RB25DET S2 hesitations , I dont know where to start....?

[ka24eracer]

Ok so I have a 180sx with a RB25DET S2 completly stock , s13 side mount IC which I swapped this summer , the car run fine almost everytime except when :

1 . I go from almost closed throtle (ie crusing) to full throtle quickly

2. I do a quick downshift from like 3rd to 2nd, again while quickly flooring it

If I do so , the car feel like there was no fuel in going to the engine ( almost dying) for like 2-3 seconds then go back to full power...

I searched but there are so many reason It could tdo this , I was wondering if my problem was specific to an engine part that could be bad...

I replaced the maf , wired the walbro directly to the battery , the hesitation is still there .

If it had an igniter , I would replace it but its an S2. I heard about TPS , i got to check it

Any help would be greatly appreciate , I almost destroyed the car yesterday because of this issue while drifting ...
Modified by ka24eracer at 3:34 PM 9/26/2009

[streeteg]

Boost/vacuum leak? Check gaskets---Grounds sometimes play a big part in hesitation. Redo all the grounds with thicker gauge, new wireWHat do your spark plugs look like?

[ka24eracer]

Ill try better ground tonight , and for boost leak I only have a stock sidemount so I dont think I have a leak but I ll check that too.

I run ngk Iridium IX plugs , i didnt gap them . BCPR6 If I remember corectly.

They seem to be black but not that much , and even when they were new the problem didnt get better

I hate the fact that I cant look for ecu codes ...

[platez808]

sounds to me like youre bogging out from being too rich..

are you running an adjustable fpr? if you arent you should jump on it soon.. may not solve your problem but its better for your engine (and wallet) in the long run.. there are a couple of threads, including a sticky about it if you didnt already read it

other than that i would say to check timing if you didnt already do that..

[mxkid54]

I had a very simmilar problem and I checked the throttle position sensor setting. I was off on the closed throttle setting. The voltage should be between .4 and .5 volts. This was for a S1 RB25DET with Q45 Throttle Body. Hope this helps.

[treymeiste]

had same prob with mine... check for boost leaks with shop air and leakdown tester... iac screws like to leak alot.. also pull top cover off coil packs and let run in dark if they are sparking out coat them in neoprene or plastidip, fixed my problem

[ka24eracer]

Checked for leak with wd40 , cant find any , Ill have to build a leakdown tester.

I installed a lot of ground , nothing .

ran the car at night , no sign of spark.

I have a nismo fpr....

On the TPS i got 0.36 v to 4.4 v

Any ideas ?

[mxkid54]

Adjust your TPS so that at closed throttle you have between .4v and .5v. I was was only a little out of range and had a similar problem.

[ka24eracer]

Interesting !

Oh and It seem to be worst when it rain , that could be in my head

[ka24eracer]

The Tps have been ajusted , the problem is still there ...

Any idea ?

think ill go for the GM coil conversion tomorow , Ill know for sure if its about the coils...

[kouki-gymkhana]

You have a boost leak...I had the exact same problem on my S2 RB25 and it turned out to be a boost leak. I was ready to replace the coils and everything but I'm happy that I built a proper boost leak tester first. Google it and you will see how to make a good one. There's even a video on youtube.

How about this...When you are cruising on the highway and you gradually lay into the throttle does the hesitation start as you build boost? Does the car run fine when not in boost? Can you free rev it without any issues? If any of the above are true then you, my friend, have a boost leak until proven otherwise.

Good luck!

[ka24eracer]

Sure Ill have to build a leak tester , but now I have a BIG BIG HINT !!

We found out that the problem only occur a 100% throttle !!! If you floor it to about 95% there is no problem accelerating through the gears !

No matter how soft or hard I accelerate , if I go to 100 % WOT , the car misfire and feel like no fuel the to engine !

This new discovery take my mind away from the boost leak....

Oh and my tps has been checked , I tried 0.5 v to 4.5 and 0.5 to 5.0 v , no difference , If I go 100 % throttle , It will hesitate

[ka24eracer]

I was sure that somebody would came up and say something like : Oh well ok then, its your ...

[rb25det250sx]

wierd...kinda sounds like leaky injectors, yet bad coil packs, or bad plugs... check them all

[ka24eracer]

Somebody know why there is 2 plug on the tps ?

Also , I tried the car with both tps unplugged and the problem is still there

[rb25det250sx]

one of them is for the auto transmission. dont worry bout it.

[DrifterProdigy85]

My S1 does the same thing. 43psi fuel pressure. No boost leaks. Timing at 15*. New coilpacks. Tried bcpr6es and bkr7eix plugs. Pulls hard at part throttle but misses at WOT. Kinda wierd.

[ka24eracer]

Any hints ?

[DrifterProdigy85]

I think my TPS is messed up. I just hooked up my AVCR that was in my SR and the car is showing 3-4% throttle at idle @ .45 volts. To get it down to 0% i have to hae the voltage around .1-.2 volts and then it will only show 89% throttle when its fully opened. This would cause my hesitation. Basically its not seeing full timing at WOT since its only showing 89% throttle.

[ka24eracer]

Pretty interesting!

[DrifterProdigy85]

I put a new TPS on and still does the voltage drop thing but its reading 100% throttle now. It didnt fix my problem though. Ive eliminated just about everything except for the MAF and Ignitor to check.

[ka24eracer]

I did replace the maf , I dont have a separate igniter on my rb25 , but I recommend you to try the igniter on your engine first . It solve my hesitation problem on my rb20

[DrifterProdigy85]

To help you with yours, Check around the TPS on your Q45 TB. I had one on my SR20 and it leaked at the TPS. If it does leak there, use some RTV on the outer collar of the TPS and adjust the voltage before it drys. It fixed the air leak on mine.

[synergy]

Its funny because i had this exact same issue!. Had...have haha i cant get rid of it either dont feel bad buddy

I launched the car front a stop light at WOT shifted hard to 2nd and all the sudden....nothing... car just stoped i let go of the throttle a little bit and all the sudden shes back and running....

[DrifterProdigy85]

I think i might have fixed mine. Put a wideband in yesterday and found out it was running at a 12.8-13.0 @ WOT. This would definitly cause detonation and make the ECU pull timing. So i increased the fuel pressure to 50psi and that dropped the AFR down to around an 11.5 @ WOT.

[synergy]

My car has more isssues than that though

I somehow have a valve tick. My turbo whines like a supercharger was told compressor blades were hitting the housing and my car is so underpowered...

[DrifterProdigy85]

Take off your intake pipe and check the compressor play. Check for any exhaust leaks at the manifold too. That can cause the turbo to spool louder and be down on power.

[ka24eracer]

I set the fuel pressure to 50 psi ,but I still hit a wall when I go WOT . Since ive changed and look for every single part on this engine , Im starting to suspect the ECU .

I had a drift event last night and my engine was the main problems ...Its pretty hard to drift on the track when you can't go wide open throttle...

[DrifterProdigy85]

Use a wideband. Im finding the stock ecu is all over the place on AFR. Maybe something is just wrong with mine. There is definitly alot of room for improvement with a good way to tune.

[ka24eracer]

Could it be knock sensor related ?