fuel pump problems

joe_mnJuly 30, 2006

the saga continues. chevy bigblock motorhome would not start. carbed engine. no fuel. we changed fuel pump. no fuel. disconnect fuel lines on pump, crank motor, only 1 suction pulse can be felt. took off fuel pump and cranked motor and FP pushrod will extend but we have to force it up into block. hmm, bent pushrod? not good. we cannot get it out. took out access plug but its almost impossible to grab onto pushrod to try and extract it. ok, plan #2. put on electric fuel pump. not too hard but time consuming. run new fuel lines to carb and now when we run pump, it only spurts/spits out of the line. gas tank is 1/2 full. is something messed up with 2 tank fuel selector switch? and its 93 degrees out. not fun job. the FP really bugs me. who bends a pushrod?

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gary__

I bet it's not bent, just gummed up. Never heard of one of those getting bent. I'd try shooting some kind of light lubricant on the rod, work it back and forth, and wipe it off with a rag a few times. Since you're not getting fuel with an electric pump, your problem is else where anyway as you already know.

    Bookmark   July 30, 2006 at 7:09PM
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joe_mn

seems the electric FP has lousy suction. we tried using the stock gas tank fuel pickup which comes out the top of the tank. not good. supposed to use a bottom outlet fitting and mount the FP below the tank. huh? i don't want to drop the tank to install the fitting or change the tank since its a 50 gallon tank or install an intank electric FP. the pushrod is about 5" long and we can see maybe 1/2 to 3/4 inch. that means a whole bunch is inside the block. every bit of info i find on the pushrod says it usually will fall out of the block and people put grease on it to make it stay up to put in a new FP.

    Bookmark   July 30, 2006 at 9:52PM
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gary__

I've used electric fuel pumps before on trucks with big blocks and they always pumped like crazy. Perhaps you have another issue like a split or crushed line somewhere, or the sock in the tank is full of junk. To test I'd just scab on a piece of fuel line from the inlet to either your electric or mechanical pump, and run the other end to a gas can or something and see how it pumps then. I bet you'll confirm both pumps are fine. Then I'd reinstall the line to the pump as it should be and scab my test fuel line at another location you think is questionable. Ahead of or behind your selector switch for example. If ok, try it as far back as you can. If still ok, then you know it's time to drop the tank. Just for kicks, remove the gas cap when doing anything to make sure there isn't a venting problem.

That's correct about the fuel pump rod. One usually has to put some grease on it to hold it up into place while installing the pump. The rod usually falls out till it hits the casting of the block. I'm assuming this thing has set for a while.

    Bookmark   July 30, 2006 at 10:51PM
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joe_mn

the mechanical pump is not doing any pumping until the pushrod is fixed. we bumped the engine and felt the cam lobe go "up" so the pushrod does move but very hard. it does extend about 1/2" inch so we know the cam lobe is not gone. this is on a full rebuild less than 10k miles ago. we just drove 400 miles 2 weeks ago to a car show and the engine would stumble about every 1/2 hr or so. we thought it was bad gas. you should be able to push the pushrod back into the motor with almost no effort. not here. i see that a HP mech fuel pump should have about 100lbs of spring force. i read that at a HP website. supposed to keep the FP from floating at high rpm. anyway, the elec FP should pump water as a test just fine with a 2 ft piece of hose in a bucket? right? I mean with a short piece of tubing on the inlet and outlet, the pump should do something?

    Bookmark   July 31, 2006 at 7:30AM
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gary__

**the elec FP should pump water as a test just fine with a 2 ft piece of hose in a bucket? right? I mean with a short piece of tubing on the inlet and outlet, the pump should do something?**

Yep

    Bookmark   July 31, 2006 at 11:07AM
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joe_mn

the FP is a carter P4070. I called their tech line. they said it should be mounted below the gas tank and close to it if possible. I am going to try and fab up a bracket to drop the pump. right now the pump is about level with the top of the tank. they said the feed line does not have to come out the bottom of the tank. coming out the stock top exit should work ok. thats a big should too me.

    Bookmark   July 31, 2006 at 1:07PM
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gary__

Don't know about any particular brand I've used, but put in several from NAPA in Ford 800's with the Louisville cab. Was trying to correct problems with vapor lock on warm days. I mounted them high on the fire wall to keep the fuel line as far from the engine as I could. No problem. I also purchased one to pump mineral oil out of leaking transformers into 55 gallon drums. That one sucks liquid much heavier than gasoline up hill no problem too. If what you have has to be practically gravity fed to operate, I'd say it's a piece of cr*p.

    Bookmark   July 31, 2006 at 4:31PM
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joe_mn

ok. we got the pushrod out. it was scuffed on one side. the tip looked ok. we put in a new one and it slides nice and easy. put on the new mech fuel pump. engine started. great. we let it idle for 10 mins or so and shut it off. we decided to go for a drive later this afternoon and got about a block and the engine died again. it seems to idle but does not like any rpm above idle. maybe the new fuel pump is funky. i am going to put another fuel pump on tomorrow after engine cools down. 101 degrees today.

    Bookmark   July 31, 2006 at 9:51PM
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earthworm

Check the flex lines, internally they can disintegrate and block the fuel flow, also they can leak air.
Assure that the fuel tank is vented.
Both these conditions can be erratic.

Use Gary's test, the electric pump should generate a 5/16" column 2' to 3' high..
If flex fuel hoses are used, they should be changed after 7 to 10 years.. or so....

    Bookmark   August 1, 2006 at 2:04PM
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joe_mn

my dad put on a new ac/delco mech pump and it seems to run fine now. his house is 100 miles from mine and he is meeting me halfway tonite to exchange the motorhome. i am going to a 4 day concert tomorrow. I would like to change all the fuel lines and hope I don't have any more problems this week. maybe next week. The tank selector switch on the dash does not work so we have a toggle switch wired in so we can use both tanks. the gas gauge works for the front main tank but not the rear. we just fill it up and switch it when we hit our mileage figure. i would like to fix the switch issue so both tanks read properly and than replace the fuel lines.

    Bookmark   August 1, 2006 at 6:44PM
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