No power to inertia switch

[LARRYBOMB]

I bought a '88 reg cab 2.9L auto tranny. I originally bought the truck because I needed a solid cab with a good title to put on a different frame. My brother gave me an abandoned project he started a long time ago. So I have Ranger frame with a 302 waiting for a cab.
Anyways I got the '88 for $500 and the previous owner replaced alternator, fuel rail, fuel injecters, IAC, map sensor, in-tank fuel pump, ignition coil and never could get it to run. So I got it home and first thing I do is hooked up a battery and turned the key to listen for fuels pumps. Nothing but the eec relay doing it's 2 clicks. I checked for power going to the inertia switch and had nothing. The inertia switch has a Org/LtBlu and Pnk/Blk wires. The org/ltblu comes from the fuel pump relay shouldn't that be power going to the inertia switch? I hooked up a test light and got nothing. So I put test light on + and touched the org/blu wire and light came on. So the org/blu wire is grounded. The fuel pump relay has ylw wire for constant 12v and there is a red wire for 12v with key on.

I have been reading different posts on the forum trying to get some ideas what to do. The truck's interior is pretty nice and the body is fair (not to rusty just some dents and clear coat peel). The title and odometer says 95,000 but you never really know if it's accurate. The motor does look fairly clean though. I do need a cab for my project but I'm not going to tear this truck up if it turns out to be a good runner. I bought a '90 2.3L 5spd over a year and a half ago for $450 and had to put a timing belt on it and have been driving it ever since. If the timing belt didnt fix it I was gonna use that cab. (lol my daily driver now)

 

[RonD]

If the O/LtB wire was hooked up it would show as a Ground since the fuel pump is hooked up and it is a Ground.
Electric motor is just a spool of wire .

Constant 12v in the FP relay socket is from a 30amp fuse in the power box, that is for Fuel Pump power.
The 12v with key on is the Relay power, it comes from EEC relay, but this does not turn fuel pump relay on.
There should be a light blue/orange wire, that is the relay ground wire, it runs to the computer(PCM), pin 22, the computer uses an internal ground to turn on the relay for two seconds when key is turned on, and then it will ground it again when rpms are above 500, and keep it grounded until key is turn off or rpms fall below 500.

There should be a VIP test connector on the drivers side near firewall, could be on passenger side, it's how you read OBD I codes

There is a diagram of it here: http://www.therangerstation.com/tech_library/OBD_I.shtml

The Fuel Pump port is marked on the diagram, if you were to put a jumper on that port and then ground it fuel pump relay should close and fuel pump should get power.

This port's wire is spliced into the light blue/orange wire that runs from relay to pin 22 on the computer, so it is a test port to turn on fuel pump relay

 

[LARRYBOMB]

Thanks for the response Ron. I just tried the jumper method on the test connector(passenger side) and the fuel pump relay just clicks. When I first got the truck the fuel pump relay was no good. I took one out of my '86 and swapped it.

 

[RonD]

When the relay clicks do you see power at the inertia switch?

If not either Fuel Pump fuse(30amp) is burned out or wire from relay to inertia switch is bad.

 

[LARRYBOMB]

I tried the jumper method again and when fuel pump relay clicks there is power to the inertia switch.

If my high pressure fuel pump is bad could it cause the fuel pump in the tank to not work?

I have another high pressure pump on my parts truck that I know works if I need it.

 

[RonD]

Near the High pressure pump in the frame rail is where the factory added a splice to tap into the inertia switch power wire going to the in tank fuel pump.
This splice can get corroded causing 1 or both pumps to quit.

Follow the high pressure pump wire to find the splice

I think both pumps share the same Ground wire, but check that, it would be the Black wire in the 4 wires running back to the fuel tank.
4 wires are:
1. Pink/black stripe - fuel pump power(from inertia switch)
2. Black - fuel pump ground(often grounded near inertia switch)

3. Yellow/white stripe - fuel gauge power(5volt pulse from dash cluster)
4. Orange - fuel gauge ground(often grounded with #2 Black wire)

High pressure pump could just be grounded to the frame rail, follow that wire to check, if so then in tank pump ground(#2 wire) would need to be checked.

 

[LARRYBOMB]

Hey Ron. I was in the garage messing with the truck before I go to work.(I work 2nd shift) I came back in and saw your post.

This is what I tried today. I pulled the plug to the high pressure pump and checked and I am getting power to the pump. I tried jumping the pump and it didn't make a sound. So I guess this whole time the pump was bad. I got a parts truck that I can get a pump from.

 

[RonD]

good work

Do you hear the in tank pump?
You should, if it is working, the two pumps are independent, they share common power wire and sometimes ground wire, but if the motor on one fails you should still hear the other one running.

 

[LARRYBOMB]

No I didn't hear anything. I do have the bed off so everything is easy to get to. I'll recheck the in tank pump plug when I get home. The in tank pump is new so I need to find out why it isn't getting power.

 

[LARRYBOMB]

This is what I know.

-Inertia switch is getting power.
-High pressure fuel pump is getting power but doesn't work.
-Jumped power to hp fuel pump and still doesn't work.(okay bad pump)
-I'm getting power to the in-tank fuel pump. I checked the ground in that plug also and it is good. It's a new pump but is not working.

(edit: I just checked Rockauto and LMC catalog and the part numbers for my '86 in-tank pump will work in the '88. I bought that pump new. It has been sitting for a couple of years but it is in a near empty brand new tank. I wish it was the weekend.)

Maybe it's the wrong pump even though the plug fits maybe the wiring is different. I'm going to jump power to the pump and see if I can get it to run. I'm sure it won't run but it's just one of those things I need to check. I have a new in-tank pump in a '86 super cab but I think their part numbers are different.*(part numbers are the same) I also have a high pressure fuel pump I can grab off that truck. To me it looks like if I change out both pumps it will start right up. One thing I did figure out when I first got the truck was the inertia switch was bad. I tested it in my Dad's '86 STX and his truck wouldn't start. I tested the one from my '86 parts truck and it didn't work. I took his good inertia switch and tried it in my '88 and it didn't help.(cause fuel pumps don't work lol) Anyways I was at the junkyard getting a wiper motor for my '91 F150 and picked up a newer style inertia switch(with red button) I spliced in the new plug and the screw holes line up to the old switch holes. So basically all I have done was put on a new inertia switch so far.

 

[RonD]

I would get a test light or volt meter and test for power using the 12v wire AND the ground wire.

A Ground is only a Ground if it is connected all the way back to the Battery "-"

You could have a bad ground strap.
Main ground is from Battery "-" to Engine block on most vehicles and that is isolated from body and frame by rubber mounts.
Ground strap is needed from Engine to Firewall(body ground) and also from Engine to Frame.
Rad support usually has a ground strap for the head lights.

When vehicles are assembled the parts are already painted, so the bolts don't provide metal to metal grounds and many have rubber grommets in any case.

 

[LARRYBOMB]

I checked the ground in the tank pump plug yesterday. I hooked the test light to the ground and the power wire in the plug and turned the key and light came on for 2 seconds. I jumped power to in-tank pump and it didn't make any sound. I haven't tried a voltmeter so far I've just been using a test light. I think I'm going to swap out the fuel pumps this weekend.

 

[Chris_1]

Yeah, swap out the pump and see where you're at. Sitting for a while you should throw a fuel filter at it too

 

[RonD]

Two failed pumps would be an oddity

 

[LARRYBOMB]

Two failed pumps would be an oddity

I agree. Especially when one is a shiny new one. I'll find out Thursday if I have to work Saturday or not. If I get a 2 day weekend I'm not going to mess with it until then. I will keep this post updated on my progress. I may check some wires with my voltmeter before then.

Oh yeah just got my title for this truck in the mail today.