Electrical Problem

91 gt 5.0 · April 15th, 2009, 11:25 AM

To start off, my friend and I looked at the Tmoss electrical diagrams and tested voltage and power for a few hours last night trying to solve this problem so I'm not blindly asking this question. My fuel pump doesn't turn on when I turn the key to run. Everything else seemingly works: wipers, windows, starter, we're getting spark, but the fuel pump doesn't turn on. We tried a pump that we know works, so we've eliminated the pump being the problem. At the pump we're only getting [U]8 volts[U]. I forgot if how much voltage the fuel pump relay is getting, but I know the relay is good because I switched that out with a known good one. Now I did accidently touch the starter wire directly to the power wires on the starter solenoid, which cause some big sparks, but it didn't blow the fusible link on the 18g orange/light blue fuel pump wire. I guess my question is, is this drop in voltage a bad ground? or is it possibly something computer related? (We did change the computer out with a known good one with the same result.) When I turn the key to run, I hear a pretty loud clicking right near the computer. Could the relay right above the computer be bad?

5.slowliter · November 13th, 2009, 10:47 PM

ecm is fubar replace i know from experience

wraitherx · November 14th, 2009, 01:22 AM

I thought the fuel pump relay was under the drivers seat

you can attribute that drop in voltage to be a bad ground. If you are sure that the relay and comp were good then it something in the wiring.

ironsteed5.0 · November 14th, 2009, 04:27 AM

If the wire is chafed somewhere along the line, it may be grounding out on the frame, causing the drop in voltage.

JBIGBOOTSY · November 14th, 2009, 04:30 AM

Inertia switch

ironsteed5.0 · November 14th, 2009, 04:36 AM

Originally Posted by JBIGBOOTSY

Inertia switch

Interesting..... care to elaborate?

mxnate116 · November 14th, 2009, 05:03 AM

switch infront of the drivers tailight behind the plastic. it trips if there is a big g force hit to turn the fuel pump off, take the panel off and see if its tripped

wraitherx · November 14th, 2009, 09:02 AM

yes, try that as well.

91 gt 5.0 · November 14th, 2009, 04:39 PM

Holy old thread. The problem ended up being that someone had cut a one of the wires to the relay to add in a fuel pump cutoff switch, but there was not switch there and the wires were hidden in the loom. I simply connected the two ends of the wire and it worked perfectly.

mxnate116 · November 14th, 2009, 06:26 PM

holy shit this is old 5.slow dug deep to find it haha

April 15th, 2009, 11:25 AM	#1
91 gt 5.0 Regular Join Date: Feb 2008 Location: CT Posts: 131 iTrader: 0 reviews	Electrical Problem To start off, my friend and I looked at the Tmoss electrical diagrams and tested voltage and power for a few hours last night trying to solve this problem so I'm not blindly asking this question. My fuel pump doesn't turn on when I turn the key to run. Everything else seemingly works: wipers, windows, starter, we're getting spark, but the fuel pump doesn't turn on. We tried a pump that we know works, so we've eliminated the pump being the problem. At the pump we're only getting [U]8 volts[U]. I forgot if how much voltage the fuel pump relay is getting, but I know the relay is good because I switched that out with a known good one. Now I did accidently touch the starter wire directly to the power wires on the starter solenoid, which cause some big sparks, but it didn't blow the fusible link on the 18g orange/light blue fuel pump wire. I guess my question is, is this drop in voltage a bad ground? or is it possibly something computer related? (We did change the computer out with a known good one with the same result.) When I turn the key to run, I hear a pretty loud clicking right near the computer. Could the relay right above the computer be bad?

November 14th, 2009, 01:22 AM	#3
wraitherx Moderator '99 SVT Cobra Join Date: Nov 2006 Location: Virginia Beach, VA Posts: 9,568 iTrader: 11 reviews	I thought the fuel pump relay was under the drivers seat you can attribute that drop in voltage to be a bad ground. If you are sure that the relay and comp were good then it something in the wiring. __________________ BUILD 2 IN PROGRESS

November 14th, 2009, 04:30 AM	#5
JBIGBOOTSY MM Fanatic 1990 LX hatch Join Date: Aug 2006 Location: Hobart Indiana Posts: 4,391 iTrader: 0 reviews	Inertia switch __________________ Bolt-on Abraham Lincoln Log motor. With extra wiring.

November 14th, 2009, 05:03 AM	#7
mxnate116 Hardcore Enthusiast SVTfocus, F250 Join Date: Jun 2007 Location: Spokane, WA Posts: 2,971 iTrader: 1 reviews	switch infront of the drivers tailight behind the plastic. it trips if there is a big g force hit to turn the fuel pump off, take the panel off and see if its tripped __________________

November 14th, 2009, 09:02 AM	#8
wraitherx Moderator '99 SVT Cobra Join Date: Nov 2006 Location: Virginia Beach, VA Posts: 9,568 iTrader: 11 reviews	yes, try that as well. __________________ BUILD 2 IN PROGRESS

November 13th, 2009, 10:47 PM	#2
5.slowliter Newbie 1991 mustang gt 13.76@108.58 Join Date: Jul 2009 Location: syracuse new york Posts: 4 iTrader: 0 reviews	ecm is fubar replace i know from experience

November 14th, 2009, 04:27 AM	#4
ironsteed5.0 Regular 91' 5.0 LX Join Date: Oct 2009 Location: Tucson, AZ Posts: 231 iTrader: 1 reviews	If the wire is chafed somewhere along the line, it may be grounding out on the frame, causing the drop in voltage.

November 14th, 2009, 04:39 PM	#9
91 gt 5.0 Regular Join Date: Feb 2008 Location: CT Posts: 131 iTrader: 0 reviews	Holy old thread. The problem ended up being that someone had cut a one of the wires to the relay to add in a fuel pump cutoff switch, but there was not switch there and the wires were hidden in the loom. I simply connected the two ends of the wire and it worked perfectly. __________________

November 14th, 2009, 06:26 PM	#10
mxnate116 Hardcore Enthusiast SVTfocus, F250 Join Date: Jun 2007 Location: Spokane, WA Posts: 2,971 iTrader: 1 reviews	holy shit this is old 5.slow dug deep to find it haha __________________

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