'03 Manual N/A - Throttle Response is intermitent

[PHNTMPHCKHD]

Gday, long time listener first time caller
Hope you can help me with an issue.

As stated, the problem is in a 5Spd BA XR6
My pedal doesnt seem to want to work until halfway pressed, in which it immediately jumps up the revs
I'd assume this'd be an issue with the potentiometer in either the TB, or pedal

I have replaced all the intake gaskets and tightened in that ol Fibonacci spiral, cleaned the TB and MAP/F
Replaced the TB three times (albiet secondhand units, all worked before I installed them)
Replaced my Accelerator with an auto BA XR6 pedal (also secondhand, but functioned correctly last time I used it)

I'm short of ideas, besides a wire rubbing through the conduit and grounding out somewhere, but I REALLY dont want to buy a harness, unless its got Haltech printed on it.

The codes I have are referring to
P0812 - Reverse input circuit: Caused by my LED reverse lights.

P1131 - PCM attempting to correct a constant lean

P1572 - Brake switch sensor: I bent the bracket, as it wasnt reaching the pedal and activating my brake lights. I suspect the PCM is detecting a discrepency between the two sensors.

U1900 - CANBUS fault. Not touching that with a 10 ft barge pole. Suspect it is caused by the canbus module on my Kayhan head unit, but cannot, and will not, be sure.

Regardless of all my codes, I cannot think of what can cause this issue.
Perhaps the leaning is due to faulty injectors, but at $300< that's not a leap I'm willing to commit to without advice pointing me there.

Anyone else have issues like this?

[El Andrew]

I reckon that lean code is where to start looking. I've had a car (albeit a Toyota, not my Falcon) with a similar code. Was a bit easier as it was reporting both banks were lean which eliminated a faulty O2 sensor or blocked injector as they would have triggered just one bank.

That car drove a bit the same - sluggish until throttle widened a bit.

I reckon if you had a blocked injector it would be running rough.

The u1900 is a pretty common code.to get triggered by a scan tool so I think ignore that for now.

Things I would try (without being an expert) :
-pressure test the fuel system to check for weak pump, blocked fuel filter or faulty reg. Or if your fuel filter is old no harm in putting a new one in anyway. (Fuel filter was my issue. Happened again so I dropped the tank and cleaned it and problem gone)
-get a multimeter out and make sure you are getting voltage changes from the pedal and at the TB which will isolate loom/TB/pedal position sensor
-check vac lines for damage or loose connections

[PHNTMPHCKHD]

Legend

I hadnt considered a voltage check, do you believe the voltage should correlate 1:1

I suppose I could look up what the norm is, hopefully the Haynes has that in it

I have a 255 sitting around gathering dust, and a 4bar FPR, though I fear increase rail pressure on stock tune/injectors may cause more issues

 

Ill do what I can and report back in a few weeks/however long I can keep my finger in

 

Cheers for the reply 😁👍

[El Andrew]

No worries.

Not sure on voltage - I *think* they both fluctuate between 0 and 5 volts but someone else might chime in. I think as long as you saw the voltage move as the pedal moves you'd be happy as a first round check.

You definitely can't use the 4 bar reg on your NA tune without causing issues. A new reg is only 60 bucks or so but I reckon the reg is less likely to be the problem.

[Puffwagon]

I somewhat recently aka probably 6 months ago, measured the throttle voltages and posted about it. You can see them in forscan anyway.

[El Andrew]

Some bloke said this...
https://www.fordxr6turbo.com/forum/topic/96915-tps-diagnosis/?do=findComment&comment=1717500

[PHNTMPHCKHD]

Checking back in

Replaced Timing chain (Unrelated, but equally pressing issue), both cam sensors, and re-lubed all the seals in the engine
The issue persists.

Panic bought a new accel pedal, might keep it for a spare, you never know.
My next guess on where to go would be fuel pump, then injectors.

I want to do the fuel pump, because the thing is just sitting there.
I can't rationale putting it in, as I don't have issues starting, nor does it ever feel like the car isn't receiving fuel.
The pedal issue merely sounds like 'voltage lag' between the pedal and the injectors.
It's like the ECU gets the throttle signal, and just maintains 0% throttle for a second and a half until it decides to limmi and make me look like a flog.

I know how an XR6 should feel at however much throttle is being applied, and that's just not what im getting back.
I bet dollars to donuts its the bloody injectors, or the entire computer system (ECU, PCM)

EDIT: Also measured voltage outputs to both the TPS, and PPS. Both looked in spec, and the voltage was moving 1:1 in terms of movement. (Throttle volts up, TPS Volts down) Range was 0.8 - 3.0 on pedal, and 4.0 - 1.2> on throttle. It was a few weeks ago so pardon if that seems off.

Edited 06/11/23 03:57 AM by PHNTMPHCKHD