Car won’t idle, dies, P025B code!

[txgt]

My 2018 GT has always run perfectly! Zero issues with the motor, purrs like a kitten.

However, yesterday problems started. I went to leave work and did my normal warm-up routine: Start the car and let her idle until the RPMs drop below 1K. Less than a minute into the warm up, the engine started running rough and the RPMs started dropping until the engine eventually just died. I let it sit a little before starting again. I started it back up and things seemed to be back to normal and idled normal. I baby’d the car all the way home “just in case” but nothing abnormal happened, but the whole situation left me worried. No check engine light

This morning I started her up, let her warm up and took her for a drive around the block and everything was perfectly normal.

But… tonight she did the exact same thing! Started fine, rough idle, RPMs dropped and the engine died

This time the CEL did come on, so I pulled the code and got: P025B Fuel Pump Module “A” Control Circuit Range/Performance

I searched the forums but have so far come up empty on this… still searching the interwebs for some help, but hopefully someone here can provide me with some direction.

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[txgt]

Started the car again just now, and she idled perfectly fine.

To try something out, I removed the rear seat to inspect whatever the hell is underneath there (yeah, fuel stuff). I found what I believe to be the “Fuel Pump Module “A” Control Circuit“ thing:

I unplugged it and then started the car, and as expected the car started but quickly died. That triggered a P025A Fuel Pump Module “A” Control Circuit/Open code. That just verified to me that it’s the right part.

I plugged it back in, and the car started right up and idled perfectly. I guess that the module could be intermittently bad, triggering the P025B code?

 

[Garfy]

Possibly yes. Solid-state stuff won't always stay dead; they will commonly go intermittent so as long as you don't see any issues with the wiring or connector, I'd replace it and see how it goes.

 

[txgt]

Drove around a few times yesterday and everything seemed to be fine. Started up and idled perfectly every time. However, after a 20 minute drive it started to rough idle and then died at a stop sign. Tried re-starting several times (unsuccessfully) before pushing her into a parking lot. I let her sit for a while (grabbed some lunch nearby) before trying again.

Luckily I got her started again and stopped by a local Ford dealership nearby and picked up and installed a new Fuel Pump Controller (FU5Z-9D370-G). So far, so good… but being an intermittent problem, I’ll have to drive around and hope that this fixed it.

 

[txgt]

Well, $#!^.

Seems the Fuel Pump Controller/Driver Module did not fix it… idled fine for about a minute this morning before rough idling and died again…

The problem is pretty intermittent and so I was able to start it and idle successfully many times after that issue this morning.

I'm just did a drive while data logging with my BlueDriver OBD-II tool. I was able to capture data when I lost fuel pressure, however, I'm really not sure what "normal" data is suppose to look like.

Looks like I'm averaging around ~950 PSI for Fuel Rail Pressure when things are running good... no idea if that is "normal"

Here is the data (link to sheet):

Things get interesting around line 1161 where we drop to 566 PSI before further plummeting:

 

[WildHorse]

driver rarely goes, but will compensate for a bad fuel pump to the point where it'll throw that code. Replace the pump.

 

[txgt]

driver rarely goes, but will compensate for a bad fuel pump to the point where it'll throw that code. Replace the pump.

What's killing me about this is the seemingly random times when I lose fuel pressure. I have no problem replacing a bad fuel pump... I'm just struggling with "is the pump bad?"

I wish there was more of a smoking gun here...

 

[WildHorse]

I wish there was more of a smoking gun here...

There won't be.

 

[txgt]

There won't be.

Yeah, it's looking that way, but would be good to see if there is a way to test this.

So, according to my data, the Fuel Rail Pressure drops during the "event". That leads me to believe that (A) either the fuel pump is getting the correct voltage, but fails to deliver the right amount of fuel/fuel pressure from the tank, or (B) the fuel pump is not receiving the correct voltage during the event, which would possibly point to another failure in the system.

Is there a good way to test those scenarios? I could try to reproduce the intermittent issue and read voltage coming into fuel pump harness?

 

[WildHorse]

Is there a good way to test those scenarios?

Yeah, no factory Schrader valve so get a mechanical fuel pressure gauge, adapters, lines, & watch it. Or replace the pump. Either way you'll know.

 

[luca1290]

The pressure you already know from the sensors in the car, the voltage you know by tapping into the wires.
I don't think the car measures the output voltage of the module BUT before slicing and dicing you had better check that Forscan does not have a PID that may sound like "fuel pump commanded voltage / duty cycle".

If it's feasible and you don't want (like me) to slice open the harness I'll go around with a multimeter, quickly disconnect the pump (if there is a disconnect) and measure the voltage without turning anything off.

Anyway it's either the driver or the pump, being that you already replaced the driver...

 

[WildHorse]

The pressure you already know from the sensors in the car

Those are inferred, not actual.

 

[txgt]

Well, she's with the Lord now...

Oh wait, I mean the Ford dealership. Will update everyone on what they find/replace. Thanks for all the help!

 

[luca1290]

Those are inferred, not actual.

You are right. My bad, I've seen it on mine but it's a 2018+ thing. Probably before the double injection all this precision was not needed for the PCM to calculate the injection flow...

 

[txgt]

Update: Just dropped off the second key to the dealership. They are replacing the PCM and need both keys for the procedure. The PCM has been ordered, hopefully they’ll get it in this week and get me back on the road before the weekend!

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