89 GT Fuel Pump Voltage - Vintage Mustang Forums
 
Thread Tools
post #1 of 6 (permalink) Old 08-25-2019, 09:43 PM Thread Starter
Junior Member
 
kakn's Avatar
 
Join Date: Jan 2017
Location: Illinois
Posts: 10
89 GT Fuel Pump Voltage

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??

In memory of shelbycarz

Last edited by kakn; 08-25-2019 at 09:45 PM.
kakn is offline  
Sponsored Links
Advertisement
 
post #2 of 6 (permalink) Old 08-25-2019, 10:03 PM
Senior Member
 
665spd's Avatar
 
Join Date: Aug 2017
Location: NW Florida
Posts: 257
Garage
The voltage (12 from relay) primes then drops off if the ecm doesn't see ignition pulse. Sounds like ignition(TFI?)


It's just a little rust...

1966 secretary special originally 6cyl 3 spd coupe.(Goes to work twice a week)
5.0 SEFI complete from 1988 Mustang GT, world class T-5, 9 inch with 3.50 Trac Lok and Shelby style traction bars. Old Air A/C system.
Build thread:https://forums.vintage-mustang.com/b...5-0-resto.html

1969 Mach 1: 1000 miles (almost) to get it....in progress(slow)
https://forums.vintage-mustang.com/b...long-term.html
665spd is offline  
post #3 of 6 (permalink) Old 08-25-2019, 10:25 PM Thread Starter
Junior Member
 
kakn's Avatar
 
Join Date: Jan 2017
Location: Illinois
Posts: 10
Quote:
Originally Posted by 665spd View Post
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.

In memory of shelbycarz
kakn is offline  
 
post #4 of 6 (permalink) Old 08-25-2019, 10:34 PM
Senior Member
 
665spd's Avatar
 
Join Date: Aug 2017
Location: NW Florida
Posts: 257
Garage
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!


It's just a little rust...

1966 secretary special originally 6cyl 3 spd coupe.(Goes to work twice a week)
5.0 SEFI complete from 1988 Mustang GT, world class T-5, 9 inch with 3.50 Trac Lok and Shelby style traction bars. Old Air A/C system.
Build thread:https://forums.vintage-mustang.com/b...5-0-resto.html

1969 Mach 1: 1000 miles (almost) to get it....in progress(slow)
https://forums.vintage-mustang.com/b...long-term.html
665spd is offline  
post #5 of 6 (permalink) Old 08-25-2019, 10:42 PM Thread Starter
Junior Member
 
kakn's Avatar
 
Join Date: Jan 2017
Location: Illinois
Posts: 10
Quote:
Originally Posted by 665spd View Post
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.
Attached Images
File Type: jpg IMG_3975.jpg (357.3 KB, 0 views)

In memory of shelbycarz
kakn is offline  
post #6 of 6 (permalink) Old 08-25-2019, 10:52 PM
Senior Member
 
665spd's Avatar
 
Join Date: Aug 2017
Location: NW Florida
Posts: 257
Garage
Quote:
Originally Posted by kakn View Post
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!


It's just a little rust...

1966 secretary special originally 6cyl 3 spd coupe.(Goes to work twice a week)
5.0 SEFI complete from 1988 Mustang GT, world class T-5, 9 inch with 3.50 Trac Lok and Shelby style traction bars. Old Air A/C system.
Build thread:https://forums.vintage-mustang.com/b...5-0-resto.html

1969 Mach 1: 1000 miles (almost) to get it....in progress(slow)
https://forums.vintage-mustang.com/b...long-term.html
665spd is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Vintage Mustang Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome