Possible misfire on cold starts question.

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DstryEvrytng

New member
So my 2015 SHO feels like it has a small misfire at idle on cold starts. It only lasts for about 30 seconds or untill the high idle settles down. Feels like rough idle, you can see the tach jumping 100 or so rpm’s.

Anyone else have this?

Plugs are new and gapped .030. Its done it since i got it at 27k miles and now has 30.5k.

Im almost thinking it is just idling rough untill the turbos get spooled and moving proper air to idle right but idk.
 
My PI and now my new SHO do the same thing. Only reason I noticed mine though was because I have full cat-less exhaust on both cars and I could hear it. I changed some parts on the PI to try to fix that and other issues and never could get the high idle thing to go away. I'm not that worried about it anymore since my new car does the same thing.
 
I found out overtime that the GTDI engines are quite stubborn on the quality of Fuel that goes in.....
To the OP do you have access to 93 octane fuel!  I would also make certain to put in Top Tier Gas such as Shell or Chevron 93 octane fuel @ preferably a high busy turnover fuel station.  Z
 
Thx guys.

Ill check all the clamps i can find on my next day off.

I use 89 from the same station always, it is the busiest station in my area. I ran one tank of 93 just to check milage and i get better milage with 89, ill try 93 again and see what happens with the idle.

Funny side note. The dealer was only getting 17.5 mpg on regular (salseman had been driving it). First tank of 89 the milage went to 23.5, now after 3k miles on 89 its getting a hair over 24 mpg.
 
I don't think it has anything to do with your fuel.

All 3 of mine exhibit/ed that behavior but there was never an actual misfire.

I've ran every fuel/E85 mix one could think of and it never changed across three different vehicles.

No idea what causes it but I really don't think its anything to worry about.

 
I have it on my '13 SHO as well.  I have not watched the tach when it is happening, but it is clearly audible on cold start for a min or so.
 
I wouldn’t worry too much....I think it’s fords idle strategy ...it kind of regulates the torque of idle and idle speed with spark. Also I think fueling and combustion can be finicky until warmed because of fuel sticking to the walls

Also your wild swings in fuel economy are due to the testing. There is no way it can swing that much from octane.

If anything the higher octane will get ever so slightly more economy due to the car making a bit more part throttle power because of higher spark allowed ...if you make more part throttle power you will use less pedal to get up to speed which will use less fuel
 
From day one I had the same issue on my 2015 SHO ..chkd clamps they were fine...did it the entire time I had it.  I always use top tier 91 or 93 octane juice.  My 2018 SHO does not have this issue. Odd.
 
Im glad to hear im not the only one with this odd miss. Now im not worried about it but i am going to attempt to chase it down, because im an idiot like that. Lol

Im pretty sure my mech’s scan tool is updated to the hilt so if all else fails ill see of he can pull the mode 6 data ( as ZSHO suggested)  and then go from there.

Last time it was in the stealer for a warranty issue (brake rotors where pooched bad when i bought it and coolant was low) i told the desk lady about the idle. For some reason she wrote it down as a cold acceleration miss tho so no idle testing was done.
 
Good luck on chasing it down. I changed the fuel injectors, coils, plugs, pcv oil separator and valve, O2 sensors and installed new hot pipes on my PI to fix other issues and the high idle thing persisted through all of it.
 
FWIW try to fix any ongoing issues before the Factory 3YR/36,000 warranty expires,since your @ 30.5K IIRC!  Best of luck.  Z
 
I am able to view mode 6, never showed any issue.

Through the 3 cars I've only seen one Misfire ever.

There is a ton of emissions stuff going on during cold start and I would suspect that is the culprit.
 
My car was doing the same thing until I put 1 stage cooler plugs gapped at 0.028 in it. Idles like a brand new car now xD no more super low rpm misfiring. Try these brisk plugs pregapped to 0.028 imo their the best plug for our application unless anyone else knows of better plugs always like suggestions!
https://www.briskracing.com/brisk-spark-plugs/brisk-silver-spark-plugs/brisk-silver-racing-rr14s-spark-plug-detail

Sent from my SM-N950U using Tapatalk

 
And my SHO saga continues.

Brakes acting ike worse than not having power brakes and the abs seems to be dragging. Almost no stopping power at all and with the brakes dragging. Really odd.

Almost rear ended a tractor, had to get a tow. Flat bed luckily.
 
It could be the brake booster line check valve!  Who changed the spark plugs!
    There is a vacuum line near the rear spark plugs on bank 2!
I hope they get it fixed Pronto! Please keep us updated.  Z

Highlighted in Red below!

Se5tibXh.jpg
 
I had my normal mech change the plugs who has done a lot of work on other vehicles for me with zero issues. I trust him 100%.

Is that booster line close to that driver side rear plug?
Id be very suprised if he f’d it up. Ive put 500+ miles on since he changed the plugs with no problems untill this morning.

Edit = your pic just now showed up for me. I guess that line could have gotten knocked around.

Its at the stealer now so ill update when i find out wtf is going on.

Edit 2= if the brake booster had a leak the brakes wouldnt drag though right? Just loose power?
 
DstryEvrytng said:
I had my normal mech change the plugs who has done a lot of work on other vehicles for me with zero issues. I trust him 100%.

Is that booster line close to that driver side rear plug?
Id be very suprised if he f’d it up. Ive put 500+ miles on since he changed the plugs with no problems untill this morning.

Edit = your pic just now showed up for me. I guess that line could have gotten knocked around.

Its at the stealer now so ill update when i find out wtf is going on.

Edit 2= if the brake booster had a leak the brakes wouldnt drag though right? Just loose power?
Click to expand...
It would feel like metal to metal contact depending how severe !  Z
 
It did kinda feel and act like there was no pad left on all corners.  Shyt, time to go talk to my mech i guess.

It also felt like they where dragging. And after maybe 5-10 minutes of me calling the wife and stuff i felt the rotors and the fronts i could only touch for a cpl seconds. In my hot o meter thats way too hot (for the circumstance and braking i did to get the car off the road).  the rears where also really hot/ way hotter than i think they should be unless dragging.

The first dash lamp that lit was the ABS. I didnt look again untill it was safe to do so and by then the big red “fix the brakes now” message was lit.
 
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