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Author
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Topic: Hot Wire fuel pump?
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infoseeker
Journeyman Posts: 12
From: cleveland, ohio, usa
Registered: Aug 2001
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posted 09-27-2001 10:54 PM
  
Hey im haveing a lil problem with a project of mine... the fuel pump wont fire up... so i was wundering would it run right if i was to hot wire the fuel pump.. and just hook a switch upto it? i here that also make your fuel pump push more psi (im running a blower and a 255lph fuel pump) has anyone here every hot wired there fuel pump?
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infoseeker
Journeyman Posts: 12
From: cleveland, ohio, usa
Registered: Aug 2001
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posted 09-29-2001 07:10 PM
welll i desided to give it a try... couldnt hurt... infact it seems to of helped sofar... i should be takeing the thing to the track next week i hope. if i get everything done.. all i need to do now is swap rear ends (iv got a new one with 3.73's) and add some type f to the 5spd. and off to the track i go.
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FISHTAIL
Gearhead Posts: 297
From: Waldorf MD USA
Registered: Sep 2000
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posted 09-30-2001 05:05 PM
Well, you CAN hotwire it, but by doing so you may make the pump work alot harder than it has too. The computer adjusts fuel pressure by turning the pump on/off and up/down by varing the voltage. You also bypass the emergency cutoff when you hotwire it. I would be more concerned with why it won't come on. It's really not a hard problem to trace. The relay for the pump is under the drivers seat. So, first thing you need to do, is unhook the harness at the rear of the car, check for power with a test light. If there isn't any, unhook the relay, and check for power there. If you have power at the relay, and not the pump, replace the relay. It's not an expensive part. If after doing this you still have a problem, you'll need to trace a few wires, but that's not likely. It's also possible that the harness near the tank has corroded, this happens sometimes if the dielectric grease dries out and water gets in. Start checking some wires, and let me know what you find.------------------
-FISHTAIL
92GT "The Ghetto Sled"
CMPS major @ University of MD college park
Best ET/MPH thus far: 14.40/100.67mph....damn wheel spin.
VP and co-founder of CMTC www.stangbirds.com
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cpmaverick
Moderator Posts: 970
From: Auburn, AL.
Registered: Jan 2000
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posted 09-30-2001 08:34 PM
quote:
Originally posted by FISHTAIL:
The computer adjusts fuel pressure by turning the pump on/off and up/down by varing the voltage.
I don't know a nice way to put it; you're wrong. I don't know where you learned this but it couldn't be farther than the truth. The computer turns the fuel pump on through a relay. It is impossible for the computer to vary voltage that is outputted by a relay. There is no reason that the pump should ever turn off. It doesn't. Not when the car is running; that's why it has a return line. The fuel pressure is regulated by the regulator only, which references off of vacuum. The computer adjusts fuel by changing injector-on-time (pulsewidth). It does not and cannot adjust fuel pressure. About hotwiring, yes you can do it, but you have to do it right, and doing it safely would probably be more work than fixing the original problem. (you'd want to implement a relay) Running a larger-gauge wire to the fuel pump does increase fuel volume because there is less voltage drop so the pump sees more voltage. More voltage=more fuel. But, with the 255 pump you shouldn't need it and you should have an adjustable fuel pressure regulator with a supercharger anyway so you probably won't see any benefit. infoseeker, since the pump obviously works, its probably going to be a fuse or the relay. You should probably also check your emergency shutoff switch. Not too hard to do.
Anyway, I agree with you fishtail about repairing his original problem, but thats some bad info you're spreading.
------------------
-Charlie Ping
1970 Maverick Grabber
[email protected]
Daily Driver
http://www.maverickgrabber.com
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FISHTAIL
Gearhead Posts: 297
From: Waldorf MD USA
Registered: Sep 2000
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posted 10-01-2001 05:59 PM
Well thanks for correcting my mistake  I have no idea where I got that from. I know better than that I think? lol, I knew fuel pressure was controlled by the regulator on the pass side fuel rail and that it was vaccum draw that affected it. I guess I was under the impression that somehow the computer did something with the relay to deactivate the pump when the line was at pressure(like when you first turn the key on and the pump primes up). I certianly don't pretend to know everything, but I"m always happy to help, and share what I do (and in this case don't) know . Even so, I still say that if you are going to hotwire the pump you need to find a way to incorperate the emergency cut off switch into the system. You dont want to get into an accident and have that high volume pump back there buzzin' away having a good ole time.------------------
-FISHTAIL
92GT "The Ghetto Sled"
CMPS major @ University of MD college park
Best ET/MPH thus far: 14.40/100.67mph....damn wheel spin.
VP and co-founder of CMTC www.stangbirds.com [This message has been edited by FISHTAIL (edited 10-01-2001).]
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infoseeker
Journeyman Posts: 12
From: cleveland, ohio, usa
Registered: Aug 2001
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posted 10-02-2001 02:12 PM
fuel safty cut off switch?? hmmmm never seen one on a stang b4.. the wireing i am useing for the fuel pump/dash bored is from a 88 gt. iv replaced the fuel pump relay thinking that was teh problem. but thats didnt change a thing... iv checked grounds.. there all good... but i also checked da cop pulling outy behind me and pulled me over and inpounded the car! lol but if i ever get it back. ill try to add a relay to the fuel pump.. and thanks alot for all the info. but when i was driveing it b4 i got puylled over. it seems to run grate with the fuel pump hot wired with 8g wire.
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FISHTAIL
Gearhead Posts: 297
From: Waldorf MD USA
Registered: Sep 2000
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posted 10-02-2001 05:05 PM
That sucks about the impound.....what did you do? Anyway, the cutoff is in the back of the car in front of the drivers side taillight. You'll see a rubber grommet in the panel attached to the rear of the trunk/hatch. If you pull it out, you should be able to see a small switch that you can press down(if it's poped up that is). This is the emergency cutoff. When it gets enough of a jolt it will pop the switch and cut power to the pump. You simply reset it by depressing the button. Check it out when you get the car back.------------------
-FISHTAIL
92GT "The Ghetto Sled"
CMPS major @ University of MD college park
Best ET/MPH thus far: 14.40/100.67mph....damn wheel spin.
VP and co-founder of CMTC www.stangbirds.com
IP: Logged |
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