose on the tank and pulled up the filter to check found the the supply hose had broke off about a few inches from the top so when i filled it it would run for a while then die ,i replace the hose 9 1/2 inches is what the service manual said to cut it at its been woking great since. hope i can help
 
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