boost cut solenoid???

[bmadd2402]

first of all, I am Brendan, and usually go to club240's forums, but there is a lot more info and people over here. I have a rb25det in my 92 240. It was the first major venture with a nissan, and the first time I ever swapped engines with a car it wasnt supposed to be in. I did a 89 integra turbo, and a Accord si-r swap, but hondas are completely different beasts. well, My rb is runnin like crap. Its only boosting to 5 psi, and when its cold, in 1st and 2nd, when you first push on the gas, it ... Bucks? stumbles? I dont really know what to call it but you push on the gas and it feels almost like you down shift. then you let off a little and ease into it, and by about 3500 rpm, its gone. almost like the care is out of tune and vtec kicks in. I read some one else was having similar problems (Boost wise) and some one said it might be the boost cut solenoid. then I start to think, what is that? I dont even know what it looks like. so, in my quest to get my car running nice, I must figure out what this is. can anyone tell me, or better yet have a pic? I have scoured the pics of other members rb240s and tried to follow the vaccum routing but had no luck there either. I'm really in a test phase I suppose, but I dont want to stop and pull out the motor again and start trying to make big power If I'm not sure the engine is good to go. This is one hell of a way to enter the forum huh!

[JonPowell]

sounds very possibly that you are detonating and the ECU is pulling timing. The engine you have might have been tuned for different fuel that you can get.

Tell us ALL your mods & if its a tuned ECU or stock ECU and we will try to give you a hand.

[bmadd2402]

no mods whatsoever. when I swapped my sir motor, I started putting on parts immediately and stuff started breaking because the motor had obviously been sitting for a long time. I havent replaced anything yet as far as timing belt or water pump. I put the motor in, Mckinney did the wiring, put some mineral 5w30 in it, did a radiator flush, checked bolts and turbos lines and such, and drove it a little, then changed to synthetic 10w30. oh, and electric fan. I have no intercooler yet. just a piece of pipe jumping the 2 intake pipes. but I have driven the thing only a few "Test drives". never pushed, never even tried to race yet. But I'm concerned about this boost cut solenoid. more than that my vaccum routing. really I need someone to look at my stuff and tell me if they see anything I did, but there are only 3 rb swaps around here, and I have the only 25, and the only 1 of the other 2's runs... sometimes.

the reason for no intercooler is that I want to do the greddy plenum and q45 TB, and I'm on a budget. dont want to make 2 sets of pipes.

I am so frustrated. this is my goal/plan. I want a 400-450 street/strip toy, not daily driver. I want to find out if everything is running ok before I go any further, and put some serious bank into this project, and if I even CAN complete it. I am planning on a turbo upgrade, along with cams and some head work and a few bolt ons like the plenum, etc. managed by a power fc.but I was gonna pull the motor out, clean up the engine bay, paint etc. but I dont want to do that yet until I feel the motor is running good enough to start trying to make power. I'm a noob. I f**ed up this time. I wish I could go back and start over right.

[Joe]

no intercooler?

bingo.

you are detonating, the air comming into the engine is too hot and preignting. do NOT BOOST WITHOUT AN INTERCOOLER

[bmadd2402]

I have seen a few honda setups that run no intercooler. greddy's turbo kit dosnt even have an intercooler. and it only happens when its cold (the problem). I figured itd be ok for a bit if I didnt push it.

[Joe]

well you dont drive a honda

you drive an engine whos ecu was programed to run with an intercooler from the factory. the greddy kit you speak of for a honda is an extremley conservative kit, i think it only runs 4lbs of boost.

[bmadd2402]

true. would that cause something like that?

[Joe]

absolutley! a turbocharger heats the air an incredible amount, the IC is there to cool it down because cooler air = denser charge. since you have this superheated air going into your engine you arent getting enough air in there so the burn isnt complete OR its SO hot its igniting the mixture before the spark plug even goes off. thats really really bad. you can blow the engine to pieces like that.

[bmadd2402]

the ecu is also tuned for running 8# boost, but I'm only boosting 5. I heard that when the boost cut solenoid kicks in to failsafe mode, it will only boost 5 psi.

[bmadd2402]

I know I'm messing up, but I'm just trying to shave a few bucks off what is gonna be an expensive project anyways. at the expense of my engine's wellbeing. not too smart.

[Joe]

the ecu is also tuned for running 8# boost, but I'm only boosting 5. I heard that when the boost cut solenoid kicks in to failsafe mode, it will only boost 5 psi.

it dosent matter what its tuned for because it meters the air going into the engine also the boost, if it only sees 5 it runs on a basemap for 5 lbs and an airflow for 5lbs.