A week ago, my '08 2.3L Ranger shut off while coasting down the road. No CEL is on, but I did have codes P0231 and P0232 display. Voltage at alternator is 14.1. Voltage at battery is 12.5. Voltage with key off is 12.5 to one relay terminal and with KOEO the other terminal is at 11.5ish.

The issue I'm having is that the voltage to the inertia switch connector is 18.5 with KOEO. If I try starting it, the voltage will drop to 12.5. I'm not sure if this is related to the stalling that I'm having, but I assume it is.

I've had the engine stall on me twice and nearly stall several times. I can pump the gas pedal when i notice the truck losing power and it will recover. I'm guessing I need to replace the fuel pump, but the 18.5V at the fuel shutoff connector has me second guessing the issue. Any suggestions for pinpointing this?

 

Welcome to the forum

First, you measure voltage at the battery
Key off
Key on engine running

If B+ on back of alternator showed 14v engine running then battery should show that as well

If you got 12.5v each time at battery then you have a blown fusible link
See diagram below


Key on engine off voltage at inertia switch should be 5-8volts, no amps, this is just monitor voltage from computer, it can't run the fuel pump
With engine running you should see 14volts IF(big IF) alternator is connected to the system

So I would first find out why battery is not showing alternator voltage when engine is running
And don't drive it very far it will stall and will not start until battery is recharged.

Minimum battery voltage with engine running is 13.5volts, anything lower and you are draining the battery
13.8-14.8v is normal

 

Thanks for the kind welcome! I did try searching through the forums to find similar problems (along with Google), but I haven't been able to find any similar problems. I love my Ranger (only 40k miles as well)--this is the first issue that I've had.

My apologizes for not being clear. Voltage with KOEO is 12.5. Voltage with engine running is same as alternator 14v. Key On Engine Off voltage at Inertia is 18.71V. After stalling vehicle starts back up and will run.




Once I attempt to crank the engine inertia switch connector voltage drops to 11.2ish.




Amerage was .1 mV with KOEO. Voltage at fuel pump relay is normal.

I attempted to add pictures, but I don't think it worked.

 

HI ronD

What year did Ford change the design to the wiring for the inertia switch?

All the older Ford vehicles I have worked on 2002 and earlier there is a three wire connector but only two connectors are used pin one and two.

Pin one is from the fuel pump relay which has switched battery voltage 12 volts or more.

Pin Two goes directly to the fuel pump

In fact I have found a few no start problems caused by a burnt connector at the inertia switch.

 

Inertia switch and fuel pump relay have been wired the same until 2008, maybe 2007

1994 and earlier did have the OBD1 connector in engine bay that added a wire so Fuel pump relay could be Grounded(turned on) manually

1995 and up used the newer computer and OBD2 so didn't have that wire.

All EFI Rangers had a wire from Fuel pump relay's "out to inertia switch" wire to the computer, this monitored if fuel pump relay closed and 12volts was present on that wire.

This wire could be at fuel pump relay or at inertia switch.

Computer only closes(grounds) fuel pump relay for 2 seconds when key is first turned on, when engine RPMs are above 400(engine started), then computer grounds fuel pump relay full time.
This is a safety feature, if fuel line should break in an accident then engine would stall, RPMs below 400 and computer would shut off fuel pump power.
Inertia switch is there for the same reason, cut power to the electric pump so it doesn't keep pumping out gasoline.

With key on you would see 12v at inertia switch for 2 seconds, then you would see 5-8volts after that from the computers monitor circuit, it is no amp voltage so can't power fuel pump.
After engine starts you would see system voltage, alternator on voltage, 13.5 to 14.9volts, after computer grounded fuel pump relay
Ford use a dark green wire from fuel pump relay to inertia switch for many years.

And the fuel pump relays coil got power from EEC(PCM) Relay, this relay closes when key is turned on and would send power to EEC(computer), spark system, fuel injectors, and fuel pump relay's coil.

Difference in '07/'08 and up is that the Fuel Pump Relay now powers the fuel injectors as well as the fuel pump
And fuel pump relay gets its coil power directly from the Power Diode in the cab fuse box when key is on.
Power diode sends power to EEC Relay and Fuel pump relay coils directly

Computer still has monitor wire to see if fuel pump relay is closing and power is at inertia switch and fuel injectors.


Back to NO8Ranger's issue

It is very hard to increase DC voltage without a transformer of some kind.
Key off or key on engine off, the DC voltage in a vehicle can not go above battery voltage, so getting 18volts from 12volts needs some kind of multiplier.
I would imagine that the 18volts is no amps or fuel pump would run full time when key was on, and you don't mention that.
So it could be computer monitor voltage just augmented in the monitor circuit.
If you have a 12v light bulb add it to the volt meters circuit and test inertia switch Brown/white wire again.

If voltage drops down or disappears then I wouldn't worry about that 18volts, low or no amps, so not an issue, but is a curiosity.

Pull out the fuel pump relay in the engine fuse box
Key off, inertia switch unplugged
Test each slot in the relay's base, one should have 12v, and only one, thats from 30amp fuel pump fuse(#23)
Turn key on
Test slots again, should be another slot that now has 12v, coil power, from power diode in cab fuse box(SJB).
If you see a slot with that 18volts then it is for sure coming from the computers monitor circuit
If you don't then replace Fuel Pump Relay, while I can't imagine how it would happen the relays coil could be acting as a transformer and imparting higher voltage to brown/white wire that goes to inertia switch

 

So I've confirmed no amps going to the circuit (light bulb did not lite). The relays base has 3 slots that show voltage and indeed, one is 18v and the other two are 12v. Can I ignore this electrical oddity and assume the issue is indeed with the fuel pump and not the relay/switch?

So far the stalling has happened while idling or coasting to a stop, never while accelerating. I'm not sure of any other tests I can do, although someone did mention I should check the o2 sensors--but I am skeptical of that as it would have thrown a different code than p0231/2,I think.

 

I would replace the fuel pump relay on speculation, should be $6-$10

The codes are not fuel pump codes they are fuel pump power codes

P0231 secondary circuit low - this means when computer Closed the Fuel Pump relay it did not see 12volts on monitor instantly

P0232 secondary circuit high - this means when computer Opened the fuel pump relay it still saw 12volts on monitor

So fuel pump relay could be the only issue, although that 18volts still has me curious, usually 5 to 7 volts is seen, but never tested on 2008

There really are no fuel pump codes, Lean codes would be about close as you would get if fuel pump wasn't working like it should, flat out stalling is more like power to pump is lost, P0231.


Upstream O2 sensors should be replaced every 100-120k miles, they use a chemical reaction like the battery does so they do wear out, as they get older engine will run Richer so lower MPG, happens very slowly.
So the $60-$80 for two new O2s will pay for themselves over the next 100k miles in better MPG

Downstream O2 will usually last the life of the vehicle, unless there oil in the exhaust from an engine problem

And you are right, O2s can't cause your symptoms

 

Thanks for the information RonD

 

RonD,
Impressive Rey !

 

So I changed out the relay, and that didn't fix the odd voltage. I decided to go through the fuse box and make sure all was okay. Turns out the fuse to the PCM was missing--after replacing fuse, voltage dropped back to normal. This could have been my own fault (i did pull fuses after the truck stalled the first time to see if one blew), or less likely but a possibility is the couple days before I had my battery replaced and in between testing for CCA and buying the new battery, someone pulled it out. I'd place it on my own stupidity.

I purchased a fuel pump--now I'm not sure if I should go ahead and replace it or return it. Truck only has 40k miles, but is nearly 10 years old. It did stall on me, but can't pin it down on the missing fuse or pump. I didn't have symptoms today while driving.

 

I would give it a week.

Relay wouldn't change the odd voltage it is not part of that circuit, you changed relay because of the codes.

Good info about the odd voltage dropping back to 5-7volts after PCM fuse was installed

There are 2 fuse for PCM, one fuse is for KAM(keep alive memory), gives PCM voltage 24/7 to hold learned data, same as radio pre-set voltage
Then the Key ON PCM voltage fuse which starts up the PCM, boots the computer

 

Thanks for all your help RonD. I'll report back in after I drive around some more and let you know if there are any more issues. While reading through the internet looking for help, your name pops up again and again on more than 1 site. You are the man!

With that said, fuse #39, 15a PCM Power was the fuse that was missing. The KAM fuse was in there and OK. I'd love to get ahold of a wiring diagram to see why that fuse would cause the crazy reading at the switch.

 

Hey guys--just wanted to state that RonD is a soothsayer. While coming home today, CEL came on. Lean Code P0171 came up. I had already bought a fuel pump and had it in the garage--I was about ready to return it as I haven't had any symptoms since my last post. The code was thrown and I saw okay---lets just replace it.

Can someone tell me how to make step 9 easier? I struggle way to long with it. What I eventually ended up doing was taking a hammer and mallet and knocking up the tabs to enable them to slide all the way on. After that I went around every tab i could get a bite on and slowy worked my way around. I contemplated fabricating a tool using an old 4 way lug wrench and some old steel but it didn't come to that. For future reference--how should I have went about it?

1) remove 6 bolts holding bed to frame (t55).
2) remove 3 7mm bolts holding filler to body
3) picked up tailgate and slid onto bumper.
4) disconnect tailgate lights
5) one person on bumper, two at the sides, pick up and moved bed about 3 feet back, let front of bed sit on tires.
6) disconnect fuel pump connections
7) use pry bar and mallet to disconnect retaining ring
8) remove fuel pump, insert new oring & fuel pump
9) reinsert retaining ring and struggle for 1.5 hours tightening
10) reinsert connections

 

Using the correct spanner wrench would have made your life much easier.

They make many different versions of this tool this is just one example

 

Yes, retaining rings can be a pain.

Problem is if you squeeze the ring to get a grip it clamps it to the threads tighter so even harder to get it to turn, lol.

Key is getting leverage without squeezing, thats what the retaining ring tools are all about.
Gripping the "tabs" for the leverage but not squeezing them.

Screwdriver and hammer are popular to get it loosened, tightening is another thing altogether.

The correct tool for each specific retaining ring size is expensive, especially if you will be using it one time.
There are adjustable tools and they do work but not on every ring setup.

 

Did the new fuel pump solve your surging/stalling issue? I’ve been having intermittent surging and my 02 ranger has stalled on me only twice now. I have codes P0231 and P0232. ECM and fuel pump relays are good. Inertia switch seems to be working properly and tested good. I feel like it’s a fuel pump issue but as others stated these codes are not faulty fuel pump codes. I’m thinking it’s just a matter of time before I get a running lean code.