A Fuel Pump that won't Sing...

[1shot]

Vehicle: 92 4.0 Auto 4x4 Exp

Okay on Easter Sunday I went out for a drive. Came home. Went back out to go for Easter Dinner at friends and the truck cranked over but wont start. I notice the absence of the old fuel pump hum.
- So i assume fuel system. - Got out the Haynes.

Followed the diagnose procedures.
Had voltage at pump connector at rear axle, so i knew it wasnt a fuse or Inertia switch therefore since the pump was very noisy before, I assumed it was the pump that failed.

Installed new Carter pump, connected everything back up - but no pump hum on start or run. I dry ran the pump prior to install so I knew it was good out of the box. So I confirmed by hotwiring it with 12v - yes pump is ok. It has a nice steady quiet hum compared to my old rattler.

So i double and triple checked all fuses in both locations.
Then I replaced all three relays under fuse panel. Checked and bypassed the Inertia switch.

Still no pump action.

So I get:
12.5V at battery and across all blades of fuses. I checked the relays and get either 0 or 12.5 volts depending on which relay blade and position of Ignition at that time.
I get 6.60 volts at bypass switch and I get 6.60 volts at connector at tank as well. When Pump is added to circuit the voltage drops to 0 and pump does not run. So Is the computer bagged or what? What voltage Am I supposed to see at the pump? I get 7.5 volts at the sending unit and 6.6 on the positive feed to the pump. My sending unit and gauge works properly as well. (tank is now back up to 1/4+ after Jerry canning it back up to make sure I wasnt drysuckin the pump)

Now my Haynes doesnt have anywhere near all of the electrical schematics a full ford book does, but I have seen a bunch that Shamaal has posted including the Autozone links and I am still confused.

I read somewhere in previous topics that the signal voltage is 6.6 volts, if that is the case which device creates this voltage? the relay or the computer? and if 6.6 volts is a good signal voltage, then why have I got 6.6 at my pump at the tank? Is not the voltage at the pump supposed to be 12V?

 

[MrShorty]

I don't completely understand why, but, with the relay open, you will see 6-7 V on the fuel pump power wire downstream of the relay. So here's what I understand:

1) You have 12.5 V at the battery, the fuse, and the relay.
2) You get 6.6 V at the inertia switch and the pump.

All values assume KOEO.

As a member of another forum I frequent is fond of saying: "where the voltage drop is is where the problem is." That suggests to me that your problem lies between the last point where you're getting 12.5 V and the 1st point where you are getting 6.6 V. Here's how I would proceed.

All tests KOEO
1) Ground fuel pump test lead. This should close the fuel pump relay. Does the relay close? Do you see 12.5 V at the lead that goes to the inertia switch? If not, then the relay isn't closing. go to 2.
If yes, then go to inertia switch and continue down the circuit until the voltage drops.
2) Do you get 12.5 V on the red wire that goes from the EEC relay to the fuel pump relay? If not, then see why EEC relay isn't closing. If yes, and you know you have a good ground where you grounded the test lead, then see why the fuel pump relay won't close (suspect bad relay).

That's not a complete fuel pump circuit diagnostic tree, but that's where I would start in your situation.

 

[shamaal]

With a paper clip in the inertia switch you will read about 6 VDC. This is the float from the bias resistor and transistor inside the computer. If it goes to zero with the pump attached that is not a problem. Why this happens is a fairly complicated discussion about impedances and voltage dividers that is not really germane.

When the ignition switch is turned to run (not start), the voltage should go up to +12 VDC for about two seconds. This makes the pump run. Because the engine is not turning the computer turns the pump off.

Assuming this does not occur there are a number of ways to troubleshoot. Look at the diagram below, we're working the green line. When the key is in run there should be 12 VDC at the red wire #361. Remove the Fuel Pump relay and measure the voltage at the corresponding contact on the relay connector. I don't know if the 92s have the same relay setup as the 91s so I can't be more specific.

If you have +12 VDC at this pin, the problem is the EEC is not supplying a ground to the relay or the wire between the EEC and relay is broken. The computer supplies a ground to the LB/O wire to energize the circuit.

If you do not have +12 VDC at the relay connector pin, we'll move to the EEC relay. See picture below, we'll work the red path first. Remove the EEC relay and measure the voltage at the pin corresponding to the R/LG (16) wire. With the key in run there should be +12 VDC. If not the problem is in the ignition switch or the wiring.

If there is +12 VDC, check the pin that cooresponds to the Y wire there should be +12 VDC. If not the yellow wire between the fuse and the relay is bad or the fuse is blown.

If +12VDC is at the connector pin, either the ground wire BK/W is bad (easily ohmed) or the Red wire that leaves the relay is broken before it gets to the fuel pump relay.

I've tried to make the instructions simple and have assumed some amount of troubleshooting ability on your part. Also, it has been said that the relays have been changed along with the pump; again I assume that the correct parts are installed.

Read the description and ask questions if somethings not clear before starting.

PS - While I was posting Mr. Shorty answered also. This provides two methods to troubleshoot. If there are questions ask.

 

[1shot]

thanks for your quick feedback

So I am printing off those schematics from Autozone and the ones you sent Shamaal. I did not have access to those when I was trouble shooting yesterday, since the truck is at my brothers house, now I have a better understanding what to look for, I will return and play the diagnostics game one more time.

Like I said I know the pmp runs, so I always could hotwire it in order to get truck started, but I want to fix it right.

 

[shamaal]

I'm sure you've seen the complete set of diagrams at http://www.explorerforum.com/forums/showpost.php?p=1655246&postcount=22

Good luck.

 

[Opera House]

The computer applies a small current through a resistor to provide a diagnostic code when the impact switch opens. The pump acts as a pull down for this voltage and tells the computer the circuit is complete. This test is performed only when the fuel pump relay is open. When testing, use a lamp as a load at the pump. The relay must be jumpered because the fuel pump relay only comes on for 4 seconds till the engine starts. The pump fuse is a good place to measure current, 1/4 inch spade connectors fit nicely into the fuse contacts and allow measurement by a meter. Normal current is 3-4A and increases about 1/2 amp at low vacuum (engine load). After about 5 minutes the current will drop about 1/4A as the pump heats up and resistance increases. Below about 2.5A th engine will start to falter. That relates to about an added two ohms in series resistance if there are connector problems.

Be aware that the added flow of a new pump can cause regulator problems if the valve seat has wear on only one side (non centered spring) as the regulator opens wider. The valve plate can move to the side and stick open. If the vehicle starts stalling at stops, this is the problem.

 

[clvineyard]

hey Opera House do you still have your 97 for sale?

 

[1shot]

Update + new Questions!! (re Dead Fuel Pump)

OK Here's the deal. Since I did not have access to the schematics and Diagrams b4 - I was missing some important clues. Then after testing fuses and relays I thought It might be the Computer not triggering properly, but now I am not sure if the computer is not okay and I have some other problem...Read on...

NOW I have those schematics I think I am closer but I am still not sure which way to turn.

I hooked up my meter and tested the codes - here is what I got: 54, 21, 1...1...1...1
@ O (KOEO) = code 54 (Air Charge Temp Sensor out of range) But I dont think this would kill the fuel pump...
@ C (Continuos Mem) = code 21 (Coolant Temp out of range) which is an eye-opener because I have been fighting a coolant temp problem for a few months...and I dont think this would kill the fuel pump either...
@ R (Engine Running) = Cant do that cause it wont run without fuel...

So after confirming the codes twice more - I get same codes so I went back to the digital measurements of voltages at all connectors and fuses and relays.

I get proper voltage (12.5+) at the proper wire when key is off and when key is on at both WOT and EEC relay...EXCEPT...I only get 02.5V+ at the Fuel Relay's Black/With Yellow trace wire. The Black/Yellow feed is supposed to be hot 12.5 all the time, because BOTH sides of the Fuel Pump Fuse are at 12.5 same as Positive post of battery all the time key on or off.

Now The reason I missed this before was because I read 2.5 and my eyes just told me it was 12.5 but when I tried this again today I now realise it is reading 2.5 - so I confirmed that with an analog voltmeter as well.

I am confused how to procede now because the schematics show a straight piece of wire with nothing but a connector or two on route from the fuse down to the relay. And at this point in time I dont think my computer is coming into play - maybe just a bad wire or corrosion in fuse block / relay assembly?

Any opinions ?

 

[MrShorty]

Sounds like you are up against the same problem I was up against last summer. I had power to the fuse, but none to the relay. I didn't track down the exact location of the break, but I cut the wire at the fuse and the relay, and spliced in a new wire. That fixed it. Once you've convinced yourself that the problem has to be in that wire between the fuse and relay, that's probably what I would do.

 

[1shot]

thanks - I thought I wuz going crazy again

Mr.Shorty - Thanx fer the quick reply...
I really began to doubt myself again....

Like I said - I read 6.6 volts at the pump connector - therefore I thought I had the voltage I was supposed to have there - but now that I read 2.5 at the relay instead of the previously thought 12.5 volts - lol -

That was what I was going to do tonight - splice in a hot feed to that blade of the relay from the fuse to just to see the result - but If you had same/similar problem I dont fear the action so much... and to think - I almost bought a new computer for it/her today...


By the way any thoughts on my codes? 54 and 21?

 

[javiscancino]

i have a 92 explorer too, i did all the wiring on my explorer, and physically, the wires to the fuel pump goes like this, you can start to locate the big green 30 amp fuse that feeds the relay, that's hot always, from there goes to the relay, that's the black white wire, then comes out as a dark green with yellow an goes to the inerthia switch, check for continuity there, then comes out as pink with black from there goes directly to the fuel pump but before it gets there there is a 4 wire plug, one is the pink black, the other is the ground and the other 2 are for the fuel gauge, look under your truck to find that plug, ok, now, you know physically how that works right, once you open the key, the main pcm relay suplies current to the fuel pump relay, and for two seconds the ecu provides ground to the relay, that close the circuit at the relay, from there the fuel pump shoul starts, once the engine runs the ecu detects the rpms and then keeps the ground signal constant to the fuel pump relay, if you want to bypass that, you could either ground constantly the fuel pump relay, that's the light green with orange, not sure, and if you want to bypass the turn key on, just put a switch to the red wire that goes to the relay, that will suply with current to the relay, ok, will take some pictures tomorrow ok, hope you can fix your problem.

 

[MrShorty]

By the way any thoughts on my codes? 54 and 21?

You say the 54 is KOEO and the 21 is CM??? Are you sure the 21 wasn't also KOEO with 11 for CM? If they were both KOEO codes, then I'd say it's just a result of the no start. During the KOEO test, the computer expects to see those temperature sensors at normal engine operating temperature. Because you can't start it, you can't get the engine warmed up, and the result would be KOEO 54 and 21.

If the 21 really is a CM code, I would clear CM and revisit it after you get the engine started and can test drive it and see if the CM 21 comes back.

 

[1shot]

Codes Mr. Shorty

Okay EXACTLY what codes popped are as follows:
(old style voltmeter with Analog swing needle gauge used - set at 30v max range so each swing was a definate half swing of full needle.)

Ignition off:
12.5 V
Ignition on:
Drops to 0v
+/-2 seconds later a small swing to like 2 volts then drop to 0
long pause
5 quick swings
pause
4 quick swings
pause
2 quick swings
pause
1 swing
long pause
1 swing
long pause
1 swing
long pause
1 swing
long pause
1 swing
longer pause.....
repeat all above once more only without the small 2 volt blip at the beginning...

So I figured it was
5,4,,2,1,,1,,1,,1,,1

so i took it to read 54, 21, 1, 1, 1, 1 ... repeats a 2nd time then stop.




Am I reading it wrong?

 

[1shot]

Mr. Javiscancino...

Great Info...thanks man...
Everything you said is exactly as I have percieved -

Its starting to look like I have a faulty wire between the fuse and relay or a fautly connector, cause I do not get 12 volts to the relay's black and Yellow with key off or key on.

The Black/white is the one to the EEC. it is showing 12 v when key is on. Like it's sposed to, and the 2 yellow wires feed the 12 v key off/on.

 

[shamaal]

If not fixed already, next step would be measuring wire 175 resisitance with digital ohmeter. It should be zero. If not then isolating the problem to what side of C109 would be next.

I've added the ECT resistance chart if the temp test does not clear up. The sensors are on the front of the engine, one's for the gauge the others for the computer (ECT).

 

[Opera House]

You can not diagnose your problem without inserting a jumper in place of the fuel pump relay contacts. The computer will not turn the pump on long enough for you to do any testing. Take all the results you have so far and throw them out the window, take a breath, and start over. At the relay with the key off, measure the resistance of the pump to ground. It should be about 2 ohms if I remember. Verify the value with your old pump. Check for voltage first, you don't want to be on the 12V side of the relay. Then you can continue with the jumper in place of the relay to diagnose where the voltage is lost.

 

[MrShorty]

Okay EXACTLY what codes popped are as follows:
(old style voltmeter with Analog swing needle gauge used - set at 30v max range so each swing was a definate half swing of full needle.)

Ignition off:
12.5 V
Ignition on:
Drops to 0v
+/-2 seconds later a small swing to like 2 volts then drop to 0

This is the "fast codes", which youcan ignore.

long pause
5 quick swings
pause
4 quick swings
pause
2 quick swings
pause

Because you have a '92, and I would expect a '92 to output three digit codes, I would interpret this as a KOEO 542: fuel pump circuit fault

1 swing
long pause
1 swing
long pause
1 swing
long pause
1 swing
long pause
1 swing
longer pause.....

Not the correct number of 1's, but I expect it's trying to ouput a separator pulse and a CM 111 pass code, though it doesn't quite fit into the usual sequence that I'm used to. Mine will output KOEO codes twice, then a separator pulse, then the CM codes 2ice.

repeat all above once more only without the small 2 volt blip at the beginning...

So I figured it was
5,4,,2,1,,1,,1,,1,,1

so i took it to read 54, 21, 1, 1, 1, 1 ... repeats a 2nd time then stop.




Am I reading it wrong?

Maybe, maybe not. Either way, I don't think it matters at this point. If it's a fuel pump code, you already know there's a problem with the fuel pump circuit (that's where this whole thing started). So, you're working on that. If they are temperature codes, there's no sense worrying about them until you fix the fuel pump circuit and get the engine started.

 

[1shot]

it...it...it's ALIVE!

Ok so after reading the 2.5 volt input on the hot wire to the relay yesterday -I obviously knew somthing wuz wrong.

So tonight I created another path - (a jumper) from the downstream side of the fuse to the relay power up side. Basically running a paralel line to the black/yellow traced power feed.

I hit the ignition and it started within a second or so. The crowd goes crazy!

So I ran it for an hour - started it up numerous times. All is well.

Except I still dont understand why or how it was showing 2.5 volts at the relay and 6.6 volts at the inertia switch before. Now it shows 12.5 volts at the relay and the inertia switch still shows 6.6 volts. But it works now.

Nice quiet new pump - and although I can get my old pump to spin up when hot wired - it makes so much noise that it would have died very soon if it had not already caused this problem. So the good news is it doesnt look like the computer died, or my relays, just the wires.

Im going to drive it around for a few days and then do some more investigation in a day or two. I still need to find out the why...

 

[1shot]

Mr. Shorty...

My exploder book doesnt show any 3 digit codes - only 2 digit ones. so maybe i did interpret the sweeps incorrect - you say 542 is a fuel system error code? well then that is obviously the right code then...but I definately got
5 4 2 and then 5 x 1's lol
I counted out loud and my brother wrote it down...

Anyway thanks again for EVERYONE's help - 'specially Shamaal and MrShorty - Ima gunna get to the bottom of this one cause I need to understand why stuff happens...

 

[shamaal]

Good to hear that.

Ponder it a couple days and if you still have questions, post and someone can explain.