Z does not accelerate

DIGItonium

Would you guys describe the issue as in the throttles refusing to open up or opening slowly but not at maximum even with the pedal to the floor? My engine doesn't scream in 2nd on up under 40 mph. However I notice if I floor it in 1st throttle seems to open up more in the later gears.

There was this one time I had trouble opening up the throttle. Then I heard a clunk and the engine and power surged while the pedal was nearly floored.

With my turbos it's harder to get it to spool up. When it does make some boost it feels like something is holding back power.

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carlitos_370z

Damn bro sorry to hear about your issue... Well when I notice the problem on my Z, to accelerate the car from 0-50mph its a PITA the car literally do not run... 0 check engine lights... anyway on my case the mechanic change one of the MAF sensors and the problem still coming... the last things that they do was cleaning the throttles bodys and re-calibrate them... after they do that the car runs like new... if you car is having this same issue maybe that the way to fixed.... If not maybe try this one if you not already do it...

Considering that your Z have a TT kit installed check this things.... First of all i will do a boost leak test, check if the blow off valve its not open at idle, check the adjustment of all the clamps to see if one is not loosen.

I tell you this things cause my last car before the Z was an Sti... i have experience that after and my problem was the blow valve... I install a Tial Q blow off valve on my Sti and when the car was on idle the blow off valve a little bit open... i decide to change the blow off valve and the problem go... I hope this are not your issue but i recommend you that make the boost leak test first.

Let us know ok

juld0zer

Digi! i thought you resolved your issue with a new brake switch?
That is exactly what it feels like and what it looks like. i have a datalog which managed to capture a normal drive and the lead up to a lag episode, and the aftermath which was full on lag.

I have never got any CEL or DTC either. Which suggests the ECU might be at fault because anything which strays away from its command and expected response/result should cough up a DTC. But for it not to notice, a sensor must be reporting the malfunction as normal. I guess if overheating the oil can cause a limp mode effect without DTC, there might be other failsafe/protection modes which dont trigger a DTC. I have never experienced the full on oil temp related limp mode to be able to provide any insight on how the ECU restricts RPM and performance.

Anyway, back to your question. When it happens, the engine is literally choked and gasping for air. According to my logs, it recognises that the gas pedal is floored but the throttle plates are being restricted. It definitely feels like a commanded choking restriction rather than a dodgy TPS reading. What happens to me is the throttle position seems to be limited to max 20 degrees opening up til about 3500-4000rpm upwards, at which the car screams and takes off. But the throttle plate doesnt get to 20 degrees quickly. Just like you said, it takes an eternity. So when the lag hits, i really struggle to get the car off the line. Even a shitbox can accelerate away with minimal effort. Taking off uphill or with a full load requires some careful riding of the clutch and building momentum by holding the revs at 2200rpm then riding the clutch. by doing this, the throttle opens appropriately to match the revs. If this isnt done then the throttle position stays at whatever it is at idle, eventually opening more as the rpm eventually increases.
Merging into traffic, overtaking or even just turning at intersections can be damn dangerous, because you press the gas pedal like you normally do in the same circumstances and nothing happens. You become a sitting duck for the few seconds before you get thrown back when the engine screams to life.

When it happens, i also notice the VVT system change. The change in VVT and throttle plate behaviour are the only things that stand out consistently in all my logs taken during the lag episodes. Unfortunately, i havent been able to fully explore the potential VVT and VVEL system fault path because of lack of support. I really need some datalogs from other vehicles to compare with mine. The reason is because when the car behaves normally, the VVT system does not behave like it does in most other cars - Toyotas, or even in the R35 which has CVTCS also. So currently i have concluded that due to VVEL, VVT behaviour on our cars is different to that of non VVEL engines. Without other people's logs, i cannot go further with this avenue.

Without my Scangauge, i would've not been able to pick up instantly on the throttle restriction during these lag episodes.

I hope that helps in some way. Another thing id like to mention is that i took it to the dealer and they blamed my G3 intakes. I scoffed at them and i have not removed any of my mods. I have not de-modded because the car was running fine for a while with all these mods. However, after demonstrating the lag to the tech he disgruntledly took the car into the workshop and came back 5mins later to hand the car back to me. The issue didnt come back for about 2 weeks. You can imagine the heartbreak when it happened again...

Ever since then, i've been taking a few punts, chucked some money into replacing sensors without success. The one thing that i have noticed is that after performing what i have grown to call the trifecta of relearns (gas pedal rest position, throttle body rest position and idle air volume), the issue doesnt come back for about 1.5 weeks. For me, that's about a tank and a bit. I discovered this after i replaced the gas pedal and also after trying to resolving my sagging idle. I did the trifecta again after cleaning my throttle bodies last weekend so we'll see how it goes. Im getting tired of holding my breath

DIGItonium

Yea I can see the throttle refusing to open enough causing the car to bog a bit at low RPM when getting in 1st and reverse. That definitely happens when things are too hot. Are the throttles refusing to open up because oil temps aren't warm enough? I notice this quite a bit when it's too cold or too warm, or after restarting. When it's just right (160-190F) I can get the car to open up.

At least one member talked about the ECU keeping the throttle from maxing out under 2k RPM. That's why I wonder why there's more power if I get on it or rev higher in 1st (versus taking of slow), then more throttle in the rest of the gears.

Could it be my driving habits? I'm pretty light on the throttle so I wonder if "eco-mode" has anything to do with it. All I know is when the foot is on the floor even at 4k RPM the throttle better be fully open, but it doesn't seem like it. But I do notice a difference in response if I floor it under 2k RPM versus above 3k RPM.

There's lots to do... just needing some time off to get around to dropping the bumper and doing some maintenance stuff.

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mike12002us

Im having a similar problem as everyone. My car will be a terror on the streets in the morning and when first cranked up, then I will hit the gas and the lag is there. I can floor the car from 700 rpm and it takes a moment before it shoots up. The lag is between 700 rpm and 2500. I have an uprev tune on the car and I brought it back to the tuner for this issue. He took out some of the vvel magic that he did and it fixed the problem for a few months. All of a sudden the problem is back. He is sending me another tune and see if that helps. If not I have no idea whats going on. I started wondering if I was running a low compression on a cylinder but I dont think thats the issue. It seems to be a tune issue but now im wondering if its an sensor issue. Im going to keep an eye on this post.

juld0zer

Digi, that feeling of more accessible power if you rev out 1st is probably purely due to engine momentum.
there is a programmed throttle restriction, which yes can be tuned out.
im generally a pretty laid back cruiser too but getting off the line i generally go up to 3k max.

Mike, i think yours is probably just heatsoak related. but that's just a quick conclusion. The lag we are experiencing results in a several second delay in throttle response before the engine roars to life. what mods do you have?

mike12002us

I have the Stillen G3 intakes, CNT Res TP, Injen CBE, Stillen LW pulleys, Uprev tune, Z1 Plenum, Stillen grounding kit, Rods, Wiseco Pistons. The last 2 dont add any power and ive had for 60k miles. I have a stillen 25 row oil cooler to keep the engine cool and I have a Seibon BD hood to release all the heat. I can see the heat escape from the engine when I am stopped. Ive done everything to keep heat away. I had no problems with the first time I had my car tuned but when I went and got the Z1 plenum and retuned I started with the issues. I went back and got another dyno tune because the car had these issues. This helped for a while but then 3 weeks ago the car started acting up again. It might be a tune issue but Im not sure why the car would drive fine for 2 months before acting up again.

3 things that come to mind of whats going on...

1. Low compression, if so that sucks...I need to test
2. When the Plenum was done something was not done right with the Throttle Bodies or not put on tightly IE hoses.
3. The tune is too aggressive and it pulls the timing.

Well thats what is in my mind at least.

mike12002us

Tonight I am going to clean the MAF, throttle bodies, put on my other K&N Filters for the G3's, check wiring, reinstall the tune/unbolt battery, make sure all hoses are tight. I have the Z1 silicone hoses for my car and maybe I didnt tighten something??? I will let everyone know if I find anything. Im going to change the oil tomorrow as well in case it makes any difference ( i know it wont)

juld0zer

do you have an Uprev cable to datalog?
i think you're on the right track there. Did you disconnect the throttle bodies from the loom or bump the butterfly at any point? they are incredibly sensitive and i think there must be some sort of keep alive memory in them. They must be sapping a little power when everything's switched off to keep that memory alive. Otherwise i see no other reason why they seem to make the engine run weird after reconnecting WITHOUT performing the 3 relearns i mentioned above.

Did you do the 3 relearns after you fitted the plenum? (gas pedal and throttle rest position, and idle air relearn). the first two must be done on a bone cold engine (coolant temp below 25 deg celsius). the idle relearn has to be done after a decent drive, as long as coolant temp goes over 85*c i think should suffice.

Otherwise i'd suggest cleaning the throttle bodies and the butterfly valves, check condition of the seal between plastic plenum and metal manifold undernearh, and the seals betweem the throttle bodies and the plenum itseld. Do the 3 relearns after all is reassembled. You must use a stopwatch for the idle relearn because it's very sensitive to timing

mike12002us

Small update...I only had time to clean the MAF's last night. After using half a bottle of cleaner on them I cranked the car up and it immediately felt better. I have been driving around all day ant its running perfect. I will say that I am not counting my "chickens" yet as the weather is low humidity and 72 today. I will have to see what happens over the weekend. Fingers crossed at least. I'm still going to do all of the other things to make sure though.

DIGItonium

Ugh. I've not had time and patience to work on my car, but hopefully it'll be something to do in December.

Anyhow, I've experienced limp mode for the first time yesterday afternoon in this cool weather. I was at the light when the engine died and all the warning indicators lit up. I started it back up, and it idled at 1k with the exhaust being louder than usual. I couldn't rev past 2.5k RPM. Whenever I shifted the RPMs dropped quick making it difficult to engage smoothly. S-Mode was still functional, and it could rev the engine past 2.5k. Pressing the pedal had no effect until the revs dipped below 2.5k. I was already nearing the gym so I parked my car and left it alone for a few minutes. When I got out to start it up again, it was fine.

What's interesting here is that there's no CEL, weather was around 70F, oil temps around 160-180F, and I was on a fresh tank of gas. This happened without warning other than the "lack" of power issue. Well it seems like the throttle is opening up more, and I'm able to get it to start boosting around 2k RPM. I currently have the boost controller dailed back to wastegate pressure of about 6 PSI. I was able to easily get it to hit 6 PSI at WOT in 2nd to 4k-5k RPM. Plus, it was easier to get boost at half throttle.

Who knows... I just need down time and several days worth of free time to pull stuff apart and get to cleaning. I'm seriously wondering of the crank angle sensor is on its way out as some owners experienced.

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juld0zer

the crank sensor is one thing i have not changed. partly due to lack of availability and price. cam sensors did SFA for me.
its been a week since i did the throttle cleaning

mike12002us

After a full weekend of driving I am happy to say that my issues are fixed. I would say the first thing to try is spraying the MAF's. I wish everyone luck with there problems. Hopefully its an easy fix also.

juld0zer

cleaning the throttle bodies and performing the 3 relearns did not cure my random significant drop in throttle response. Like replacing all the VVT seals and o-rings, it cured a different annoying problem - sagging idle when stationary.
After cleaning and relearning, my idle throttle position is 0* according to my Scangauge 2 device. TPS voltage is about 0.55V according to Cipher. Before it would idle around 3*/0.6ish volts. So that tells me the throttle plate was probably held slightly open by carbon build up. So not a complete waste of effort. Glad to sign off on that one. I'll probably set myself a 1.5-2 year cleaning interval for the throttle bodies.

At this point, i have no choice but to delve deeper into the workings of the VVEL system to try and resolve this ongoing issue. With no local dealer support or technical experience, i am left to battle this alone. i might make a few phone calls to some Z workshops in the US to pick their brains

P's_Z

Sorry to hear that my friend

Keep us updated on this

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Zeta