The Stovebolt Site Forums The Shop Area Engine Shop 1972 GMC 5500 not running right ... help!

My 72 gmc 5500 was running fine shut it off and now it will not run right at all I checked the oil before I drove it the last tine it was low I drove it about 5 miles the other day it was running terrible and the exhaust smelled like way to rich of gas mixture i checked the oil and it’s now over full and has a gas smell to it . I thought maybe the needle was stuck in the seat but I took the carburetor off and opened it up the needle isn’t stuck at all the bowl moves freely . The fuel pump is the only other place the gas can get into the crankcase right ? I haven’t Checked timing yet but how could timing cause gas in the oil ?

Gm 350 with gm 2g carburetor manual choke .

Does this look like correct pump

Replace the fuel pump, simple procedure and probably the most available fuel pump in the land! When you pull the old pump off, the push rod will want to fall out of the block, just before you mount the new pump, coat the push rod with sticky grease and push it back into the guide, then mount the pump.

There's a bolt hole in the front of the engine that intersects the pump pushrod hole. Put a long 3/8-16 bolt into that hole and GENTLY tighten it against the pushrod. Problem solved! There's a very short bolt installed into that hole to avoid oil leaks.
Jerry

I learned that trick in High School auto shop in 1963. Used it a week ago to help a neighbor change the fuel pump on his hot rod small block '79 Nova.

Thanks for the replies . Does the bolt need be threaded the whole length ?

Here a picture of the bolt location the bolt I used was 3/8 x 2 1/2 inches long fully threaded

Just finger tight, easy to bend the pushrod for the fuel pump.

For a lot of years I kept a piece of 3/8-16 all thread about 3 inches long in my tool box with two nuts jammed together on one end and 1/2" of threads ground off the business end. The last few threads of that hole get gummed up with sludge since the bolt plugging the hole doesn't extend that far. No telling how many fuel pumps I changed using that tool.
Jerry

I took a pair of needle nose pliers and held the rod up then carefully run the bolt in until the rod had a little resistance on it 50 years of grease and dirt I had to use a ratchet to turn the bolt in.

It definitely helps to have that bolt holding that rod up I’m pretty sure I’d have lost mind if you guys didn’t tell me that

Since the symptoms are that the carb is dumping gas into the manifold, I would chase that down first. Could be that the fuel pump pressure has jumped for some reason and forced the float level way too high. In that case it wouldn't idle well or at all. Repop 6-cyl. fuel pumps are notorious for this. I would check the FP pressure and look down the carb for flooding if you can get it to idle. I's also possible that there are two problems, high pressure and a leaking pump diaphram. Ethanol gas will attack some old rubber used in pumps.

Oil level going from low to overfull in five miles says fuel pump diaphragm to me. Engine wouldn't run with that much gas being dumped into it through the carburetor.

AND! a secondary benefit of the leaking diaphragm is a nicely flushed engine by way of Hot Rod Lincoln's solvent thrashing.

It was the lift pump . The carburetor checked out fine . The inside of the lift was full of gas swapped that pump problem solved . And yes my crankcase probably looks like It was the year 1972! Thanks for the replies I would have fought that push rod without knowing about that bolt

Did you remember to drain the contaminated oil?

Mike B

If you're running gasoline through a lift pump, that diesel engine ain't gonna' hold together very long! haha

Yes I did and there’s enough gas in it could probably dump it right back in the tank .

When it gets 40 below zero sometimes cut the diesel with a little gas to keep from gelling up . My buddy phil was always there to tell me it’s not a lift pump I said why it does the same job he never would let it go so I couldn’t either

If for some reason you let the rod fall and you can't get it slid back up. An old trick taught to me was to use a hacksaw blade against the shaft. It will catch it enough so you can slide it back up out of the cavity. You have to be ready to catch it. Usually can slide the hacksaw blade down under it before it falls again.