No fuel pump and another issue

[gavin]

Posted this in my build'ish thread, but thought it might be better to create a new thread.

Finally got around to doing some more work on my 86 B2 yesterday, but having a couple issues.

First, it will not run off the alternator. The battery that was in it died, since the truck had been sitting for ~9 years. I did start it up once a few years ago, but had to leave the jumper cables up. Soon as I disconnect, the truck died.
It should be able to run without a battery, no? I took the battery out a couple weeks ago, and yesterday we just had the cables hooked up directly to the truck's wires.

Secondly, the fuel pump ain't coming on when key is turned to On/Run. The relay is clicking, but no juice is getting to the pump apparently.

Run a jump from pos to the pos terminal on the inline pump, it runs.
Inertia switch doesn't appear to be tripped. Maybe it went bad with enough moisture?

The interior of the truck is quite... moist.
The foam cusion on the firewall is soaked; a little squeeze and water was dribbling out. Possible the moisture killed the inertia switch, maybe?

 

[gavin]

bumpity

hoping to get to work on it a bit more next week, as I'm taking a couple extra days off work to get the junk moved.
Need to pick up a new battery for it; need for find a type 34/78 that has both top and side terminals. One Wally World doesn't seem to carry any of those. Also don't want to spend big bucks on it, and I've had good luck with my EverStart MAXX.

what should I check/try for the lack of fuel pump?
To add another note to this, I had run a wire from the fuel pump relay (hot) to a switch in the cab, and another off the switch to the wiring harness in the driver's side of the engine bay that feeds the +12 to the pump. I can't remember why, honestly, but there was a reason for it!

Since flipping the switch made no difference, the relay is clicking with key on, and the pump does work when it's jumped directly from the battery, I'm not sure what else there is to check other than wiring and the inertia switch.

Disconnect the inertia switch and plug a blade fuse into the wiring connector? That should eliminate the inertia switch from being the cause.

 

[janderson4010]

Well obviously your fuel pump isnt bad, test for voltage from the battery back through the circuit for the fp, it can really only be the fp relay or the switch, unless u got some cut wires in there somewhere

 

[gavin]

it can really only be the fp relay or the switch, unless u got some cut wires in there somewhere

yeah, that's kinda what I figured.
it's possible there's a break in the line somewhere between the harness in the driver's side engine compartment and the pump.

I do have a butt-connector near the pump, can't remember why, but that's where I hooked up the jumper wire to get it running.

 

[gavin]

ok, bumping this thread cuz I just spent 3.5 hrs farting around with the junk.

wiring from fuel pump relay to fuel pump is good.
wiring from inertia switch to fuel pump is good.
inertia switch is good; or, at least not the culprit. No change when I jumper the connector in the cab.
relay is good, it clicks as it should. Also swapped it to the other relay and no change.
pump is good, because I can wire it to a 12v source and it runs.

So, I'm not sure how it can be wiring, when everything from the relay and inertia switch to the fuel pump is good. Resistance is 0'ish.

But I don't know what else to check.

I suppose the next thing to do is to how far the voltage is actually getting, if anywhere.

 

[rookieshooter]

I suppose the next thing to do is to how far the voltage is actually getting, if anywhere.

I would have done this first.

 

[gavin]

I would have done this first.

well, at one point I had it working by rigging a wire from the relay to a switch in the cab, and from the switch to the wiring harness in the dri side compartment. It doesn't actually jumper power to the fuel pump though.
But it's been years since I've done much to the thing.

So what I can't find, even looking at wiring diagrams from 2 different Chiltons, a Haynes, and the FSM, is where the 12v source actually comes from.
It looks like it comes directly from the ECM.
But I am a bit rusty attempting to understand wiring diagrams.

 

[rookieshooter]

Ok did some research, see if the below link helps. This shows 2 relays an eec and fuel pump relay. Note that both are normally opened and then when 12v is applied the electro magnets will close the switch in the relay sending power out to both yellow wires from both relays. This dia. shows that you need both relays working. The switch I'm talking about is the - - - - marking. It's shown with the switch not making contact until power is applied. It also gives the color of the wires.
This should do it. A test light should be all you need to check the voltage to and from the relays and then to pump.
It also shows somekind of testing site.
http://www.justanswer.com/ford/1hhcp-restoring-86-ford-bronco-ii-2-9-fuel-injected.html

 

[gavin]

ah ha, thanks!
Might be the other relay that's dead then.

 

[gavin]

ok, here's what I've found.
I have power leaving the fuel pump relay down to the inertia switch, but it's not coming back.
I jumpered the plug to the inertia switch, still no voltage coming back.

Yet, I see resistance between the 2 wires that go to the inertia switch.

So I'm seeing resistance, but no voltage.
I'm not sure how?

 

[gavin]

ok, so I had a dumb moment.
didn't pay enough attention to resistance; it was actually showing over 1 MOhm with the jumper.
New piece of 10 or 12 guage, and now the fuel pump starts every time.

Checked resistance between terminals on the inertia switch; only a couple ohms at first.
Tripped it a couple times and reset it, then reistance would jump up to something like 16 MOhm and slowly drop. Cleaned up the terminals, same thing.

So I'd guess that the inertia switch has been an issue.