Fuel pump issues

Topic: Fuel pump issues (Read 2126 times) previous topic - next topic

Fuel pump issues

May 16, 2009, 10:04:34 AM

When it's damp out, the fuel pump will kick on for apparently no reason... the battery has to be unhooked to prevent it from going dead...could this be a wiring issue?

Fuel pump issues

Reply #1 – May 16, 2009, 10:06:03 AM

I had the problem with my parts car. It was the ignition on mine

Fuel pump issues

Reply #2 – May 16, 2009, 10:23:49 AM

Really? hhmmm... what was your fix?

BTW, I finally revealed it to the rest of the board...

This is for the '85.

Fuel pump issues

Reply #3 – May 16, 2009, 10:27:33 AM

I didn't actually fix it, because I'm junking it. but it does it when the key comes out and the cylinder isn't in the right place.
Eric knows about those problems, and how to check and fix them. ;)

Fuel pump issues

Reply #4 – May 16, 2009, 10:39:12 AM

Ok cool...I'll check with him on it.
This turns on when the car isn't running... so for now, we just unhook the battery... that was Karl's fix.

Fuel pump issues

Reply #5 – May 16, 2009, 10:51:19 AM

go back to the fuel pump relay in the trunk and flick / tap on it and see what happens.
Do the same to the EEC relay, if its getting energized by moisture, it might kick the fuel pump relay on for its normal prime or runtime of 3 sec.

when this happens, does the pump seem to run its normal 2-3 seconds then shut off?

obiviously the pump thinks the car is getting turned on so the ign sw sounds right to me.

Another idea-
unhook the pos battery cable
rig up a small dc bulb from the positive battery post to the positive battery cable. does the light come on?

Fuel pump issues

Reply #6 – May 16, 2009, 02:48:54 PM

I would check the ignition switch. That *may* be the problem. If so it is an easy fix. If it has never been replaced it might be a good idea to do so, just incase. They have been know to burn the car down........:flame:

Fuel pump issues

Reply #7 – May 17, 2009, 09:45:17 AM

As mentioned, it's likely either the ignition switch or the fuel pump relay in the trunk. I'd lean more toward the latter. Moisture and/or cold weather can start messing with that relay (and the inertia switch, for that matter). I've had that happen several times throughout the last two decades. Besides, if I know Karl, he probably already changed the ignition switch...not that that would guarantee anything, but it's doubtful the fuel pump relay was ever changed before.

Fuel pump issues

Reply #8 – May 17, 2009, 10:52:26 AM

Thanks guys.... I'll let Roger know so he can check it.

However, can you tell me where the relay is located exactly? We don't have a book for this one yet.

Fuel pump issues

Reply #9 – May 17, 2009, 11:01:38 AM

There is almost Zero chance the Ign sw or inertia switch could be the problem... If it were causing the continuous running, there would have to be an additional problem in F/P relay circuitry(remember the fuel pump will only run briefly when the ing sw is first turned on)...

Problem just about has to be a sticking fuel pump relay...

If the pump just starts running on it's own while the car is setting, you need to have a exorcism...

Fuel pump issues

Reply #10 – May 17, 2009, 12:15:57 PM

Open trunk
fold back trunk cover near pass hinge
mounted there will be a relay

Tom
If,, just "IF"
the eec relay were getting intermittant activation, wouldnt that trigger the fuel pump relay to prime?

My gut feeling was fuel pump relay to start but for some reason I cant get my head around what would happend if the eec relay were getting power as well.
Seems reasonable because if the heater core were leaking and such, water could make its way down in that arear near the EEC.

Fuel pump issues

Reply #11 – May 17, 2009, 12:41:04 PM

If the EEC relay was continually energized, the pump should not run because there is no iginition pulse to the computer... To energize, the F/P relay, it's coil would have to be receiving both a ground signal(pin 22 ECU, the VIP connector or possibly a bare wire) and voltage, which is supplied from the EEC relay...

I'll retract what I said about the ign sw, as possibly there could be some voltage leakage through it causing the EEC relay to energize(maybe a wet EEC relay as suggested, coolant is conductive), cycling the F/P relay and it's contacts then sticking(this is a stretch)... Still there would have to be two issues causing the problem, but this could maybe explain the pump energizing on it's own(but we don't really know that it is doing so)...

Fuel pump issues

Reply #12 – May 17, 2009, 03:22:56 PM

84 relay location.

Fuel pump issues

Reply #13 – May 17, 2009, 04:17:40 PM

I love a mystery.

Is there any indication that the injectors are pulsing while the fuel pump is running?

Theory #1
If the EEC power relay contacts were bridged by something that is more conductive when damp, it could apply a voltage to the EEC.
A voltage to the EEC that is outside it's normal operating range can put the EEC into LOS mode (Limited Output Strategy) mode. Also known as limp home mode.
In LOS mode the EEC will keep the ground on the fuel pump relay and pulse the injectors without any PIP input from the distributor.
The reduced voltage to the EEC would have to be high enough to pick the fuel pump relay.

Theory #2
The EEC is broke and is always running in LOS mode.
The ignition switch is bad and is picking the EEC power relay.

With the ignition in RUN without starting the car, the pump should run for 1 or 2 seconds. If the pump runs continuously you are in LOS mode.

Fuel pump issues

Reply #14 – May 17, 2009, 09:51:25 PM

I like a good mystery too,

the situation is the pump runs for no reason. Not clear yet as to the length of time because of no reply to that yet.

does it run its normal 2-4 seconds and shut off?