2013 GT500 Coast Surging

[Lidio Iacobelli]

GH,

Have you seen if this happens only in the real world on the road, and not on a chassis Dyno (providing you have access to one).

You may want to look into this -- Some of the aftermarket air-boxes like the JLT's are known for causing big time coasting-decel surge while clutch is depressed, and just kinda goes away as you slow down and get just under ruffly 15-20mph.
Some of these boxes cause the MAF to become very sensitive to wind, ram-air, and turbulence once the vehicle starts moving well over about 20mph. JLT's actualy started coming with a diffuser a couple years back to install in them in order to cut down on the ram-air effect that becomes much more sensitive to the MAF on those when upgrading to the larger and higher flowing Air-boxes and etc. Not sure why, but some will do it very badly and others non at all with similar builds.

Iv'e chased a ton of this kind of crap... Won't do it on the Dyno (no substantial wind obliviously), customer takes the car,, and then 1/2 hour later customer calls with an idle issue when clutch depressed on coasting decel. As long as there is some load on the motor,, there is never a problem, its decel neutral ram-air effect.

Hope this helps.

[GHuggins]

I'm out of the shop all this week, but yes it does it both on the dyno and on the road - main reason the customer brought the car to me after having a few other tuners work on it... It also does have the JLT CAI, which is actually shaped a little funky from what I remember where it attaches to the TB - might be one of the earlier design flawed ones? I know I've never once had this issue that I haven't been able to tune out of one like this before and A LOT of things weren't adding up on this one, such as - increasing wheel torque errors up to 1500Nm's at idle would bring bank to bank fueling back in line and then it's wanting a ton (+6g/s) on cold starts even though I already have min air at 11g/s and then it shifts to -3 or -4 g/s of air only after moving the car on the rollers and allowing it to coast back down... Bank to bank fueling is "usually" spot on with rpm's which I just thought was part of the cams causing problems, but again - never had this problem on another cammed Ford engine? Acts like a vacuum leak, but it's not... Did order a low vacuum bypass and it's getting new widebands and injectors as a prepared future upgrade... Air not being seen correctly through the MAF would make sense - especially with everything changing like it is... You have a part number for the JLT fix?

Thank You...

[Lidio Iacobelli]

I'm out of the shop all this week, but yes it does it both on the dyno and on the road - main reason the customer brought the car to me after having a few other tuners work on it... It also does have the JLT CAI, which is actually shaped a little funky from what I remember where it attaches to the TB - might be one of the earlier design flawed ones? I know I've never once had this issue that I haven't been able to tune out of one like this before and A LOT of things weren't adding up on this one, such as - increasing wheel torque errors up to 1500Nm's at idle would bring bank to bank fueling back in line and then it's wanting a ton (+6g/s) on cold starts even though I already have min air at 11g/s and then it shifts to -3 or -4 g/s of air only after moving the car on the rollers and allowing it to coast back down... Bank to bank fueling is "usually" spot on with rpm's which I just thought was part of the cams causing problems, but again - never had this problem on another cammed Ford engine? Acts like a vacuum leak, but it's not... Did order a low vacuum bypass and it's getting new widebands and injectors as a prepared future upgrade... Air not being seen correctly through the MAF would make sense - especially with everything changing like it is... You have a part number for the JLT fix?

Thank You...

I don't know the part number on the diffuser insert from JLT, there is one for the 2011-14 5.0L Mustangs, and one for the 2010+ GT-500's too. Its included in those kits starting about 2 or 3 years ago. I actually helped those guys at JLT with this problem and worked with them for this solution, chased if for quite a while on a few cars till we finally stuffed rags in the Ram-air inlet tube and realized what was going on. As I said; some cars are more sensitive then others with this sort of coasting idle surge. Again, this is for a rolling idle surge fix. doesn't help on the Dyno or if standing still or going under about 20-25mph.

I actually own a 5.8L 2013 GT-500 that has big stage-4 crower cams, Its extremely cold blooded with anything to do with and around idle RPMs. I have mine set to idle at 1050rpm,,, just commanding that high of an idle (amongst other tuning) with those cams fixed or improved a lot of drivablity concerns. It still rumps and chops hard at that 1050 idle RPM setting, and it took me a while, but I got all the off-idle, cold-idle, and all that stuff figured out over time.
Great thing about the GT-500's is that they still use AirFlow based Dashpot parameters, and not TQ based. For me; I felt that this was easier to figure out a lot of idle related stuff.

[GHuggins]

Yeah I have fans blowing a lot of air in the front of the car to simulate driving and it's probably more than it would see at slow speeds so possibly making this problem worse. Only does it while coasting too.