RB25DET break up

[1972 240z]

My RB25DET breaks up under a load and today i put new NGK iridium spark plugs in it and that didn't seem to help. Can someone please help me?

 

Thanks,

 

Another thing i do have the stock recirculation valve on it could that be whats wrong?

Edited December 22, 2010 by 1972 240z

[1972 240z]

Okay to add to it today i recirculated the recirculation valve and tightened all the intercooler pipe clamps as much as i could and it helped a little then i tried to advance the timing and it helped a lot when gradually putting it under a load but if you floor it its still the same. So i left it like that and a couple hours later i went to go drive it and after about ten minutes it started running real bad and wouldn't let me rev it up at all and smelled like it was dumping fuel into it. someone please help, what should i test/try

 

Thanks,

[fast-datsun]

Okay to add to it today i recirculated the recirculation valve and tightened all the intercooler pipe clamps as much as i could and it helped a little then i tried to advance the timing and it helped a lot when gradually putting it under a load but if you floor it its still the same. So i left it like that and a couple hours later i went to go drive it and after about ten minutes it started running real bad and wouldn't let me rev it up at all and smelled like it was dumping fuel into it. someone please help, what should i test/try

 

Thanks,

Check plug gap.. We use .025 on std NGK Check TPS setting... Check fuel pressure 43PSI with vac unhooked , check ecu for codes.... Check fuel injector for torn o-rings..

[pat1]

Your coil packs are taking a dump. It a common thing with the rb motors.

[Canadianz]

If its not a spark issue make sure you have both the correct MAF and that its working correctly. It could be dumping fuel due to a limp mode. If there is no MAF reference then the engine will run BUT horribly.

[rayaapp2]

Check plug gap.. We use .025 on std NGK Check TPS setting... Check fuel pressure 43PSI with vac unhooked , check ecu for codes.... Check fuel injector for torn o-rings..

Confirmed Std Copper Cores for RB25DET. I have Dyno results with std coppers vs laser platinums and guess which one didnt misfire.

I gap my plugs at .033"-.035". I tried .030" and noted it would sometimes misfire randomly at idle over long periods of time.

 

Your coil packs are taking a dump. It a common thing with the rb motors.

 

They could very well be going out. The old coils in these end up with cracked insulation and in the dark watch them "leak" out to the aluminum mounting brackets. The tiniest cracks seem to leak and you can usually see the carbon outline the crank where the spark has been passing. THE best way that Ive found to make this happen with no load is a spray bottle of water in the dark. Without going into the physics of why this works I will just tell you what to do.

In the dark lightly mist the coils when the engine has reached opperating temperature and lean down and carefully watch and listen. If there is a leak from the coils it will make noise and a light of spark. You should be able to trace down the bad coils this way and even see exactly where the spark is leaking from.

I gave up on used coils and purchase a new set from Raw Brokerage.

 

To set you timing you have to put the ECU into "Base Mode". If you didnt do that, you didnt adjust the timing correctly and it can do some weird things. Basically you confuse the ecu for lack of a better statement.

Timing is 15* BTDC stock.

Early RB25's can be put into base mod by unplugging one of the TPS plugs. Check the FSM to be sure as to which one(I remember it being the brown one but there is more than 1 style).

Base Mode on a RB25det S2 can only be set with a plug in device. The old TPS trick will not work. Most high end Scan Tools, Nissan Consult, Nissan DataScan, and Im sure other lap top based softwares could do it.

I dont trust computers to give me a good timing value as its all "perceived" values that they give you(blind leading the blind thing). I pull the #1 coil off and extend the boot with a regular spark plug wire so I can clamp my inductive timing light up to it and manually check the timing at the balancer for confirmation. That's probably more than anyone really needs to do though.

 

If you have a recirc BOV system in place you should be fine either way. If your ECU is still using a MAF then it is a must that the BOV be recirculated before the turbo but after the MAF. If you do not the ECU will be getting erroneous information from the MAF at times.

 

Besides all of that you should perform the basics. Check Fuel and Air. You know you have some kind of spark and we've given you the points needed there to determine if you have good spark. Fuel. check for proper pressure and volume(flow test if needed). Air. Make sure you have a clean air filter and that nothing is preventing air from the system where it should be getting air. Likewise with a Turbo make sure you dont have any leaks letting air out of places that should be holding in air. Brake Cleaner or Carb Cleaner will go a long way to finding leaks at idle when used with precaution of course.

 

 

BTW: This all assumes that your engine is setup as its suppose to be with the correct parts or part modifications. Youve not given us much else to go on so we are left assuming its a stock RB25det setup as stock.

Edited February 3, 2011 by rayaapp2

[mr jdm]

My friend had this problem for a long time when we swapped his rb25 into his 240sx years back. A lot of people didnt have the setup at the time, after 3-4 months, he swapped out the plugs and changed the gap and it ran perfect.