The Stovebolt Site Forums The Shop Area Engine Shop Need some help with a stalling issue

Hey guys,

Need some help with a new issue. Last Friday I was off work and it was a beautiful 70 degree sunny day. So instead of tending the multiple tasks needed on the farm I decided a nice second drive of the 2021 season with my 1941 Chevy 1 1/2 ton 4x4 GI with a 1954 235 was in order. Got to keep your priorities in order, right?

So the truck performed along approximately 50 miles of seamlessly good performance over many conditions including both highway (with me screaming along at 40 mph or so) and super curvy old roads with frequent steep sections both up hill and down. On the way home I stopped to get some items at my favorite old style auto parts store. Perhaps I was at the store for about 20 minutes, and the truck starts fine considering that I was starting a pretty hot engine. The truck seems completely fine at this point. I pull out of the store and drive up the road to the town square (an approximate 6 percent incline). I sit at the traffic light waiting to take a left, and proceed when I get a gap in traffic. Right as I was crossing over the oncoming lanes, the truck starts acting like it is running out of gas (properly functioning fuel gauge shows better than 3/4 tank as I filled it up on my last drive a week prior). I push in the clutch and feather the gas to try to keep it from completely stalling. Fortunately some fancy foot work kept the engine running and it recovered and on I went, driving approximately 10 more event free miles, I start to ascend my very long and steep driveway (20 percent grade average). Here is where it got hairy. About 100 feet into the climb, the truck in second gear (1:6.77 gears in this old gal) starts to act like it is running out of gas again and this time it does stall. I put the truck in neutral apply the parking brake, and go to hit the foot starter. The truck restarts fine. I sit there contemplating what just occurred and proceed to do a first gear restart on a steep hill feathering the clutch while simultaneously releasing the parking brake (yeah, fun right?). The process goes better than expected and I proceed driving. In about 150 feet, she stalls again. Again I repeat the previously mentioned process and again it starts back up just fine. She stalled 4 times climbing that darn steep section of my driveway, but each time it started fairly easily considering it is a hot engine!!! I finally make it up the incline and the truck drives fine the rest of the time. I let the truck idle when I got home and it ran fine when not under heavy load.

The first occurrence symptom reminded me of a fuel pump that is dying, but in past experiences with crapping out mechanical fuel pumps, they don't recover at all. Yeah I know, it's never the fuel system. I am including a video of the fuel pump at idle. It looks like it is pumping okay to me, what do you all think? I also thought of a poorly venting gas cap, but unfortunately I thought of it too late (the next day) so I squandered my investigation opportunity. When checking the fuel cap about 18 hours after driving, there was no vacuum pressure in the tank. I have had history with venting fuel caps not venting properly on this truck but felt the current one (that has been on the tank for a few years) has been working okay.

So what in the devil happened? What should I check first? The fuel pump was NOS but rebuilt with modern materials about 4000 miles/6 years go. The truck has an original AC T-2 type fuel filter that has been converted to a large paper filter (GM854425 used on old saddle tanked GM trucks). I annually bleed off water from the fuel bowl but have not replaced the filter since putting the truck together 6 years ago. Tank was professionally cleaned and lined at time of build. My thoughts are to replace the fuel filter, and conduct a volume flow check on the output side of the fuel pump. I don't have access to a pressure gauge.

Sorry for the verbose question, but hopefully; all of the "who, where, what and when's" should be addressed. I appreciate your insights.

Edit, evidently stovebolt doesn't support .MOV video files, will send as a youtube link in a bit.

First of all, buy a pressure/vacuum gauge. They're about 10 bucks or so on Ebay with free delivery most of the time! It's impossible to test a fuel pump properly without one. The inlet and outlet check valves are the most common failure items on any mechanical fuel pump and a pressure/vacuum gauge is the only way to check their function.

I think you're on the right track, suspecting a fuel flow problem. I'd suggest adding another filter hidden under the cab out of sight of people who have nothing better to do than point out "That's not stock!"- - - - -like one of the 3" diameter metal canister filters Ford used for years on their fuel injected vehicles. Those things can trap a huge amount of debris and still keep flowing enough gas to keep the engine running.
Jerry

Hey Jerry,

Thanks for the confirmation on my diagnosis path. Yeah I really need to get a pressure gauge. I didn't realize that they could be bought for so cheap. Will a pressure test on a fuel pump not under load be the same as one under load? Some research on this is in my future. Currently the glass fuel bowl is completely full when not running. New filter and fuel bowl gaskets are on the way. Yeah I have hidden modern fuel filters on other vehicles in the past and I agree with you. I did such a pretty job at bending good replication hard fuel lines on this truck that I am very apprehensive to muck it up.

Movie of pump at idle the day of the problem:
https://studio.youtube.com/video/X6Wkn2Q0jIo/edit

Paul

I do a 3-part test on fuel pumps. Idle the engine for 30 seconds with the fuel line at the carburetor routed to a catch container. If the engine won't idle that long on the fuel in the float bowl, you've got other problems to fix. You should get at least a pint of gas in the catch can. Then deadhead the fuel line into the pressure gauge and idle the engine for a few seconds. You should see 2-4 PSI on the pressure side of the gauge and the pressure should remain for several seconds after shutdown. This tests the pump output check valve. Connect the gauge to the inlet side of the pump and idle for a short time. You should see 10" of vacuum or more and it should stay there for a while after shutdown. That's the inlet check valve test. If the pump passes all these tests and it isn't leaking gas anywhere it's good. Start looking for a restriction upstream of the pump somewhere. I once had a flathead Ford engine that would run about a mile, quit, and wouldn't restart for several minutes. After a huge amount of diagnosis, I found a big grasshopper lodged in the pickup tube in the gas tank!
Jerry

Inflation has hit the gauge market!

https://www.harborfreight.com/fuel-pump-and-vacuum-tester-62637.html?cid=paid_google|||62637&utm_source=bing&utm_medium=cpc&utm_campaign=&utm_content=&msclkid=2f59a26712f61a4da9a1c207a257d315

Still, not likely to break the bank, and they last forever. I'm still using a similar tool I bought in the 1970's!
Jerry

Maybe these are a few helpful Vacuum Gauge posts:

Using a Vacuum Gauge (Fuel Pump and Vacuum Tester)

How to use a Fuel Pump Pressure Tester (Fuel Pump and Vacuum Tester)

Fuel & Vacuum Pump Tester

I had an issue just like that on my 49. Turned out to be part of the rubber filler neck hose floating around in the bottom of the tank.

Gentlemen,

Thanks for the input so far. Currently sourcing the needed parts and tools. The problem that concerns me is the intermittent nature of the problem. How could the truck run without issue for 10 miles between events with the 10 miles having similar loads on the the engine. I suppose the fuel pump tests may reveal some weaknesses, and once I take the fuel filter assembly apart, if I am lucky there will be a smoking gun.

I guess a borescope is the next tool required so I can look for arrant rubber and or grasshoppers in the fuel tank!

When there is trash floating or not floating around in the gas tank it can take a few minutes for it to work it’s way to the pickup tube. Then the engine begins to starve for fuel and eventually dies. Once the fuel pump quits pumping the suction releases and the crud, whatever it is, floats/moves away from the pickup tube and the pump will be able to pull fuel through the line again. The engine will then start and run normally until the process repeats itself.

It could also be a piece of the lining failing in the tank getting sucked into the outlet of the gas tank.

Hey all,

This is a follow-up on my original post. A fuel pump tester was sourced and have some data:
1)Fuel volume-at idle the pump produced 24 oz. in 31.25 seconds
2)Fuel pressure-5 PSI at idle, and it kept the 5 PSI after shut down until I grew tired of watching the gauge (approximately 5 minutes)
3)Vacuum- 9 inches of Hg at idle without moving, with engine stopped, pressure dropped 1 inch of Hg per 70 seconds.

The last reading was the only one that caused concern as it was 1 inch Hg lower than the 10 inch Hg threshold for a decent functioning pump. But given my testing elevation of 3300 feet, that number should be corrected to approximately 12 inches of Hg (Add 1 inch HG per every 1000 feet). So it seems the fuel pump passed all of the diagnostic tests. Glad you all got me to learn how to test versus guess!

I also changed out the rather large paper element fuel filter and it looked every bit as fresh as the new one so I don't feel that had much to do with the stalling issue. The T-2 filter bowl also looked surprisingly clean given that it hasn't been removed and cleaned in over 4000 miles.

After all of these tests and replacements, I went for a 20 mile run and the truck ran fine.

Not sure what the issue was with the stalling as I didn't find any "smoking gun".

Paul