Re: 98 Fbody fuel system and ECU return voltage
Thread Starter
On The Tree
Joined: Apr 2010
Posts: 152
Likes: 17
From: Saskatchewan, Canada
Re: 98 Fbody fuel system and ECU return voltage I have a question for the more technical guys on the forum.
I understand my ECU (w just the ignition ON) sends a signal to my Fuel Pump Relay and then to my Fuel Pump for a few seconds which causes my Fuel Pump to Prime the fuel system and injectors and then the voltage should drop down.
1. What causes the voltage to drop down?
(a) Is it an internal timer in the ECU or
(b) Is it the fuel pump regulator (in tank) reading the 60 psi?
...Or (c) is there some wire in the fuel tank that sends a voltage signal BACK to the ECU letting it know to drop the voltage?
I am in need of help as no one locally can help me out.
I understand my ECU (w just the ignition ON) sends a signal to my Fuel Pump Relay and then to my Fuel Pump for a few seconds which causes my Fuel Pump to Prime the fuel system and injectors and then the voltage should drop down.
1. What causes the voltage to drop down?
(a) Is it an internal timer in the ECU or
(b) Is it the fuel pump regulator (in tank) reading the 60 psi?
...Or (c) is there some wire in the fuel tank that sends a voltage signal BACK to the ECU letting it know to drop the voltage?
I am in need of help as no one locally can help me out.
Staging Lane
Joined: Feb 2011
Posts: 95
Likes: 0
From: Detroit, MI
The voltage to the fuel pump is shut off entirely, not 'drop down', if the engine is not running after 2 second prime. The ECM receives the information of whether the engine is running or not from the crankshaft position sensor. The ECM is basically a computer hard drive that is programmed to collect data from all the various sensors and then sends information out accordingly and gives error codes if something is not within specification. The fuel pump regulator has nothing to do with fuel pump voltage, it is a mechanical device that is not much more than a diaphragm and spring.
If you think you have good connections and grounds, go ahead and install new:
Crankshaft position sensor
Oil pressure switch (redundant fuel pump voltage signal if FP relay goes open)
Fuel pump relay
Have the ECM Reflashed
Ignition switch
If you still have your problem after all that, I have no clue, your system must be wired incorrectly
If you think you have good connections and grounds, go ahead and install new:
Crankshaft position sensor
Oil pressure switch (redundant fuel pump voltage signal if FP relay goes open)
Fuel pump relay
Have the ECM Reflashed
Ignition switch
If you still have your problem after all that, I have no clue, your system must be wired incorrectly
Staging Lane
Joined: Feb 2011
Posts: 95
Likes: 0
From: Detroit, MI
Here is a great description of how it all works:
http://www.youtube.com/watch?v=Rqtfrx-HeD0
Here is a good technical thread for you to read:
http://www.automotiveforums.com/t966...l_cutoff_.html
http://www.youtube.com/watch?v=Rqtfrx-HeD0
Here is a good technical thread for you to read:
http://www.automotiveforums.com/t966...l_cutoff_.html
