2002 TJ fuel pressure issue when engine is cold

lonestar67

lonestar67

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Joined
Mar 18, 2019
Messages
4
Location
Celina TX
I am having an issue with my 02 tj 4.0.
it has no fuel pressure when you turn on the key, starts when cold after few cranks but when its warm it will crank and fire only briefly. if you crank long enough and wait long enough it finally starts and runs rough idle then smooths out, at this point it only has about 25 psi fuel pressure

have new fuel pump and sending assembly and new injectors installed

this one got me searching for an solution
 
Did the problems occur only after installing the new fuel pump assembly?
Has the fuel pump relay been replaced? If not try swapping the fuel pump relay with another relay like the fog light relay and see if the problem persists.
 
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Reactions: TJ Hunnicutt
Welcome from a fellow Texan!

Assuming you replaced the fuel pump because of this issue, have you checked the fuel lines? A clogged or kinked line could cause this. If you find and clog/kink, be sure to disconnect the line at the injector rail and, after correcting the problem, blow the line out thoroughly before reattaching to the rail. Maybe even run the pump for a while to do a complete purge of the lines (attach a hose and route to a bucket or something to catch the gas, no need in setting yourself on fire over this :)). What you don't want is to free up a bunch of gunk and send it running up to the injectors.
 
Steel City 06 said:
Did the problems occur only after installing the new fuel pump assembly?
Has the fuel pump relay been replaced? If not try swapping the fuel pump relay with another relay like the fog light relay and see if the problem persists.
Click to expand...

The problem did occur after installing a new fuel pump
I have swapped the fuel relays and there was no change

Also there is not a full 12 volts to the pump
Only like 1.8 volts
 
TJ Hunnicutt said:
Welcome from a fellow Texan!

Assuming you replaced the fuel pump because of this issue, have you checked the fuel lines? A clogged or kinked line could cause this. If you find and clog/kink, be sure to disconnect the line at the injector rail and, after correcting the problem, blow the line out thoroughly before reattaching to the rail. Maybe even run the pump for a while to do a complete purge of the lines (attach a hose and route to a bucket or something to catch the gas, no need in setting yourself on fire over this :)). What you don't want is to free up a bunch of gunk and send it running up to the injectors.
Click to expand...
TJ Hunnicutt said:
Welcome from a fellow Texan!

Assuming you replaced the fuel pump because of this issue, have you checked the fuel lines? A clogged or kinked line could cause this. If you find and clog/kink, be sure to disconnect the line at the injector rail and, after correcting the problem, blow the line out thoroughly before reattaching to the rail. Maybe even run the pump for a while to do a complete purge of the lines (attach a hose and route to a bucket or something to catch the gas, no need in setting yourself on fire over this :)). What you don't want is to free up a bunch of gunk and send it running up to the injectors.
Click to expand...

Replaced fuel pump because of the fuel sending unit
Have not checked the fuel lines , I will check that

Also I have only like 1.8 volts to the pump
Not the full 12 volts
Have swapped the fuel really as well with no change
 
Huh. Sounds like an electrical issue. Might be a loose connector somewhere.
It's possible there's an error in installation, or you have a dud.

I would chase the wires and check for any loose connections. Check the stock grounds as well. Also try a different fuse. Sometimes they can incompletely blow.

Hopefully someone else can chime in with more ideas.

My first fuel pump install I botched because I forgot to hook up the internal evap line inside the tank. My car kept stalling out at idle, and I had to hold the pedal on the gas at every stoplight to get home. (Turns out it was sucking slugs of straight gas through the evap system straight into the engine!)
 
Since you have a voltmeter (otherwise, you would not have report on the 1.8 volts), you should pick an end (at pump or at battery) and trace to the other end to see where things go South. What is the voltage just on the pump side of the relay? Halfway to the pump?, etc.

Actually, now that I think about it, I have a hard time believing the pump could even operate at all on 1.8 volts. Make sure that the ground you are using to check that voltage is sound and, if so, that the ground to the pump is equally as sound.
 
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