95 Mack won't start

[Glensts]

Have owned this truck for over 20 years so know it inside out.  Have had trouble starting it lately, crank it for 30 seconds and it won't go, crank again and it won't go. Turn key off and pump up injector pump and it'll fire up instantly. Just seemed strange.

Have now figured it out that if it doesn't start within the first 5 seconds of cranking, turn key right to off, try again and it'll fire right up.  Next time it might fire right up too.

So its almost like the fuel isn't getting turned on.

Its a 95 Mack with the E7 350.   Only thing I'm thinking is that its the computer or may be the voltage isn't right somewhere.  So it never leaves us stranded but the first time in the morning it may not start right away until you try a couple times and turn off the key all the way each time.

Any ideas???

TIA

[HeavyGunner]

You could also have a leak somewhere allowing you to lose prime. 

[Glensts]

My first thought was we were losing prime but have come to realize that we aren't.  As soon as you turn that key off and try again it'll fire right up or try one more time guaranteed.  You could crank it for 30 seconds and it'll never fire, you could do this 4 times and it'll never fire.  Turn key off and back on and crank a second and poof its running. 

[Mack Technician]

Put a pressure gauge and sight glass on the line into pump and get the actual rolling pressure reading. See if it really is a quirk. You have electronic V-Mac pump or mechanical? 

[fjh]

Sounds like the accessory relay to me!when you turn the key on is the heater fan able to run? If not replace the relay!

Edited September 14, 2019 by fjh

[Glensts]

7 hours ago, Mack Technician said:

Put a pressure gauge and sight glass on the line into pump and get the actual rolling pressure reading. See if it really is a quirk. You have electronic V-Mac pump or mechanical? 

V-Mac

 

[Mack Technician]

Did you check Fred's suggestion?

[Glensts]

Heater fan will always run, tried that, so now I'm leaning more to that we could be losing prime.  Will try and find the stuff to try the pressure and sight glass idea.

[fjh]

Check all of the connections on the fire wall also have seen the ground fault breaker cause issues like this try by passing it if you’re lost of prime theory don’t work.