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Surging Issue

MSTORMIN919

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So I have a 2017 Mustang Gt., with 36,000 miles. When I'm in 6th gear at cruising speeds, the car seems to "surge" off and on, kind of difficult to explain. Only in 6th gear though. I thought it was the fuel injectors, which I changed but it's doing the same thing. I've checked for vacuum leaks but can't find anything visually.
Not throwing up any codes, so this has me stumped.
Any ideas?
Thanks
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Proshop

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Stock, modded, tuned? Give as much information as you can before you get hammered by all those questions!
 
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MSTORMIN919

MSTORMIN919

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Sorry...
Cold air intake
Long tube headers
High Flow Cats
Lund tune
I've had all of this on for about 3-4 years and this issue just started about 2 months ago.
 

Avispa

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If you can, try putting the stock tune back in. Mine does something similar, it blips about 50 RPM in 6th when the converter is supposed to be locked, at light part throttle. Have several different tunes, and the ones from VMP have the "surging" problem.
 
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MSTORMIN919

MSTORMIN919

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The stock tune won't work with the cold air intake I have.
And like I said before, everything has been great for at least 4 years without an issue. I do have a PBD tune that I may try to see if that helps.
 

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Cory S

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The stock tune won't work with the cold air intake I have.
And like I said before, everything has been great for at least 4 years without an issue. I do have a PBD tune that I may try to see if that helps.
Possible dirty MAF element, or wheel speed/ABS sensor.
 

Cobra Jet

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Did you check for any stored codes? If so, where there any?

As Cory stated - check the MAF with multimeter ohming it to factory specs; if it's +/- the factory specs, it's starting to fail. If it's within the factory specs, then you can clean the MAF using specific EFI MAF cleaner - do NOT use anything other than specific MAF cleaner.. The MAF has been a Mustang culprit to idle issues since 1990 when MAF was first introduced to the Mustang 5.0 (1989 California, rest of the US it was 1990 for Ford Mustang MAF).

Here a few other pointers:
- Pull the plugs and "read them" via comparing what they look like to online sites that show varying degrees of plug wear. Plugs don't last forever, especially if there may be another underlying issue causing the plug to become dirty, prematurely wear or even be damaged.

- Check up on threads on here regarding the VCT system. Any minute amount of debris in the VCTs can cause idle issues. I can't recall who, but in one of the VCT threads a M6G user showed how to make a DIY VCT "flusher" that will cycle the VCT's to flush out any possible debris. It's a similar process to what a Service Center would do using Ford IDS.

- Check your throttle body too - pop off the intake tube and see if the throttle body blade is dirty (or is sticking during manual travel). If so, use only EFI Throttle Body Cleaner and clean the blade. Never use anything other than that specific product, because the TB blade and interior of the TB itself has a special coating on it and other products such as carb cleaner or even brake cleaner can destroy that coating.

- Check for any breach in the air intake tract. Check all hoses going to/from the intake and make sure any/all clamps are tight too. The slightest amount of breach before or after the MAF will cause fluctuations.

- IMRC could be a possibility - but check all the easy stuff first. Hit up the IMRC threads on here too which have a boatload of info/DIYs regarding that system. IMRC has also been a known source of idle/drivability issues since it was first introduced into the 4.6 DOHC for the Lincoln MVIII, which was eventually carried over into the first DOHC 1996 SVT Cobra - and eventually morfed into the 5.0 Coyote....

Sure, sounds like a lot of "checking" but do it methodically starting with 1 item at a time to rule out that item is not causing the issue. Don't just throw parts at the car, that never solves anything, just runs your pockets dry and causes more frustration.

Report back.
 

K4fxd

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Do a log. It might show what is going on.
 
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MSTORMIN919

MSTORMIN919

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Did you check for any stored codes? If so, where there any?

As Cory stated - check the MAF with multimeter ohming it to factory specs; if it's +/- the factory specs, it's starting to fail. If it's within the factory specs, then you can clean the MAF using specific EFI MAF cleaner - do NOT use anything other than specific MAF cleaner.. The MAF has been a Mustang culprit to idle issues since 1990 when MAF was first introduced to the Mustang 5.0 (1989 California, rest of the US it was 1990 for Ford Mustang MAF).

Here a few other pointers:
- Pull the plugs and "read them" via comparing what they look like to online sites that show varying degrees of plug wear. Plugs don't last forever, especially if there may be another underlying issue causing the plug to become dirty, prematurely wear or even be damaged.

- Check up on threads on here regarding the VCT system. Any minute amount of debris in the VCTs can cause idle issues. I can't recall who, but in one of the VCT threads a M6G user showed how to make a DIY VCT "flusher" that will cycle the VCT's to flush out any possible debris. It's a similar process to what a Service Center would do using Ford IDS.

- Check your throttle body too - pop off the intake tube and see if the throttle body blade is dirty (or is sticking during manual travel). If so, use only EFI Throttle Body Cleaner and clean the blade. Never use anything other than that specific product, because the TB blade and interior of the TB itself has a special coating on it and other products such as carb cleaner or even brake cleaner can destroy that coating.

- Check for any breach in the air intake tract. Check all hoses going to/from the intake and make sure any/all clamps are tight too. The slightest amount of breach before or after the MAF will cause fluctuations.

- IMRC could be a possibility - but check all the easy stuff first. Hit up the IMRC threads on here too which have a boatload of info/DIYs regarding that system. IMRC has also been a known source of idle/drivability issues since it was first introduced into the 4.6 DOHC for the Lincoln MVIII, which was eventually carried over into the first DOHC 1996 SVT Cobra - and eventually morfed into the 5.0 Coyote....

Sure, sounds like a lot of "checking" but do it methodically starting with 1 item at a time to rule out that item is not causing the issue. Don't just throw parts at the car, that never solves anything, just runs your pockets dry and causes more frustration.

Report back.
Wooo, that does sound like a lot but I agree at not throwing parts at it.
Question if you or anyone else knows; should the vacuum stand steady at idle? Or should there be some fluctuation? At idle the car's vacuum is jumping from 21.3-21.7 (after it's at operating temperature)
Is that normal?
 

Proshop

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Wooo, that does sound like a lot but I agree at not throwing parts at it.
Question if you or anyone else knows; should the vacuum stand steady at idle? Or should there be some fluctuation? At idle the car's vacuum is jumping from 21.3-21.7 (after it's at operating temperature)
Is that normal?
There will always be a slight fluctuation at least in my experience.
 

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MSTORMIN919

MSTORMIN919

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There will always be a slight fluctuation at least in my experience.
Thanks... yeah it idles fines, just that jerking/ surging in 6th gear going 65-70 driving me bananas.
I'll check all of those mentioned above and report back.
Thanks for the help everyone
 
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MSTORMIN919

MSTORMIN919

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So... borrowed a buddy's scanner and got a P2251 code and this while the car was running. I actually had to replace the downstreams 2 years ago from driving in some crazy downpour.
So is this telling me just that one O2 sensor is bad? I'm going to replace both but just curious

20230327_133059.jpg
 

ORRadtech

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Vacuum is dependent on engine RPM. If the idle varies even a little vacuum will too. Your only getting a 4 tenths variation, I wouldn't consider that out of the realm of possibility.
Out of curiosity how did you check for a vacuum leak? A smoke test is probably the most reliable way to hunt for a small leak.
 

Angrey

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One thing you should check is the FPDM signal. Early on, I tried to use the FPDM signal as my trigger for my fuel system (which is "standalone") and in cruising I was getting surging/cuts at a repetitive interval. I swapped over from the FPDM signal to the key on and it went away. Something in the tune logic was causing intermittent drops/rises in either the voltage or PWM signal from the FPDM and it was only noticeable at steady low level cruising. You may be getting fuel pressure variances that are a result of the FPDM cycling (if it's a consistent interval)
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