Digital Tuning Need help with returning to stock (SCT)

Paradox2018

Member
Oct 9, 2019
21
2
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20
Pennsylvania
Hi,
Can do the rest on a better day. Answer to your question- No, pressure is not too low at 39 PSI. It’s actually pretty optimal. It’s the higher side that is unusual, 50 psi. It’s within range, just a bit excessive jumping to that without slamming the GO pedal to the floor at escalating rpm’s so the pressure keeps up behind the fuel volume being used.
@ Idle, range is between 30-50 calculating various scenario’s.
Since you have a returnless system, the pump controls the fuel pressure to maintain pressure >30lbs while running through hard acceleration. You have an FPRS on the front of your drivers side fuel rail, this is to communicate actual fuel pressure in the loop It has a vacuum line & plug attached to it.
Check the connections for both.
I’m interested in what your pump’s PRIME pressure is, the fuel system pressurizing the lines on a cold start.
That will be great information. This issue started occurring suddenly, correct? Wasn’t like this when purchased?
Acceleration have any flat spots, or interruptions while driving normally, or hard?
Best!
- John
So i drove for a little bit and the check engine light remained off for awhile but then one time after turning the car off and turning it back on about 45 minutes after the check engine light was back on with the same code.

The car runs so much better now and has started without any issues since the spark plug change.

Is it possible there is still something wrong or maybe it’s being triggered for some odd reason? Should I return the car to stock now to see if that fixes anything?
 
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Onesick99GT

Active Member
Nov 20, 2018
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Dayton, Ohio
I think your plugs were in need of a change so replacing them only helped in making it run better. A good tune up always helps. I'd replace the coils too. They wear out after about 75,000 miles. The mods you have never needed a tune. Although they make tunes to help maximize power, or use less fuel for more efficiency, your car is perfectly fine to run stock. The pcm can easily make adjustments with those mods to run the car. Have you done any data logging of the oxygen sensors? These will throw an emissions code. I had 3 of my 4 oxygen sensors fail on my mustang. Replacing them all was a huge difference and cheap fix. Anything that effects spark, fuel or air will throw an emissions code. Have you check your haynes manual on troubleshooting the code? And by chance you havent deleted the EGR have you?
 
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Paradox2018

Member
Oct 9, 2019
21
2
13
20
Pennsylvania
I think your plugs were in need of a change so replacing them only helped in making it run better. A good tune up always helps. I'd replace the coils too. They wear out after about 75,000 miles. The mods you have never needed a tune. Although they make tunes to help maximize power, or use less fuel for more efficiency, your car is perfectly fine to run stock. The pcm can easily make adjustments with those mods to run the car. Have you done any data logging of the oxygen sensors? These will throw an emissions code. I had 3 of my 4 oxygen sensors fail on my mustang. Replacing them all was a huge difference and cheap fix. Anything that effects spark, fuel or air will throw an emissions code. Have you check your haynes manual on troubleshooting the code? And by chance you havent deleted the EGR have you?
I’m going to replace the coils soon too but they are aftermarket accel coils and are newer.

I haven’t logged the o2 sensors yet and have had limited data logging capabilities. My SCT tuner needs updated to connect to a laptop and I wanted my car to be stock before I updated the tuners firmware.

So my plan is right now I’m going to attempt to return the car to stock and if that goes successfully I’ll update the tuner firmware and get some good data logs with my laptop. If I run into any issues tonight I’ll just contact SCT Support tomorrow morning for help since I’m free until the afternoon tomorrow.
 

08GT500

Active Member
Jul 12, 2018
771
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Massachusetts
So i drove for a little bit and the check engine light remained off for awhile but then one time after turning the car off and turning it back on about 45 minutes after the check engine light was back on with the same code.

The car runs so much better now and has started without any issues since the spark plug change.

Is it possible there is still something wrong or maybe it’s being triggered for some odd reason? Should I return the car to stock now to see if that fixes anything?
Hi, Glad it’s running better, was there any cracked porcelain on the Plugs? What color were the electrodes?
I apologize for the lapse.
Just an FYI, Any aftermarket ignition parts, Dizzy, TFI’s(to 95’ models), Coils, etc, in the big picture, are more likely to cause issues quite often when compared to OE products.
Doesn’t mean their all bad, but look in the archives, you’ll see this trend.
Reverting components back to OE parts many times cures the issue. A wiggle test may prove/disprove a possible a Coil’s connector or FDPM wire disturbed when you changed Plugs.
Is your spark strong, nice & fat/blue, what color were the plugs when pulled?
If you’re now running well & have the code popping up, along with some erratic yet within range fuel pressure PID’s from scanning, I’d do the comparison below.
You run a return-less system, the fuel pump is not operating at 100% of its power levels all the time.
It runs the pump at various power levels, via sensors input/output to keep up with the fuel demands of the motor.
Returnless systems are run by the FPDM (Fuel Pump Driver Module), which directly creates controls varying power levels to the pump. It may also be programmed to change values
A PPRV (Positive Pressure Relief Valve) controls, mechanically, the fuel system’s pressure, purging excess fuel & maintains pressure in the lines.
This Power isn’t conventional DC, it’s PWM (pulse width modulated) & requires an Oscilloscope or frequency counter, other means to see the changes in power, a regular VOM is useless, unless checking for power present, or not
The (Drivers side rail, center) to maintain the necessary volume under adequate pressure whether sitting or running. which allows for easy start-ups, prevents excessive fuel pressure in the lines.
I’d be comparing what the Scantool is relaying pressure, and plug in a gauge into the Schraeder valve on the line, to see how accurate the rail’s pressure gauge is. Gauges are cheap, and will tell you if your sensor is correct. A freeze frame with a Scantool hooked up will automatically record all data right before, when, after the CEL flashes.
As we’d discussed, as Onesick99GT
mentioned the Tune is increasing the Bolt-on gains, but unlikely a necessity with the Bolt-on’s viewed, and mentioned.
In regards to altering the tune, if you had this code popping from the onset of the car purchase, I’d have reflashed it with a new tune, which to my knowledge it did not.
it’s not ridiculous to return it to the. stock program, or even reflashing to the program its running, could be corrupt.
I’d pull the battery cable for 20 minutes & see how she runs after that.
One thing at a time, right? You’re gaining ground
Your reflash should be simple with the stock Tune, and it should run OK, nothing visible that would prevent that.
Any tuning questions or uncertainties, please post. If a question arises, stop & ask. We don’t even sell the X3 tuners any longer, most ly push for the WIFI Rev-X. But both work just fine providing updater files are the newest. Don’t create a new Email account with the Tuner, it’s still the property of the previous owner.
May not let you update,. I’ll PM you.
- Best! John
.
 
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Onesick99GT

Active Member
Nov 20, 2018
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Dayton, Ohio
Go back to the stock coils. I had accel on mine and had issues. They are junk. Always stick with OEM when replacing parts. If your a hands on guy and want to learn buy the elm adapter from amazon prime for your mustang. You can use this to monitor everything on your car. I'll post a link below of mine when I was dataloging with it. Super helpful and this helped me find 3 of my 4 oxygen sensors were failing or had failed. You can see this from the picture. Also found out I had 3 injectors failing.
 
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Onesick99GT

Active Member
Nov 20, 2018
359
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33
Dayton, Ohio
You can see from the datalog the 4 oxygen sensors below. Oxygen sensor 1,3 and 4 were bad. Oxygen sensor 2 had the correct heart beats(orange in color on graph), which they all should have that heartbeat. I was chasing my tail trying to correct issues when I should have data logged to find the source. Very valuable information to be learned using the elm adapter. Download forscan software and with a little bit of patience you can learn a whole lot about your car and the issues your having. 20 dollar cure to instead of throwing parts at it and guessing.
Oxygen Sensors Voltage.PNG
 
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08GT500

Active Member
Jul 12, 2018
771
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Hi, Good info Onesick99GT. +1.
FlashTuners are great for their intended use, and can give you a basic code & reset, but they lack the troubleshooting tools you need to see what’s really occurring.
What was 400-600$ even a few years back is now cost effective for most everyone, validates PID’s (streaming data), freeze frame data records what set off a CEL, drive cycles, graphing & much more, user friendly to boot.
They are an essential tool in any modern toolbox, it will pay for itself many times over.
Bonus is they Work on other OBD-2 vehicles you may also own. They rival what a shop uses & keeps you away from their ridiculous prices, saving you $$ (For the ‘extra HP fund’) lol!
Best!
John
 
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