Fuel Pump Relay Won't Switch

roach5050 · #1 09-18-2010, 10:50 AM

I've a 92 ranger xlt 3.0v6
I'm now looking for wiring diagrams, if there's one around here please point me to it.

When I try to start it, the fuel pump won't 'wind up'.
I break out the voltmeter and see that I have power (12vdc) on the switch side of the pump relay. However when i turn the ignition on, the relay coil terminals has only 2.x volts...I assume it should be about 12vdc to switch the relay and send power to the pump. Where does this power come from and what could be causing the drop?

The wires that bring the relay on are _red_ and _blue+orange stripe_. Looks like the blue+stripe is #24 at the firewall Tstrip.
I've jumped out the rlay and the pump is working, but still won't start.

Thanks for any help.

ranger5572 · #2 09-18-2010, 12:32 PM

Could you just get a new relay?

roach5050 · #3 09-18-2010, 12:37 PM

I've replaced the pump and the relay.

sorry i should've said that.

ranger5572 · #4 09-19-2010, 07:24 AM

Oh. I don't know then. But I'll tell you that electrical problems are the worst. You'll just have to track the problem down. I'll see what I can come up with as far as wiring schematics.

roach5050 · #5 09-19-2010, 08:01 PM

So I had taken the negative terminal off the battery, and left it off overnight. I suppose that reset the eecm. I go back out this morning, hooked the neg back up to try and trace the voltages...and guess what. Drove it around all day, started it numerous times. This truck has never given me any trouble at almost 200k.

The coil voltage of the pump relay still reads 2.something vdc. I was assuming it took more to switch that relay. Guess not. And seeing that it comes straight from the eecm....I dunno.

This bugs me tho because I don't know what I fixed, or what was wrong. I have the haynes book for 85thru92... but the diagrams in the back stop at 90, 3.0. The wire colors are different it seems...so that alone makes me not want to fully trust the drawing there. So I'd still appreciate a good diagram.

Thanks for trying to help.

ranger5572 · #6 09-20-2010, 03:58 AM

I did't have much time for hunting around the net this weekend. As soon as I have time I'll look. I've heard before that leaving the battery unhooked for a few hours resets the pcm, but that came from a GM mechanic...who knows. Maybe what you fixed was nothing more than a sensor or something acting up and a reset was all it needed.

FireRanger · #7 09-20-2010, 04:18 AM

I'm not familiar with the fuel pump wiring either, however I doubt it is a signal from the computer. It's more likely coming from a circuit that is on when the key is in the on position and probably through the inertia switch too. You should check that as well. It's on the passenger side under the dash and has a reset button.

roach5050 · #8 09-20-2010, 06:07 AM

yessir I checked out the inertia switch. In the circuit that's between the relay and the pump, the only thing actually.

I am now leaning more to the side of some sensor acting up, or a physical/mechanical problem in the fuel system. After all day yesterday of it starting without a hitch (after battery was disconnected), I jump in it this morning for work and it had trouble starting after just sitting there overnight. At least now I can hear the pump wind up like it should...and eventually, after some spit sputtering it did even out, so I drove it the 15miles to work.

Maybe the filter next, or like said maybe the idle sensor or some other sensor. No check engine light tho. I wasn't thinking in this direction before because before I couldn't even get the pump to come on (without jumping it thru the relay socket).

Maybe gremlins nest in it at night...

FireRanger · #9 09-20-2010, 07:02 AM

The fuel filter is cheap and easy so definately do that. There is also a schrader valve somewhere that you can check the fuel pressure with. I'm not familiar with the process but it's worth looking up. I'm still curious about the 2 volts at your relay. That should all be 12v switching, so it is odd that it's actually working.

ranger5572 · #10 09-20-2010, 11:04 AM

Quote:

Originally Posted by FireRanger

I'm not familiar with the fuel pump wiring either, however I doubt it is a signal from the computer. It's more likely coming from a circuit that is on when the key is in the on position and probably through the inertia switch too. You should check that as well. It's on the passenger side under the dash and has a reset button.

If it was the inertia switch a.k.a. fuel shut-off switch, he wouldn't have been able to drive around...unless the switch itself is faulty and is causing it to engage and disengage all willy-nilly...I guess its worth checking out.

roach5050 · #11 09-23-2010, 05:38 AM

So I've been driving it this week. Here's what I notice.

When I go to start first thing in the morning: turn the key 1click (not to start, just accessories)...I won't hear the pump or the relay. I also notice that the check engine light should be on at this point. If it is not on, it won't start, if it is on it will start.

Now once it's going, everything is fine, I've even dogged it out some to see if it sputters... runs great. The idle is a little rough, but other than that it's gold.

Seems if I let it sit for overnight, or all day at work... then I have to try a few times of turning the key one click, hear the pump / relay / or see the engine light. After that all is good.

Could this be a pressure problem? Sensor or actual pressure? I'm assuming (again) that if the fuel pressure isn't there then the eecm won't kick the pump relay on.

*** oh and btw yeah I agree in the assumption that the pump relay should be ~12vdc on the coil instead of the 2.5vdc (but it seems to work more often than not). I can't find a straight answer on it.

Again thanks for the input guys...

AntGreenHEY · #12 10-10-2010, 04:32 PM

I don't know if it's the same problem, but whenever I drove my '05 from Texas to San Diego, it would just shut off everything every 3-4 hours. I thought it was a faulty inertia switch as well and had it working for a long time. Didn't happen again until I drove it a long distance back over to Georgia. Well, I realized in both instances, I had someone in the passenger's seat for an extended period. My dad and I instantly went for the switch and what he noted is that the wiring harness on the switch itself becomes loose and sometimes works, sometimes doesn't depending on the amount of contact made. Probably happened from accidental kicking or something. My dad reconnected them and shifted em a little and I haven't had problems since. Sounds like this may be your problem.

stephensimmons · #13 10-10-2010, 04:39 PM

check your EEC relay. Its by the fuel pump relay and looks just like it except on is brown and one is green! Thats what my problem was.