Need a little help regarding RB26DETT Choking issue!

[91GTRR32]

I have a 91 r32 with an rb26dett in it and im having a small issue with performance...

In 1st gear she pulls hard from 1-8k rpm, but in the rest of the gears when i rev to 4k RPM she starts to choke and bog out, i cant get anymore power out of it when it hits 4k rpm. i was told to check a few things, but shes under a cover under some now right now so i cant touch her till the spring. The few things i was told to check were: Spark plugs, Fuel pump and/or fuel filter, Coil Packs, Boost Leak, waste gate, injectors, or an electrical problem..

On a cold start she idles at 1,100rpm and makes her way down to 1000rpm but its very very steady it doesnt move up n down at all. The boost up to 4-4.5rpm feels very raw. It doesnt have any other issues at all except for this one, and she has a great launch and very powerful first gear, can i get some input please...I could use as much information from as many people possible who have knowledge in this engine.

Thanks for reading/viewing!

[bobbo]

It sounds like it's in limp mode if it falls over at 4G but I think it would be acting the same in 1st gear. Is/was it holding boost?
If it was an ignition problem it would be noticable any time the car was under load and would be misfiring on one or more cylinders.
Could be a fueling issue so checking the filter would be an idea.
What you didn't mention and is critical to diagnosing problems is any mods that are made to the car.
Also have a read through this... http://forums.gtrcanada.com/gts-tech...esitation.html

[amnash]

first off i wanna say im jealous or your solid idle...

my bet is its a fueling issue. probably filter or pump. do you have a fuel pressure gauge? if you didnt have the rock solid idle i would say to check your TPS cuz that effects fuel maps too.

[91GTRR32]

I don't have a fuel pressure gauge, and thanks hehee. I only drove it for the last 3 weeks of summer before i Covered it and during that period its always been choking...so I don't truly know the power of gt-r's yet... :/ Im hoping to get it 100% in the spring, so you think its fueling? I do have a very minor leak in injectors, and still manage to get 660km per fill up..does that help with your assumption?

Mods:
Twin k&n Air filters, split twin turbo pipe, mashimoto allu rad, hks bov's, still holds the 100 octane jap tune, yellow jacket coil packs, arc cooling plate, unknown brand big front mount intercooler, fujitsubo exhaust system, oil filter relocation, boost restrictor removed (idk what that even is), hicas delete bar, and other mods that arent related to drive-train (suspension, wheels, brakes etc)

And was it holding boost? The boost id get from 2.5-4k rpm was very consistant but as soon as it hit 4-4.5k rpm (cant remember exaaactly the value) it started to bog, same for every gear past 1, in 1st I can rev 1k-8k np.

[Skym]

If R32 ECU detect's knock via knock sensors on side of engine or picks up excessive noise (missing coilpack, anything banging against engine, etc) it pulls ignition timing up until 6000rpm which makes the engine feel like it bogs in midrange. Also usually pulls ignition timing when engine runs lean, engine knocks around peak boost which is at around 4000rpm with stock GTR turbo's. On dyno graph you'll notice a big drop in torque like a inverted mountain, which matches exactly the amount of ignition timing that's pulled.

Other things that can cause the above are fitting bigger turbo's or aftermarket FMIC without retuning ECU to inject more fuel into engine to match the extra air, weak fuelpump or voltage to fuelpump is not enough, weak FPR (Fuel Pressure Regulator) on fuelrail. Also on RB26 there's the intake gaskets that can blow when boost level is raised, leaking exhaust manifolds, etc.

[Dakota_gsx]

Didnt feel like reading what everyone has said so far, but I know that with the Vipec i have in my two cars, i had a problem in my eclipse where i was hitting my map limit and it would bog out. only in third or fourth gear though becuase the car is under more load and could reach higher boost levels. Im not sure what ecu youre running but maybe try knocking down the boost a little bit. I dunno, just a suggestion.

[91GTRR32]

Skym, how come i can rev to 8k in first gear? I do have a slight 'ticking' noise coming from the engine but everyone i asked said theyve heard it before and its a common tick/ Even the videos ive seen from the tyee imports skylines all have the same ticking, as well as a couple on youtube. Other than that idk.... But yeah Skym if i can hit 8k rpm in first does that mean your theory could be in-correct? or.... what exactly would you do in my situation. Also, it doesnt choke when i rev it when its sitting.

cmon guys help a fellow gtr'er in need >.<

[GTRADDICT]

When you did pulls, did you always start from first gear? I'm asking this because it seems like a lack of fuel. Try to get around 4k rpm in 2nd or third slowly and then punch it. If its lacking fuel it will go for 2-3 sec and bog.

[91GTRR32]

When you did pulls, did you always start from first gear? I'm asking this because it seems like a lack of fuel. Try to get around 4k rpm in 2nd or third slowly and then punch it. If its lacking fuel it will go for 2-3 sec and bog.

Hmm cant remember exactly, but in every gear its the same thing same bogging, like ill go hard from 1st to 5th even while its like this to get SOME fun outta her, and she bogs the same way every gear. Boost guage reads +7 throughout all gears as a peak. Bov's scream real loud. But once she hits 4-4.5k rpm it just chokes, like its tryina go but its got asthma or something. Even when i continue to gas while its choking it doesnt gain any speed, i have to shift then it boosts till 4th and chokes again, shift boost choke, shift boost choke...

PS - I've done donuts in the rain with her shes a beasssst in first, spun like a dang tornado...thats pretty much all the power i can get outta her..1st gear.

[GTRADDICT]

Get a fuel pressure gauge. first thing.

[91GTRR32]

Will do, any other suggestions folks? Could use all the input I can get..

[RSTuning]

Install a aem uego wideband, it will tell you if your afr's are correct.

if you have a stock fuel pump, change it to atleast a walbro, if a customer comes to me for tuning with a stock 20
year old pump, i wont tune the car until changed.


Once you have ruled the above out, you need to get someone with consult and check your maf sensors and all other sensors.

Lastly if that fails check mechanical. Compression test, boost leak test.

[RSTuning]

I just read your mods post.

please do a compression test. and for god sakes dont kill the throttle until you have that car retuned, 100 octane timing from our shitty 94 octane will blow your engine.

if the car was tuned for 100 octane, that means the timing values are very advanced, and just to give you a comparison the stock gtr ecu timing values are overly advanced for our canadian fuel.

the bogging could be a result of too high cylinder pressures caused by to much heat due to the advanced timing.

If you have any questions you can email me at info@rstuning.ca

Thanks.