Fuel pump not working?

[Saskadude]

Sent: 5/14/2008

Here's one for the mechanically savvy group here at Classic Winnebago's.  I recently had a breakdown in my GMC chassis class 'C'.  At first I thought it was the fuel filter (which was fouled), but I replaced it and it would still not start.  I took the tank off to check the lines and the tube in the tank everything looks fine (I did accidentally break the ground strap for the fuel tank though and some help on how I should fix that would be great).  I reconnected the tank and all the lines and tried to start it up.  It still wouldn't start.  I disconnected the line from the fuel pump to the carb and it will run for a few seconds ( I guess until the fuel in the bowl is burned up).  I looked at the pump with the engine turning over, and only a little spit of fuel was coming out.  I'm thinking fuel pump, but some advice would be appreciated.  Also, this thing has dual tanks with a switch on the floor to go back and forth.  The fuel gauge only works with the main tank and not the rear one.  Not sure how to test to see which tank I am running off of, etc.  Hope you fine folks can help so I can be driving this thing instead and scratching my head every time I look at it in my yard...

[ontheroadagain]

Sent: 5/15/2008

Do you have a fuel pressure/ vacuum gauge?

[Slantsixness]

Sent: 5/15/2008

I have two ideas...
but a question first:
Are you using a mechanical fuel pump, or an electric?


The clogged filter on a GM vehicle may be all your problem is, however.... you do know there is a filter in the input to the Quadrajet carb (if it's still there). That's what's behind the big 7/8" float bowl connection....

But.... a torn or ripped diaphragm in the mechanical fuel pump will also show the same results (little or no fuel flow). Sometimes (pretty seldom actually) you used to be able to get a car home by pinching off the fuel inlet side of the mechanical pump, about 1/2 to 3/4 of the way, and the pump would run enough to get you home... if you do that, and the engine seems to run and fuel pressure comes back, then the echanical pump is definitely bad....

Ok.. so if it's an after market electric pump.... my first question is... Why? but if you do, that's fine, but you don't need it... check the power connections to the pump. it may be incorporated with the fuel selector switch too, so given that the selector is not reading one tank, the solenoid or witch contacts may be bad... and of course electric fuel pumps just tend to die at the most unfortunate times, so it could also be just a bad or failing electric fuel pump.

To fix your selector switch, first you need to find out where the tank gauge wiring is going. sometimes, it's just a loose wire under the dash on a simple switch. then again, newe systems switch tank senders on the selector valve itself, so that gives you a couple places to look into that.
Due to the age of all these motor homes, keep in mind that the wiring, sending units and ground straps to the tanks all fall apart, so you could have a loose wire or bad tank float/sensor too..

Ok.. hopefully something of this is familiar to you... and helpful. If not, then We can attack it with simple tools and simple instructions one step at a time, but it's certainly not the end of the world for your rig!

You should have spoke up in the chat last night..(just type... we'll read...I promise!). Glenn and I we're just gabbing... wasn't anything really important, just shootin' the "stuff"!

Tom

[Saskadude]

Sent: 5/15/2008

Thanks for the advice Tom.  I'll try a couple of steps to see what results I get.  The filter on the inlet bowl of the carburetor is good and there are no other filters between, so I don't think that is the problem.  When I replaced it with a new one it wouldn't run again anyway...   If it's the pump, it can wait until payday next week.  The wiring I can fix over the weekend, with some help from my trusty wiring diagram.  I'll repost soon with some results.

Oh yeah, it's a mechanical fuel pump.

[ClydesdaleKevin]

Sent: 5/17/2008

When you turn your motor over, you should have lot more than a "little spit" of fuel coming out of your mechanical fuel pump.  It should gush out!

So you have a bad mechanical fuel pump!

Replace it...they are cheap!

A few words of advice though...First, use RTV sealer on both sides of the gasket so you won't have an oil leak...a very thin layer, and make sure you clean up the gasket mating surface.

Second, there is a push rod that comes out of the engine block when you remove the fuel pump...and it is at a downward angle, so it will want to slide out when you are trying to line up and put in the new pump.  SLATHER it in wheel bearing grease, reinsert it in the hole it goes in, and it will stay in place when you install the new pump, prelubed, and the grease won't damage any engine components.

Kev

[Saskadude]

Sent: 5/18/2008

thanks Kev.  I went out and got the Haynes manual and the troubleshooting procedure that I followed in the book led me to the same conclusion: fuel pump.  My bigger concern now is seeing how the two tanks are wired and plumbed so that I know which tank I am pulling fuel from.  Thanks for the tip on putting the push rod back in, I'll use it!

[ontheroadagain]

Sent: 5/19/2008

there is a bolt hole in the front of the block that goes through to the pump rod passage there is a short bolt in it to keep it from leaking oil just remove it and install a longer bolt  2-3 inches before removing the old pump and just snug it up pretty tight to hold the pump rod in place after you put the new pump in just put the original bolt back here is a picture of the bolt hole

[71CTwinnebago]

Sent: 5/19/2008

I would definitely change the fuel pump.  I have a 71 winnie in excellent shape, been having trouble when running lately . Everyone told me electrical. I Started changing everything I could think of, from voltage reg. to wires , plugs. Winnie backfiring through carburetor and or exhaust. Opened up carburetor to check excel, pump good. made mistake of not connecting gas line, and cranked over engine 50 times to start,and then got a spit from the gas line and realized it was unconnected. Then it hit me . All the times I let the engine crank I should have gotten soaked as the pump pumps off the cam every turn. Just ordered new one for 16 dollars. good luck .

[Saskadude]

Sent: 5/19/2008

I'm feeling very stupid today.  I got the rig running without having to replace the fuel pump.  There is a manual switch between the main tank and the auxiliary tank that was clogged and not allowing fuel to pump from the main tank (or so it seemed).  So I bypassed the valve and BOOM, it started right and ran perfect.  Oh well, live and learn I guess...  Thanks for the info everyone, it certainly helped me pin point the problem.

[lucidsodemite]

Sent: 5/27/2008

could everyone please list where they are getting fuel pumps from. i am getting quoted very high amounts from parts stores. now they are for holley and edelbrock pumps but i still cannot justify paying $210.00 for a pump. last time i bought one it was for a small block chev and i paid like $20.00 for it. i have 440 dodge so i know i will pay more than the chev guys but it should not be that much. all help is greatly appreciated

[ontheroadagain]

Sent: 5/28/2008


this place is pretty good and they ship to you I didn't know your location when I sent that other link http://www.rockauto.com/