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76 bus- can't get fuel pump to buzz
Posted: Sat Jul 18, 2009 6:23 am
by cellobus
I just removed the engine from my 76 bus to install a new fuel gauge sending unit. Everything is allegedly in place on the reinstall, but when I turn the key, the fuel pump doesn't "buzz," like it always did before. Motor turns over very nicely, though. Could crossed wires at the coil be the culprit? or a fuse? or did the pump (or, God forbid, the computer) just coincidentally pick this time to die? I'm thinking wiring; are there any guides to which wire goes where, just in case my marking system failed?
Thank you.
Posted: Sat Jul 18, 2009 6:42 am
by fusername
well the pump should only buzz while the engine is running or the key is in the start position. to check quickly, put the key in the on position, and either stick a pencil intothe afm, you'll need to remove the filter, or pop the cap off the wiper\ box and move the arm by hand. when it moves the pump should kick on.
Posted: Sat Jul 18, 2009 6:56 am
by david58
Posted: Sat Jul 18, 2009 9:32 am
by cellobus
Thanks for the help. I'll have time tomorrow to dig into it.
cb
76 wiring snafu
Posted: Thu Sep 17, 2009 4:34 pm
by cellobus
I know it has been a while, still no luck. I guess I should say that there is a wire that I can't account for. It's a double black wire combined onto a single female connector. It comes out of a bundle from the right, and it is not long enough to connect to the coil. I'll admit that even though I labelled these wires, the markings got smudged and don't exist any more. The double black wire combined onto a single terminal from the left is the only such wire that retained its label, goes to coil terminal 15. I'll also say that neither the back-up lights nor the heater blower work.
cellobus
Posted: Fri Sep 18, 2009 11:13 am
by Volswagon
Cello-the wires for the heat blower (including fuse holder) come from the right side. The fuse holder for the backup lites plus the trigger wire for the pump/ECU relay on the left side plug into the coil, at least on this '75. Where in Ktown are you? I have a manual with diagrams if you need to look. Marc
Posted: Fri Sep 18, 2009 12:41 pm
by david58
Ok if it was me I would hot wire the pump just to make sure the pump works. Here is a wiring diagram and the legend for it.
Here are the wire colors at the pump.
So if you power up the red/blue wire and ground the brown wire the pump should run if it is still good. You will still need to track down the wiring.
Posted: Fri Sep 18, 2009 1:01 pm
by cellobus
I'm in Parkridge, on the near east side. I have the Bentley manual with the color diagram but it doesn't describe how things look. I think photos are going to be what saves me here.
cb
Posted: Fri Sep 18, 2009 1:13 pm
by david58
15.2) Close-up of the starter wiring partially removed. It's hard to mix up the wires because of the ring terminals but on terminal 30 you should have (1) large red wire for the alternator, (1) large black wire for the battery, (1) red wire for the heater booster fan and (1) thick red/white stripped wire for the fuse box. The large cables are usually wrapped in a beige sheath.
The red/white wire triggers the fuel pump via the double relay. In this photo you can see that I've got a hot start relay installed and the blue arrow points to one of the relay's wires. Normally the black/red wire which is connected to the blue wire of the relay connects to terminal 50 where I have the black wire from the relay. An large red wire on terminal 30 powers the double relay. All the red wires can be confusing but again remember all the ring terminals connect to 30.
http://www.ratwell.com/technical/EngineRemoval.html
Posted: Fri Sep 18, 2009 1:45 pm
by david58
dtrumbo wrote:Assuming no one has hacked up your wiring any more than has already been identified, there should be a blue and red wire that goes directly from the double relay to the other (+, not the ground) terminal on your fuel pump. In addition, make sure the "new" ground wire that your mechanic added is firmly attached to the nut you referenced. I don't know exactly what you're describing by "nut on body", but if they hooked the wire to some place on the body that was painted, that's not a good ground. I'd be curious as to why the original ground wire was abandoned in favor of a new one.
All of that said, if it turns out the connections are good, it still sounds like a double relay problem to me. Do you have a voltmeter and/or a test light? If not, pick one up cheap at your friendly local auto parts store (FLAPS). It will pay for itself the very first time you use it.
Posted: Fri Sep 18, 2009 2:13 pm
by cellobus
Thanks very much for your helpful and timely replies!
-cellobus
Posted: Sun Sep 20, 2009 4:47 am
by david58
Have you hot wired the pump to see if it works?
