after highway pull, ecu detuning/boosting low rpm/low power on accel

[evolution23]

Alright so, the car runs amazing in the city..boost it all day long in 1st - 3rd, but while cruising on highway in lets say 5th at 110kph and 0psi reading on my boost gauge and at about 2800rpm...everything will be running great, until i go to pass someone. Ill give it about 3/4 throttle, car speeds up and the boost increases (10psi) as it should, i pass the person and ease off the throttle to go back to cruising again at 2800rpm but now i'll running 10psi boost while cruising and the car runs like a bag of sh!t (feels like a strong head wind, no misfires, no boost leak). If i even touch the throttle i will immediatley see 10psi boost and it will slowly lurch and increase the speed, if i get up around 5000rpm it will suddenly slingshots back to life and almost gives you whiplash, but as soon as i let off the throttle and the rpms drop below 5000, it runs like crap again. Accelerating from a dead stop will be very slow and lurchy and will be at 10psi by about 1500 rpm.

Coming to a stop and shutting the car off for a 3 seconds resets it and it runs amazing again until i try to pass someone on the highway..again. at which point i will have to stop and shut the car off for a few seconds and get going..again.

No engine light
showing 55 when i jump the OBD plug
1992 RB26DETT mostly stock
stock twins and piping, no restriction so about 12psi
Nistune ecu to accommodate the injectors
800cc injectors
chevron 94 (have tried chevron 91 and shell v-power and it will do the same with both)
it is not misfiring

Any other info you might need to know just ask and ill be happy to answer!

[Dragon Humper]

Stockish tune? Fuel? Sounds like a big detination and the ECU yanking a ton of timing out.



Jon.

[Skym]

Turn knock control off, o2 feedback off before tuning. Contact Nistune and ask how to turn it off, as I think it's different for each ECU.

Also check for intake airleaks just behind MAF's. If there's a intake airleak there the engine starts to stutter (similar to a coilpack missfiring and can be easily mistaken for that). Also check for intake airleak just before MAF's, as it makes ECU hit boost cut earlier that it should.

[Dragon Humper]

Yes...and try to do that same pull with a gallon of Tolulene in a half tank of 94 and see if it still happens. Massive turbo shuffle always seems to come back to grossly retarded ign. timing.


Jon.

[evolution23]

I should add. The car runs perfectly and flawlessly under normal driving. And while boosting in 1 - 3. But if I'm on the highway and I hold about 10 - 12psi boost in 4/5 for say 7 seconds, the ecu kicks out. I have no boost leaks, no misfires, etc. Car runs amazingly. It's only after a long boost pull that it kicks the ecu out. While on the highway with the timing pulled it runs like a crap, but once the RPM gets upwards 4-5000 it suddenly snaps back to life and almost gives you whiplash. I'm quite certain it's pulling the timing when it kicks out, just looking for suggesting on where to look for what might be causing the ecu to pull timing under long boost pulls. My first 2 thoughts are 1. Failing knock sensor, or 2. Working knock sensor detecting knock.

After reading some more last night and this morning I'm quite certain it's knock. Either the sensor is failing or I am getting knock during long boost pulls on the highway.

Nistune was installed for the 800cc injectors, so basically a stock tune. And it does this with chevron 91, 94 and shell v-power.

[evolution23]

Found an exhaust leek off my rear turbo where the dp bolts up. I can hear the "tick" noise from the leak while I am driving. Just wondering if this could potentially cause my issue?

Dp looks slightly warped by about 1/8" where it is leaking, any recommended sealing methods out there for a dp? High temp silicon?

[Coombsy]

That's most likely not going to cause a problem beyond being annoying. Silicone isn't going to do ****. You can try tightening all the bolts but beyond that, you're going to have to remove it and straighten it and replace the gasket.

[Skym]

Sounds like the knock control is not turned off. Monitor knock count via Nistune and see if the knock count rises when it happens. Nistune allows you to display knock count on any cell on maps, so easier to track down which cell is the cause (knock sensor might pick up on excessive engine noise at higher rpm). Ask Nistune, as they can explain how to do that.

Exhaust leak can seem to make engine run leaner if have a wideband plumbed into exhaust, but it can be the wideband picking up on the exhaust leak (more oxygen).

[evolution23]

Yeah I have wideband but it's reading a nice 14.7 at idle and cruising once warm. Under boost it richens up. It's a very small leak I have found, sounds like a playing card hitting the spokes as I drive lol, hardly noticeable. I will order a consult cable and see what I can find via Nistune.

But while boosting I have no audible misfires, no shuttering, etc. The car runs great until it suddenly pulls the timing and runs in this limp mode until I shut it off and back on, then it's back to running great. So I'll see what I can find with Nistune.

[evolution23]

No more exhaust leak, problem still persists. waiting on Nissan consult cable now.. cleaned up the first post as it sounded a little confusing, should be more clear now.

[Coombsy]

Try running the car on wastegate pressure to see if the problem still happens? Also try unplugging the knock sensor?

[evolution23]

Try running the car on wastegate pressure to see if the problem still happens? Also try unplugging the knock sensor?

Can you just simply bypass the knock sensors by unplugging them? Or do you need to do a little wiring and fool them? Going to run 1gal of VP C12 with 30L of chevron 94 tomorrow and see if it still kicks out. I am thinking it's probably just my ecu tune.

Also checked all of my plugs, look great, #4 had a tiny bit of oil. Compression numbers are 150 - 152psi cold/dry test. No visual signs of detonation. Sitting at 18deg timing, advanced it to 20deg but the car doesn't like that. Will try retarding it a couple degrees tomorrow if the race fuel doesn't work.

Not sure where else to look. What else could cause this? It's got all the symptoms of knock pulling my timing.

All new fluids were put in just last year along with new filters. I'm just clueless for diagnosing this.

[Coombsy]

Not sure if the knock sensor works that way or not...I would just try it to rule it out though, then plug it back in when you see what happens. I would try running wastegate pressure first though because if it can handle that fine, you most likely are getting knock. Also might want to try cleaning the MAF.

Also, I would advise against advancing the base timing until you get this problem sorted.

[Skym]

Can you just simply bypass the knock sensors by unplugging them? Or do you need to do a little wiring and fool them? Going to run 1gal of VP C12 with 30L of chevron 94 tomorrow and see if it still kicks out. I am thinking it's probably just my ecu tune.

ECU could engage the revlimiter around 5000rpm if unplug the knock sensors (ECU is known to do this when knock sensor is faulty).

Not sure where else to look. What else could cause this? It's got all the symptoms of knock pulling my timing.

Lack of fuel (Fuel pump, FPR), internal problems with engine, anything knocking against engine, sparkplug gap is too wide to name a few area's to look at.

I'm just clueless for diagnosing this.

Best way to check is on dyno with wideband, etc (they usually do the basic fuel pressure, etc checks before dyno). The torque graph will have a V in it if the ECU is pulling ignition timing.

[evolution23]

Alright so.

ran 2 gallons of C12 (108 octane) with 30 Litres of Chevron 94..if my math is correct thats approximately 98 octane. Then did a highway run (of course on a closed road) and the car pulled at 11psi all the way through, and again, and again. Did NOT pull my timing or kick the ecu out, and it runs damn amazing.

My theory...

When the previous owner removed the boost restriction, the fuel mapping was not adjusted for the extra boost, thus causing the car to run a little lean from 7psi ~ 12psi causing (detonation?) knock which my ecu then goes in to limp mode and retards my timing.

Does that sound like my issue? Simply needs retuned for the added boost?