RB25 Help!

[Nissan 250sx]

Hello everybody. My names Rafael and I was wondering if you guys could help me out with my little situation i have here. I live in the states (southern california) and since the motor was never offered legally here, help has been very limited and information scarce. I've only had a chance to read on here and try to learn from people with first hand experience with these beasts! I have some friends that are known to deal with these motors such as motorex and mckinney motorsports but to you guys they probably mean nothing. They are just too shop busy usually to stop and give me a hand. well, heres my adventure into RB25ville.

Some background information first:

• Chassis is a 1990 180sx hatchback
  

• Motor is a series 1 RB25det
  

• Running on OEM ECU
  

Upgrades to motor include:

• Greddy intake manifold
  

• Q45 Throttle Body
  

• Front Mount Intercooler
  

General Maintanance for swap

• New N1 Water Pump
  

• New Power Enterprise Timing belt
  

• New Tensioner and idler pulley
  

• New 6 puck clutch
  

The Story:

OK, Here's my RB25 experience. I owned a sr20det 240 but came across a deal on a RB25 clip i just couldn't miss. I thought, what do i have to lose? I gain 2 more cylinders and a bunch of torque! So i sold the SR20 and got me the RB25. I tried to go the cheap route and install this thing at a friends house (doing it at my own residence is not an option). After some drama between him, his parents, and my car. . ..i ended up paying $100 to tow it to another location (i had pulled out the sr20 there so it would not move)

Ok, lesson learned, Don't take on big messy car projects in 1)a gated community with neighbors that complain 2)your friends PARENTS house 3)anywhere where you have a time limit of 1 weekend for a first time swap. ok, whatever. . .i ate those $100, learned my lesson. Now being in southern california, i am spoiled with shops everywhere, good and bad. Ok, i say f*** it and splurge, i take it to a very reputable shop with guys who know what they're doing since they do these swaps all day long. So anywho, another $100 tow truck bill gets my car to the shop. Now here's the doozy. . .the tow truck drops my car off right?. . ..then backs into it right before he leaves. ..lol! I'm like wtf??!! Well, he's taking care of the bill once the car comes out of the shop. I'll probably just end up getting a carbon fiber unit rather then repair and respray the stock one. ..who knows. on with the story. . .

$2500 for the swap. ...install the motor,do the wiring, install Greddy Intake Manifold and Q45 TB, FMIC piping and install Mckinney Motormounts and driveshaft(which were included in the price and installed flawlessly btw). Time was great. .it only took a few days to drop in the motor and get it wired up. I got that call, your car is ready to pick up! I was stoked to say the least.

When i drove it home, it felt kind of funny(no power) but was afraid my expectations might of been too high so i drove it home anyway(not that far). I called the shop and told them my concern and they told me to bring it on down to make sure everything was cool. So i said great! I take it a day later and end up overheating by the time i get there. Now thats my fault because i provided the fan they used which was enough for my Turbo 4cyl but not this car. luckily, it wasn't THAT bad to cause damage. Since we were running on no guages he said it'd be a good idea to install these so we know whats going on (which makes plenty of sense to me and i agreed) I bought a water temp, boost pressure, and oil pressure.

oh yeah, before i forget. I got the car back with no knock sensor harness! apparently, my clip didnt come with one? I was really tripped out but luckily got one off my friends extra RB20 harness and ran it straight to the ecu spliced since i couldnt find the plug that contains the sheilded wire for the knock sensors

I took the car home later (once the temp came down from this sunny 100 degree cali weather). eventually got around to install them and install another better fan. Overheating solved Vacuum reads ~20 hg, boosts ~7 lbs. I checked timing with a timing light and verified 15 degrees also. But it's still not running right. TPS is at 5.0-5.1 at idle.

Idle is weird. It drops sometimes temporarily and sometimes seem to be searching for idle. I have no BOV right now so im getting some MASSIVE compressor surge (working on that ASAP) but it dies on me upon deceleration sometimes as if it was running an open atmosphere BOV. I suspect its running rich because sometimes i have to kind of pump the gas pedal to get the thing back up and running after one of these decel stops. I don't think there is any vacuum leaks and pretty sure there are no boost leaks either.

The other day, i took my intercooler off just out of a hunch and found oil puddled in the endtanks. enough to drop out when you hold the intercooler sideways on both sides. I immediately thought turbo but it has no problem holding boost pressure at 7lbs. There is no smoke coming out of the tailpipe at all. I cleaned it up and drove it hard for a day then checked again, nothing. weird! My friend brought up a faulty PVC causing blowby from the valve cover going back into the intake stream which is also possible. Anyone know how to check for a faulty PVC? and where to replace it?

The other/main thing is power. The turbo spools, holds boost, but just doesnt go! I mean, it doesnt have nearly the power and torque that an inline 6 turbo motor should be capable of. My friend has a turbo from a spare RB20 that i'm thinking of swapping just to see if its possible the turbo could be causing me any greif. I haven't done a compression test since i purchased the motor when it read around 140 with less then 5 variance across all cylinders (done motor cold and in clip before i purchased it) I've also done the infamous carb cleaner can in search of leaks on vital motor gaskets. ECU shows 55, all good in my neighborhood!

If someone has some good deeds to claim i could sure use some help. Anyone have any tips online they could help me with and should try i would GREATLY appreciate it. Thanks for taking the time to read my journey into the land of RB25. any and all responses welcome. thank you

Rafael Gonzalez

[51jay]

Are you running stock exhaust ? why no bov?...you need it. Which OEM ECU is it If it's R33 you can't tune it and I don't think it will cope very well with the Q45 throttlebody, Greddy Manifold and fmic. I assume it's the R33 stock turbo. Your idling problems sound like a malfunctioning AAC valve or you could try running through the ECU learning process a couple of times or 3. My R33 with many performance mods in place is currently making about 160rwhp instead of near 300 and it is entirely due to it's current state of tune or I should say lack of tune. The first thing you need to do is get it on a dyno and see where you'r at .....I think you'll need an aftermarket ECU to utilise your current and future mods.

Brouse the Teck forums here and at WWW.skylinesdownunder.com for heaps of info

[Nissan 250sx]

No, exhaust is Apexi GT spec exhaust (95mm) currently connected to the stock catalytic converter. I was advised to "punch out" the cat to help eliminate some uneccesary back pressure. The only reason i dont have a BOV is because i own an HKS SSQV unit but am waiting for the flange so i can have it welded onto the intercooler piping. You are correct, it is the stock R33 computer and stock Turbocharger as well. After doing some searching as you suggested it seems i might as well clean out the AAC valve and check if it is functioning well. I plan on buying an APEX power fc computer but funds depend on how much this repair is going to cost me! Thanks for your input.

Rafael Gonzalez

[SteveL]

TPS is at 5.0-5.1 at idle.

You say your running the OEM RB25DET ECU (right ??).....that being the case the above doesn't make sense. The TPS on these engines simply tells the ECU whether the throttle is closed (ie idle) or not. It is simply an open or closed switch. If you have a reading like the above it means your using a variable resistor TPS which is not suitable for your ECU and would probably explain your erratic idle/dying, etc. I'd suggest putting the original TPS on your current TB or if that can't be done put the entire original TB back on and work from there in terms of your other problems.

[Nissan 250sx]

are you sure Steve L? I took your advice and switched the TPS sensor to the sensor that came with the original Throttle but still had to initially set it to factory spec .5 volts and i'm positive it is the factory piece. It's definately a step forward though as the car seemed to pick up some noticable power but still not quite there yet. We tried to advance timing a bit but it performed less so we're still hovering around 15 degrees. Anything else it could possible be? oh, and ECU is still giving me a 55!

Rafael Gonzalez

[the phantom]

Raphael, the standard ECU wont handle the Q45 AFM, the mapping for it will be all wrong. Even on an FC if you temporarily switch to the Q45 whilst running the standard AFM it runs bad. The TPS is a pot. It tells the ECU when you let off the throttle, but also controls acceleration enrichment. At idle the TPS should be about 0.5v increasing with throttle to usually just under 5v. This also ties in with idle control performance.

[Nissan 250sx]

phantom, Im running the RB25 AFM not Q45. I understand they are not simply interchangeable like that. The TPS is what i changed and it seemed to respond well thinking that i was either running the Q45 TPS or it was faulty. I swapped it out for the OEM original that came from my front cut, set it to .5v at idle and was on my way! thanks

Rafael Gonzalez

[the phantom]

Ok Rafael, got the wrong idea there somewhere along the story about the Q45...maybe it was late!!!