Harsh manual downshift and hesitation -- not the usual
07-31-2017, 10:28 PM
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Harsh manual downshift and hesitation -- not the usual
I'm having a weird issue that seemed similar ish to what other people experience, but at the same time the conditions and circumstances are quite different IMO.
I drive an '11 G37 IPL Coupe, 7AT.
Let's say I decide to downshift manually when going down a hill. If I'm coasting (no brake, no gas) and do it, there's about two whole seconds of delay, sometimes three, and I'm not making this up I can sit there and count Mississippis, and then a big THUMP. Sometimes more intense than others, but it's always there. This began happening AFTER getting the tranny TSB updates done, which did noticeably improve the auto driving.
During the delay, it feels like I'm in freefall, i.e. coasting in neutral. During the delay, before the thump, my RPMs do increase, so it seems that it's trying to rev match but physically can't complete the shift, which seems to point away from a software/logic issue IMO.
I was going to say that this does NOT happen in full auto mode, but I do get the freefall coasting feeling sometimes on slight downward slopes right over the crest, but there's no thumps or anything.
I finally went to do something about it (vs just leave it alone for a while and just....not do the thing that prompts the issue) but then in traffic I had an issue where I tried to really gun it from about 25 and for about two seconds my car just would not accelerate, like my engine didn't even react (I've had an issue in an Audi where I was stuck at like 30 at redline and only restarting the engine fixed it, it wasn't like that). That was scary. This also was completely unlike the gear hunting issue causing throttle lag that the transmission updates fixed. It was way worse. It hasn't happened since, so I'm gonna hope it was a one off thing from bad gas or something (I have filled my fuel tank a couple of times since).
Anyway, I had Nissan diagnose it, and they said bad tranny throttle valve body (before the traffic incident I just mentioned, which made me tie them together, bad throttle valve and lack of throttle response?? Hmm...). I gave this paperwork to Infiniti along with my paperwork for my third party warranty. They could not reproduce the issue and also could not file a warranty claim to do the work Nissan quoted me because my car was not throwing any error codes, which is what the warranty company would want before proceeding with a repair. Makes sense to me.
I can still reproduce the issue, so either they didn't grasp the specific nature of it and really try, or it's just me. I'm not super experienced with engine braking or manually choosing gears. Is it normal to expect this reaction when downshifting while the car is being pulled downhill by gravity? Is it throwing off the auto rev matching?
What might be up? Do I just need a transmission flush? Neither shop clarified which one they were talking about but I'm aware that there's a pressure flush and a 3x drain and fill which are not the same. My car is at 42k miles and I bought it at 31k. Nissan recommended (in line with people on this forum IIRC) every 30k and said it'd be 50 bucks to do. Infiniti quoted me about $350.
As I was Uber-ing back and forth to the dealership, one driver told me they had a similar issue, a mechanic said the transmission was fine but it was likely her shift modulator, a cheap electronic part she got for $15 that he replaced for free. Sound applicable?
I drive my car every day during work for work, and this is my only car. I don't have the time to make an appointment and take the Infiniti tech (I'm building a history with the same guy, he also did my TSBs) on a test drive to demonstrate. That might be my only option at this point, but before going through that hell I wanted to ask you guys.
Disclosure: I had a deer collision on the front right of my car about a month ago. Infiniti told me I needed new rear brake pads when I got the updates done, and the next day I went to Firestone and they said (and showed me) my rear left caliper was leaking fluid and needed replaced. In their opinion the collision and this failure we're a coincidence, but who knows. Tossing it out there in case it's relevant. I noticed the issue while playing around with engine braking a couple hours after I picked up my car from the brake work.
Thanks for your time!!
I drive an '11 G37 IPL Coupe, 7AT.
Let's say I decide to downshift manually when going down a hill. If I'm coasting (no brake, no gas) and do it, there's about two whole seconds of delay, sometimes three, and I'm not making this up I can sit there and count Mississippis, and then a big THUMP. Sometimes more intense than others, but it's always there. This began happening AFTER getting the tranny TSB updates done, which did noticeably improve the auto driving.
During the delay, it feels like I'm in freefall, i.e. coasting in neutral. During the delay, before the thump, my RPMs do increase, so it seems that it's trying to rev match but physically can't complete the shift, which seems to point away from a software/logic issue IMO.
I was going to say that this does NOT happen in full auto mode, but I do get the freefall coasting feeling sometimes on slight downward slopes right over the crest, but there's no thumps or anything.
I finally went to do something about it (vs just leave it alone for a while and just....not do the thing that prompts the issue) but then in traffic I had an issue where I tried to really gun it from about 25 and for about two seconds my car just would not accelerate, like my engine didn't even react (I've had an issue in an Audi where I was stuck at like 30 at redline and only restarting the engine fixed it, it wasn't like that). That was scary. This also was completely unlike the gear hunting issue causing throttle lag that the transmission updates fixed. It was way worse. It hasn't happened since, so I'm gonna hope it was a one off thing from bad gas or something (I have filled my fuel tank a couple of times since).
Anyway, I had Nissan diagnose it, and they said bad tranny throttle valve body (before the traffic incident I just mentioned, which made me tie them together, bad throttle valve and lack of throttle response?? Hmm...). I gave this paperwork to Infiniti along with my paperwork for my third party warranty. They could not reproduce the issue and also could not file a warranty claim to do the work Nissan quoted me because my car was not throwing any error codes, which is what the warranty company would want before proceeding with a repair. Makes sense to me.
I can still reproduce the issue, so either they didn't grasp the specific nature of it and really try, or it's just me. I'm not super experienced with engine braking or manually choosing gears. Is it normal to expect this reaction when downshifting while the car is being pulled downhill by gravity? Is it throwing off the auto rev matching?
What might be up? Do I just need a transmission flush? Neither shop clarified which one they were talking about but I'm aware that there's a pressure flush and a 3x drain and fill which are not the same. My car is at 42k miles and I bought it at 31k. Nissan recommended (in line with people on this forum IIRC) every 30k and said it'd be 50 bucks to do. Infiniti quoted me about $350.
As I was Uber-ing back and forth to the dealership, one driver told me they had a similar issue, a mechanic said the transmission was fine but it was likely her shift modulator, a cheap electronic part she got for $15 that he replaced for free. Sound applicable?
I drive my car every day during work for work, and this is my only car. I don't have the time to make an appointment and take the Infiniti tech (I'm building a history with the same guy, he also did my TSBs) on a test drive to demonstrate. That might be my only option at this point, but before going through that hell I wanted to ask you guys.
Disclosure: I had a deer collision on the front right of my car about a month ago. Infiniti told me I needed new rear brake pads when I got the updates done, and the next day I went to Firestone and they said (and showed me) my rear left caliper was leaking fluid and needed replaced. In their opinion the collision and this failure we're a coincidence, but who knows. Tossing it out there in case it's relevant. I noticed the issue while playing around with engine braking a couple hours after I picked up my car from the brake work.
Thanks for your time!!
