Fuel pump will not stop running

[MustangGT1990]

The other day I started my Mustang and when I turned the motor off my fuel pump was still running. I started it back up and cut it off again. It was still running. I got out and disconnected my negative battery cable. I tapped on the fuel pump relay a few times then reconnected my battery cable and started it again. It seemed to be alright for a little while then it did it again. I bought a new fuel pump relay and put it in. It did the exact same thing. Now it has gotten worse, it will NOT stop running. What could be causing the problem? Is it my ignition switch?

Just to sum it up for you, with my keys in my pocket the fuel pump runs non-stop if the battery is hooked up.


Thanks for any help!

[crazypete]

Go up front and check the eec-iv hook up connector near the brake booster. There is a port on it that if you hook up to ground then the fuel pump will run on it's own, even with the motor off. Otherwise, the computer module controls fuel pump operation, but with the power off, the computer relay would be off too. This works because the wires to the relay are always hot.

You probably got this wire chafed and grounded somewhere.
See attachment. I would check this wire and trace it back (easier said than done) to the relay under the seat.

[MustangGT1990]

Crazypete:

Thanks, I'll give it a look tomorrow evening and report back. Is it possible that I am having computer issues? I have been having some serious problems with my car anyways. Try this one on for size:

It is a 90 GT with a factory 5 speed. When I pushed the clutch in to start the engine it would start up just fine and idle perfect in neutral with the clutch out. As soon as I pushed the clutch in it would start idling down basically to the point of stalling. But if it did manage to idle on its own with the cluth pushed in, as soon as I put the T-5 into ANY gear 1-5 or R it would IMMEDIATELY kill the engine. I ran the KOEO tests and got a code 67 for the Neutral Switch circuit. I tested the switch on the tranny and it tested OK. I am beginning to wonder if my computer is hammered.

[bigred90gt]

got a code 67 for the Neutral Switch circuit

If I'm not mistaken, the neutral switch is on the top of the cluth. There is a grey plug with 3 red wires, one or two have a blue tracer. I cut off the plug and spliced all three wires together to override the switch, thinking it would solve a past problem I was having, and now I don't need the clutch to start it at all. Just turn the key and go. That's all fine and dandy, but you have to remember when it is in gear to take it out or mash the clutch, I almost hit my truck like that.

Caymon

[MustangGT1990]

BigRed90GT:

I have already replaced the clutch position switch in my many attempts to remedy my problem. Then I found out that my T-5 also has a neutral position switch mounted on top of the transmission itself (apparently only used during part of 1990 from what I can find out so far) that senses if you are in neutral or a gear. My understanding of this switch is it is closed when it's in neutral and open the rest of the time. (Or it could be the other way around, can't member right now). Anyways, my car is not safe to drive right now because when you start slowing down and down shift you take a chance on the engine stopping unless you keep the RPMs up. I'm beginning to wonder if the computer is damged or if I have an open circuit or a short.

[srv1]

It is your EEC Power relay that is causing that problem. Replace that and it will stop running when the key is off.

[crazypete]

Here's my take on the early eec fords (granted this doesnt help you much).....

These cars are extremely solid and regardless of what people say about the quality of these early 90's american musclecars, they are extremely durable and I've seen these motors do over 200,000. The problem is that ford had really weak electronics components. It's usually the sensors and computer chips that go first. I basically had the reverse of the same problem: the computer would shut off the relay at random times, killing the fuel pump. Then, after hard wiring the relay, the computer started telling me my MAF voltage was too low. I checked voltage manually and, if anything, it was too high. I kept tinkering with it, trying to figure out why nothing was working the way it should. All of a sudden, all of the black ground wires in the computer/sensor wiring harness went hot. Manually grounding it would get some very strange behaviour from the eec.....blah blah blah.

Got tired of it all, ripped it all out and did a nice carb conversion. I have NEVER had a mysterious stall since. The car ALWAYS starts now. I am no longer at the whim of some computer, I can walk up front and turn a screw if I feel it's too lean or too rich. If someone were to do everything right... $150 intake/$350 carb and $150 for mechanical fuel pump = $650 = The cost of replacing a computer and a mass air sensor + a little and total confidence in the vehicle from that point on.

For the neutral switch... The computer does not need to know what gear the vehicle is in or not in. It is an Engine control module. Just hard wire it off if it is causing problems.

[MustangGT1990]

Well I put in a new EEC Relay and still have te same problem: my fuel pump runs ALL the time. So I have a new fuel pump relay and a new EEC relay. I also checked for bare wires, etc... and no luck. As soon as I reconnect the battery cable my fuel pumps starts running. So, is it the computer or not\/ hehe Any ideas?