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Discussion Starter #1 (Edited)
Question for you fox guys.


What is the voltage supposed to be at the pump when key is first turned to prime the pump?


I have a 70 Mustang with a 89 5.0 and 5 speed installed along with a Painless EFI harness. When I first turn the key to run the voltage is around 12 volts, tried starting it many times with no luck, then drops down and sits around 6.87 volts.



The fuel pump does kick on and run then shuts off like it's supposed to.



I did a fuel pressure check today and at first I got around 8 PSI. A few more prime cycles and it sat around 20 but then quickly dropped off. I ran straight 12 volts to the pump and it held around 40psi but the car still wouldn't start. Removal of the 12 volts the pressure dropped to almost nothing. I have a new pump and pressure regulator on their way.



Any who, voltage at the pump when key first turned??
 

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Discussion Starter #3
The voltage (12 from relay) primes then drops off if the ecm doesn't see ignition pulse. Sounds like ignition(TFI?)



That's the thing tho, I'm not trying to start it. I'm just testing things by myself at the moment and don't have the ability to crank the car over and test the wires at the pump at the same time.



I had my 12 year old son helping earlier and he was affraid of starting the car, even tho it wouldn't start because of the low fuel pressure.
 

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If you don't crank it, you will lose voltage in a few seconds. I'm not familiar with the painless setup, but my fuel pump relay is situated in the trunk. I used bungee cords to hold in view the relay and test light in the cavity that feeds the pump while I cranked. My issue was a poorly grounded TFI. Some parts stores still have the machine to test the ignition module off the car. I'd setup a spark tester where you could see it while cranking and check spark. These things are great when they run, frustrating when they don't!
 

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If you don't crank it, you will lose voltage in a few seconds. I'm not familiar with the painless setup, but my fuel pump relay is situated in the trunk. I used bungee cords to hold in view the relay and test light in the cavity that feeds the pump while I cranked. My issue was a poorly grounded TFI. Some parts stores still have the machine to test the ignition module off the car. I'd setup a spark tester where you could see it while cranking and check spark. These things are great when they run, frustrating when they don't!

My relays and the fuses for the Painless harness are going to be mounted in the glove box. The ECM is mounted behind the dash as well. I agree about being frustrating. At one time I got the car to run, rather rough, and eventually found out the ECM was bad. Sent it out and got it fixed and now I can't get it to run at all, even like crap. Today we tested the fuel pressure and it was really low so a new fuel pump will be going in once it arrives. Fingers crossed that's the problem. If not, I'll look into the TFI and see if Autozone or Oreillys can test it.
 

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My relays and the fuses for the Painless harness are going to be mounted in the glove box. The ECM is mounted behind the dash as well. I agree about being frustrating. At one time I got the car to run, rather rough, and eventually found out the ECM was bad. Sent it out and got it fixed and now I can't get it to run at all, even like crap. Today we tested the fuel pressure and it was really low so a new fuel pump will be going in once it arrives. Fingers crossed that's the problem. If not, I'll look into the TFI and see if Autozone or Oreillys can test it.
It sounds as if, when energized, your pump ran 40psi. Don't know about the rest of your setup, but if it consists of used components, anything can get ya'. My donor car sat 20 years. Pinfit and bad injectors drove me nuts. Keep pounding it out, it's worth it. BTW call around before you run all over with this module. Only one Advanced auto had the machine AND the adapter to test. These fox bodies are classics now; I saw one yesterday with an antique tag!
 

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65 Fastback 289 4 spd, 65 convertible 5.0L 5 spd. 3.73 8.8
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Question for you fox guys.


What is the voltage supposed to be at the pump when key is first turned to prime the pump?


I have a 70 Mustang with a 89 5.0 and 5 speed installed along with a Painless EFI harness. When I first turn the key to run the voltage is around 12 volts, tried starting it many times with no luck, then drops down and sits around 6.87 volts.



The fuel pump does kick on and run then shuts off like it's supposed to.



I did a fuel pressure check today and at first I got around 8 PSI. A few more prime cycles and it sat around 20 but then quickly dropped off. I ran straight 12 volts to the pump and it held around 40psi but the car still wouldn't start. Removal of the 12 volts the pressure dropped to almost nothing. I have a new pump and pressure regulator on their way.



Any who, voltage at the pump when key first turned??
You have a voltage drop somewhere. With a volt meter ck at the fuse, then the relay, then at the pump. Also ck the ground side. So to ck a voltage drop for instance if you take a volt meter across the fuse one prong on one side and the other on the other sid, set to volts you should have very small amount of drop (.oo1) would be good. across any connector, fuse, etc. if you show 5 volts that is your problem.
 

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You have a voltage drop somewhere. With a volt meter ck at the fuse, then the relay, then at the pump. Also ck the ground side. So to ck a voltage drop for instance if you take a volt meter across the fuse one prong on one side and the other on the other sid, set to volts you should have very small amount of drop (.oo1) would be good. across any connector, fuse, etc. if you show 5 volts that is your problem.
5 month old post.....
 

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You have to get in the have to get in the habit of checking the thread origination dates. At least if you are browsing the forum in the traditional way. I don't use the new/trending posts feature myself.
You have to admit kakn never did come back to close this out. In fact, now that I look, he basically didn't come back at all.
 
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