3.8l Engine: Random Misfires, Inconsistent Codes

Gray

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Greetings everyone, thanks in advance for any insight you can provide.

Quick background on recent work:

Oil Change, New Air Filter, Transmission Rebuild, New Spark Plugs, New Plug Wires, Coolant Flush, New Lifters, Cleaned MAF, Injector Cleaning + O-rings, Connecting Rod Bearings

The vehicle drove beautifully for about a week - when driving home I began to notice a slight hesitation on throttle which grew rapidly worse over the course of 5 miles. I arrived at my home and checked the codes, and returned the following:

P1233, Fuel Pump Driver Module Disabled or Offline
P1406, DPFE Sensor Circuit Downstream Hose (Already remedied, I had broken off a stem and had yet to repair this at the time)

P0300, Random Misfire
P0303, Cyl 3 Misfire
P0304, Cyl 4 Misfire

I checked the inertia switch: Not tripped, receiving and sending 12v.
I then gave a good solid... 'tap' to the CCRM, the engine levelled out for a moment before going rough. I assumed at this point it was a faulty relay. I soldered in a new relay (confirmed 100% exact match) and threw it all back together.

Now, there's an aggressive misfire on 'Random' cylinders... and new codes.

P0316, Misfire Detected On Startup, First 1000 Revolutions
P0300
P0303
P0304
P0113 Intake Air Temperature Sensor Circuit High Input

Now, P0113 I can't make any sense of. The information I have found leads me to believe that the MAF is a combination of IAT and MAF on this vehicle. Disconnecting it and restarting the engine resulted in no noticeable change, no new codes. Restarting the engine with the sensor reconnected results in no change, and no new codes. I then had to drive the vehicle for about 60 miles to get the computer to send me a new batch of codes after a reset. Post-reset codes are same as above.

I cleaned the MAF -again- just to rule out possible dirty sensor, no change.

Let me know if there's something I'm missing. Tomorrow I plan on pulling the Fuel Pump Driver Module just to rule that out.
 
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Gray

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Okay... I'm stumped. Fuel pump is putting out 78lbs when it's jumped to deliver full power. The inertia switch is functioning properly, the CCRM is functioning properly.

Does this indicate a failed FPDM? I can't seem to find a way to actively test the module.
 
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Gray

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Update: after pulling apart the FPDM and testing each component for continuity I have found a broken circuit. If someone can provide further insight as to "C10" on the underside of the board, I would be grateful. Should C10 be default open? Or should it have a closed reading like every single other chip? If someone has a functioning FPDM and can tell me what this particular chip is, I am hoping I can repair the board.


*** Sorry, I left out some important info:
Model '04, Board No. XS7F 141608 DA
 

01yellercobra

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C=capacitor. Depending on how you're measuring it, it's going to read open. Do you have any local Mustang buddies that would let you borrow their FPDM. They're all the same 99-04.
 
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Gray

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C=capacitor. Depending on how you're measuring it, it's going to read open. Do you have any local Mustang buddies that would let you borrow their FPDM. They're all the same 99-04.

Aha... the other capacitors gave me a resistance reading. This is the -only- chip the did not return a resistance. I don't know anyone in the area with a mustang in the same year as mine. I'll have to call around and see if a scrapyard has a board I can inspect. Thanks!
 

01yellercobra

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If the other capacitors were showing resistance then there are probably other branches in the circuit that connected it. Really the best way to test this stuff is to remove at least one side from the board. It isolates the component.

And capacitors have a positive and a negative side.
 
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Gray

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If the other capacitors were showing resistance then there are probably other branches in the circuit that connected it. Really the best way to test this stuff is to remove at least one side from the board. It isolates the component.

And capacitors have a positive and a negative side.

Gotcha.... Will remove the chip and test again.
As far as pos/neg sides, I did reverse the connection to test, just in case.

Cheers
 

Gemini

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Had something similar to this when I first got my used 1997. I had replaced the coil pack as preventative maintenance but the one I installed was bad. Swapped it for the original and problem solved.
 
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Gray

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Had something similar to this when I first got my used 1997. I had replaced the coil pack as preventative maintenance but the one I installed was bad. Swapped it for the original and problem solved.
Would this have thrown a code of any sort? I am STILL stuck with this...

New FPDM installed, problem not fixed. I changed my fuel filter and the fuel that came out was a rusty brown color. I flushed some out of the tank and it ran clear, or as clear as gasoline gets. Engine still misfires. After reset, no codes. Very irritated with this. I cannot afford to throw money at this car, if there is a way to test the coil pack, please let me know.
 
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Gray

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is it still showing the same codes?

It wouldn't give me any codes for a while, but now I have a new one... the only code it's throwing is P1235 - Fuel Pump Control Out of Range

What in the hell is going on with this thing... According to Ford: Faulty FPDM. I JUST REPLACED THIS THING! Could this mean my PCM is shot? :mad:
 
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Gray

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where does it read the pressure at?

Key on engine off - 38- 45
Engine on - 30 - 35, and it dances violently for a little while upon startup.

This is strange, when I jumped it last time I got a MUCH higher reading...
** Perhaps because jumped at full voltage causes it to run at a much greater pressure than intended for normal operation?

**Also, someone siphoned my tank while I was away. Super happy about that.
 
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Gray

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I've checked:
Voltage between Red/Blk and Brown/Pink - OK
Black to Frame Ground - OK
Light Blue/Orange to PCM continuity - OK
Light Blue/Orange to Frame Continuity - Open Circuit; OK
Light Blue/Orange to Frame Voltage - Duty Cycle Indicates Fault - NOT OK

I forgot to mention - before resetting all codes, the last pull gave me these three:
P1233, P1235, and P1237

Now all I receive is a P1235.

PS., alternative repair methods that I have tried with no success:
Stroking and pleading with the PCM to summon the genie inside to grant me a wish
Screaming threats at various parts / in the general vicinity of the vehicle
Percussive Maintenance
Staring Match with Headlights
Attempting to flip vehicle with bare hands
Willing the entire thing to explode using the power of my mind
Crying gently into the engine compartment in the hopes that the taste of my tears will appease the demon trapped within
 
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ttocs

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What I meant by where it measures pressure at was phisically, where is the sensor that measures pressure. Check it.

checking for continuity to ground really isn't good enough. Measure resistance and see how low it is. It almost sounds like a bad wire connection in a harness or somewhere. Try connecting the meter to check resistance and then get technical with the harness. Push/pull/twist on the harness connections and see if the resistance changes.
 

01yellercobra

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Pull the FRPS and see if you can blow through the vacuum nipple. If you can then it's bad. A bad FRPS will cause all kinds of issues. Also, has the fuel pump been replaced? I've had those start doing random things before they die.

If you're datalogging you want to watch FPDC and pressure drop across the injectors. You want the second one around 40psi. Those two will tell you a lot.

My apologies if this has been mentioned. I didn't read the whole thread.
 
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Gray

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Pull the FRPS and see if you can blow through the vacuum nipple. If you can then it's bad. A bad FRPS will cause all kinds of issues. Also, has the fuel pump been replaced? I've had those start doing random things before they die.

If you're datalogging you want to watch FPDC and pressure drop across the injectors. You want the second one around 40psi. Those two will tell you a lot.

My apologies if this has been mentioned. I didn't read the whole thread.

Resistance is low - low enough that the multimeter doesn't register it beyond .000.

The sensor seems okay - the internal diaphragm is intact, as far as I can tell by blowing through the vacuum line. No scent of fuel in there either.

The fuel pump has not been replaced... though that seems a likely culprit here. The fuel pressure being delivered seems highly erratic, yet the codes don't seem to back up a failed pump. Rather, they tell me that EVERYTHING ELSE has failed. I'm making no progress here, as I've checked what I can find online as suggestions.

Any further suggestions, please, let me know.

***EDIT:

If I'm shopping for a pump, is there any reason to replace the whole unit rather than just the pump? Please let me know what you think. Cheers
 

01yellercobra

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You'll never get lower than 0.0 ohms. That's a dead short.

If nothing else replacing only the pump will save you a few bucks. I remember I worked on a V6 that was doing some random things. Until it left the owner stranded on an on ramp. Then it was really easy to figure out the pump was the issue.
 
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Gray

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You'll never get lower than 0.0 ohms. That's a dead short.

If nothing else replacing only the pump will save you a few bucks. I remember I worked on a V6 that was doing some random things. Until it left the owner stranded on an on ramp. Then it was really easy to figure out the pump was the issue.

As far as pricing goes, I'm seeing assemblies for 109 +, whereas I found a Bosch standalone pump for $50. Just curious, is there any real reason to spend extra money on the plastic shell and fuel level sensor?
 

01yellercobra

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As far as pricing goes, I'm seeing assemblies for 109 +, whereas I found a Bosch standalone pump for $50. Just curious, is there any real reason to spend extra money on the plastic shell and fuel level sensor?
IMO no there isn't.
 

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