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Fuel Pressure leak off


Tagg

Active Member
Joined
Aug 2, 2009
Messages
35
City
Muse, Pa.
Vehicle Year
1996
1995
Transmission
Automatic
Ok, I have a 95 Ranger 4.0L 4x4. It is running rough at idle in traffic or at a traffic light stop. Checked the fuel rail pressure today and it shows about 36#. The problem appears to be that the gauge drops to 0 # when the key is turned off. We also checked another trucks fuel rail and the pressure stays at 40#. There is no CEL, the emissions station advised the truck isn't holding a steady enough idle to pass. Is there a check valve somewhere in the fuel rail or regulator or fuel pump that ie causing this bleed off? We also changed out the fuel filter, but when putting it back together it felt like the downstream side of the filter connector appeared to be loose however it is not leaking. Any HELP is Appreciated. Thanks.:icon_confused:
 
There is a check valve in the pump that is supposed to prevent pressure bleed off.

How easy does it start? It should take more than a few seconds for it to bleed back like that.
 
When Cold the truck will start right up and stahl out about 2-3 times. When Warm it is hard starting by cranking 2-3 times. Like I said when stopped at a traffic light it will slightly surge while idling. We have done a complete tuneup, changed the TPS, IAC and MAF. Still same problem. Also checked vacuum lines, which seem ok after replacing a couple that were slightly bad. It takes about 10 seconds to bleed off pressure to 0#. Thanks.
 
Did you change the PCV valve and three things are in play with the fuel pressure, check valve in fuel pump,leaky injectors and fuel pressure regulator. Do you smell fuel on the dipstick if so you need to change the oil and either have the injectors cleaned or replaced. Pull the plugs right after it bleeds down to zero smell for fuel and compare colors. They should all be the same. Probably the cheapest is the regulator when you check the fuel pressure did you disconnect the vacuum line to the regulator while it is running and what is the pressure difference with vacuum and without.
 
OK, the PCV is good, the plugs where just changed out and appeared to be all the same color. The regulator didn't appear to have a vacuum line attached to it. The injectors have had a fuel system flush done on them. Therefore, I believe it has to be in the fuel pump check valve, The truck has a 3" lift kit on it, Is that enough room to pull the fuel pump without pulling the bed to get to it ? Thanks.:dunno:
 
http://www.therangerstation.com/tech_library/diagrams/95-99_Ranger_4-0_vacuum_hose_diagram.gif

Here is the vacuum diagram for 95-99 4.0 it shows a line to the regulator is this the same as the one under your hood. You need to find the vacuum line and hook it up if it isnt you have both a vacuum leak and fuel pressure issues. Find out for sure before you pull the fuel pump someone else here can tell you for sure I am just going by I assume all regulators use vacuum pressure and a vacuum leak will cause starting problems. Fix the obvious first.
 
Also you didnt mention you reset the computer when you changed the sensors. Disconnect the battery for 1/2 an hour to set new values for the new sensors. You need to do this every time you change or clean a sensor the computer dosent go backwards.
 
pull the vacuum line off the fuel pressure regulator, its on the fuel rail. check to see if there is fuel in the vacuum line and if so replace the regulator.

if you don't find any fuel then watch your pressure gauge as you unplug the vacuum line from the regulator, it should increase the pressure with the vacuum line off, if it doesn't then replace the regulator.

if you still don't find anything wrong. block off the return line(usually smaller) and see if pressure holds, if it doesn't then block off the supply line(usually bigger).

if it holds pressure with the return line blocked off then you need to replace the fuel pressure regulator, if it holds pressure with the supply line blocked off you need a fuel pump.

if it DOESN'T hold pressure with both lines blocked off then you have a leaking fuel injector

do all this with the key on, engine off. except the vacuum line test
 
Last edited:
He said the pressure regulator dont have a vacuum hooked up to it. I am thinking the line popped off somehow or someone didnt hook it up that still leaves a vacuum leak if it is not plugged. That is why I say fix the obvious first maybe it was disconnected because it was sucking fuel into the intake and disconnecting it made it run better.
 
He said the pressure regulator dont have a vacuum hooked up to it. I am thinking the line popped off somehow or someone didnt hook it up that still leaves a vacuum leak if it is not plugged. That is why I say fix the obvious first maybe it was disconnected because it was sucking fuel into the intake and disconnecting it made it run better.

still need to find the cause of the leak down
 
Yea but if he changes the fuel pump and it turns out to be the regulator I know I`d be pissed. I say get the vacuum connected and check the regulator for proper operation first.
 
It takes about 10 seconds to bleed off pressure to 0#. Thanks.

That really sounds like a fuel pump. I hate to tell someone that it's likely a part that expensive without looking at it myself first, but that is really my best guess at this point.
 

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