rb20 problems..... out of ideas

[91240sx rb20det]

i have a 91 240sx w/ a rb20, and its been acting like it has no power. I'm not sure why cause everything is hooked up. When i give it full throttle it just doesnt want to pick up and go. I took it to a performance shop to get it dyno'd and it ran 128hp at 10-11 psi of boost, and 9.8-1 a/f so i know its running a little rich but not enough to kill 75 hp. only mods are 3" downpipe and walbro 255. the performance shop said to get a new ecu but i'm not sure can someone help out...thanks....

[Acecool]

Too much fuel might be an issue... do you have an AFTERMARKET adjustable Fuel pressure regulator?

Make sure you adjust it to 43psi or whatever with the vacuum hose OFF!!!!!!

Josh

[91240sx rb20det]

no after market fpr i still shoudn't lose that much power right now it runs like crap when i try to get on it, and its boosting fine

[Carl H]

check base timing and intercooler piping for leaks.

[91240sx rb20det]

timing is good because i just put in a water pump, and the boost gauge is registering 10-11psi isn't that mean its good?

[Carl H]

no, if you havent stuck a timing gun on it do so.and check for charge pipe leaks, it sounds like you've got a massive leak somewhere.

[91240sx rb20det]

ok i will thanks.....so you don't think i need a new ecu??

[91240sx rb20det]

also when i crack the throttle just a little bit and hold it after a couple of secs it picks up a little, does that mean anything

[Joe]

ok i will thanks.....so you don't think i need a new ecu??

the ecu isnt a cure all for your problems. they VERY rarely go bad.

check your ignition timing and for boost leaks. these are the most common issues with RB's.

[Acecool]

If you have a 255, you are most likely getting too much fuel, you can get an FPR pretty cheap, try the easy stuff first ;-)

[91240sx rb20det]

but what i don't understand is that when we ran it on the dyno it did not "crackle" or backfire at all isn't that saying that my timing is close to dead on. because i did the timing when i replaced the water pump.

[Carl H]

there is a diffrence between _ignition_ timing and _cam_ timing, your ignition timing (as set by the cas) might be off but seriously sounds like a nasty boost leak.

[91240sx rb20det]

how do i know when its set right??? do i just move it a little and drive it?? oh thanks for clearing that up for me... ya its got no power i hate it

[mello88]

Hello 91240sx rb20det, I sympathize with your problem... A close friend went thru similar issues with his RB, so here are some ideas for you.

First off read the FSM chapter on setting your timing, it's pretty simple if you have a timing light. You'll know when it's set right, because when the timing light flashes the bump on the lower timing cover lines up with the correct mark on the crank pulley.

Like they suggested, having a boost leak is very likely. You should consider build/buying/borrowing a boost leak tester to pressurize your hotpipe/fmic/coldpipe/intake manifolds to see where you have any leaks. Don't forget to block off your PCV when you do this otherwise it won't work how you want it to...

Running rich is probably because of two things. One, your stock FPR + Walboro is a potential problem considering the age of the FPR. Replace it eventually with a Nismo (or whatever other brand you trust) and set your fuel rail pressure to 43psi (3 bar) without the vac hose hooked up. The second thing is the stock ECU runs really rich under load anyways. What AFR do you have, from your motor (in the past) to reference to where it is now?

Check your coilpacks to make sure one of them isn't cracked and leaking spark under high load. I suggest this because of your comment about when you just crack the throttle and your motor feeling better... At WOT there is a lot more load on the coilpack vs at idle or part throttle, so sometimes the car will idle and part-throttle cruise with "full power" but whenever you step on it it'll sputter or feel like it lost power. Does your car miss occasionally at idle?

BTW your "performance shop" telling you that your ECU needs replacing is a give away that they have no clue what they're talking about... What diagnostics did they perform to arrive at that conclusion? It's not like the ECU just forgets part of it's memory... It's a lot more likely that a sensor went bad, or you have a short or something mechanical failed...

If you really wanna play around with the ecu, swap yours with a known-good one from an RB20 friend. Also check that your harness bolt (connects the harness to the ECU) is tight. Next you should unbolt it from the kick panel, flip it around and use a flatblade screwdriver to put it into diagnostic mode and read the DTC codes off of it (read the FSM for instructions on how, plus a list of code #s). DTCs are useful for finding out if you have a wiring short to one of the sensors, plus it's a quick and free diagnostic you can do any where. I'm assuming that a code 34 [for knock sensor/KS wiring] would probably put the ECU into a safe mode and retard spark timing.. Which kills your power. At least that's what happens on the KA so I assume the RB ECU handles code 34 similarly...

GL hope these suggestions help... When you find your problem pls update your thread so other ppl can learn from ur troubles!

Modified by mello88 at 3:54 PM 10/29/2007
Modified by mello88 at 3:57 PM 10/29/2007

[91240sx rb20det]

thanks guys for the input.....i turned the cas alittle bit and then i test drove it and it ran perfect.