need help sounds like missfire under boost

[lanerjo]

ok let's start from the beginning on this one...

Stock rb20det transplanted into 89 240sxcustom intercooler pipingrb25 turbo running 12 psi (changed because the stock turbo had a bad oil seal)slight exhaust leak between the dump pipe and the downpipe... (the exhaust shop got a little over zealous with the welder on the flange)

the miss/hesitation under full boost/throttle (i can hit full boost at partial throttle ie 75% no problems... pulls great)No vacuum or boost leaksplugs nkg iridium proper heat range with a decreased gap to .033plugs look right not too hot not too cold not to lean maybe a little rich according to the color on the insulator nice and brown no signs of pinging or detonationchanged to J30 ignitorchecked the throttle body it is clean. the maf is clean too.

I am stumpedany help would be greatly appreciatedalso does anyone know where i can get a good chip for the computer? tuned for my setup?but i really need to get the whole full throttle thing figured out

[fast_s14]

You might have a couple weak coils and check to make sure your timing is dead on. Double check for boost leaks, they are sometimes hard to find.

[lanerjo]

I have double and triple checked for boost leaks had a friend rev the motor to boost while i physically checked every single connection...

I figured it may be a weak coil but i have no clue how to check to see if they are good or not... if it was an american motor or there was more information on how to check the coils that would be great, i can't find the oem resistance between each connection, even then it is not entirely accurate as to whether or not the coil is weak.

The issue did not start until i swapped the rb20 turbo for the rb25 turbo...

[fast_s14]

you need to make a boost leak checker. Reving the engine will not build boost to check for leaks.

[lanerjo]

i beg to differ with that statement... if you rev the engine to boost then it does create boost. I know this is not the most reliable way to check for boost leaks but it can and does work. Logically you could just check for vacuum leaks and any vacuum leaks would therefore be a leak under boost... since the car at idle pulls about the same vacuum (20in/hg) as boost 10psi... the conversion relates to 20in/hg = 9.8psi... This is also theory here but it stands to reason that one could be diagnosed by the other... Not that I live by that rule but you get what I mean

soap and water help too.

i'm not trying to be a smart arse... but i do know what i mean when i say it. If i am not sure about what i am saying i will not say it...

[fast_s14]

ok how much boost are you creating with no load on the engine?

[lanerjo]

i can reach full boost 12 psi... only for a second with no load for fear of over rev...

[lanerjo]

I guess my main question is how do i check to make sure the coils are good?

I have checked on older domestic vehicles but those vehicles are also easy to find chilton's or haynes manuals for... a rb20det motor was never in the us officially thus no chiltons or haynes that i can find... nor have i been able to find spec for the coils online

[fast_s14]

What kind of tune do you have? Go make a boost leak tester so can find a leak if you have one. Reving to get 12 psi only for a second isnt enough to find a leak. Your just asking for problems trying to find a leak like that.

[lanerjo]

i never said it was the best way to check for a leak... the tune is still stock... I am looking for a reasonably priced way to tune the engine... not safc or piggyback. I would prefer to chip it...

[fast_s14]

Try taking the boots off of the coils and cleaning the contact of each coil. Also try turning the boost down a little to see if the problem goes away.

[lanerjo]

i turned the boost down to 8psi to see if that helped... made no noticable difference... and yes the contacts have all been cleaned...

[Booztd 3]

33 thou seems like way to much gap.....

Buy some new plugs and I'd go down to 25 thousandths and see if that helps........if everything is running fine and you're misfiring under a heavy load, you're either:

1. Not giving it enough fuel (detonation)2. Giving it too much fuel (so rich its blowing spark)3. Having an issue with spark (not timed right, or to much plug gap)

Seems how you're on a stock ECU and you've tried running stock boost, I'm going to rule out issues 1 and 2

Double check your engine timing, put a timing light on the crank pulley and verify it reads what nissan spec is (i think 15 degrees at idle, fully warm?)

This is adjustable via the cam angle sensor

Easiest way to check the coils is to just pull them out, stick some plugs in the ends of the coils, pull your fuel pump fuse, and spin the CAS over by hand. If you can see a decent spark come from the plug, then they're not weak....

[ANVIL]

if u need some coilpacks i saw a set of 6 on zilvia yesterday for $100

[lanerjo]

I thought pretty much the same thing... as i stated the plugs look good though. which right there, for me eliminates #1.

The timing should not have changed, as i have not touched it. I will check though...

Too rich is a posibility, but once again with everything stock except the turbo i don't see it, and if it was a leaky injector would do it at other loads, i would think.

Too much gap? is a posibility.. the .032-.033 gap was after i decreased the original gap. I will try going down to .025 though...

Blowing spark that is my initial and ongoing assumption... thus the reason i put the j30 ignitor on it. also the reason i tried decreasing the gap on the plugs.

I did not think of checking the coils like that... I am all about the ohm meter... I don't know why it did not dawn on me I used to check domestics like that all the time... matter of fact i have a tool that replaces the plug and has a ground attachment to make it easier to check the spark like that. I kinda feel like an idiot for not thinking of that sooner.

Wouldn't checking like that be a little bit redundant though as this condition only happens under full throttle and full boost?

[lanerjo]

i might have to check out those coilpacks...

[Booztd 3]

Wouldn't checking like that be a little bit redundant though as this condition only happens under full throttle and full boost?

Someone said to check to see if the coils were weak, it was just my thoughts on how to check them reasonably quick

You're going to have to pull the coils to get to the spark plugs anyways, its an easy test

You said you gapped them "down" to .033, what were they originally? If you're going off of what the spark plug comes from the factory, its going to be nowhere near what you'll need to run, they dont come "Pre-gapped" for your application

I'd say decrease the gap to mid 20s, if not lower (I run .018) and have fun driving your car

[lanerjo]

I am not putting down any ideas here... I appreciate any help i can get with this... nor was i saying i was not going to check them... I do plan on decreasing the gap down to probably around .020 or so... and i will check the coils at the same time...

btw .9mm is what the plugs are supposed to be gapped to which is .035 inches when i decreased the gap last time i was mostly checking for consistent gap and color of the plugs... the plugs have about 500 miles on them changed when i did the swap... and about 200 miles on them since the turbo change... enough that i would be able to see any signs of pinging or detonation...