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Discussion Starter · #1 ·
I wasn't sure where to post this, but this is the closest place i could find. I have a freightliner box truck with a caterpillar motor that is driving me nuts here. It has about 320,000 miles or so on it and it doesn't want to start sometimes. It cranks over good but just wont fire up. I took it to the freightliner dealership before the holidays and they had it three days and it was ok for about a week and now is worse than ever. They put a new fuel line on it thinking it was deteriated and drawing air in somehow. They claimed the shut off solenoid was working ok and that that wasn't it. If i put a strong mixture of a diesel additive in it like fuel injection cleaner then it seems to help, but to me that doesn't make any sense. It doesn't help 100% ,but it probably helps 80% or better. Everybody tells me it is probably one of two things. The shut off solenoid or it is drawing in air somehow. I can take the primer pump and pump it really hard a few times and it will start, but there is pressure on the pump. Not like it is pumping up or anything. Anybody got any ideas? I can't afford to let those clowns at freightliner have it again.
 

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Discussion Starter · #3 ·
Originally posted by Argee
I'm going to state the obvious....FUEL PUMP????

Have you done a compression test???
Thanks for the reply Argee. Once it starts it has never died on me and runs good. If it was the fuel pump wouldn't it not run either? They had the thing three days at freightliner so i would think they would have checked all that.
 

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I don't know to much about diesels but seeing how cold y'all are over there i take it you put a fuel additive in it to keep the fuel from jelling.
 

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Discussion Starter · #5 ·
Originally posted by jodyand
I don't know to much about diesels but seeing how cold y'all are over there i take it you put a fuel additive in it to keep the fuel from jelling.
Actually i use a seperate additive for that Jody. Between the antigel additive and the fuel injector additive plus the almost $2.00 a gallon fuel, fillups are real expensive. :dazed:
 

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Discussion Starter · #7 ·
Originally posted by Chief
What do your fuel filters look like when this happens?
I had just replaced the fuel filters Chief and it made no difference. Is that what you are asking ?
 

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Discussion Starter · #9 ·
Originally posted by Chief
That should eliminate iced up or contaminated fuel filters. Is the CAT in your truck a 3126B?
That sounds right Chief, but not 100% without looking at it. I'll be trying to get it started again tomorrow so i'll see what it says on it.

Dur
 

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Nearly all CAT engines us HEUI type injectors to fire the engine. These injectors are usually pressurized by a high pressure oil pump separate from the engine oil pump. If the high pressure oil pump is weak or not functioning properly, I would think this may effect initial start up.
 

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Discussion Starter · #11 ·
Originally posted by Chief
Nearly all CAT engines us HEUI type injectors to fire the engine. These injectors are usually pressurized by a high pressure oil pump separate from the engine oil pump. If the high pressure oil pump is weak or not functioning properly, I would think this may effect initial start up.
Thanks Chief, that gives me something else to look into. I wonder if by using the fuel injection cleaner, it might be why it is starting if that is the case.

Dur
 

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Durwood
It sounds to me like your getting air in the system, so after it sets for a couple of hours you are getting an air lock in the pressure side of the pump so you won't build enough pressure to make the injector work (when you hand pump it you disspell the air and it starts) You say you have new filters, could be a lose filter or a bad gasket if they're spin ons check the filter heads for small cracks or the gasket and cover if it's a canister type. Another thing I've had a problem with is some systems run a check valve on the suction line that can go bad

Archie
 

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Discussion Starter · #13 ·
Originally posted by archyb2
Durwood
It sounds to me like your getting air in the system, so after it sets for a couple of hours you are getting an air lock in the pressure side of the pump so you won't build enough pressure to make the injector work (when you hand pump it you disspell the air and it starts) You say you have new filters, could be a lose filter or a bad gasket if they're spin ons check the filter heads for small cracks or the gasket and cover if it's a canister type. Another thing I've had a problem with is some systems run a check valve on the suction line that can go bad

Archie
Thanks Archy, i know it is probably something simple. Yet freightliner had it 3 days and didn't get it right. I probably should have taken it to a Cat dealer instead. It has cost me too much money already.
 

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Bob, it sounds like Archy is onto something. I am no expert on CAT's but if you recently had the filters changed, this could be an area to look at closely as already mentioned. I am not exactly sure how the fuel supply system on your truck is configured but could it be that there is a pocket of air somewhere between the filters and the pump that could be defeating any anti-leak down check valves? In the event this might be the case, purging the fuel lines may resolve this issue.
 

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Discussion Starter · #15 ·
Originally posted by Chief
Bob, it sounds like Archy is onto something. I am no expert on CAT's but if you recently had the filters changed, this could be an area to look at closely as already mentioned. I am not exactly sure how the fuel supply system on your truck is configured but could it be that there is a pocket of air somewhere between the filters and the pump that could be defeating any anti-leak down check valves? In the event this might be the case, purging the fuel lines may resolve this issue.
I guess i wasn't clear before Chief. It had the same problem before the fillters were changed and was still there after the filters were changed. Also, when they put the new fuel line on it they would have purged the system. The check valve on the suction line that Archy was talking about could be a possibility. It just seems funny that after it starts it runs fine and has never died on me.
 

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Bob
What your discribing is classic of a small leak /crack, it does not cause any problems when running, only at startup after a period of down time. It most certainly is between the tank and the point of suction in the pump and since this problem developed on it's own would suggest a crack or loose fitting from vibration. Since you have a new suction line that only leaves the filter heads/ fittings and the connection to the pump. You will have to pressure or vaccum test them One other thing to check is that hand pump they can start to leak, or is it closed properly.

Good Luck
Archie
 

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Discussion Starter · #17 ·
I finally got it started today. I pumped the dog crap out of the primer pump and it finally started. Here is something else that doesn't make any sense on the air part of it. I can run it then shut it off and sometimes it won't start even a minute after i shut it off and then sometimes it can be shut off for several days and start.
The engine is a 3126 Chief , but there is no B behind it.

Durwood
 

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it could be that there is a bad spot in the injection pump causing a leakdown and it only leaks down if the engine happens to stop in that spot. its a long shot
 
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