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Recently I notice that under full throttle my car feels like it hesitates and surges a bit. At first I thought maybe it was pulling timing because it is pretty hot here in Phoenix in the summer. But a few days ago it rained and was about 80 degrees but the hesitation was still there, so I don't think it's pulling timing for heat reasons. This morning it hit me that maybe the clutch is starting to slip. I've never had a car feel this way with a clutch slip though, usually you hit gas, RPM goes up and speed doesn't match. But maybe the way the RS is tuned it backs off when clutch is slipping?
Anyway, just wondering if clutch slip on this car feels like a hesitation or what. If this is clutch it is very premature, is that usually covered under powertrain warranty? I have about 29k miles in 4 years, I've never lost a clutch before 100k miles.
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FOMOCO usually wont warranty the clutch unless you get lucky...But like you I doubt its the clutch.. uncontrolled spike in the RPM is the normal sign...Good luck OP
 

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Doesn't sound like clutch slip to me (although I wouldn't put it past the Ford ECU engineers). Are you tuned or have access to data logging (Cobb AP, etc.)? That can give you more information on what's going on.

Could just be our terrible gas (assuming 91ACN since you mentioned being in Phoenix) and just your ECU pulling timing up top after detecting some knock.
 

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Discussion Starter #5
Completely stock.
Bad gas is a good thought, I believe it was a pretty fresh tank when I first noticed it and haven't filled up again yet. I'll update when I fill up again.

Sent from my moto x4 using Tapatalk
 

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The stock tune will fall on its face at random times. It's been discussed at length on here.

Consider regapping your spark plugs to .026", or just getting new ones and gapping them. It helps.
 

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Try to notice if it’s worth with a full tank versus a half tank. Multiple RS have had stalling/hesitation issues which seem related to the purge valve or something (which was a base model/ST recall)
 

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I just did the purge valve, I had rough idle even after spark plugs.. gapped.. etc.. still a problem, threw a cel when in 2-3rd gear, half throttle... then poop.. cel came on there was a hesitation... it’s a cheap part to do yourself.. $50 I think.. not covered under my warranty.. paid much more through the dealer.. dumbass.. time to get an AP..
 

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Try to notice if it’s worth with a full tank versus a half tank. Multiple RS have had stalling/hesitation issues which seem related to the purge valve or something (which was a base model/ST recall)
I never paid attention but when this happend to me I was around quarter tank, if that means anything...
 

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Discussion Starter #10
Try to notice if it’s worth with a full tank versus a half tank. Multiple RS have had stalling/hesitation issues which seem related to the purge valve or something (which was a base model/ST recall)
My last fill up was only a day or two before I noticed the hesitation so a nearly full tank. This morning I'm at about half a tank and hesitation is about the same. If it's purge valve I think that was not venting the tank so after gas goes down the pump couldn't overcome the vacuum right? This doesn't seem likely as it is fairly consistent.

Plugs are pretty new and gapped to 26, about 2k miles on them. I suppose something could have gone wrong with them but I think I'll just get another tank of gas this weekend and see if that helps first.
 

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Ah ok. Yeah reported by owners the venting issue is only with a full tank, and if you keep it at 3/4 or less the problem goes away. So yours would be something different
 

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Recently I notice that under full throttle my car feels like it hesitates and surges a bit. At first I thought maybe it was pulling timing because it is pretty hot here in Phoenix in the summer. But a few days ago it rained and was about 80 degrees but the hesitation was still there, so I don't think it's pulling timing for heat reasons. This morning it hit me that maybe the clutch is starting to slip. I've never had a car feel this way with a clutch slip though, usually you hit gas, RPM goes up and speed doesn't match. But maybe the way the RS is tuned it backs off when clutch is slipping?
Anyway, just wondering if clutch slip on this car feels like a hesitation or what. If this is clutch it is very premature, is that usually covered under powertrain warranty? I have about 29k miles in 4 years, I've never lost a clutch before 100k miles. View attachment 343268
Here's how to test for clutch slip. Drive in say 3rd gear at 2500 rpm and apply full throttle quickly and watch rpm V the drive. The engine needs to be under high load. Clutches don't generally slip at high rpms and speeds because that's not where the maximum load is. So a slipping clutch will be most noticeable on a fast shift from say 2nd to 3rd at a moderate speed and when you release the clutch after the shift into 3rd you go WOT immediately and quickly. The sudden additional load and WOT combined will produce the sudden surge of load that will trigger a slipping clutch to slip. If you keep your foot into it a moderately slipping clutch will quite quickly begin to grip again until its hooked up at which point another quick shift into 4th and repeat will often produce the same result. The moderately slipping clutch grips again as the friction and pressure plate heat up due to slippage and increase in dimension and create a little more clamping load and the speed increases and the load reduces. When the clutch is really bad this wont happen and when it slips at WOT under load it will just keep slipping and then the additional heat generated accelerates the eventual failure.
This is why you can nurse a slipping clutch for many miles if you treat it nice and dont load it too much at low speeds and high throttle openings. If you wait till you have some speed and rpm up it wont slip and you can still get a fair amount more mileage out of it.
Ciao
 

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Discussion Starter #13
Yesterday I I was at half tank and decided to fill up to see if things improved. I still have some hesitation but it's not anywhere near as bad as before for the couple of 2nd/3rd gear pulls I was able to do. Will just take it easy the rest of this tank and burn it off, hopefully completely gone with the next tank.
 

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Yesterday I I was at half tank and decided to fill up to see if things improved. I still have some hesitation but it's not anywhere near as bad as before for the couple of 2nd/3rd gear pulls I was able to do. Will just take it easy the rest of this tank and burn it off, hopefully completely gone with the next tank.
If you have e85 available nearby, another way to check is to "splash blend" (add 1 gal of e85 to the tank and fill the rest with 91). This should bump up the octane enough where knock shouldn't be an issue and should rule out "bad gas" as a factor.
 

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Discussion Starter #19
I don't have OBD2 reader or Torque app. I could get one, but by the time I do I will have another full tank of gas or gallon of E85. I'll not worry much about this until that time, probably in a week or so.
Thanks for the suggestions. I'm confident my clutch isn't a problem and a bad tank of gas is likely the issue. No check engine light reinforces that it's not some other problem causing a misfire or lean condition. I'll update again next fill up.
 

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I'll accelerate up an onramp and it always pulls power/torque in second gear under full boost/overboost. What gear does yours seem to fall flat? I don't get that same response in first or third. I think I read somewhere that the ECU pulls power under some conditions, then again, I could be wrong and it may be fuel. Good Luck :)
 
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