Need help for rb25det....

[RayCorn]

I am sorry if i am posting in the wrong forum as i am not driving a skyline coz cant afford 1 yet but i am having a a31 with rb25det,i have some problem with the engine and i hope i can find some solution and some help from sifu sifu here,ok get back to the topic,my rb25det is stock except for fmic and the problem i had is when i start my car in the morning (cold start)the car hardly climb to 1100-1200 rpm as normal car does,it will climb from 700-800-slowly to 1200 rpm,and it will sound like boxer engine,but if i step on the gas pedal and start then it will be normal,after a while everything will be smooth and sound like normal,it happen on hot startup too,on hot startup the car jerking so badly for a while then settle at 700-800 rpm,driving,boosting never been a problem,idling also no problem,anyone here been to tis problem before and if u been there before please share the solution to this problem,haunted me for almost 5 month,checked by few mechanic,none of them know wats the problem,i dont think is maf and aac valve problem,as those 2 stuff problem my car wont be idling perfectly,i am suspecting fuel pump check valve,leaky injector,cold start valve under the intake manifold,anything that i miss?please share,thank you for viewing and ur comments will be appreciated,thank you

 

[cosmicgate]

i thought that is normal for rb engines?

If it ain't broken, don't fix it.

 

[yams727]

i'm no sifu,

but based on experience and what i've read - your engine idling at 800-900 rpm is normal.

the only problem i see based on your thread is the car jerking - maybe you should see if there is anything wrong with your fuel pump.

do you have the same jerking problem when accelerating?

 

[RayCorn]

i thought that is normal for rb engines?

If it ain't broken, don't fix it.

i dont think is normal for the engine to vibrate at cold/hot start,it just seems cant find the right idling on the few second of starting up the car

i'm no sifu,

but based on experience and what i've read - your engine idling at 800-900 rpm is normal.

the only problem i see based on your thread is the car jerking - maybe you should see if there is anything wrong with your fuel pump.

do you have the same jerking problem when accelerating?

nope i dont have jerking when accelerating,on on startup,i think my few pump is working,as i can hear the fuel pump whinning quite loud

 

[yams727]

before u start the engine, try letting the fuel pump whine for a few extra seconds (10-15secs), only then start the engine.

see if got any difference.

i assume u're using an rb25 fuel pump yeah?

 

[RayCorn]

yes before i start the engine i turn on the ignition and wait for 5-6 second,the fuel pump will whine about 5-6 second then stop then i just start the engine,dont make any different also

 

[ckwanloong]

in common i think cold start valve or fuel filter. fuel filter jam will influence fuel supply, so when u start ur car in the morning the fuel hav to be pumped from ur tank through filter,pipes then fuel rail. Or mayb u can try switch on ignition but not to start and then switch off...do it several times then u start see whether it's ok...if it works, then i think u can check these two things...just my 2 sense.

---------- Post added at 08:11 PM ---------- Previous post was at 08:08 PM ----------

the problem you r having sounds like lack of fuel supply when u leave it for a period. hope it helps!

 

[RayCorn]

in common i think cold start valve or fuel filter. fuel filter jam will influence fuel supply, so when u start ur car in the morning the fuel hav to be pumped from ur tank through filter,pipes then fuel rail. Or mayb u can try switch on ignition but not to start and then switch off...do it several times then u start see whether it's ok...if it works, then i think u can check these two things...just my 2 sense.

---------- Post added at 08:11 PM ---------- Previous post was at 08:08 PM ----------

the problem you r having sounds like lack of fuel supply when u leave it for a period. hope it helps!

fuel filter change new already but still the same problem,if fuel pump is failing would it cost the car hard to start on cold/hot?

 

[kaminari]

There is one thing control idling mechanism on RB engine ...we call it AAC(Auxiliary Air Control) valve...maybe can try check it out too.

Are you running normal thermostat?Have try swap ECU?

 

[ckwanloong]

yes, it would cause the car hard to start. in my opinion, ask ur mechanic to check ur fuel pressure using the fuel press meter. when u switch on ignition see the fuel press will be rise,then when u crank the engine the fuel press will increase then engine starts. then u can figure out whether there is something wrong with ur fuel supply. if there is no prom with tht,mayb u can go for others like ignition system...

---------- Post added at 10:21 PM ---------- Previous post was at 10:20 PM ----------

even the mixture is too lean or rich with cause it...check ur co as well

 

[RayCorn]

There is one thing control idling mechanism on RB engine ...we call it AAC(Auxiliary Air Control) valve...maybe can try check it out too.

Are you running normal thermostat?Have try swap ECU?

yes i am running normal thermostat..will tis cause the problem?i swap ecu before but still the same thing,nothing changes

yes, it would cause the car hard to start. in my opinion, ask ur mechanic to check ur fuel pressure using the fuel press meter. when u switch on ignition see the fuel press will be rise,then when u crank the engine the fuel press will increase then engine starts. then u can figure out whether there is something wrong with ur fuel supply. if there is no prom with tht,mayb u can go for others like ignition system...

---------- Post added at 10:21 PM ---------- Previous post was at 10:20 PM ----------

even the mixture is too lean or rich with cause it...check ur co as well
Yesterday 10:15 PM

i got fuel pressure regulator,pressure will increase whenever i rev the engine,after i off the engine pressure remain there for a hour or more then will slighty drop,tats why i didnt suspect my fuel pump

 

[iexit]

Aside form the other suggestions, also chk if your car has been wired properly. Seems that the ECU is not able to perform a smooth cold start.

 

[reintel]

yes i am running normal thermostat..will tis cause the problem?i swap ecu before but still the same thing,nothing changes



i got fuel pressure regulator,pressure will increase whenever i rev the engine,after i off the engine pressure remain there for a hour or more then will slighty drop,tats why i didnt suspect my fuel pump

It is normal for fuel pressure increase when u rev the car. If it doesn't, ur pump not working or something choking.

My opinion would be the AAC sensor need to replace or clean as mentioned earlier by Kaminari. If u plan to clean it, dont soak it in petrol.

 

[RayCorn]

Aside form the other suggestions, also chk if your car has been wired properly. Seems that the ECU is not able to perform a smooth cold start.

i will check on it thank you for ur suggestion

It is normal for fuel pressure increase when u rev the car. If it doesn't, ur pump not working or something choking.

My opinion would be the AAC sensor need to replace or clean as mentioned earlier by Kaminari. If u plan to clean it, dont soak it in petrol.

i will try to clean it,tomorrow will try open the whole intake manifold side to see wats wrong,but its not easy to take out rb25det intake manifold,the manifold design seems stupid to me :stupid:

 

[a31gtst]

dude,

there is no need to open the entire intake manifold! just opening the AAC valve in itself can be a challenge if you dont have the right tools. I have taken apart much of the head myself and its something you would likely wanna avoid unless you are doing a rebuild and have all the necessary tools, knowledge, gaskets and replacements you need.

I have had similar problems before and you should be able to find the root cause with some patience.
If you are using a stock ecu, you can simply locate the ecu and run a diagnostic test...pls google for more info...the diagnostic check will light up the led/s on a stock ecu and alert you to any sensor or part that is not working within its range.

If that doesn't give you any answers then perhaps hook up with a workshop that handle's RB's and will likely have spare's...you should be able to borrow the spares and eliminate the faulty part one by one...

AAC valve, O2 sensor, coil pack, ignitor, ecu...etc...


like many on the forum have said before...if it aint broken, dont fix it...just focus on finding the necessary part that is causing the headache...and should you still not be able to find the problem and seem to lose hope...just ask around the forum and you will likely be given quite a number of reputable contacts/mechanics that should be able to help you.


Cheers.

 

[owtaman]

I have a RB25DET, yes it does behave erratically at 650rpm when the aircon is off, try to pump RON97 it will reduce the symptom a little.

 

[owtaman]

Hi Guys,
Does anyone else having this problem with RB25DET ? Just want to see if this is a 'known issue' that is perceive as normal or it does indicate a problem.

Engine does not stall, at idle, occasionally the idling speed would slowly drop below the 650RPM(standard idle speed), then it would automatically attempt to raise the idling but will then immediately drop below the standard 650RPM again, making the car vibrate more than usually would expected, leave it to behave like this for awhile and it will stabilize it self but after a few minutes the symptom comes again... feels like the ECU is trying to run lean at idle speed to save petrol but it does not able to do so properly, give it a quick step on the throttle it will be fine but will resume the symptom again.

 

[a31gtst]

Its called hunting.
Your ecu is not getting a signal from one of the sensor's and is trying to search for it, thats why you notice the idle going up and down.

Check your AFM, O2 sensor and the AAC valve. Do a search and you should get all the answers you need. If you have a good mechanic who is familiar with RB's than just get him to swap out the mentioned sensors above with spare ones one at a time to eliminate which is the faulty one. If its not any of the above you could have some wiring issue.

 

[Dr.D]

do diagnostic on ur ecu n check if any sensors not performing up to par..

 

[owtaman]

Thanks for all the inputs, I plan to bring the car to Ah Man in USJ industrial area to run a diagnostic, heard that he is the wiring king in Subang area, anyone use his service before ? Care to share ?