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ricardo hohl
ricardo hohl, ASE Certified Technician
Category: Dodge
Satisfied Customers: 4078
Experience:  ase master tech / and dodge ,jeep,and chrysler certified thec,with 28 years exp on general automotiv
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1996 dodge neon: finally does it idles extremely rough

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I have a 1996 dodge neon 2.0 automatic it is very hard to start and when it finally does it idles extremely rough. after a few minutes of running if i leave it idleing it will smooth out but if i put my foot on accelerator it runs rough or dies and if i put it in gear it dies or if i put foot on brake pedal it will die
hi, you seem to have a fuel problem have you replace the fuel pump, or check for pressure?
Customer: replied 6 years ago.
the fuel pump is new and the return filter is new the fuel pressure is close to 40 psi with key on engine off with engine idleing it hovers around 20 and does'nt stay steady
ok that is not good you should have from 45to 55 psi when running and 40 psi with key on engine off, you must have a bad fuel pump or filter clogged.
Customer: replied 6 years ago.
i recently bought the car from my friend you can see the fuel pump is new it is an airtex plus I have the receipt it is only a couple of weeks old
ok, it can be new and defective and the pressure its showing means you need another one , make sure you check the fuel filter to.
Customer: replied 6 years ago.
i just called my friend he told me the car was dying randomly and his dad put the pump and filter in he said the car still wouldnt run like it should
Customer: replied 6 years ago.
i was wondering what are the odds the pcm are bad or the throttle postition sensor
hi, sorry for the delay, you say the fuel pressure is around 20 psi when running, and if so i tell you right know that is the problem on this vehicle you need to check the fuel pump operation it needs to go back to 45 psi if you change the fuel pump it is possible there may be a restriction some ware, can you do a fuel pressure test again and confirm the pressure for sure ?
Customer: replied 6 years ago.
fuel pressure just past 40 and if i turn the key off and on it raises past 40 but when you start the car 20
ok, then you need a pressure regulator it is not reserving pressure at the rail, those the fuel regulator at the rail has a vacuum connected to it?.
Customer: replied 6 years ago.
i don't see a regulator on the fuel rail just the supply line and the injectors coming out of it
Customer: replied 6 years ago.
i figured out that the regulator is on the pump in the tank and is new with the pump which brings me back to car running rough and dying before the pump was even replaced
Customer: replied 6 years ago.
today i read on the internet how to read codes without scntool i have several codes but i don't know what they mean 12,51,42 and 55

i am sending you this picture and information just to show you that the fuel pump pressure should be more then 20 psi , the reason for the engine lights and codes is because the low fuel pressure problem is affecting other sensors like 02 sensor and map sensor


Fig. 2 Side View-Filter/Regulator

A combination fuel filter and fuel pressure regulator is used on all gas powered engines. It is located on the top of the fuel pump module.

  • A separate frame mounted fuel filter is not used.

Fuel Pressure Regulator Operation: The pressure regulator is a mechanical device that is calibrated to maintain fuel system operating pressure of approximately 338 kPa (49 psi) at the fuel injectors.

It contains a diaphragm, calibrated springs and a fuel return valve. The internal fuel filter (Fig. 2) is also part of the assembly

Fuel is supplied to the filter/regulator by the electric fuel pump through an opening tube at the bottom of filter/regulator.

The fuel pump module contains a check valve to maintain some fuel pressure when the engine is not operating. This will help to start the engine.

If fuel pressure at the pressure regulator exceeds approximately 49 psi, an internal diaphragm closes and excess fuel pressure is routed back into the tank through the pressure regulator. A separate fuel return line is not used with any gas powered engine.


Customer: replied 6 years ago.
ok I traded fuel pumps and installed new one ran fine for about ten minutes and same problem reocurred runs rough after i killed it and went to start it again it was really hard to start
ok, do you have a fuel presure tested with you right know?
Customer: replied 6 years ago.
it has 40psi when key is on but when idleling it hovers around 25 so it is pretty much the same as before
ok so its still at low presure when on drive . ok do you have a voltmeter we need to check if the voltage to the fuel pump changes also when shifted, if you do i will gide you on checking by testing the fuel pump relay
Customer: replied 6 years ago.

yeah i have a volt ohm meter i have checked voltage at the fuel pump at the key on position and it is at 12 volts

how about when running?
Customer: replied 6 years ago.

it has 12 volts briefly then fluctates after testing this i checked and replaced the relays bothe fuel and auto shutdown relay

do the voltage fluctuates between 14 volts and 9 volts?
Customer: replied 6 years ago.
no between 7 and 12 volts
ok if this is the voltage when engine is running then its wrong you should have 12 volts with key on and ENGINE NOT RUNNING and 14 .3 volts with key on ENGINE RUNNING ok can you check the voltage at the battery with engine running?
Customer: replied 6 years ago.

voltage at the battery is 14.52 volts when engine is running


good then that is the voltage we need to have at the fuel pump . somenthing is shorting out the power to the fuel pump , lest check the fuses at the outside fuse box with the voltmeter see if they have 14.5 volts also with engine running .
Customer: replied 6 years ago.

ok at the fuel pump fuse i have just over 14 volts

and at the fuel pump it goes from 12 to an average of 10

Customer: replied 6 years ago.

i just checked all wires at the fuel pump one has 13 volts one has 10 the other has 10 and on has 9

you need to check for a ground missing one of those wires is supposed to have a ground , here is the schematic you are supost to have 2 power wires and 2 ground wires its posibl
e for one ground to be missing.
Customer: replied 6 years ago.
ok 2 are hot and two are ground i checked two for continuity to chassis and i have two grounds

what is the voltage at dose 2 wires that have power?

Customer: replied 6 years ago.
10 and 9
Customer: replied 6 years ago.
i need to add to that if the car has been running for a few minutes the voltage goes up to almost thirteen and 10 but when just started 10 and 9
ok, lest first check for how many volts are precent at the fuel pump relay with a voltmeter check for two powers at the fuel pump relay with key on use the schematic i am sending you it shows the location of the relay and the powers on the conectors test them and let me know what you get.make sure you copy or print this page.

Fuel Pump Relay

Fig. 15 Power Distribution Center (PDC)

The fuel pump relay is located in the Power Distribution Center (PDC) . The inside top of the PDC cover has a label showing relay and fuse location.


you copy or print this page.
Customer: replied 6 years ago.
ok one is 11.80 the other is 11.91
ok voltage is ok, withing battery voltage, can you replace the relay and check the voltage at the fuel pump again you can use any relay in the same box.
Customer: replied 6 years ago.
i have actually already done that it doesnt matter i have the same result i actually bought two new ones just to be sure
oklest check the power output from that relay to the fuel pump, install awire in to cavity #52 and insert the relay over it and check how many volts are present with key on?
Customer: replied 6 years ago.
ok i have 11.90 with key on but it drops to nothing right away but when cycling key it goes back up to 11.90 then drops again
ok how about with engine running?
Customer: replied 6 years ago.
just over 14 volts

one last voltage check , disconect the fuel pump and with key on check power.

Customer: replied 6 years ago.
just over 10 volts
ok you have a wire between the relay and the pump conector open or shorte causing a voltage drop and this is affecting the fuel pump ability to maintaine can try ussing a jumper wire from the relay output, and to the fuel pump conector you will have to cut the wire that powers the fuel pump and replace with this wire just to try.
Customer: replied 6 years ago.
does the voltage go through the pcm after the relay or before im just wondering the last time i experienced low volts to fuel pump on my truck the pcm was actually bad i went through the hole ordeal of tracing wire and it turned out that there was a short in the pcm
no this wire comes out of the relay and goes strate to the pump the computer only grounds the relayto turn the pump on.
Customer: replied 6 years ago.
is it possible there is a bad ground in the computer
no because if it was the relay would not activate the pump.the relay needs full ground to switch power to the fuel pump, have you check for a fuel filter posibly clogged?
Customer: replied 6 years ago.
the fuel filter is brand new

ok, we cover all the basis of posible fuel restrictions and electrical flows and found no problems but still cant explane the lost of presure, one last thing we can do is baypass the circuit and run a wire strait from the positive side of the battery, and another wire for grownd start the car and check fuel presure again.

Customer: replied 6 years ago.
ok i ran a wire from relay to the pump car runs great that way what next
Customer: replied 6 years ago.
ok ive figured out that i have voltage at my ground connections to the fuel pump i believe this is voltage from a shorted power wire. my question is where does the wire go from the relay to the pump what route does it take through the car and what colors does it change to
ok, that shous you that you have a shorted wire from the relay to the fuel pump,you are going to have to replace that wire from the relay output on to the fuel pump and the same with the ground wire.can you check the fuse shown on this schematic with a voltmeter and see if voltage is there when runing 14 volts and not running key on 12.5 volts fuse 10 inside the vehicles fuse box.

Fuel/Ignition Systems (Part 12 Of 13)

Fuel/Ignition Systems (Part 13 Of 13)

NOTE: To view sheets referred to in these diagrams, see Diagram Information and Instructions/Complete Body and Chassis Diagrams .
Customer: replied 6 years ago.
ok there is 14 running and 12 koeo
ok, that fuse is ok the problem is like i sad on that wire going to the fuel pump you are going to need to cut the wire right from the relay and cut right at the fuel pump conector and run another wire to bypass that wire and just tape up the wire in the harness nice and neat. you mention before somenthing about having power at the groundwire?
Customer: replied 6 years ago.
yeah both ground wires to the pump show voltage as well as having continuity to ground
ok that is were the short may be just run the wire from the relay to the pump and eliminate the old wire .
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