40mopar Posted November 16, 2020 Share Posted November 16, 2020 My '46 Merc died on me. mechanical fuel pump had a grass bowl and I could see there was no fuel. Checked the fuel line and there was no obstruction. Gas tank is about 1/2 full. I replaced the pump with a 6v Airtech pump wired directly to the ignition. When I turn on the ignition without the engine running, I get about 5 PSI of pressure. As soon as I start the engine, the pressure slowly drops to zero. The engine continues to run for about a minute, then dies. Checked the carb. It's clean and float seems to be ok. Would sure appreciate some help.😔 Link to comment Share on other sites More sharing options...
TerryB Posted November 16, 2020 Share Posted November 16, 2020 Check to see if you really have gas in the tank, fuel gauge can go bad. Sounds like fuel line or tank pickup might be blocked. Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted November 16, 2020 Share Posted November 16, 2020 Where is the pump mounted. works best if mounted close to the tank. Ben 1 Link to comment Share on other sites More sharing options...
Marty Roth Posted November 16, 2020 Share Posted November 16, 2020 As Ben noted, mount electric pump as close to the tank, but also as low as possible. Electric pumps are a good "Pusher", BUT NOT SO MUCH AS PULLING. Rather than bypass your mechanical pump, leave it as the primary, and wire the electric pump on a switch to use is as an addition when needed, such as priming the system after sitting for some time, and for when vapor lock affects your flathead which is prone to this condition. Also, the Airtex you used is a cheaper type pulse pump, and in my years of experience is prone to failure, even in the short term. You should strongly consider the rotary-vane type pump such as the Carter, available for a few bucks more through Amazon. This is a Free-flow design, and your mechanical puimp will pull fuel through it just fine. switch on the electric when your fuel system needs a temporary boost. The rotary vane type pump is far better than the cheaper pulse (bullet) type, and will last many years longer. My choice is the Carter P4259 - $78.11 & FREE Shipping at Amazon.com I use this model on my 1930 Packard, 1937 Buick Roadmaster, and 1941 Cadillac https://www.amazon.com/Carter-P4259-Line-Electric-Fuel/dp/B000CIS4IU/ref=sr_1_4?dchild=1&gclid=Cj0KCQiAwMP9BRCzARIsAPWTJ_EVycjP6Y_TX2aDAx_qM6aEgNOYBimwB3t4kdE0jYQzVTnHNCcqun8aAkX4EALw_wcB&hvadid=177570362789&hvdev=c&hvlocphy=9025155&hvnetw=g&hvqmt=e&hvrand=7371372844440783517&hvtargid=kwd-3628355007&hydadcr=5739_9590425&keywords=6+volt+electric+fuel+pump&qid=1605486563&sr=8-4&tag=googhydr-20 Link to comment Share on other sites More sharing options...
dalef62 Posted November 16, 2020 Share Posted November 16, 2020 Sounds like there is an obstruction in the tank or line(maybe even a rubber hose is collapsing) somewhere. When you checked for on obstruction did you blow back through the line? If so you could have just pushed the obstruction out of the way. Link to comment Share on other sites More sharing options...
JACK M Posted November 16, 2020 Share Posted November 16, 2020 Filters doing their job? Link to comment Share on other sites More sharing options...
Graham Man Posted November 16, 2020 Share Posted November 16, 2020 I had a similar problem, it was garbage in the tank plugging the pickup. You can put a light amount of air pressure by the mechanical fuel pump and blow the gas back into the tank, you should hear bubbles in the tank. If you have a glass bowl, I have had the cork seal dry out but that would not explain the electric fuel pump problem. I do not like electric fuel pumps, unless you also include an impact detector, they automatically turn off the pump in an accident, the race car guys use them all the time, most tracks require them. I would guess they are required for vintage racing also? Link to comment Share on other sites More sharing options...
40mopar Posted November 16, 2020 Author Share Posted November 16, 2020 6 hours ago, TerryB said: Check to see if you really have gas in the tank, fuel gauge can go bad. Sounds like fuel line or tank pickup might be blocked. I don't use the fuel gauge. I added fuel to the tank as soon s the problem came up. I blew back the line with a compressor and also used a vacuum pull to pull fuel forward. Both showed no obstruction. 1 Link to comment Share on other sites More sharing options...
40mopar Posted November 16, 2020 Author Share Posted November 16, 2020 6 hours ago, Ben Bruce aka First Born said: Where is the pump mounted. works best if mounted close to the tank. Ben Pump is mounted on the rear frame about 3 feet forward of the tank and lower than the tank. 2 Link to comment Share on other sites More sharing options...
40mopar Posted November 16, 2020 Author Share Posted November 16, 2020 5 hours ago, Marty Roth said: As Ben noted, mount electric pump as close to the tank, but also as low as possible. Electric pumps are a good "Pusher", BUT NOT SO MUCH AS PULLING. Rather than bypass your mechanical pump, leave it as the primary, and wire the electric pump on a switch to use is as an addition when needed, such as priming the system after sitting for some time, and for when vapor lock affects your flathead which is prone to this condition. Also, the Airtex you used is a cheaper type pulse pump, and in my years of experience is prone to failure, even in the short term. You should strongly consider the rotary-vane type pump such as the Carter, available for a few bucks more through Amazon. This is a Free-flow design, and your mechanical puimp will pull fuel through it just fine. switch on the electric when your fuel system needs a temporary boost. The rotary vane type pump is far better than the cheaper pulse (bullet) type, and will last many years longer. My choice is the Carter P4259 - $78.11 & FREE Shipping at Amazon.com I use this model on my 1930 Packard, 1937 Buick Roadmaster, and 1941 Cadillac https://www.amazon.com/Carter-P4259-Line-Electric-Fuel/dp/B000CIS4IU/ref=sr_1_4?dchild=1&gclid=Cj0KCQiAwMP9BRCzARIsAPWTJ_EVycjP6Y_TX2aDAx_qM6aEgNOYBimwB3t4kdE0jYQzVTnHNCcqun8aAkX4EALw_wcB&hvadid=177570362789&hvdev=c&hvlocphy=9025155&hvnetw=g&hvqmt=e&hvrand=7371372844440783517&hvtargid=kwd-3628355007&hydadcr=5739_9590425&keywords=6+volt+electric+fuel+pump&qid=1605486563&sr=8-4&tag=googhydr-20 Before reconnecting the fuel line to the carb, I ran the pump and got a good steady flow of fuel. How could the pump be defective if it produces 5 psi of pressure before starting the engine? Link to comment Share on other sites More sharing options...
TerryB Posted November 16, 2020 Share Posted November 16, 2020 Will it pump fuel with the electric right up to where the fuel line connects to the carb? Can you run the fuel from the open line to a container to see if the pump gradually quits pumping? 1 Link to comment Share on other sites More sharing options...
vermontboy Posted November 16, 2020 Share Posted November 16, 2020 In the "probably not" category make certain the gas cap vent isn't clogged just for kicks - doesn't sound like the right symptoms but .... Link to comment Share on other sites More sharing options...
Guest Posted November 16, 2020 Share Posted November 16, 2020 Most/many carb fuel problems are electric/ignition. Just an old saying that is true 90% of the time. Link to comment Share on other sites More sharing options...
padgett Posted November 16, 2020 Share Posted November 16, 2020 Just a thought but "As soon as I start the engine, the pressure slowly drops to zero" certainly sounds like a clogged vent. What happens if you leave the gas cap loose ? Link to comment Share on other sites More sharing options...
John348 Posted November 17, 2020 Share Posted November 17, 2020 Are there any rubber hoses connecting the lines? I had a similar (not identical) and it turned out that there was hairline crack in one of the rubber lines sucking air in and causing the pressure to drop. I discovered this by blowing air backwards to the tank (with the cap loose) I then heard the air hissing out. Just a thought... Link to comment Share on other sites More sharing options...
dalef62 Posted November 17, 2020 Share Posted November 17, 2020 40 minutes ago, John348 said: Are there any rubber hoses connecting the lines? I had a similar (not identical) and it turned out that there was hairline crack in one of the rubber lines sucking air in and causing the pressure to drop. I discovered this by blowing air backwards to the tank (with the cap loose) I then heard the air hissing out. Just a thought... Along those same lines, I had a 41 Olds that would idle and cruise around perfectly, but any kind of load it would die out. Turns out there were holes in the metal fuel line as it went over the rear axle, never leaked just sucked air. Link to comment Share on other sites More sharing options...
wmsue Posted November 17, 2020 Share Posted November 17, 2020 What terminal did you use to wire it to the ignition? Does that terminal have power during 'start' and 'run' occurrence? Or only have power when cranking? Good Luck Bill Link to comment Share on other sites More sharing options...
40mopar Posted November 17, 2020 Author Share Posted November 17, 2020 17 hours ago, padgett said: Just a thought but "As soon as I start the engine, the pressure slowly drops to zero" certainly sounds like a clogged vent. What happens if you leave the gas cap loose ? Just tried your suggestion and the car ran! Not for long, but a significant improvement. Ran for about 3 or 4 minutes with the pressure fluctuating between 2 and 4 psi. I located the fill pipe vent and it was plugged shut with a long bolt with tape over the end to keep the bolt from falling out! Looks to have been done a long time ago. I removed the bolt and also cleaned out the gas cap vent. Put the cap back on and the car started and ran, but again not for long. Runs fairly good at high RMP, but will not idle. Anyway, looks like you got me headed in the right direction. Thanks very much. 1 Link to comment Share on other sites More sharing options...
40mopar Posted November 17, 2020 Author Share Posted November 17, 2020 17 hours ago, vermontboy said: In the "probably not" category make certain the gas cap vent isn't clogged just for kicks - doesn't sound like the right symptoms but .... Done, and I think that was part of the problem. Thanks. Link to comment Share on other sites More sharing options...
40mopar Posted November 17, 2020 Author Share Posted November 17, 2020 1 hour ago, John348 said: Are there any rubber hoses connecting the lines? I had a similar (not identical) and it turned out that there was hairline crack in one of the rubber lines sucking air in and causing the pressure to drop. I discovered this by blowing air backwards to the tank (with the cap loose) I then heard the air hissing out. Just a thought... There are the rubber hoses used to connect the fuel pump and also some under the hood. The ones under the hood are fairly old and I'm going to replace them. Thanks. 3 Link to comment Share on other sites More sharing options...
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