Old 753 won't start

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eriksat1

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Jul 10, 2014
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We have a old Bob Cat 753 at work it has been sitting for about 3 years not running because of a bad starter. We finally got a new starter put on charged up batterys and it started right up. I ran it about 15 mins. it seemed to be ok maybe smoking a bit much (blue smoke rich diesel smoke) They tried running it down the road a bit to a job site but the operator said it started losing power sputtering then died out and won't start again. I changed fuel filter, air filter is new, primed up fuel line and filter. I even cracked the injector lines to make sure they were bled. Still won't start, not even with ether. For the short time it ran it seemed ok. I don't have a compression tester for a diesel, is there anything else I might try? When I cracked the injector lines and crank it over it was spraying fuel out of all 4 lines.
 

antfarmer2

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Oct 28, 2013
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Do not use either!!!!!..... you can use wd40 I would look for a bad connection chewed wire or crudded up fuse or relay on the running circuit
 

Tazza

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Make sure you have fuel and not water
As you said it primed ok, it sounds like the fuel lines are good.
Sitting for so long, i'd suspect a stuck injector. I'd pull the injectors and ensure tehy are free to move or get a shop to do it for you. On injectors that have been sitting for a while, i find that the nozzles stick, so they will not open or if they do, they stick open.
If you ae handy, dismantle them one at a time and ensure the nozzle and top are free to move in and out, lube with WD40 or diesel and re-install.
 
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eriksat1

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As you said it primed ok, it sounds like the fuel lines are good.
Sitting for so long, i'd suspect a stuck injector. I'd pull the injectors and ensure tehy are free to move or get a shop to do it for you. On injectors that have been sitting for a while, i find that the nozzles stick, so they will not open or if they do, they stick open.
If you ae handy, dismantle them one at a time and ensure the nozzle and top are free to move in and out, lube with WD40 or diesel and re-install.
It just seems to me that if I can't even get it to run for a few seconds on ether the fuel is not the problem? This is a old basic diesel engine the only thing electrical on it as far as the engine running or not is the shut off solenoid on the injection pump, and that is working ok. I agree on pulling the injector's the nozzles might be stuck, but I am starting to think maybe the piston rings are stuck also, before wasting money on injectors I am going to try and check compression and then maybe try and soak the piston rings with the injectors out. What would be a good solution to try and free up the rings? Maybe seafoam, or ATF?
 
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eriksat1

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It just seems to me that if I can't even get it to run for a few seconds on ether the fuel is not the problem? This is a old basic diesel engine the only thing electrical on it as far as the engine running or not is the shut off solenoid on the injection pump, and that is working ok. I agree on pulling the injector's the nozzles might be stuck, but I am starting to think maybe the piston rings are stuck also, before wasting money on injectors I am going to try and check compression and then maybe try and soak the piston rings with the injectors out. What would be a good solution to try and free up the rings? Maybe seafoam, or ATF?
I know for a fact low compression will cause very hard starting and rich blue diesel smoke like it was. Air, fuel, and compression, it should run. It is missing one of the 3. Unless something mechanical broke as far as injection pump or timing. I'll keep you posted. The machine has about 3,000 hours on it. Btw I am a mechanic by trade just not real familiar with bob cats.
 

SkidRoe

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I know for a fact low compression will cause very hard starting and rich blue diesel smoke like it was. Air, fuel, and compression, it should run. It is missing one of the 3. Unless something mechanical broke as far as injection pump or timing. I'll keep you posted. The machine has about 3,000 hours on it. Btw I am a mechanic by trade just not real familiar with bob cats.
That was my thought exactly - could the injection timing be off? I don't know how that could of happened, unless the drive gear has come loose and slipped a bit on the injection pump.
Weird one. Do you have a manual for your machine? There should be a method listed for checking the injection timing in the engine section.
Keep us posted - SR
 

antfarmer2

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That was my thought exactly - could the injection timing be off? I don't know how that could of happened, unless the drive gear has come loose and slipped a bit on the injection pump.
Weird one. Do you have a manual for your machine? There should be a method listed for checking the injection timing in the engine section.
Keep us posted - SR
I have had good luck with marvel mystrey oil
 

Tazza

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I have had good luck with marvel mystrey oil
On a Kubota, for it to slip a tooth on the timing, something major is wrong, it's all done with gears. The injector pump is timed with a cam shaft that goes to these gears.
Do you get any smoke as it's cranking?
I found that spraying in WD40 and winding it over should get it to jump too. I was cleaning an engine one day on a bench, it had carbon on the inlet manifold. I took the manifold off and sprayed WD40 in the inlet ports and brushed with a tooth brush, i wound it over to blow the crud out. guess what tried to jump off the bench?......... No fuel was hooked up, it had not been started in years, the WD sure woke it up from it's slumber.
Checking the compression isn't a bad idea, but as it started and ran, i really can't see why it would suddenly drop compression on all 4 pots.
 

biggie

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Jul 28, 2011
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There's a screen in the fuel pick-up line. Try a separate fuel source, to the lift pump. STOP with the ETHER!!!!
 

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