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Rudolph Diesel, ASE ,Master Heavy Truck Technichian
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97 mack truck hard start first thing..starts fine..primary lift pump

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97 mack truck hard start first thing in the morning!
Once started,it starts fine the rest of day.
Haven't looked at it yet.
Does it have a priXXXXX XXXXXft pump?


Welcome to JA!

Witch engine do you have in the MACK

When it does start the first time what color is the smoke?

are you using any coolant or oil

How may miles on the engine



Customer: replied 6 years ago.

I haven't looked at the truck yet,so I don't know which engine it has.

I only had verbal communication with the owner.

He told me that it will start right away with either,

that's why I was wondering if it had a electric or mechanical lift pump.

I'm probably will take the filter off to see if it's full or bleeding back somehow.

I will look at it sometime next week.



Yes that would be something to check before you start it is if it is bleeding back into the tank

Also if this is duel tanks then check the splitter return valve if this fails this will cause the fuel to drew back


And also look by the smoke when it does start if were sending raw fuel out the exhaust then we have injectors leaking.


Fuel pressure too im sure it has a mechanical pump if there has been any contaminated fuel problems in the past i bet there is some bad o rings in the pump.


Let me know if i can help more!


Customer: replied 6 years ago.

I think I need to check the electrical system out some more.

The truck would not start yesterday afternoon until I put the accel. to the floor.

then it started right up but would not shut off with key.

It's been cobbled up a bit.

There has been a new fuel regulator put on by someone else,

and they said that would cure the hard start but didn't.

It looks like it has a fuel shutoff solenoid on it but I don't think it works right.

I believe this is what is causing the problem.

Couldn't drive it because it has chucked both belts off and

they wonder why it overheats!

It hasa 2 fuel filters on it and a mechanical lift pump,only 1 fuel tank


yes i would start at the ignition feed and go out,

I would also when you go to first start it and it does not start see if there is power to the fuel shut off solenoid. ans dbl check there is power from the ignition switch, I have see where there is no power to the solenoid but when you either the engine it tricks it in running.

It does sound electrical on this Let me know what your seeing from the ignition switch this might be the problem,


Customer: replied 6 years ago.

I did some checking this afternoon.

The fuel shutoff solenoid is air actuated,

so without anyair the solenoid stays in the run position.

I did check another thing,it seems someone put on 2 springs

on the fuel pump lever instead of 1,which I think is pulling the lever closed.

But you crank it over and then hit the throttle it starts right up!

I also found the ball and socket on the pump linkage is very sloppy

which keeps the lever closed because of return spring pressure.

I'm going to havew the owner get the right spring and a new socket.

I think this will cure the problem!

I want to thank you for your input on this!


Good for you

This must have the E7 engine,

Yes the pump lever should have 1 spring.

I have run into where the tuck wont hold air over night so it will keep the fuel shut off closed to when first started.

Let me know if i can help more!


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