M56 feels like it's braking after full throttle for 5 seconds+

Tryptameme · Post by **Tryptameme** » Mon Jan 30, 2023 4:25 am

I have a 2012 M56x with 105k miles, bought just a few months ago at 100k from an Infiniti dealer. The car was always dealer serviced and seems to have been maintained pretty great. The thing rides and accelerates incredibly smooth, even at 120+.

But I'm starting to have an issue that's happened twice to me in the last week. When I'm accelerating full throttle for around 5 seconds+, suddenly the car will feel like it starts to brake. Both times it happened on an on ramp, accelerating from ~40 to ~100. Initially I thought it was the IBA being weird, because I was driving directly into the sun. I fully disabled it after that, and it was off when it happened the second time. Now I'm beginning to fear it's something mechanical. No engine codes are thrown, and I don't hear any strange noises from the engine or trans after it happens. I can't say for sure if there was a noise while it happened, because there was music playing both times.

I'm a little bit afraid to cause damage to my engine or trans by replicating this again to try to get more information. But if I do... What should I be looking for to try and debug the issue? I know this most recent time it happened that it was around 100mph, and the tac read a little over 5k. It happens while my foot is still on the gas full throttle, and it definitely feels like it's braking, rather than just taking my foot off the gas.

Does anyone have any clue what could be causing this? It's worth noting I hit a deer and had bodywork done very recently, and they had to recalibrate the safety systems for that. However, I have all the safety crap turned off in the settings, and the IBA OFF button disabling that too. Is there any way it could be IBA still, or would it be mechanical?

Tryptameme · Post by **Tryptameme** » Mon Jan 30, 2023 4:26 pm

I guess I can't edit a post, but I just wanted to describe it a little better. It might not feel like braking exactly, more like a sudden switch from full max power to nothing instantly. So when it happens it's a slight jolt that gives the feeling of braking.

I'm thinking maybe it's a transmission issue, because the shifts on this thing have always felt.... A little weird. Nothing concerning, but a little jumpy. It's more pronounced in sport mode, so I thought maybe that was just how it's supposed to be.

I think I'll try and replicate it happening on video at some point in the near future

Post by **Yoda's Master** » Mon Jan 30, 2023 8:53 pm

traction control? it is cold so maybe you're slipping?

Tryptameme · Post by **Tryptameme** » Tue Jan 31, 2023 5:13 pm

Yoda's Master wrote: ↑
Mon Jan 30, 2023 8:53 pm
traction control? it is cold so maybe you're slipping?

Hmm, I don't think so although that's a good point. I'm almost positive it's not slipping, as both times it was very dry, and I didn't see the dash light turn on to indicate that. I've also been driving an M35 for the past 4 years and that thing slips a lot, and it doesn't feel anything like that.

I'll try keeping an eye out for the light next time, but I don't think that's it

Post by **crrraaig** » Thu Feb 02, 2023 7:59 am

Your first post described it more as a miss (shaking), but in your second post it sounds more like a full cut out of multiple cylinders for several ignitions? I would suspect a miss could be a coil with the mileage, full cut out of a number of cylinders is not likely ignition, I would think.

Because you mentioned Sport mode and suspect transmission, why not do a Learned Behavior reset just to rule that out.
howto-perform-an-ecu-reset-learned-beha ... 69-30.html

Also, consider dogging it to see if it is a engine load issue - heading up hill at a low speed, shift into the highest gear it will take and floor it. I've used this approach to find bad coils on a few of my cars. Good Luck!

Post by **Yoda's Master** » Thu Feb 02, 2023 8:04 am

Are you saying braking or breaking? Words matter.

Tryptameme · Post by **Tryptameme** » Thu Feb 02, 2023 2:37 pm

crrraaig wrote: ↑
Thu Feb 02, 2023 7:59 am
Your first post described it more as a miss (shaking), but in your second post it sounds more like a full cut out of multiple cylinders for several ignitions? I would suspect a miss could be a coil with the mileage, full cut out of a number of cylinders is not likely ignition, I would think.

Because you mentioned Sport mode and suspect transmission, why not do a Learned Behavior reset just to rule that out.
howto-perform-an-ecu-reset-learned-beha ... 69-30.html

Also, consider dogging it to see if it is a engine load issue - heading up hill at a low speed, shift into the highest gear it will take and floor it. I've used this approach to find bad coils on a few of my cars. Good Luck!

Thank you for the recommendations! Wow I had no idea the car had learned behavior! This explains a lot considering the 2 previous owners were definitely grandpas. The MPG average when I got the car was 19.2, and mine has been around 17. I will try this reset before I drive home from work tonight and see if it helps. Definitely going to also try the hill thing tomorrow as well, I appreciate the tips and I'll update once I do this.

Yoda's Master wrote: ↑
Thu Feb 02, 2023 8:04 am
Are you saying braking or breaking? Words matter.

Braking

Post by **Shanehsmp** » Sun Feb 26, 2023 11:09 pm

This is exactly what was happening to my car back in 2021 with about 60k on the engine. I thought it was a a transmission issue, but turned out that I have low compression in 3 cylinders....I even get the shake you describe. I know this is an older post, but feel free to message me for more info. I also did a leak down test to determine if it's the valves, rings, head and the air is leaking from the crankcase which would signify bad rings. I also did a visual scope of the affected cylinders and they all have scratch marks and what looks to be gouges in the cylinder walls.

I've yet to tear down the engine, but that will happen sometime this year.

Tryptameme · Post by **Tryptameme** » Mon Mar 20, 2023 6:39 pm

Shanehsmp wrote: ↑
Sun Feb 26, 2023 11:09 pm
This is exactly what was happening to my car back in 2021 with about 60k on the engine. I thought it was a a transmission issue, but turned out that I have low compression in 3 cylinders....I even get the shake you describe. I know this is an older post, but feel free to message me for more info. I also did a leak down test to determine if it's the valves, rings, head and the air is leaking from the crankcase which would signify bad rings. I also did a visual scope of the affected cylinders and they all have scratch marks and what looks to be gouges in the cylinder walls.

I've yet to tear down the engine, but that will happen sometime this year.

Damn, that's crazy. Did you hear any noise from the cylinder walls getting scratched?

So I've been driving this thing every day since the post, and I go WOT pretty much every time I drive it, and I've yet to have the problem happen again. However, these last 2 mornings have been cold, and when I start my car, the engine starts and immediately dies. If I press on the throttle a little bit as it's starting, it's fine. Prior to these last 2 days, all winter when I would start it in the cold mornings it would sound like it was about it die, but recovered right before hand.

I'm starting to wonder if both of these issues are related, and may be symptoms of a bad high pressure fuel pump. Does anyone know of how i can test the HPFP, and does it sound like it could be the cause of both these issues? I'm worrying because it seems to be a huge killer of these cars, and I should probably be replacing it ASAP if it is the problem. But I also don't love the idea of spending upwards of 3k for something that may not be the problem.

Post by **fontana dan** » Mon Mar 20, 2023 6:55 pm

Are you able to recreate this problem for a video? Take a data log of vehicle speed during this event. O2 sensors will tell you if it is running out of fuel.
When you say the car feels like it is "braking" you need to know if the ABS pump is activating in these conditions. I would recommend pulling fuse for ABS and test driving. Scan for codes in all modules.

Tryptameme · Post by **Tryptameme** » Mon Mar 20, 2023 7:11 pm

fontana dan wrote: ↑
Mon Mar 20, 2023 6:55 pm
Are you able to recreate this problem for a video? Take a data log of vehicle speed during this event. O2 sensors will tell you if it is running out of fuel.
When you say the car feels like it is "braking" you need to know if the ABS pump is activating in these conditions. I would recommend pulling fuse for ABS and test driving. Scan for codes in all modules.

I haven't been able to recreate this issue since the initial post. I just posted an update in the comment above yours, do you think the HPFP could be the problem here? I don't think the car was actually braking, it just felt like that to go from full throttle to nothing instantly. Thinking maybe the car was running out of fuel due to the HPFP

Post by **fontana dan** » Mon Mar 20, 2023 7:39 pm

A loss of fuel pressure will make the engine stall or cut out at WOT. Same symptom if the PCM loses signal from any of the number of sensors that control the fuel injection/spark timing.
I will always recommend AGAINST the parts swapping game. Wait until the car is broken so you can confirm the issue and not waste money.

Post by **Shanehsmp** » Mon Mar 20, 2023 10:09 pm

Tryptameme wrote: ↑
Mon Mar 20, 2023 6:39 pm
Damn, that's crazy. Did you hear any noise from the cylinder walls getting scratched?

So I've been driving this thing every day since the post, and I go WOT pretty much every time I drive it, and I've yet to have the problem happen again. However, these last 2 mornings have been cold, and when I start my car, the engine starts and immediately dies. If I press on the throttle a little bit as it's starting, it's fine. Prior to these last 2 days, all winter when I would start it in the cold mornings it would sound like it was about it die, but recovered right before hand.

I'm starting to wonder if both of these issues are related, and may be symptoms of a bad high pressure fuel pump. Does anyone know of how i can test the HPFP, and does it sound like it could be the cause of both these issues? I'm worrying because it seems to be a huge killer of these cars, and I should probably be replacing it ASAP if it is the problem. But I also don't love the idea of spending upwards of 3k for something that may not be the problem.

So the car shutting off on itself was also happening to me...

Does your oil level change or does it always seem high?

I have this all documented in this forum and on Facebook as well. But I have scanner/app that logs my fuel pressure and I was noticing this weird occurrence each time the car started engine breaking....anyhow, it turned out my HPFP was leaking from the piston and dumping fuel into my crankcase (causing other damage). My oil level was always high and I couldn't understand why until changing it, as it reeked of fuel. After I changed it and the HPFP, that starting problem went away. But I now have other issues due to the fuel mixing with oil....I don't have an audible knock, however it is getting worse as I drive, but something is off based on the scope I did on the cylinders with low compression. I'm just waiting until the summer so that I can start tearing it apart for the rebuild.

Before you go replacing parts like I did...get a scanner that can read real time values. The one I have can read similar to the dealer's all for under $50. I used one called Veepeak OBD2 Bluetooth dongle and an app called "Car Scanner"

Btw, when I pulled my HPFP it dumped fuel from the bottom and that isn't supposed to happen - shouldn't be hard for a mechanic to diagnose either via the scanner (fuel pressure, especially when you let off the gas) or via visual inspection. .

Like I said, feel free to PM me with any questions, maybe I can help point you in the right direction.

Post by **Shanehsmp** » Mon Mar 20, 2023 10:18 pm

Btw the braking you are seeing is likely the car retarding timing when you let off the throttle or whenever it feels itself knocking too much or detonating. Again, a log will show all of these things at once and you can overlap to tell if the issues are related.

Check out this thread

https://ecomodder.com/forum/showthread. ... 38960.html

Post by **ken in az** » Thu Mar 23, 2023 11:04 am

Are you in manual mode when this happens? I bet you are hitting either the rev limiter or the speed limiter. A 5 second pull will get you to either places and make it seem like you hit the brakes for sure.

I agree with the other posts - get a data logger and see what's happening when you encounter this problem again. That's the only way to know for sure.

good luck and be sure to report back!

Tryptameme wrote: ↑
Mon Jan 30, 2023 4:25 am
I have a 2012 M56x with 105k miles, bought just a few months ago at 100k from an Infiniti dealer. The car was always dealer serviced and seems to have been maintained pretty great. The thing rides and accelerates incredibly smooth, even at 120+.

But I'm starting to have an issue that's happened twice to me in the last week. When I'm accelerating full throttle for around 5 seconds+, suddenly the car will feel like it starts to brake. Both times it happened on an on ramp, accelerating from ~40 to ~100. Initially I thought it was the IBA being weird, because I was driving directly into the sun. I fully disabled it after that, and it was off when it happened the second time. Now I'm beginning to fear it's something mechanical. No engine codes are thrown, and I don't hear any strange noises from the engine or trans after it happens. I can't say for sure if there was a noise while it happened, because there was music playing both times.

I'm a little bit afraid to cause damage to my engine or trans by replicating this again to try to get more information. But if I do... What should I be looking for to try and debug the issue? I know this most recent time it happened that it was around 100mph, and the tac read a little over 5k. It happens while my foot is still on the gas full throttle, and it definitely feels like it's braking, rather than just taking my foot off the gas.

Does anyone have any clue what could be causing this? It's worth noting I hit a deer and had bodywork done very recently, and they had to recalibrate the safety systems for that. However, I have all the safety crap turned off in the settings, and the IBA OFF button disabling that too. Is there any way it could be IBA still, or would it be mechanical?

M56 feels like it's braking after full throttle for 5 seconds+

M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

Re: M56 feels like it's braking after full throttle for 5 seconds+

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