Fuel pump won't come on

[geoph1986]

Fuel pump won't come on...Update

My truck has been sitting for a few months, because the front end got too much play and was getting scary. The battery has been disconnected the whole time. I finally got all the front end stuff done and went to start it and the fuel pump won't come on. I checked all the fuses (both under the dash and in the power distribution box), tried swapping relays and bypassed the inertia switch with a jumper. It seems that I'm not getting power to the rear of the truck. However, I did have minor success as the pump will run if I connect power directly to it. The truck was running fine when I parked it and now nothing. :scratch:Any ideas? I'm sure this is a simple fix that I'm not seeing, and I did use the search button. I guess the OBA will have to wait until this issue is sorted. Thanks for any and all help.

 

[94Sport5Sp]

Hi:

When you say "I'm not getting power to the rear of the truck" how did you test and where did you test. Remember that power to the fuel pump only comes on briefly when you initially turn the key on and after that only as needed.

When you say "bypassed the inertia switch with a jumper" does that mean you connected the input side of the jumper to the output side or did you apply independent power to the wires?

PaMnd

 

[MrShorty]

Will the pump run if you ground the fuel pump test lead in the self-test connector (KOEO)? Do you have a wiring diagram?

 

[geoph1986]

94Sport5Sp:
I tested the pump by connecting a battery directly to the fuel pump wiring harness, at the rear of the truck (I took a battery to the rear of the truck and connected the + to the pink w/ strip and the - to the black), and the pump came on. the plug that comes off the frame "looked" suspect, so I replaced it with one I know is good (I was using it to connect the battery to the pump), and plugged it back into the pump harness. I turned the key to the "run" position, with no pump prime noise, no start, and no pressure on the fuel rail.
I then unplugged the inertia switch and put a jumper from one pin of the plug to the other, turned the key to the "run" position, with no pump prime noise, no start, and no pressure on the fuel rail. It seems that there is no power at the harness for the the fuel pump, but the gas gauge works. I need to get a new circuit tester, as I can't find mine, and do some more testing. By the time I came inside last night it was dark and I was *****y.

MrShorty:
I didn't ground the fuel pump test lead in the self-test connector, and I don't have a wiring diagram. Any time I've had problems, I've been able to find my answers via the internet. How do I perform this KOEO test?

One other question, could a bad fuel pump run when connected directly to a battery and not when connected to the vehicles harness? I won't be able to do any testing today, as my son takes up quite a bit of time, but hopefully I can get this sorted tomorrow or on the weekend. This site ROCKS!

 

[marragtop]

You need to check to see if you are getting power to the inertia switch when you turn the key on. If not, then problem is in front of the inertia switch would could mean that it's the fuel pump relay, PCM relay, ignition switch, or associated wiring or fuses.

 

[geoph1986]

You need to check to see if you are getting power to the inertia switch when you turn the key on. If not, then problem is in front of the inertia switch

I've been doing some more searching and reading, and that is the conclusion I've come to. I will try to do some more testing tonight.

could mean that it's the fuel pump relay, PCM relay, ignition switch, or associated wiring or fuses.

I've already checked the fuses and relays, they seem good. I hate tracing down wiring problems.:frustrate

 

[marragtop]

When you turn the key to the ON position, does the CEL come on? If it doesn't then the PCM relay could be bad. If you are testing relays by switching the PCM and FP relays, you could be moving the problem which would still result in no power to the FP.

Start by checking power to the inertia switch.

 

[geoph1986]

There's no check engine light on. In fact, up until I had my dash apart to run carputer wires, there was no bulb in the dash for it (someone before me had removed it). I put a bulb in, but it doesn't come on. I swapped the relays with spare relays I had. I will check the inertia switch and post back later.

 

[geoph1986]

OK, I checked the inertia switch, and my multimeter displays 1.45 when set to 20 volt range and the key is turned on. Now what?

EDIT: I just read that I need to use an ANALOG multimeter or a test light to check the "electric pulse" for the fuel system. Is this true?

 

[geoph1986]

I used a test light and it seems that there is no power to the inertia switch. So that means it has to be somewhere between that and the power distribution box. Can someone tell me where to go from here?

 

[MrShorty]

There's no check engine light on. In fact, up until I had my dash apart to run carputer wires, there was no bulb in the dash for it (someone before me had removed it). I put a bulb in, but it doesn't come on.

The CEL never comes on. The CEL is supposed to come on key on engine off as an indication that the main computer has power and is ready to go. If the computer doesn't have power, it can't tell the fuel pump relay to close (amongst other things) and the engine won't run.

You say you don't have power to the inertia switch. The next step I would probably take would be to see if the fuel pump relay is closing. If the relay isn't closing, then you see if you can figure out why the relay isn't closing (including making sure the main computer has power). If the relay is closing, then you trace the wiring up towards the battery post until you find the break in the wiring. This is where an actual wiring diagram is better (IMO) than searching over the internet, you don't have to wait for someone to tell you what the next component in the circuit is. I've had good success with the diagram in Chiltons as far as the fuel pump circuit goes.

 

[geoph1986]

MrShorty:
I've been using the diagram in post #18 in this link.
http://www.explorerforum.com/forums/showthread.php?t=163224&highlight=TESTING+INERTIA
I have power at the fuel pump fuse (20 amp mini in the PDB). So would it be safe to say that my problem probably lies between that fuse and the inertia switch? As for the check engine light. It hasn't worked since I've had the truck. Before I got my hands on it, someone removed the bulb from the cluster, and when I had the dash apart, I replaced it. The truck hasn't been started since. Maybe there's a reason the bulb was removed. I don't know how to test relays, I know it's simple...but I can't grasp it. If I had someone give me a procedure written for dummies, or could show me pictorially, I could do it. Vehicle electrical isn't one of my strong points.

 

[MrShorty]

I have power at the fuel pump fuse (20 amp mini in the PDB). So would it be safe to say that my problem probably lies between that fuse and the inertia switch?

It's a basic DC circuit, so, yes, the problem almost certainly lies between the fuse and the inertia switch. As you can see from the wiring diagram, there's only the fuel pump relay and some wire between those two components.

I don't know how to test relays, I know it's simple...but I can't grasp it.

In this case in particular, it is really easy.
Relays are basically electronic switches. One side of the relay is a simple electromagnet (the R and LB/O side. The C is coming from the EEC relay. The LB/O wire ends up at the PCM). When current flows through this side of the relay (when the PCM applies ground to the LB/O wire), the magnet is activated and pulls the switch closed, allowing current to go to the fuel pump.
Testing the relay is as simple as getting current through the magnet circuit and using a voltmeter to see if the relay closes. There's a branch off of the LB/O wire that goes to the self-test connector (short end of the trapezoid if memory serves), that you can ground with a jumper wire. Assuming there is power at C, then this allows us to test the relay.
With that in mind, here's a basic set of steps for testing the fuel pump relay:

1) Check for power on R and BK/Y at the relay. If either doesn't have power, look upstream in those circuits to find out why.
2) Apply ground to LB/O at self-test connector and use a voltmeter DG/Y to see if the relay closed. If the relay closes, then the problem is elsewhere. If the relay doesn't close, replace the relay.
3) If the relay closes when you manually apply ground to LB/O, then use a voltmeter to see if the computer is applying ground to LB/O when it should.

 

[geoph1986]

Update

OK here's the latest and greatest.

I tried applying ground to the LB/O wire via the self test connector, but nothing happened (I might be doing it wrong). I then tried to apply the ground from the battery, and nothing happened. This was done KOEO. I removed the relay and connected it straight to the battery, and it closes. If I apply a jumper from the BK/Y wire to the DG/Y wire the fuel pump runs.

I used a multimeter and tested each fuse on either side, and on all of them I get 12V on both sides, excet on the ECC fuse. I get 12V on the unfused side and 2V on the fused side. I checked the red wire on the computer and get 2V there too. BTW, there are 2 LB/O wires at the computer that goe to different pins.

As far as the fuel pump relay goes, I get 12V on the Bk/Y wire and 4V on the R wire and the relay doesn't get the signal to close. The ECC relay is engaging properly.

I've also cleaned the grounds on the fender by the battery, and that didn't help either. I also have no CEL ever. The batt, and ABS lights come on when the key is in the run position, but no CEL.

I'm really stumped on this.

P.S. The wiring diagram I have been using is on post 18 in the link.
http://www.explorerforum.com/forums/showthread.php?t=163224&highlight=TESTING+INERTIA

Does anyone have a wiring diagram of the computer wiring?

 

[MrShorty]

I checked the red wire on the computer and get 2V there too. BTW, there are 2 LB/O wires at the computer that goe to different pins.

As far as the fuel pump relay goes, I get 12V on the Bk/Y wire and 4V on the R wire and the relay doesn't get the signal to close. The ECC relay is engaging properly.

Is there a typo in there, because that red wire should have +12 V on it with the key on, not 2 V. If that really is only 2 V, it suggests to me that the EEC relay isn't closing properly. The absence of the CEL also suggests that the computer isn't getting power. As noted previously, if the computer isn't getting power, the pump won't come on as it should.

I've used the wiring diagram in Chiltons for a lot of the basic computer wiring (including computer power and ground circuits). Autozone used to have a free electronic version of Chiltons on their website. I haven't used it in a while, but it seems like it's still there, you may just have to "register" with them to gain access.

 

[geoph1986]

Is there a typo in there, because that red wire should have +12 V on it with the key on, not 2 V. If that really is only 2 V, it suggests to me that the EEC relay isn't closing properly. The absence of the CEL also suggests that the computer isn't getting power.

MrShorty,
Yes that's a typo. I am getting .02V on the yellow wire (fuse 4) coming out of the PDB. On the other side of the fuse I get 12V. I'm also only getting .02V at pins 37 & 57 at the PCM. All grounds I have tested (off battery, at each side of connector going to passenger fender, at passenger fender, and at PCM) are 12V. For fun I by passed the relay for the EEC and I still only get .02V. What would cause the EEC power at the PDB to go from 12V on one side of the fuse to the .02v on the other side of the fuse?
Here's the engine wiring diagram I'm using.

 

[MrShorty]

What would cause the EEC power at the PDB to go from 12V on one side of the fuse to the .02v on the other side of the fuse?

Bad fuse seems the most obvious explanation? If the fuse itself is good, something not making connection/broken in the connectors.

 

[chilliwackwestie]

I don't mean to dumb things down but this happened to me and all it was after all the over thinking on my part was the connector from the truck to the pump was dirty i just cleaned it bent the contacts a bit to be sure of a good connection and boom no worries
just my 2 cents
cheers
Glen

 

[geoph1986]

Fixed it yesterday evening. The connector on the fused side was bad. It looked good on both the top and the bottom, but when I removed it from the PDB, it became obvious that it was bad (corrosion). I replaced it, and the truck runs. The CEL comes on with the key now too, but now it is always on. I will pull codes in the next day or two. I guess this is why there was no bulb in the socket. I would like to thank everyone, especially MrShorty, for all their help. This has been quite a learning experience for me, as this was the most electrical trouble shooting I've ever done. Thanks again.