Power deadspot

[krystalized_jdm]

To explain more in detail

This is not turbo lag, I will be boosting @ full 9-10 psi (depending on gear) when this happens.

Basically, if I do a 2nd gear pull doing about 3k, it'll pick up fast to 4k, between 4-5.5kish it seems to be laggy....less power. Once it hits above that, car pulls like a mofo.

THIS IS NOT HESITATION, car is firing, it is not misfiring, it sounds fine.

Not sure if it is a problem or if this is normal? It's been so long since I've had my car in great running condition.

Probable causes I am going to address is a vacuum leak. Currently at -20 vacuum, and I am quite sure it is supposed to be -30?

Any input is appreciated

Thanks guys
- Stephen

[Supraclean]

What condition is your fuel pump in? And or what are you running?

Dont think a vaccum issue will effect you while under boost.

[krystalized_jdm]

I'm not sure how to check fuel pump? Car pulls like a mofo once its out of that range like I said.

Set up
- Apexi intake
- Fmic
- 3" cat back

[Skym]

That's normal with those mods and is ECU reacting to engine knocking (probably find that engine is running very lean, up to 13.5:1 or higher when on boost). It's just ECU pulling ignition timing, running engine slightly richer (knock maps). My car did the same thing with similar mods, stock ECU tune and can see a big V in torque graph due to ECU pulling ignition timing. It's the stock ECU protecting engine from blowing up.

To fix this problem you need to retune ECU (Nistune). Or minimum fit a bigger lph fuelpump, hardwire fuelpump to run engine richer at mid to high rpm (it will feel more boggy when you do this, but should save blowing engine up until can get a ECU retune).

[ToroGTS]

You could probably go cheap and install apexi SAFC to tune this out. Would need a wide band as well. Both will run you like $400 if you can install yourself.

Edit: I also wouldn't call this 'normal'. To me that seems like a weak oem fuel pump (install in line pressure gauge and you should see 38psi or better at idle), or maybe as simple as a clogged fuel filter (replace with 300zx filter, lose the stock filter bracket). I had mine running on 12-14 psi boost (even 16 at one point, for two pulls), hks air filter, 3'' straight pipe, intercooler, did not have this stumble issue.

[krystalized_jdm]

Nistune is an option for me this season, I will look into this.

This is helpful, thank you guys.

[Skym]

Apexi SAFC plays with MAF signal (makes ECU select richer or leaner cells on fuelmap and same cells on ignition map). Still limited to what's on fuelmap. In the past before PowerFC was released they had Apexi SITC that adjusted ignition (I think adjusted CAS signal).

What I mean by "normal", as I have seen similar V happened on dynochart (torque) with FMIC, stock turbo, split dumpipe, 3" exhaust from split dumppipe (boost was dropping off at higher rpm, somewhere below 10psi at higher rpm which is normal with leaking stock BOV, stock turbo). But he did change to stock GTR fuel pump and was way richer on dynochart.

My car was running similar mods and same V (torque) thing happened, but still was a safe 11.8:1 at peak hp (obviously fuel pump was ok). Checking fuel pressure afterwards confirmed that.

But you could be right with fuel pump, fuel filter (I thought he has already changed fuel filter, but might not have) on his car. If fuel pump was weak or on the way out, it would be running into 14's at peak hp (stock turbo, stock airbox, catback exhaust) or way leaner at peak hp with what his car has as far as mods go.

[ToroGTS]

In my experience, extreme lean and knock detection results in massive timing retard under boost and the engine 'revs out' to redline but makes no power, where as an overly rich condition or ignition problem results in these type of 'stumbles'. Hard to say when just getting a description of the issue over the interwebz.

[Skym]

On R33 ECU (I think R34 ECU is the same) it can pull ignition timing to 0 which should stop engine accelerating when on knock maps. R32 ECU doesn't pull ignition timing that much and engine can still accelerate, yet you feel a drop in torque in that rpm range (with my car it was 3500rpm-6000rpm on torque plot where the V was and power plot looked normal, yet a very slight dip in power graph in that rpm range). When ECU is tuned it can be very violent / responsive (depends on mods) on and off throttle in that rpm range.

Hesitation before accelerating can sometimes be due to engine going suddenly lean (transient fuel enrichment problem, which is sometimes caused by a stuffed TPS). I have been through 2x TPS on my car so far (depends on how you drive car, as to how long they last). He said he adjusted TPS, but not fully to 0.44V, something like 0.46V (from memory, mentioned in another thread) which could be the cause of hesitation or TPS is stuffed.

When my car ran rich due to o2 sensor problem, I didn't notice much of a bog (it might of bogged, but maybe just used to driving it with a bog due to other problems it had at the time, hence didn't notice it being any different). You have to try both running correctly, not to really notice the difference.

That's true with description over the internet. We are just giving area's to look at, check.

[ToroGTS]

Speaking of TPS, where does one get a replacement TPS. Is there a compatible north american vehicle or are you stuck with wrecked skylines and online?

[krystalized_jdm]

I am currently waiting on an o2 sensor from a 300zx driver side (everyone was saying it was compatible) I ordered it last week.

I am talking to a vendor about nistune now, hopefully it will line up good.

Thanks guys

Edit - Is there anyway of turning boost down? The running lean is obviously because of the mods causing more boost. I bought a turbosmart manual controller, not 100% on how this bad boy works. Haha

[plankworx]

^ use an rb25 oem wastegate regulator. An additional short-term fix for lean condition ( did this myself, works) is add a fuel pressure regulator and increase pressure to the injectors. Decreases leaning out across revs a little bit.

[Skym]

RB25DET auto internal wastegate actuator is around 5psi.

[krystalized_jdm]

Okay, so I talked to the dealer about nistune. Looking at about a grand to get a 100% plug and play unit. (new ecu)

That is not an option for me at this time.

I am however looking into a SAFC at the moment.

I can see about getting a in-line fuel pressure tester. Although not sure how I would test it as it would be in the engine bay?

Thanks guys.

[Skym]

Aftermarket fuel pressure gauge.

It's not that much, around 600 max (Nistune board + socket, internal cable, install, tuning software, Consult cable). Less if you take out the Consult cable, tuning software (tuner has those). Unless that includes a tune for the mods, which sounds about right (300 for parts and install, 700 for tune)????

You can install Nistune and run stock maps. Then retune later on when you can afford it.