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Old 09-14-2019, 03:41 PM
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leeklm leeklm is offline
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Default Electric fuel pump wiring??

Hello,

This one has me baffled! As you may have seen in my Chassis Dyno post, I stared blowing fuses in my fuel pump relay circuit while at the dyno. This system has worked well for the past few years in 2 different cars wired as shown in the first diagram.

After some troubleshooting, i was convinced the problem was the oil pressure sending unit, which I replaced. Problem still there. About 3 seconds after starting car, the fuse blows that supplies 12v on left side of diagram below.

I then added a manual override switch to the circuit, and replaced oil sending unit with a basic switch with no provision for the starter solenoid, which is shown in 2nd pic. Fuel pump powers up fine to prime the bowls. Shut the manual switch off, start the car, and the 12v supply fuse blows again.

Now here is the strange part, I can leave the manual switch on (with the 12v supply on left side disconnected), start the car and everything keeps running like it should. Of course I could run it this way, but would like to correct the problem.

My next thought is some type of short in the relay, but if that was the case, it should still blow the manual switch fuse wired as shown in the 2nd pic.

I have now used 3 different oil switches, replaced a couple of feed wires just to be sure, checked wiring 10 times, but cannot keep the oil switch in the circuit as it has been running all summer.

Am I missing something obvious here???

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68 Firebird-- Street/Strip - 400/461 Eagle Forged Bottom End & Ross Flat top pistons. KRE 325 CFM D port, Ultradyne 263/271 @.050, .4267 lift. Crower Solid roller lifters and 1.65 stainless rockers. Quickfuel 1000 on Torker2 intake and 2" open spacer. Hedman 1.75" headers. TH400 w/brake. Ford 9" w/3.80 gears & 28x9 Hoosier pro bracket drag radial. Best ET: 1.35 60ft, 6.29 @ 107.20 mph, 9.99 @132.33 mph. 3,300 race weight
  #2  
Old 09-14-2019, 03:46 PM
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New photo....

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68 Firebird-- Street/Strip - 400/461 Eagle Forged Bottom End & Ross Flat top pistons. KRE 325 CFM D port, Ultradyne 263/271 @.050, .4267 lift. Crower Solid roller lifters and 1.65 stainless rockers. Quickfuel 1000 on Torker2 intake and 2" open spacer. Hedman 1.75" headers. TH400 w/brake. Ford 9" w/3.80 gears & 28x9 Hoosier pro bracket drag radial. Best ET: 1.35 60ft, 6.29 @ 107.20 mph, 9.99 @132.33 mph. 3,300 race weight
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Old 09-14-2019, 07:31 PM
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Not sure what all the 12v things are?

Here is a link to a page that has a wiring diagram:

Fuel Shutoff




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Old 09-14-2019, 07:44 PM
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Quote:
Originally Posted by johnta1 View Post
Not sure what all the 12v things are?

Here is a link to a page that has a wiring diagram:

Fuel Shutoff



12v is my ignition on source. This system is connected as shown in your link and has worked for years, which is why this is so baffling.

I have 2 of the Carter brand oil pressure switches that summit sells, which allow you to connect a terminal to the starter solenoid so it pumps fuel while cranking. Only problem with doing it that way is you cannot have the bypass switch connected, otherwise you power your starter when flipping the bypass switch

For troubleshooting this problem, I removed the starter wire so I can use the bypass switch.

It is almost like the oil pressure switch is shorting the 12v ignition source to ground once the engine starts. However, it all tests correctly with an ohm meter when testing out of the car and applying pressure with an air hose to the oil switch.

Again, all works fine with the oil safety switch disconnected.

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68 Firebird-- Street/Strip - 400/461 Eagle Forged Bottom End & Ross Flat top pistons. KRE 325 CFM D port, Ultradyne 263/271 @.050, .4267 lift. Crower Solid roller lifters and 1.65 stainless rockers. Quickfuel 1000 on Torker2 intake and 2" open spacer. Hedman 1.75" headers. TH400 w/brake. Ford 9" w/3.80 gears & 28x9 Hoosier pro bracket drag radial. Best ET: 1.35 60ft, 6.29 @ 107.20 mph, 9.99 @132.33 mph. 3,300 race weight
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Old 09-14-2019, 08:16 PM
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They give a schematic for the oil pressure switch?
Also how is the relay wired?


Most pressure switches work by grounding/ungrounding when the pressure is at some pressure point (like say 8 pounds).
Maybe the switch is closing at different times?


I'd try a different brand of switch?



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Pontiac Power RULES !!!
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Winner of Top Class at Pontiac Nationals, 2004 Cordova
Winner of Quick 16 At Ames 2004 Pontiac Tripower Nats

KRE's MR-1 - 1st 5 second Pontiac block ever!


"Every man has a right to his own opinion, but no man has a right to be wrong in his facts."

"People demand freedom of speech to make up for the freedom of thought which they avoid." – Socrates
  #6  
Old 10-16-2019, 09:29 PM
punkin punkin is offline
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This is how I have mine wired...it's worked well for me.
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Old 10-16-2019, 10:23 PM
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Interesting. Mine is wired the same way, but I have never used the inline diodes. Would not hurt for me to solder a couple in.

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68 Firebird-- Street/Strip - 400/461 Eagle Forged Bottom End & Ross Flat top pistons. KRE 325 CFM D port, Ultradyne 263/271 @.050, .4267 lift. Crower Solid roller lifters and 1.65 stainless rockers. Quickfuel 1000 on Torker2 intake and 2" open spacer. Hedman 1.75" headers. TH400 w/brake. Ford 9" w/3.80 gears & 28x9 Hoosier pro bracket drag radial. Best ET: 1.35 60ft, 6.29 @ 107.20 mph, 9.99 @132.33 mph. 3,300 race weight
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