The Good ol' RB25 studdering problem

[mentordrift]

Okay, so I have been reading common posts on this for about the last 2 hours now, and just have a few questions about some of the stuff I have been reading.

What is happening, is any time I go into boost over 9 psi, the engine seems to do a very stong pulsing/lurching ordeal.

HOWEVER, since I haven't taken the car out pretty much at all since we finished the swap, and the few times that I have, boost has been only 7.5psi on a manual boost controller, I still have yet to swap the FPR and fuel pump for my Nismo and Walbro units (The pains of wedding planning).

The car idles a bit high, but I have not had the tachometer calibrated to the RB25 from KA24DE - I think I read that a failing/failed intake manifold gasket can cause this, as well as the lurching/surging/pulsing that I am feeling in the car.

I checked dang-near everything for a boost leak, and all of my connections are good (MAF, etc). ECU is stock still.The car is managable and fine under a certain boost limit, but when boost is turned up, it immediately stumbles around, but is still driveable and does not die out or stall. I thought at first I was overspooling the turbo somehow, but the more I read, the more it seems like a possible fueling issue, followed by the intake mani. gasket.

[240z4u]

Where are you plugs gapped and how old are they? Thats the first thing that comes to mind.

Evan

[lilskyline240]

exactly the same thing i was thinking. Plug heat range, and gap can cause a whole ton of problems when raising boost levels. Try some new plugs and gap then down a bit

[mentordrift]

I dont know it off the top of my head, but they are stock part number NGK's from a Murray's auto. "Lasersomething" I think lolGapping is stock gapping also.The plugs were brand new when we installed the motor, back in november and have less than 100 miles on them.For alternatives to spark plugs on the Rb25, what is a good plug heat range? I paid $9.95 per plug on those suckers. As for gapping, about how much should I close the gap? It seemed pretty tight for stock tolerences, but a little bit goes a long way I guess.

[lilskyline240]

im guessing they are Iridiums your running or something for them to be 9.95 a piece. Try some regular NGK plugs. I am personally not a fan of Iridiums at all. I have seen alot of ppl have problems with them

[240z4u]

If you search around, you will find the popular plug everyone likes. I have a spare set, but they are a heat range colder so you don't want them.

Like Ben said, people have trouble with iridiums. I have had poor luck with iridiums in TWO previous turbo motors.

Gap IS tight, do a search. Its kind of common knowledge that stock gap is too wide.

Evan

[lilskyline240]

i really dont even pay attention to what stock Gap is on a car/engine. Anything turbo that i know im using for performance i gap the plugs down to about .026 then test it out and if im still gettin bad spark ive gone all the way down to .020.

it all depends on your setup. Every motor IS different. I am also not a fan of NGK plugs in general. Ive had probably 3-4 bad NGK spark plugs since ive started working on cars.

[WhatsADSM]

If I were you I would get those fuel components in ASAP. I have had a few walbros fail on me and it would cause a shudder under medium-high boost levels because the pump was dying/running out.

As a side note in my DSM this issue caused me 2 blown motors so I would say rather be safe than sorry and swap in your FPR and walbro

[mentordrift]

gap was .036, or something huge like that. Fixed A LOT.Walbro is sitting in the trunk (tomorrow's project), fpr is on the engine....

Found a marble sized hole in the radiator plastic trim on the bottom about an inch from the drain plug. It's on the back side, and I have no idea wtf it's from lol

Will wait to start up when the new rad. gets here.

[rb25drag]

I have this problem with my motor just about every climate change. Basically it comes down to me re-adjusting my AFC and Timing. The Stock ECU is pulling timing on you also under boost probably not helping your spark problem. But your gap is way too high. So Bring it down around .026-.028 and try that. If it still studders, Check the timing.

[BEST1TUNING.COM]

^ yes HUGE timing losses when upping the boost on a factory mapped ECU.

[mentordrift]

okay, so the plugs are gapped and the car is buttoned up, sans the radiator.The company that I ordered it from was backordered and it's not coming till the 7th

Another thought I had was my weakening alternator.We just swapped the 110amp Quest alternator onto the RB25 at the same time as everything else that we were doing (air intake, different MBC, and new turbo elbow).Could the failing alternator been a big issue? Because I will feel like a total tool if that was a big factor

Oh well, we'll see what she does in a few days now.Also - if the spark needs a little "kick" ... has anyone heard good things about those "pulse plugs" I keep seeing adverts. for them on websites now, and I'm curious. If no one has tried them, I'm willing to take the $125 bullet