Ranger Fuel System Woes

[ltbenji]

Hey Guys

Today ended day two of trying to diagnose my Ranger. I've extensively searched the forums but cannot find the information I need. Here's the story.

The truck is a 88 Ext Cab, single fuel tank, 89 engine and modified 88 wiring harness. 196k on the truck and about 60k on the engine. The swap was done over a year ago.

Last sunday the truck died in the road, started back up when a little gas was added, cut out again, waited a few hours and then ran for a final few minutes. It had to be towed home Fuel pressure was tested when it was dropped off, first cycle nothing, eventually worked up to 40 but only after many cycles.

Fuses checked out fine and I replaced both relays.
Fuel pump - Autozone - Duralast 19911
EEC Relay - Advance Auto - BWD R3080
Nothing changed with the new relays and mixing and matching the new and old ones. Further investigation showed that the connectors were very corroded so $40 later the pigtails were replaced. Again the truck would't start.

My next thought was fuel pump(s). Almost 200k miles seems a good life. So off came the bed and the in tank pump and strainer assembly was replaced followed by the high pressure frame mounted pump as well as both filters.

Primed the system six or seven times and tried to crank it. The truck caught two or three times but would not run. It would choke out and eventually it would not start at all.

The current state is the fuel pumps will not even prime now. The relays both have at least one constant hot. No power is read at the inertia switch and bypassing the inertia switch doesn't help anything.

The wiring diagrams on the site have helped some but not tremendously. I've got a volt meter and have been chasing some wires but have not come to any solid conclusions.

What do I start with tomorrow?

 

[adsm08]

Near the steering column out in the engine bay is a round plug that has one wire going in and two coming out I would start by applying power directly to the two-wire side.

 

[ltbenji]

I'll look for that....sorry for the noob question, but how should I be applying the power to this plug....run a wire temporarily from the battery?

 

[adsm08]

That's how I have been doing it all week.

Look into a set of these:

www.amazon.com/Hand-Tools-1129-Retr...4?s=automotive&ie=UTF8&qid=1374329265&sr=1-24

They are nice to have to chasing wiring problems because you can hook them up in place of a suspect section of wire, or just hook things to the battery.

 

[RonD]

The fuel system power can be a bit confusing.
When the key is turned on the EEC relay closes and sends 12v to the Fuel Pump relay(and alot of other stuff), this is not Fuel pump power it is just power for the fuel pump relay to work.

Inside of any mechanical relay there is a metal contact bar that is held "open" by a spring, and there is an electro-magnet(apply power and it becomes a magnet), when the electro-magnet is powered it pulls down the metal bar and "closes" the switched contacts(that's the click you hear), when power to the electro-magnet is stopped the spring pushes the switched contacts "open"
There are generally 4 connections on a relay.
2 connections for the switched contacts, for the device you want to send power to.
2 connections to power the electro-magnet

The Fuel pump power comes from the fuel pump fuse this fuse is connected to the fuel pump relay's switched contact, the open/close contacts inside the fuel pump relay, this is the constant power you see at this relay.
When the relay is activated by the computer the contacts close and this fused 12v is sent to the inertia switch.

So with key off the fuel pump relay base should have
Switched contacts
12v(from fuse)
0v(to inertia switch)

Relay power
0v(from EEC relay)
0v

With key on and a delay of 5 seconds
12v(from fuse)
0v(to inertia switch)

12v(from EEC relay)
0v

With key on instantly measured, the computer will ground(activate) the relay for a few seconds to prime the system, so contacts will close and you get
12v(from fuse)
12v(to inertia switch)

12v(from EEC relay)
Ground(but only for a few seconds, each time key is turned on)

You can put a jumper wire between
Switched contacts
12v(from fuse)
0v(to inertia switch)

This would send the 12v power to the inertia switch regardless of key on or off, so just used for testing.

I have seen lower voltage coming out of the EEC relay to the fuel pump relay, bad wire, this lower voltage prevents relay from closing.
With fuel pump relay in place, each time the key is turned on you should feel or hear it click, BUT.......the EEC relay is next to the fuel pump relay and it "clicks" at the same time, so make sure fuel pump relay is clicking(closing)

 

[ltbenji]

Adsm, I don't see the plug you mentioned. I have one round connector coming from the underside of the truck that has a dark green with white stripe and a light green with a white stripe. There is a single line that goes from the firewall down the frame with what looks like a pink and black wire. If I remember correctly from wiring diagrams pink and black is the hot for the fuel pumps

 

[ltbenji]

Ron, I'm doing my best to understand your post and I think I have almost got it. I have a constant hot at both the EEC and the fuel pump relay. According to my Haynes manual, there is a switched hot that goes from the EEC relay to the fuel pump relay, a solid red wire. This does become hot when the key is cycled. However I am not finding a switched hot going from the fuel pump relay to the inertia switch. Do I have the right train of thought here?

Next steps?

 

[ltbenji]

Update. I removed the wires from the inertia pun clip and ran a wire from the battery to the pink/black wire and at least one of the pumps primed

 

[ltbenji]

One more update. Removed the individual wires from the relay clip, wired the inertia switch clip straight through and touched the yellow constant hot and the orange/blue that goes the inertia switch and at least one pump was priming. Off to get a new relay from a different parts store and cross my fingers

 

[ltbenji]

Good news!!! The truck now starts and runs!!!!
Replaced the duralast relay with a BWD relay and it fired up

On a not quite so joyous note.....it only shows 27 psi on the first prime...any ideas for finding those 13 missing psi?

 

[Mark_88]

did you check the Fuel Pressure Regulator (FPR)? pull the vacuum line off it and sniff...if you smell gas then the FPR is the problem now...

It's not unusual to have more than one thing go wrong at or about the same time as others...

 

[ltbenji]

Mark, I checked it like you said and there was a slight gas smell.....it's strange because I replaced the FPR about two weeks ago.

Would you recommend me getting another one anyway?
And on a side note, I checked the volts at the high pressure pump, and it is getting 12v

 

[RonD]

Glad you found the problem.

Yes, if you have a fuel pressure gauge hook it up and with engine idling pull off the vacuum line on the FPR, put your finger over the end of the line so engine doesn't get open vacuum.
Pressure gauge should jump up when vacuum line is removed, if not then FPR is bad.

FPR is just a valve and a spring
Engine at idle has a highest vacuum and is using less fuel
Engine at 3,000rpm has low vacuum and is using more fuel

So the vacuum line is used to pull open the FPR valve(spring closes it), sending fuel back to the tank when its not needed, like at idle.
As RPMs go up vacuum goes down so FPR closes a bit keeping fuel pressure up while more fuel is being used.

Since the fuel pumps do not run all the time there is also a check valve on the high pressure pump, this prevents fuel from being push backwards into the tank when the pump is off during driving but also when the key is off.
After testing FPR, shut of engine/key off, and watch if the pressure starts to drop, if it does then check valve may be leaking(could also be FPR)

 

[ltbenji]

Mark and Ron

I checked the FPR like both of you said and when the vacuum line was removed the gauge climbed from 27 to 40 every time. So back to O'Reillys to try and get this one replaced under warranty. I'll keep you all posted.

 

[ltbenji]

Wait wait, I just caught my mistake. So the FPR is supposed to climb when the vacuum line is removed. So should I take the HP pump back for a new one?