Severe bucking/jerking when accelerating in a turn

[Christian]

This has happened numerous times over the course of the last few months.

An example: stopped in an intersection waiting to make a left turn. When the time comes to turn, I accelerate hard and shortly after (split second), the car jerks badly and hesitates. Obviously dangerous if there was a car coming towards me.

Another: entering an on-ramp that has a sharp turn/curve in it at full throttle.....same result. This never happens in straightline acceleration.

Any ideas???

No mods whatsoever. Cam phasers, timing chain, water pump all replaced last Summer. 65k miles on the odo.

 

[Joshw0000]

Do you see your RPM's fluttering when it happens? It sounds like the torque converter is going out (common for this car). But it wouldn't matter if you were turning or not. The issue would be present at lower RPM's (i.e. acceleration) or when going uphill. When was the transmission fluid last serviced? If it's been a while, sometimes fresh tranny fluid will remedy it. You should confirm (with the engine at operating temp) that it's not low or overfilled. You could also add a tube or 2 of Shudder Fixx. If the torque converter is failing, that will significantly help it almost instantly. If the issue comes back it's time for a new torque converter.

Your comment about it only happening when you turn makes me think maybe it's suspension related. Do you feel the front end jump at all? I.e. some components are buckling.

Sent from my Pixel 8 Pro using Tapatalk

 

[SHOrod]

Is it always a turn in the same direction, or will it happen in both left and right turns? If only on left hand turns, I'd suspect an outer CV joint. If it's both directions, and since you mention on hard acceleration, I'd suggest checking / servicing the fluid in your rear differential unit as well as checking and servicing the fluid in your PTU. Does the Traction light come on at the same time?

-Rod

 

[Christian]

Trans fluid has been replaced/flushed twice since new - most recently this past Summer. PTU as well.

Yes...it only happens in a left turn or curve. I did'nt notice the RPM's when it happened.

Thanks for the ideas.....I'll have the dealer take a look at the CV joints.

 

[SHOrod]

If the dealership has a ChassisEar or similar, they should be able to at least narrow down the proximity of the noise pretty quickly.

-Rod

 

[Christian]

No noise per se. It's a violent Jerking/stumble/hesitation.

 

[SHO@Sparks]

Some questions, more than answers....

Assuming all fluids are full, particularly the transmission, I wouldn't think it would be a CV joint as it should bind turning the other direction too.

If you have a decent scan tool or Forscan, have you scanned the modules for any codes, particularly the PCM?

Even without misfire DTCs it can trigger misfire data in Mode 6. Have you reviewed Mode 6 Data for any misfires?

These 3.5 L Ecoboost engines can be ******* spark plugs, especially under load or hard accel. If the plugs haven't been done I would replace them.

Again with a comparable scan tool, you can monitor several different engine and transmission related PIDS for ignition, misfires, fuel pressure, injector faults, TP, BP, turbo charger boost pressure, torque converter clutch lock up/slippage, shifts, gear, etc.

Regarding fuel pressure you should monitor FLP ACT vs FLP DES for the low side fuel pressure and FRP ACT vs FRP DES for the high side fuel pressure, just to see if one or both are dying off on accel when making a turn.

There are multiple different directions this can go, but hopefully as others have given their thoughts, maybe these details can be helpful.

God bless, Mike

 

[SHOrod]

Some questions, more than answers....

Assuming all fluids are full, particularly the transmission, I wouldn't think it would be a CV joint as it should bind turning the other direction too.

I'm not sure how the steering geometry on the SHO deals with Ackermann angle, but it's possible that an outer CV joint might be stressed more in one steering direction than the other. But, that would only come into play on a pretty sharp turn.

Not to cast stones, but misfires wouldn't be steering dependent either. ;P

-Rod

 

[SHO@Sparks]

I'm not sure how the steering geometry on the SHO deals with Ackermann angle, but it's possible that an outer CV joint might be stressed more in one steering direction than the other. But, that would only come into play on a pretty sharp turn.

Not to cast stones, but misfires wouldn't be steering dependent either. ;P

-Rod

Thanks for tossing the stones, as I appreciate those that challenge me to think outside the box or to just question my thought process.

I agree with your thoughts, as a whole, but I've seen some weird issues as a technician of 34 years......so, in my book, nothing is impossible.

I've been wrong a number of times and yet learned from many years of mistakes due to my assumptions. As much as I try to use questioning, logic and fact finding in my diagnosis of vehicles, the answer isn't always obvious.

Also, if there was an intermittent wiring or internal electrical issue with the EPAS rack that only occurred on turns on accel and it caused a network or momentary power loss of power, it could cause weird issues to say the least.

I appreciate challenging issues like this, but it is hard doing it remotely and not being sure of a member's skill level, let alone what testing equipment they have on hand.

Mike

 

[Christian]

Thanks all....
I have a decent scan tool. I will use it to see if anything shows.

 

[SHOrod]

Also, if there was an intermittent wiring or internal electrical issue with the EPAS rack that only occurred on turns on accel and it caused a network or momentary power loss of power, it could cause weird issues to say the least.

That's a really valid point. Years ago I had a Lincoln LS with VAPS and several miles after having the valve body replaced in the transmission under warranty, I had a very strange feeling on turns, and I think that was only on right hand turns. The issue ended up being that the VAPS connector was not fully seated. It was seated well enough for them to pull it out of the dealership, but after a few expansion joints in the road, it vibrated loose. Power steering that comes and goes could pretty easily be interpreted as a bucking or jerking when powering into or through a turn.

-Rod

 

[Austin2013SHO]

Little advice I’d jack up that side of car and see if u have any play in the cv. Try moving it back and forth and compare to other side. Same amount of play prob not the issue but much different I’d try that. I’d also go drive a few mile like u casually would and get a temp gun out see if anything on that side if much hotter than other parts like a shot wheel bearing. Look at lower control arm mount as well those like to dry rot and crumble apart or tear from time to time. I definitely want it to be suspension for you as trans and PTU issues are a PITA ask me how I know lol good luck let us know what u find.