m1008 only starts when pointing down hill

[CUCVLOVER]

I have a 1986 m1008 with a completely stock drive train. I drove the truck most of the day yesterday, all around town and some longer runs. I got home and let the truck set for a few hours and it wouldn't start. It has done this once before when pointed up hill and I was a little low on fuel. But when I got the truck pointing nose down it started like a brand new one. This is one of those problems that comes and goes as it pleases.
I have already put a new pickup in the tank, the old one very nasty and the truck actually got a little more power, but it still hasn't solved my problem.

So has anyone ever had this problem? If so how did you fix it?

I wondering if the check valve in the lift pump is going out and when pointing up hill the valve doesn't hold the fuel pressure but when down hill it lets it run away.

Also I was thinking about adding an electric fuel pump between the lift pump and tank is this a good idea?

thank you all

 

[Gunzy]

I would suspect the mechanical lift pump, but you may have a pin hole in a fuel delivery line. If you have a way to put compressed air to the tank and then inspect for fuel leaks. If there are no leaks I would replace the lift pump and retest.

 

[olly hondro]

Mine did that when I had the stock fuel filter with the rectangular seal. Switching to spin-on filter made that issue go away.

 

[CUCVLOVER]

Thanks guys.
I was thinking it could be the filter.
I have a spin on with base I just haven't never felt like installing it.

How hard is changing the lift pump?

Thanks

 

[CUCVLOVER]

Well I ended up getting it going.
A new lift pump, spin on filter setup and a new tank solved all the starting issues.
Thanks guys.

 

[KansasBobcat]

Don't if same problem but H1 refused to start hot when parked pointing up grade. Tried cooling the pump but did not work as it had when parked level. Had it towed to dealer and it started ok there!

 

[Mainsail]

Mine did that when I had the stock fuel filter with the rectangular seal. Switching to spin-on filter made that issue go away.

Same here. I spent considerable time and effort keeping it nose-down. What I think is happening is that there is a very minor seep. Parked nose down fuel seeps out - parked nose up air seeps in.

 

[CUCVLOVER]

I just thought I liked the box filter until i put the spin on filter setup on. It is makes such a difference.
Thanks for all the help.