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Category: Heavy Equipment
Satisfied Customers: 3527
Experience:  16 Years working on Cummins Diesel engines,
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3126 cat fuel question?? starts on ether only then dies

Customer Question

3126 cat fuel question?? starts on ether only then dies
Submitted: 6 years ago.
Category: Heavy Equipment
Expert:  DR.Cummins replied 6 years ago.
have you done anything to it prior?ie fuel filters ect? are you getting fuel to pump? is there smoke while cranking engine over? after reviewing your other post i can tell that the broken transfer pump is the problem, The fuel transfer pump assists in fuel delivery to the engine from the tank. My suggestion is to replace both filters, fuel transfer pump and with the fuel supply line off blow back the fuel line to tank. But first i'd run the engine from a clean bucket of fuel right to the pump, bypass all filters and fuel lines from the tank, This ensures the enging is ok.

Edited by DR.Cummins on 1/16/2010 at 11:18 PM EST
Customer: replied 6 years ago.

Which part is the transfer pump it looks like a big component. What are the 2 wires going into it ? Is it just a bolt up.


There should be fuel coming out of the pump after the second fuel filter shouldnt there? this is while cranking?

How can you tell if the ecm has shut down the heui pump due to another issue, or if the heui pump is bad. HOw do you tell if there is a transfer pump issue or a heui pump issue?

If I change the heui pump is it just a bolt up, do you have to reset up timing etc or just unbolt etc and go for it.


Is there a way to prove the fuel pump is bad.

Expert:  DR.Cummins replied 6 years ago.


Let's start from the beginning, There are many reasons these engines won't start,

Do you have any check engine lights?

Oil and Coolant levels full

Smoke while cranking?

Filters Full? You might have to drop filters and check , I'd still replace them,

Good Cranking ?

Customer: replied 6 years ago.

Tiny bit of smoke comes out. Oil level is a bit low I actually just topped it up with some lucas oil addidtive (Thick) before it wouldnt start its still a bit below the add mark. fuel filters are full . Engine cranks fine. Engine light Ill have to check.


How can you tell if one of these other sensors have shut down the huie pump? so it wont start. There are 2 wires going to the pump is this the circuit that can disable the pump?


I was told I can change the transfer pump without doing the complete pump any input on this?

Expert:  DR.Cummins replied 6 years ago.

The ECM will set the check engine light on dash if faults occurs,This makes trouble shooting go a bit faster. Yes the wires on the pump are for the fuel shutoff solenoid, You might have to pump manually for a while.

Customer: replied 6 years ago.

When will the engine light go off to see if it is in alarm or just the light on before the engine starts?


I get 10.8 volts at the 2 wires on the heui pump when the engine is cranking, so does this eliminate the chance of any of the other sensors i.e. oil sensor, coolant sensors etc disabling the heui pump?


With that said my fuel line comes from the tank to the fuel/water seperater then to the fuel pump (I think the transfer pump section that is bolted on the heui pump) then it goes to the secondary fuel filter where the manual primer is and then to the block. If I crack the discharge side of the primer pump (the line going to the block) and pump the primer there is plenty of fuel and no bubbles coming out. If I leave this same fitting cracked and crank the engine NO fuel comes out of the fitting telling me engine isnt getting fuel because of bad fuel pump or disabled fuel pump because of ecm shutdown.

I dont think its a air issue since there is plenty of fuel when the primer is pumped.


I had started the truck then it stalled 5 seconds later, I then restarted it , it ran fine I moved it about 40 feet away , shut it off topped up the oil and it wouldnt restart, I used that thick lucas oil addititive so I thought maybe it wasnt making the oil sensor so it wouldnt let it start , but then I did have voltage at the heui wires so I figured all was ok on that end.


Im thinking about just changing out the heui pump and then puting on new fuel filters. I just want to somhow prove the pump is bad first and make sure it isnt a different alarm holding it off.

Thanks for your help so far

Expert:  DR.Cummins replied 6 years ago.

Your welcome

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Customer: replied 6 years ago.

does my last response sound right to you. With the heui pump is it just a bolt up etc...there isnt any timing etc needed is there?

Expert:  DR.Cummins replied 6 years ago.

it's easy bolt up, I'd still check ecm for codes if someone can for you.

Customer: replied 6 years ago.
can I buy a tool to retrieve the codes.. Its a frieightliner fl170 Its got the round plug in deal under the steering wheel
Expert:  DR.Cummins replied 6 years ago.
That gets pricey Than you need the Cat Program to read Cat codes. It's all about money with them.

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