View Full Version : Fuel pump keeps running in "on" position

01-15-2012, 05:00 PM
I have checked the relay, under the driver's seat...good

Replaced the ignition switch...no change

The fuel pump is new, according to previous owner...

I also have good pressure to the rails, the car starts and runs...

It continues to act like it's trying to build pressure just like any other mustang, but just keeps running (not like the 7 secs it's supposed to).

I got nothin'...

What do you guys think I should check next...I haven't hooked it up to a diagnostic tool yet so I don't know if/what codes it's throwing, so...

01-16-2012, 06:08 AM
Just to be clear, you turn the key on, the pump keeps running without starting the engine?

If you start the engine, and then shut it off, does the pump shut off?

01-16-2012, 08:11 AM
The fuel pump continues to run, even after it builds initial pressure in the "on" position...

It, obviously, ha, runs when the car starts and runs...

and it runs even after engine stalls (during diagnostic tests like VAM, etc.)

once the ignition is turned past the "on" it runs constantly...

01-16-2012, 11:54 AM
When the car is OFF, does the pump stop running?

01-16-2012, 12:28 PM
So it switches off when the ignition switch is off?

That function is controlled inside the EEC - there is a drive transistor that completes the ground side of the fuel pump relay to engage the pump(s). It should run for about 2 seconds in initial igntion on - strictly time controlled as there are no fuel pressure sensors.

Do you get any KOEO/KOER codes? The fuel pump always on is also symptom of limp mode (damaged EEC) so if it makes [accurate] codes, then the driver transistor in the EEC is shorted.

If you're skilled with multi-layer circuit board soldering, replace the driver. otherwise replace the EEC.

01-16-2012, 12:54 PM
Agree with NotBud. I can sell you my PE eec if you need one, $100 shipped. 100% working, I swapped to the LA3.

01-16-2012, 01:01 PM
Yep, it turns off when the ignition switch is off...crap!

If you can hold on to that PE, I'll pick it up in a few weeks, if you need to sell it, don't wait for me...but I guess that's my problem...

Thanks guys!

01-16-2012, 01:27 PM
I can hold it, just give me a shout when you're ready. Just make sure there are no issues with the harness, hate to see you fry another eec (and waste a 100).

01-25-2012, 07:28 PM
I opened the ECU just for poops and giggles (what's the worst that can happen, it doesn't work!)...there doesn't appear to be anything fried, I know what that looks like, I've seen me do it!! I'd give the driver replacement a try, but I can't find any schematic that shows where it is in this ECU...I would just look for the fried one, but, like I said earlier, I can't find even a connection line burned??

I also can't find PE, LA3, etc. anywhere on this thing...beginning to think it's just a 2.3 ECU. I have a plain old 2.3 ECU laying around, could I hook it up and see if the fuel pump does the same thing, just to be sure that it's the ECU, or will it cause bad ju-ju with everything else?

Serenity Now, Serenity Now!!

01-26-2012, 06:09 AM
Schematic? That's funny!

Find the appropriate pin on the 60-pin connector that enables the fuel pump ground. Then trace that pin-to-foil trace to the 3-pin TO220 device that's bolted to the case (for heat sink purposes). Then take that TO220 driver out (remember your multi-layered soldering skills - after dissolving all the humiseal coating from the entire EEC board) and test that driver using a transistor tester.

Repair/replace as needed.

And No, it's not an easy task nor a job for the timid.

01-26-2012, 06:32 AM
I wouldn't just plug in the 2.3 non-turbo EEC. If the pinouts are different, you could fry it. I know I had to move a couple of wires to go from the PE to the LA3 eec. Let me see if I can dig up those instructions, it may help.

01-26-2012, 06:43 AM
Fuel pump control is pin 22 http://www.gt350mustang.com/eecspecsturbo.htm

Found my docs Download here ( 2 pdf's in a zip.

01-29-2012, 04:14 AM
Wow, that may be a little above my skill level...

I followed that pin and foil to the driver...still doesn't look fried.

I was swapping out the seats from this car into my 84 (cause it's running) and noticed a ground wire spliced into the fuel pump relay under the seat and into the seat mount bolt on the floor pan...WTF???

Would that have anything to do with the issue??

01-29-2012, 05:03 AM
If that splice is indeed on the same circuit as pin 22, then sure, that's why the pump keeps running. The big question is WHY was that added? I can only speculate that the pump was not coming on.
At this point, I would remove the added 'riggin' and start from square one. Make sure there are no other 'alterations' to the factory wiring, and begin troubleshooting.

01-29-2012, 09:04 AM
I found this on another forum from way back, makes me wonder if this is what the PO was trying to do...what do you think?

..."The Gree/Tan wire goes to the EEC and the EEC ground that wire to pick up the relay secondary curuit (coil) and turn on the pump (primary power circuit). Sounds like the solid state device in your computer that grounds the relay coil might be bad. You can fix this if you don't want to buy a new EEC just for that problem by running the Green/Tan wire through the primary circuit of a new relay and using an ignition "run" source to pick up the new relays secondary circuit. When the key is on the pump will be on and the inertia switch is still in the circuit for protection. Down side is the pump is on anytime the key is on. you could also wire a switch between the "run" power source and the secondary circuit of the new relay so that you could override the pump run in the key on position." ...

He has the shut off bypasses as well, a staple in the pigtail????

This whole harness has been butchered!!

01-29-2012, 12:46 PM
OUCH, that' sucks. But atleast you are making progress in getting it straigtened out. It shouldn't be a big deal to get an inertia switch, you need that working for safety.

01-29-2012, 12:50 PM
Okay...removed the spliced wire that was "grounded" to the seat mounting post...haven't reconnected the emergency shut off (that's next)...fuel pump runs for the 2 seconds and shuts off as it's supposed to!!!

Not the computer after all...I'll definately connect the emergency shutoff...

We have a winner!!

Thanks for all the help, guys!!

01-29-2012, 05:31 PM
Gosh - a pre-modified SVO.

Who woulda thought?

01-30-2012, 07:57 AM
Makes me appreciate my bone stock 84...got it from a Ford technician that serviced it its whole life with original owner...he left things alone or replaced with OEM!

I'm a little nervous to see what has been done under the hood, when I really get into it...

Got the fuel pump working right and the engine running, now it leaks water like a sprinkler from every hose connection I can see!! Hopefully not from the head gasket!

One thing at a time, I guess...