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Discussion Starter #1
OK .. I'm having problems with my 87 F-150 ( A.K.A. Mustang tow vehicle ). It seems my fuel pumps are not working , it has 3 of them. Well I started with the high pressure pump , took the leads off and I get 12 volts to the pump after jumping the relay to make the pump run constant. When I plug the pump in voltage goes to zero. Ah ha I thought , bad pump , well I got a new pump and it does the same thing. So my question is , if I had a short in the system I would not get twelve volts to pump at all, right? It seems to me that I might have an open circuit in the harness somewhere and the pump draws too much juice so the voltage goes to zero. Seems logical right? IF I remove the relay and run a hot lead from the battery to the OUT side of the relay plug the pump works fine. If I run a wire from the hot IN side of the relay plug I get the same problem , 12 volts to the pump until I plug it in. Anyone have any ideas , this is driving me nuts.

70 SCJ R-CODE MACH 1
88 GT
 
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Had a similar problem on my 88 Bronco. Tell you what I know, which is limited. When the ignition key is first turned on the EEC turns on the fuel relay for one second to prepressurize the system. If working, the pump can be heard. During cranking and when started, the pump continues to run. My symptoms were unanticipated flameouts in traffic. When trying to restart it would start if I heard the pump whine and not start if the pump did not whine. After considerable headscratching and knuckle busting turns out the problem was an intermittent EEC ground. The EEC is grounded by a fine wre that goes directly to the negative lug on the battery. There are two fine wires on my negative post, one is the ground for the EEC and the other is the ground for the ABS. Those two wires go to a double connector on the radiator support. When I touched the connector it fell apart due to serious corrosion. Soldering the wires togather fixed my problem. HTH

Mustang Lovers ---- A Box-O-Choclates !!!
 
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As far as I know your Bronco and my F-150 share similar wiring harness. I'll check that out , but I thought that the EEC on my tuck gets a ground from under the hood hinge on the driver side. Maybe this ground is for something else? Well , I'll have a look see. Thanks for the response.

70 SCJ R-CODE MACH 1
88 GT
 

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Hi Marc, Have you checked the impact/rollover switch? By memory it seems it's located under the dash on the passanger side somewhere below and to the left of the glove box on an '87. It is a little square relay looking box about 1" x 1-1/2" and has a reset botton on it. Push the button in and see what you get.

They install these on all FI equiped vehicles to cut the power to the fuel pumps by way of the relay in case of an accedent. Sometimes they are just activated by the strangest things like a passanger kicking the floor, a hard bump in the road or my favorite, me dropping my hand held tool box on the passanger floor, (ask me how I know?......*G*). Since you have lost power on all the pumps by way of the relay it is highly possible this is your problem.

Hal
Love hard, drive fast, wear your seat belt.

PS, that's my 'bird...... My Mustang is too ugly to take pictures of yet........*G*.

http://www.teleport.com/~cosa/bird2.jpg
 
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If I understand your question,you are applying 12V to back side of the relay connector and getting the pump to run yet when applied to the front or relay side the pump quits. this sounds like a bad termial in the relay connector.You can remove the terminal from the plastic to check for corrosion. To remove the terminal you must pull out the plastic key lock in the center of the connector ,you can the depress the small tab and pull the wire and termial from the hard shell.

Chris Sowden 1965 Fastback
 
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Hmmmm... I'll try that. If the terminal is indeed bad this would create an OPEN in the harness , right ??

70 SCJ R-CODE MACH 1
88 GT
 
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Discussion Starter #7
Whisperer , I bypassed the inertia switch. I have also noticed that my inertia switch is very sensitive. Sometimes if I drop something heavy in the bed of the truck , or jerk the clutch around in creeper gear I can get the inertia switch to trigger. Once I removed the connector and cleaned it up it seems to be less sensitive , I'm not sure why , but if it aint broke , dont fix it.

70 SCJ R-CODE MACH 1
88 GT
 
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