Fuel system problem

[Dulis]

Okay so I've got a no start condition right now in my '89 b2 with single pump, I've narrowed it down to the fuel system. It's not making enough pressure so I did a voltage drop test on everything from battery to pump. It looks good until I get to the inertia switch as in when I do the test on it I pulled the connector and tested the input wire because I'm lazy but assuming I had a good ground the meter read from key on, 12 something volts for all of half a second, then about 6 and a half volts continuous until key off (the fuel pump reads the same) . From what I've seen here the things upstream from that are the relay and computer, and I know the relay is getting the right power so I think it would mean the computer isn't working right for whatever reason. Anyway I'm kinda stuck here so what should I do next? Thanks in advance!

 

[Curious Hound]

Try swapping a different relay in there and see what happens.

 

[Dulis]

Which one would work, I went to the parts store looking for a ry610 and they said the closest one they have was in British Columbia

 

[Curious Hound]

It should be a common 5 pin relay. Do you have fog lights? Fog light relay would work. A/C WOT relay, if you have air conditioning.
Horn relay if you have cruise.

 

[Dulis]

The one that's in there is a 4 pin, would those still work?

 

[Curious Hound]

Should. There us probably an unpinned empty hole in the relay block. The extra pin on the relay will harmlessly slip down in there.

 

[Dulis]

Alright I'll give that a try after work sometime I'll post results when I get to it, Thanks

 

[Dulis]

Alright I couldn't get one of those other relays to work so instead I jumpered it and tried starting like that, the pump now has correct voltage but it still doesn't fire. I'm really starting to think it's that computer

 

[Curious Hound]

You need a fuel pressure guage that you can use to measure fuel pressure at the fuel rail. Might be able to get a "loaner" Guage from a local parts store. I think you should have 30-35 psi. If your fuel pump is really getting the right voltage and has a good ground, you should have good pressure. If not, bad pump.

 

[Dulis]

But that doesn't explain the weird voltage it had before I bypassed the computer though (I think), if the computer was bad then wouldn't that mean the injector's aren't working right either? Or am I missing something here, I'll see if I can't grab a cheap fuel pressure gauge when my schedule allows thanks.

 

[sheep herder]

When you turn the key on without starting the motor, the computer only turns on the fuel pump for a couple of seconds. Basically just filling the lines. Once the motor actually starts, the fuel pump will stay running.

 

[wildbill23c]

If you were getting 6 volts through the fuel pump shut off switch that's most likely your problem. Those things get weak and fail over time. Had to replace the one in my 88 Bronco 2 a while back....pretty easy replacement job.

 

[Dulis]

I tested the input wire not output wire

 

[MikeG]

Then test the output wire. The voltage should be the same, or nearly so, across that switch. It shouldn't have any resistance to speak of. It's just a 'fail' switch.

 

[Dulis]

I picked up a fuel pressure tester and with the jumper in the relay plug I'm getting around 1-2psi so I have a new one on the way