Can not get correct fuel pressure

[junkyardjeff]

I have a 88 full size bronco with a 5.0 and the fuel pressure is too low,its supposed to be 30 to 45 with motor running with regulator vacumn hose on and all I can get is 29 so I run it with the vacumn line plugged and unhooked.  It originally had two fuel pumps so I converted it to the 90 to 96 single pump system and still the same,just got done installing a new pump/sending unit because the gauge quit and I still have to keep the regulator disconnected or it will surge when first started. I was told it could have a few weak injectors causing low fuel pressure so should I look there next.

[wayne petty]

do you know where the fuel pump relay is..?

it has a green connector usually..

the brown connector is the EECIV main relay..


the brown main relay and the green fuel pump relay get their power for their switched contacts from DIFFERENT WIRES.  i have had terrible issues with the fuel pump relay power wires..  

can i get you to perform a voltage drop test after you wire brush clean both sides of the  multiple ring terminals at the starter relay



now onward to the  voltage drop test..   engine running.. headlights on..

positive battery post to the wire to the fuel pumps..  hint.. toss your jumper cables under the truck.. clip only the positive lead to the battery terminal.. you can now clip the one under the truck to one of your meter test leads so hopefully you can probe the power wire to the fuel pump with the other lead..    write down the voltage you get..     less that 0.2 volts is great..

unclip from the end of the jumper cable..   measure the voltage on that wire when you touch that and the frame rail.. over 13.0 volts is great..

then measure the fuel tank to the frame rail..  that should really read close to 0.00.  

get up and disconnect the jumper cable at the battery.. then measure the voltage drop between the negative battery post and the front bumper or frame rail.

when you have a slow build up of fuel pressure. you have some resistance in the fuel pump power circuit..  either on the positive or the negative side.

why am i having you check UNDER the truck at the closest wire to the fuel pump.. because this checks most of the circuit.  if you end up with voltage drop to the pump.. you will have to narrow the test positions.

[junkyardjeff]

I will do that tomorrow,I have to give a young couple a ride in my 55 sunliner today to the church where they are getting married.

[kb426]

I'm not familiar with the 90-96 Bronco. It it an eecv system rather than a eeciv? If that is a pump designed for eecv, it is for a returnless system and the pump runs on variable voltage.

[rooster]

I have a 88 full size bronco with a 5.0 and the fuel pressure is too low, I still have to keep the regulator disconnected or it will surge when first started.

You might take that plug off the regulator, and watch that port where it was plugged with the engine running and see if it spits out fuel! That would cause surging. You might have to wait for afew minutes to see the leak of a broken diaframe or a bad seat in the regulator.

What does the fuel pressure do on a snap throtle? Should not drop!

[wayne petty]

http://i1207.photobucket.com/albums/bb476/waynep712/mustang/1987_89F_Series_50_58_460_zpsf148923c.jpg

right click and open the link above in a new window

[junkyardjeff]

I am going to check pressure tomorrow.

[junkyardjeff]

30 with regulator hooked up and 40 not,when I snap the throttle with the regulator hooked it will go up and little then drop down some and will not move when the regulator is not hooked up. Will do the voltage tests later today  and wondering if I got a regulator for a throttle body system since I think they have a lower pressure.

[kb426]

I always checked mine with the engine shut off and the vacuum line unhooked. That's where the 40 lbs. was correct. With the engine running at idle, if you unhook the vacuum line, I believe you should have 40 lbs. but with the vacuum line connected, you will be at reduced pressure. The 40 lbs. is for full throttle.

[rooster]

wondering if I got a regulator for a throttle body system since I think they have a lower pressure.

Did you watch that Vacume port for leaking fuel while engine was running?

pump wiring:

[junkyardjeff]

I do not think its a ruptured diaphram in the regulator since I have been driving it a year with the vacumn line unplugged and have not smelled any gas but will check and will look for the ground and check it out. Since it does not have the front pump now I checked the voltage at the connector and got 13.8 while at the battery it was 14.6 while running but forgot to turn on the lights,I was using the ground at the connector but will check again going straight to the battery.

[junkyardjeff]

Its had the regulator hooked up all week and seems to be doing ok,I am getting a little surging when its fired back up when warm but the cold start is like it should be.