Strange hesitation between idle and 3000 rpm

[xxsurvivalism]

I'll try to explain this the best I can. 2008 GT Deluxe 5 spd. Occassionally, I have a strange hesitation between idle and 3000. It only happens after the car has been driven and is shut off and restarted in a short period of time (getting fuel, or grabbing groceries for example). I'll restart the car, hit the road, and it hesitates til it gets to 3,000 rpm. After that, it runs like a champ from idle to wherever. "Alright, lets crack 3,000 in first gear to get rid of the hesitation." Super strange to me. Other than that, I've never had a better running vehicle in my life, runs like an old Singer sewing machine. And again, it only does it every once in a while. I have hopped in after a short stop and it ran completely normal.

Here are the mods that would matter in this situation:
- S&B CAI
- FRPP 62mm TB
- FRPP Intake Manifold
- Comp Cams XFI Camshafts
- BBK Long Tube Headers
- Offroad X pipe to Magnaflow mufflers
- Fresh Motorcraft plugs
- MSD Blaster Coils
- Fresh header gaskets
- Fresh intake manifold gaskets

Now about the TUNE. I bought this car pretty blindly. Previous owner had no idea what they had gotten into, I had to save the damn thing before something bad happened lol. I have no idea what tune it has on it. But I DO know that it would need a tune to run as amazing as it does with these mods. It loves a belly full of 92 octane, tried a few gallons of 87 on an empty stomach and it ran noticably different. Another clue to a tune might be a VGA cable and a USB female cable inside the center console? They've been routed under the console to somewhere under the dash. No idea where they go, maybe the VGA is hooked up to the OBDII port?




Hesitation aside, it runs pretty mild between idle and 3,000 rpm. A possible loss in bottom-end due to that Ford Racing Intake Manifold. Honestly makes it pretty streetable, good cruising speeds I suppose. Once you crack three grand, it's on like Donkey Kong. That engine really comes alive, like some kind of wack-ass 2 stroke power band. It's fairly impressive for a naturally aspirated 3V (4:10 gears, all the suspension mods and a FRPP 1 piece aluminium driveshaft help with that lol).

Any help or advice would be appreciated!

 

[Dino Dino Bambino]

Which cams do you have? Any bottom end torque loss is due to the cams rather than the intake manifold. The latter tends to cause a loss of torque in the midrange (3300-5200rpm).
I agree that the tune is the most likely issue so I suggest you contact Lito and perform some data logging to see if you can pinpoint it.
@GlassTop09 recently alluded to the Evap port in the FRPP intake manifold being a potential design flaw in his Lunati Voodoo cams thread and I think he's onto something. You might want to read his comments.

 

[xxsurvivalism]

Which cams do you have? Any bottom end torque loss is due to the cams rather than the intake manifold.

Mid-range torque is actually pretty outstanding.
They're the Comp Cams XFI Stage 2 set.

Interesting, I'll go read through the thread, thank you.

 

[Dino Dino Bambino]

Mid-range torque is actually pretty outstanding.

The BBK full-length long tube headers with off-road mid-pipe would offset any midrange torque loss from the FRPP IM. Your HP & TQ curves would probably look something like this:



I didn't see you list underdrive pulleys, so here's another simulation with the pulleys included.

 

[xxsurvivalism]

I did forget to mention, yes I do have Roush underdrive pullies.

 

[Dino Dino Bambino]

I did forget to mention, yes I do have Roush underdrive pullies.

Therefore by my reckoning you have an estimated 357rwhp & 331rwtq. I'd be interested to see what you get on a real dyno.

 

[07 Boss]

I have had a similar issue pop up every once in a while. Seems like when it's up to temp and I make a quick stop sometimes she is hard to start or runs rough till I give her some gas The times it hasn't started I have held the pedal down while cranking to clear the cylinders. It only happens once or every couple of months or so. Less now that she is not my daily. I haven't been able to duplicate it or diagnose it as it is so sporadic. I have mad a couple of conjectures but nothing solid.

 

[xxsurvivalism]

I have had a similar issue pop up every once in a while. Seems like when it's up to temp and I make a quick stop sometimes she is hard to start or runs rough till I give her some gas The times it hasn't started I have held the pedal down while cranking to clear the cylinders. It only happens once or every couple of months or so. Less now that she is not my daily. I haven't been able to duplicate it or diagnose it as it is so sporadic. I have mad a couple of conjectures but nothing solid.

Strange, sounds very similar. I haven't had any issues with starting at all, not even a small misfire. But I agree, it does seem like clearing the cylinders makes it go away. Wish I knew what tune was on this dang car.

 

[xxsurvivalism]

Therefore by my reckoning you have an estimated 357rwhp & 331rwtq. I'd be interested to see what you get on a real dyno.

I definitely plan on a Lito tune + dyno. I'd be all smiles at 357rwhp on a NA 3v with no head work. Been having a very difficult time finding a good speed shop/dyno after moving to the Spokane/Coeur d'Alene area. If anyone is into modding cars, it's carbureted classics or subarus. I called a few 'renound' shops in the area and asked them if they knew the 3v 2 piece spark plug removal procedure and they all had never even heard of 2 piece spark plugs. Scary haha.

 

[xxsurvivalism]

I'd read another post on here about a similar issue (post is about 8 years old lol). Almost same setup, turned out to be O2 sensors.

Took the Mustang out today on a very mild cruise. Threw a P2197 02 Sensor Signal Stuck Lean code... hopefully it's just a bad O2 sensor creating the hesitation. I'm going to change them out with some Motorcraft sensors and I'll update.

 

[Dino Dino Bambino]

Your O2 sensor is probably fine and something else is triggering the lean code. Since P2197 is from the front sensor on the driver's side, the likely cause is going to be side specific e.g. vacuum leak (intake manifold gasket on driver's side or leak from brake booster, Evap, or PCV vacuum line), header collector leak, shorted O2 sensor wiring.
The latter often occurs if the tranny has recently been removed e.g. to do clutch replacement, and the wiring gets pinched as the tranny is reinstalled.
If the wiring looks OK, hire a smoke machine and start looking for a vacuum leak.

 

[Pentalab]

I definitely plan on a Lito tune + dyno. I'd be all smiles at 357rwhp on a NA 3v with no head work. Been having a very difficult time finding a good speed shop/dyno after moving to the Spokane/Coeur d'Alene area. If anyone is into modding cars, it's carbureted classics or subarus. I called a few 'renound' shops in the area and asked them if they knew the 3v 2 piece spark plug removal procedure and they all had never even heard of 2 piece spark plugs. Scary haha.

Buddy in Wash state sez there is a dyno in Marysville, just north of Arlington.

 

[xxsurvivalism]

Buddy in Wash state sez there is a dyno in Marysville, just north of Arlington.

That's about 6 hours from me unfortunately.

 

[xxsurvivalism]

Last night, I was leaving a car meet after the car had been sitting for maybe 30 or 40 minutes. Pulled out onto the road and it hesitated so bad when I laid into the accelerator, it actually DEcelerated. Just started popping and slowing down. Downshifted into 2nd to creep her up to 3,000 RPM and it went away, ran like butter the rest of the night.

Super strange, I've visually inspected under the hood multiple times. Changed the 02 sensors to Motorcraft. The old ones were a narrow-band on the driverside header, and a wide-band on the passenger side... Dunno what's up with that.

The hesitation/misfire happened AFTER new 02 sensors. Doesn't throw a code either.

 

[Laga]

Check filter sock in gas tank and fuel filter under drivers side. It might not be getting gas all the time. Can you datalog and check fuel pressure?

 

[xxsurvivalism]

I have Torque Pro and a Wifi OBDII adapter, I should be able to see fuel pressure, I'll check it out. I changed the fuel filter anyways.

It did it again today leaving my kids' school. Went to leave the parking lot in first and as soon as it grabbed 1st, it fell flat on it's face. Almost stalled. I slowly got it up to around 3,000 rpm and again it went away and ran great.

I did notice something though. Every time this happens, there's a really faint squeak under the hood. Like a belt squeak or a pulley squeak. I'll start the car, it'll run normal for a second. Then choppy and the little squeak under the hood and hesitating. Then it all goes away and runs great lol.

Strange.

 

[Oliver Vigil]

Any inconsistency in RPM with idle?
Id highly recommend changing your plugs. Had a similar issue, Motocrafts they run too hot. For your set up, colder plugs makes a worlds difference. Would recommend Brisk or NGKs.

 

[xxsurvivalism]

Any inconsistency in RPM with idle?
Id highly recommend changing your plugs. Had a similar issue, Motocrafts they run too hot. For your set up, colder plugs makes a worlds difference. Would recommend Brisk or NGKs.

I was actually just looking at Brisk plugs debating if I should grab some. Spendy but sounds like they're worth it from the reviews.

 

[xxsurvivalism]

Every once in a while the idle will fluctuate but it's not a very common occurrence. Seems to idle a tad higher than some other S197's I've seen, possibly because of the tune? It sits right at 900 most of the time.

 

[Pentalab]

I was actually just looking at Brisk plugs debating if I should grab some. Spendy but sounds like they're worth it from the reviews.

I use Brisk plugs on my 2010 GT automatic...+ Roush M90 blower. And no, you don't require plugs that are one step colder. VMP ran a lot of tests , and colder plugs are only required once the boost exceeds 10.2 psi. I only have 5.8 psi boost. Plugs are gapped at .035". For a NA car, plugs are gapped at .060". With 9 psi, plugs are gapped at .032".

I did notice asap, that with the new plugs installed, the misfires dropped to ZERO. I monitor misfires on the aeroforce gauge, plugged into the OBD port. It resets to zero, with eng off. Typ I would get 6-9 misfires every time I used the car. With the new brisk plugs, zero misfires. Runs like a swiss watch. Correct Brisk plugs are not overly expensive.