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Curtis B.
Curtis B., Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 26026
Experience:  Technician turned service manager on multiple lines of trucks and engines, used in industry.
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We have a mercedes benz mbe 4000 460 that is losing its

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We have a mercedes benz mbe 4000 460 that is losing its prime. It will not crank without a little assistance. Freightliner has changed fuel filters and checked filter housing. Still didnt fix problem. They replaced a piece up on the top of the engine that they thought was the problem. Nope. Now they want to start with the six fuel pumps on each cylinder and each line. Still no guarantee that is the problem. Going from a $1000. bill to a $4500 bill. and this is just the next guessing step. Any thoughts that may help us.
JA: Is the fuel filter an external one, or is it inside the tank?
Customer: It has two external fuel filters, a spin on filter and a sock filter in the fuel water separator unit.
JA: What year is your 4000?
Customer: 2005
JA: Are you fixing your 4000 yourself? What have you tried so far?
Customer: No, it is at the freightliner dealer.
JA: Anything else you want the mechanic to know before I connect you?
Customer: i guess not, don't know what to ask at this point.

Welcome to JUST ANSWER heavy equipment. With years of experience, I look forward to doing my best to help.

Does the engine loose prime and it has to be reprimed before it will start. How long does it have to sit before it has to be reprimed/ Diesel engine can loose prime through the fuel suction hoses, and can have an external fuel check valve installed between the tank and the fuel transfer pump. Most engine today have fuel check valve in the system already, but a separate check valve can be installed and is a cheap fix. worth looking into.

Customer: replied 1 month ago.
The freightliner shop said they took the fuel system loose and connected it to an instore fuel system. It still wouldn't start. They installed some part on top of the engine and that didn't help. They said the next step is to check each fuel pump attached to each cylinder. Each has a o ring and gasket. But they are just playing the elimination game, because they don't know what the problem is. They are just following a mercedes repair manual.
Customer: replied 1 month ago.
My husband is on the road today and he would be the one to talk to. The truck is still sitting at the freightliner shop. We have to go pick it up. Right now the bill is about $700. If we had let them do the other part, that would have been an additional $3500. and no guarantee that was the problem. After that, they said new injectors were called for. The truck runs too good for injectors to be the problem. We changed out the filters and they changed the filters. It just acts like it loses its prime. To get it home the other day we had to use a squirt of ether. Then it cranked right up and ran like crazy. It loses its prime fairly fast. I know you aren't supposed to use ether, but we were sitting alongside the highway. I can't afford the guessing game. Do you have any other suggestions? If you give me a phone number, I can have my husband call you tomorrow.

For a quick test, use a pair of locking pliers and pinch off the fuel supply line from the fuel tank to he engine, when you shutoff the unit. Then when you are ready to start engine, remove the locking pliers, and if engine fires right up, you know the fuel check valve is not working A phone call is extra charger and i'm not sure it would be worth it for you. Run the rest and let's see where this takes us.

Customer: replied 1 month ago.
ok

This was always common problem, even going back to the mid 60's when I worked as truck mechanic. Not as common no, but is often overlooked by techs who are not looking for the easy fix, but just throwing dollars at the unit!

Customer: replied 1 month ago.
where exactly is this fuel check valve located?

On the typical engine it is part of the fuel transfer pump. But an extra one can be added, anywhere after the fuel tank outlet line and the inlet to the primer pump. The intent is to keep the fuel from bleeding back into the tank on engine shutoff.

Customer: replied 1 month ago.
We just got the truck out of the freightliner shop and will have to try your suggestion later today or tomorrow. I will let you know as soon as we get it done. Thanks.

OK> Thanks!

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