Fuel system question -Please help

MDempsey · Post by **MDempsey** » Tue Apr 08, 2003 3:53 pm

Hi everyone. I own a '78 Campmobile and I just replaced the fuel pump. The old one was plugged as was the filter (which i also replaced) and when I put the new pump on I can't get any power to the new pump. If I run a cord from the battery to the pump to test, it works fine. I also noticed that the pump doesn't bypass so could this be a problem with the computer thinking that fuel preassure is too high and not sending power to the pump?

Guest · Post by **Guest** » Tue Apr 08, 2003 8:01 pm

The pump only gets power from the relay when
-the starter motor is turning
or
-the flap in the intake system tells it that the motor is pulling through air

it will not just run with the ignition on (if iverything is stock and working)
Jeff

MDempsey · Post by **MDempsey** » Tue Apr 08, 2003 9:26 pm

but when I turn the key, the engine turns over. and when the cord is hooked up the pump pumps but if I take the cord off, the pump quits. shouldn't it kick on after the engine fires and it's idling?

Guest · Post by **Guest** » Tue Apr 08, 2003 10:39 pm

yes it should
You can either hotwire the pump direct to ignition power or get a circuit diagram and start tracing the problem
probably either the double relay or the flapper
jeff

MDempsey · Post by **MDempsey** » Wed Apr 09, 2003 5:16 am

I've been trying to find a good diagram, like you said. Any idea where I can get a good one on the net?

Guest · Post by **Guest** » Wed Apr 09, 2003 6:51 am

do yourself a favour and buy a bentley manual, you can't be a bus mechanic without one!

in the mean time:

http://www.vintagebus.com/wiring/index.html

to test the pump 'in situ', have everything installed and connected. remove the air filter. you can leave the front part of the plastic filter housing attached to the air flow meter. look into the filter housing. with the eraser end of a pencil, move the flap in the afm. when this flap moves, it will switch the pump on. the reason why this is a good test is that it tests all of the components in the pump circuit - the pump, the double relay and the wiring. IMPORTANT: the pump will only operate with the key in the 'run' position, but do all of the steps with the key off first, just to familiarise yourself with everything, then finally do the test with the key in 'run'. leaving the key on for a long time is bad for the ignition system.

if the pump fails this test you have a bad pump, bad wiring or a bad relay. the bentley manual has a step-by-step procedure for the FI system which will find any of these faults quickly.

scott lyons

MDempsey · Post by **MDempsey** » Wed Apr 09, 2003 3:26 pm

Hey Scott and Jeff. I just want to thank you two for replying. You both were really helpful and I'm going to do what you two said. I'll let you know what happens when I get to work on the van this weekend.

Thanks again,

Matt

Melina1973 · Post by **Melina1973** » Wed Apr 16, 2003 11:25 am

I have a different question:

My pump runs as soon as I turn the key to the on postion before I engage the starter motor. It does not seem right, is it?

Thanks,

Post by **Marc** » Wed Apr 16, 2003 11:42 am

Michael, a `73 bus didn't have an electric fuel pump - someone must've added one without any kind of safety circuit.

http://www.shoptalkforums.com/viewtopic ... highlight=

Melina1973 · Post by **Melina1973** » Wed Apr 16, 2003 12:15 pm

Thanks Marc, the pump is out of an 84 Jetta, it seemed to work correctly before I removed the engine though.

Post by **Marc** » Wed Apr 16, 2003 12:55 pm

Hmmmm. That's a lot of fuel pump pressure for a carbureted engine, but let's move on for now.
If the pump didn't run until you cranked/started the engine before, it must have some sort of safety circuit installed (as discussed in that other thread)....and if it's coming on with the key now, that means whatever the safety circuit is, it chose this moment to fail - heckuva coincidence.
I'd be more inclined to believe that there's some connection between this problem and the alternator light problem you mentioned in the other thread, but without knowing how they set up the fuelpump circuit I can't envision what it might be. Maybe you should disconnect any non-stock wiring (for the fuelpump) and see if the alternator light problem goes away.

raygreenwood · Post by **raygreenwood** » Wed Apr 16, 2003 9:14 pm

Don't worry too much. Though the Jetta pump is capable of high pressure for CIS injection, the fuel pressure regulator is responsible for how much restriction is on the line and therefore how muchpressure it builds. It shoul be no problem. You forgot to mention how long the pump runs for when you turn the key to the first position. It is supposed to run for about 1.5 seconds or so to charge the line..before the starter turns. Ray

Melina1973 · Post by **Melina1973** » Thu Apr 17, 2003 5:11 am

Thanks guys, the pump just runs and runs as long as the key is turned I tried to wait it out but I got worried and stopped.

I am going to try that fuel pump connection to see if that fixes my alternator light.

Post by **Marc** » Thu Apr 17, 2003 6:05 am

Ray, this thread started out talking about a `78 Campmobile but it was highjacked and now we're on a `73 bus; it's never been confirmed that it's still carbureted but that's my assumption.

Melina1973 · Post by **Melina1973** » Thu Apr 17, 2003 6:39 am

Hey man I only 'highjacked' this thread after I thought the creator was satified with your responses, and I had a similar problem I figured you and Ray could answer.

My 1973 bus has a 1776 (non-Upright) with 2 solex carbs, I believe the distributor and the fuel pump were the only things changed from original equipment.

Disconnecting the fuel pump did not turn off the (G) light.

Fuel system question -Please help

Fuel system question -Please help

MDempsey