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Discussion Starter #1
I have a 1998 mustang GT that is pulling numerous codes although most parts have been replaced. I'm out of ideas as to what to do next. It has been having fueling issues lately. The fuel pressure will be just fine, drop down to about 5 psi, stall the car, then go back up to where it should.

Specs of car:
4.6L
79K miles
5 speed
4:10 gears
Cold air intake

Codes pulled from car:
P1260 Theft detected vehicle immobilized (car was broken into 2 days ago)
P0161 Heated oxygen sensor, sensor bank 2
P1506 IAC over speed error
P0122 TPS sensor "A" circuit low
P0231 Fuel Pump secondary circuit low


I have replaced the fuel pump and filter, the iac, the TPS, and bypassed the inertia shutoff switch just to be sure it wasn't a faulty unit.

I have no idea how to go about fixing the fuel pressure issue. Any help and/or suggestions are greatly appreciated.
 

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Did the problems begin after the break in? What damage was done to the car? Is the Theft DTC still happening? Which DTC codes were happening before the break in?

Note, the 1998 GT has a two speed fuel pump controlled via a relay and ballast resister. The P0231 comes from a failure in the high/low speed relay circuit. Likely this is why the fuel pressure is dropping. IE the PCM is commanding high speed while the relay is still in low speed mode.

Have you performed a visual inspection of the area around the PCM? Look for evidence of water/rodent activity.

How about the grounds around the radiator core support? Are they clean and tight?

From looking at all the parts replaced, it would appear that your preferred method of trouble shooting is to replace parts. There is a possibility that all of your issues has a common electrical root cause. Proper trouble shooting will involve detailed tests using a Volt-Ohm Meter. A set of wiring diagrams are almost required.

If interested in getting a full set of wiring diagrams and service manual I maybe able to help. PM if interested.
 

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Discussion Starter #3
Well before the break in, it wouldn't even start. As far as the damage due to the break in, just the radio is missing and there's a couple wires dangling out of the dash. No broken windows and it doesn't appear that they tried to take the whole car or start it or anything of that nature.

It wasn't until after this occurred that I really cracked down and tried to get it running. The only parts that cost me any money was the fuel pump and filter (replaced these because previously I wouldn't get any fuel pressure) all other parts were given to me.

But all electrical connections and grounds appear to be good. I went ahead and cleaned all the dirt around and under the ground wires mounting locations and made sure it was getting good contact.

Would it be possible to wire the fuel pump directly to the battery with a toggle switch? I know it's not the most safe way to do things, but if it'd get the car able to drive without losing pressure I could do that until I can find time to fix it all the right way. In my neighborhood, the longer a car sits in one spot, the more it tends to get broken into. (Found this out from experience with a jeep we owned).
 

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Discussion Starter #4
The previous owner said the car ran great until it was in an accident. He had replaced all damaged parts (or so he says). Would it be possible that it being in an accident could cause some of the trouble codes mentioned above?
 

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Well the lack of fuel pressure is related to the P1260 anti theft code. I dont want to sound silly but is this the only ignition key you have for the car? If you have a second key try to start it using the 2nd key. The key is chipped for the anti-theft and it is very common for the chip to go bad or crack and fall out of the key. Let us know if you can get it running after trying this.
 

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Well...... Just try and wire the fuel pump "hot" and you will get a lesson in just how smart a modern PCM controlled car really is. There are circuits that are designed to verify that devices and sensors are producing the expected results. No more commanding a relay to close and "assuming" that it did. The PCM monitors system states and takes action. For proof see DTC P0231. If you were to wire the fuel pump direct, it would create a constant P0231 thus trading one problem for another. The difference being is now your car will have a hacked electrical.

Further, this would do nothing to fix the other DTC's in the original symptom list.

If looking for something to do that may help, try monitoring the voltage at the trunk mounted IFS switch. What we are trying to see is if the voltage drops real low when this problem occurs. If monitoring voltage at the IFS seems too hard, start with ANY fuse. Get yourself an "add a fuse" and wire up a VOM and set it on the front seat where you can see it. Any drop on voltage indicates a problem.

Today's cars simply will not run right without a strong battery and charging system.

You also didn't answer any of the questions regarding possible water/rodent activity in the area around the PCM.

If the car was hit around the front right this is the area around the CCRM.

Note, there's a ground behind the center console that's shared by multiple devices including the cluster, GEM, PATS module and the RADIO. This ground is frequently messed up during a radio install when done by ppl that care about their car. Do you get where this is going?

Regarding the lack of fuel pressure. This is NOT related to PATS only. Why? Because PATS on the 1996+ model year does not withhold power to the fuel pump. It works by withholding injector pulse. So in cases of low fuel pressure, it's not a PATS problem.

Here's a crank with no start check list:

http://www.allfordmustangs.com/forums/4-6l-tech/336452-1997-mustang-wont-ignite.html#2984838

However this is of questionable use since in all likely hood your car has deeper issues. If asked to handicap, there's a weak ground somewhere. Or your alternator's output is cutting out.
 

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Discussion Starter #7
This is the only key I have. So trying another is not an option unless I get a new one from the ford stealership.


And it appears as though there is no rodent activity or moisture damage on/around the PCM. I will have to test the IFS today after work and will let you know what happens. I will also look into the ground that is near the center console.

Could it be possible that the loss of pressure could be a FPR problem?

Thank you for all your help and suggestions.
 

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Check the fuel pump resistor which should be in the dark green with yellow stripe wire coming off the fuel pump relay. I am looking at Alldata to get this information for you.
 

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Discussion Starter #9
Check the fuel pump resistor which should be in the dark green with yellow stripe wire coming off the fuel pump relay. I am looking at Alldata to get this information for you.
Is there anything specific I should be looking for to tell if it's bad? This is my first computer controlled vehicle so this all very new to me. I'm use to having carbureted cars with minimal wiring
 

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Discussion Starter #10
From looking at all the parts replaced, it would appear that your preferred method of trouble shooting is to replace parts. There is a possibility that all of your issues has a common electrical root cause. Proper trouble shooting will involve detailed tests using a Volt-Ohm Meter. A set of wiring diagrams are almost required.

If interested in getting a full set of wiring diagrams and service manual I maybe able to help. PM if interested.

I hooked up a volt meter to the inertia shutoff switch and it runs a constant 12.75 Volts until right before it dies at which point it drops to about 1 volt.
 

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Discussion Starter #11
Well I have discovered that the fuel pump resistor was gone. So I put one on, car runs now. But if I give it too much throttle, it wants to stall out.. Any possible reason this could be happening? I'd like to assume it's because I have no air filter on it currently so it's pulling in too much air.

Any other help/suggestions is greatly appreciated
 
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