M813A1 fuel leak under load

[kylenobes]

Hello guys,

I am new here but have been using your forums for information for a while. I have a 72 M813A1 and I am having a fuel system problem. The truck starts and runs great. BUT as soon as I drive down the road I get a major fuel leak from the lift pump area. When I run it in the driveway and rev it up I dont get a drop of fuel but I drive a mile down the road and back and the entire drivers side of engine/fender/frame is dripping in fuel. I cannot tell where it is coming from because there is so much.

One other thing I noticed is that once it has started to leak like that the rpms will hang for a second or so after I rev it up.

Any tips on where I should look first?

 

[73m819]

rpms hang because you are sucking air, the leak is because what ever is leaking expands when hot, hence the leak, get the truck to operating temp. clean around the ip, you should see the leak, look for a crack or a loose screw.

 

[kylenobes]

Thanks for the advice. The strange thing is... even after I took it down the road I could not find the leak. When I got back home I left it running in the driveway, wiped all the fuel away from around the IP, and had someone rev the engine. I could not see anything dripping.

It just shocks me how I cant find anything in the driveway but I go on a half mile drive and its dripping fuel all over the place. Maybe a blocked up return line??

 

[kylenobes]

Is there any type of relief valve on the injector pump or lift pump? I don't understand how I am getting this much fuel in such little time, but then not getting a drip when its idling/revving in driveway.

 

[MyothersanM1]

Do you have power loss? Sucking air into the supply line will cause this and this does not sound like this is your issue.

Check your return line. I understand from a Cummins guru that RPM's will hang if there is blockage/restriction in the return line hence not allowing excess fuel to flow back to the tank fast enough leaving a residual fuel source. Maybe this excess fuel is finding a least path of resistance in the return line under load and is giving your truck it's oily bath.

 

[mbent1911]

Is it on the hood also?? Mine was leaking in front of the engine where the IP output goes in to the block.

 

[Floridianson]

I believe the 250 PT can not build up the 172lbs or maybe a little higher psi when there is a no load rpm given. You might try and do a snap the throttel test and see if she will build some good pressure. If you cleaned the PT and area real good and dusted the PT with baby powder it might show up. There is a weep hole on front of the PT that can leak but sometimes when it starts leaking there it stays leaking there I believe. I don't know if you have a plastic primer line that comes off the PT and goes to the primer pump but that might leak too I believe. Just rember strong a bull smart as tractor.

 

[kungfu dave]

Did you ever figure out where and why the fuel was leaking?

 

[R Racing]

Not sure if the 250s have it. But my 400 has a screw on the top of the pump ( its about 3/4 to 1 inch in dia) Towards the rear . underneath it is a filter screen . Maybe that screen is plugged ??

 

[Farmallmilitary]

If you say it leaks under a load maybe try revving on the engine with the trans in drive and the brakes on and then look for the leak. Be careful, you don't want to get run over.

 

[randygk]

I had a leak at the pulse damper on the back of the pump. For a year it didn't leak fuel, but truck was losing prime when sitting for a while. Then one day it started leaking fuel out at a pretty good rate. I rebuilt it and solved the prime loss problem.