Jump to content
SAU Community

Boost Cut 'appears' To Be Cutting In A Little Earlier Than Usual?

superspit

By superspit,
in Engines & Forced Induction

 Share

Recommended Posts

superspit Mentor

superspit

Posted
Posted

I wonder what's changed?

Hi guys, been a while.

I had my car running nicely for almost 2 years at 11-12 psi..via a bleed valve...(PS.I'm not a lead foot, very occasionally would give it a squirt)....All good.

Just recently I have found that when going up-hills, for a test example, in a high gear, she'll cough just as you'd expect to happen IF the boost cut was cutting in....btw, this never use to be a problem.

I have since wound everything back to 7-8psi (accurate, as both stock and a/m guages concur), now I can get up that hill in 5th with no problem....but with a lot less 'joy'.....as you'd expect when lowering a car's performance.

Just as a side note: I did the 'solenoid conversion' 3 years ago, so it's always on bypass...I've had much success with that simple mod..so it stays. (unless....????)

I just can't think of anything else I've done to suddenly make it 'not like' the higher boost levels she use to run on, and very well.

I've performed 're-sets', checked IC piping for bleed, and generally just checked things over.

Turbo still appears 'strong', no smoke etc...plenty of typical Skline power.....but....as above.

I'll throw it into the 'lion's den', see what you guys might come up with..

Sincere thanx in advance to you all!

Superspit.

superspit Mentor

superspit

Posted
  • Author
Posted (edited)
Fuel pump, spark plugs, fuel filter, cracked coils, blocked catalytic converter. Most likely one of these

Thanx for quick response Adriano,

replaced my fuel filter this morning.

I've not done my plugs in ages, prolly more like 18-24 months...(Nissan platinum), could that be a cause?...geeesh....I will look at those.

Coil packs seem fine, there is no missing, or roughness....I won't bother with that.

Cat?.....geeesh....I had know idea that could cause a problem with boost cut, but then again, when thought about, it could do something with the back pressure...??? I will look at that.

Pump..?....I can't see that as an issue at the moment...sounds fine (I can't hear it..LOL!)..just doesnt seem fuel pumpish!!.....car can sit at high speeds for as long as I want it, with no issues. (done in remote areas)

So, plugs...and cat...I will check these.

Thankyou so much.....Adriano!!!!

Others...Please, anything else, ideas, suggestions?????

Edited by superspit
Adriano Grand Master

Adriano

Posted
Posted

Close your plug gaps down to .8mm, to check the coils remove the cover over them, give it a quick brap of the throttle at night while watching the coils, you will most likely see sparks(where there shouldn't be). Fuel pump can sound fine and drive fine, but only loose power under boost. Nissan's dont have any boost cut, not until you start running high power levels that max out the airflow meter, which is unlikely. Sitting at high speeds doesn't run on boost, so most of these symptoms would not show.

superspit Mentor

superspit

Posted
  • Author
Posted (edited)

Ok...fair points...but allow me to clarify...

Gaps are at .75, and have been like that since I've had the car, with all plugs changed....as in my signature.

so that's cool.

Yes, I did the 'spark cover off at nite' thing....saw no traces of spark or flashback...so, all good there.

Fuel pumps, in my little exparience, regardless of boost conditions, can be easily tracked down to fault. The car comes up thru the rev range wonderfully, with no hesitation.. (I've had pumps fail on me before, and it just didn't feel that way, at all.)

As soon as guage goes to a very consistant 12psi....the engine shudders, then wham, off she goes until you hit that 'Hi' boost again.

Now she'll sit beautifully at the new 'hi' boost of only 7-8psi. ...but.. but...the joy was at 12-13psi!!! ( I miss it!..and more importantly, I want to know why this has changed)

I believed that there was a boost cut on these engines, and at a very conservative and safe level.....? Is that not right Adriano?

Thanx again Adriano...

Close your plug gaps down to .8mm, to check the coils remove the cover over them, give it a quick brap of the throttle at night while watching the coils, you will most likely see sparks(where there shouldn't be). Fuel pump can sound fine and drive fine, but only loose power under boost. Nissan's dont have any boost cut, not until you start running high power levels that max out the airflow meter, which is unlikely. Sitting at high speeds doesn't run on boost, so most of these symptoms would not show.
Edited by superspit
Adriano Grand Master

Adriano

Posted
Posted

Do a search of "rich and retard", there are about 100 threads on this exact thing. There is no boost cut, it just accesses load points that cause it to run rich(er) and retard the timing, maybe its a bad batch of fuel?

When did you last gap your plugs?

superspit Mentor

superspit

Posted
  • Author
Posted
Do a search of "rich and retard", there are about 100 threads on this exact thing. There is no boost cut, it just accesses load points that cause it to run rich(er) and retard the timing, maybe its a bad batch of fuel?

When did you last gap your plugs?

mmmmmm...no boost cut?........ok....

Fuel?...no, I've done many tanks, with the same results.

Last time I gapped the plugs was when I last installed them...as per above.

Car is great now, just won't boost like it use to.

Thankyou.

R33silverS2 Mentor

R33silverS2

Posted
Posted

People always seem to say that there is no such thing as boost cut in skylines and its just rich and retard, but im still not convinced. Ive hit rich and retard many times and it is nothing like the boost / fuel cut. The whole car comes to a hault and switches the power fully off momentarily - basically if you aint got a seatbelt on and hit the fuel cut you could go flying forward into the damn windshield. Now that is not R&R

superspit Mentor

superspit

Posted
  • Author
Posted
People always seem to say that there is no such thing as boost cut in skylines and its just rich and retard, but im still not convinced. Ive hit rich and retard many times and it is nothing like the boost / fuel cut. The whole car comes to a hault and switches the power fully off momentarily - basically if you aint got a seatbelt on and hit the fuel cut you could go flying forward into the damn windshield. Now that is not R&R

there you go....I'm sure of the same thing too. (that is, I'm not entirely convinced).

Your description is perfect, as far as I'm concerned, I feel/get the same action/re-action in the car under certain 'boost' conditions. (if I may call it that!) LOL!

thanx silvers2,

even if we both are incorrect, we may at least get some clarification on this subject.

Thanks

Spit.

R33silverS2 Mentor

R33silverS2

Posted
Posted

No Probs I hit it for the first time the other day had me scratching my head also >_< A lot of people i think believe R&R and whatever cut we must of experienced is the same thing...

RB30 Ceffy Enthusiast

RB30 Ceffy

Posted
Posted

maby you have a small slit in your pipeing and only opens up a little when on high boost and then you just have a simple boost leak. Ive had this problem before on a 32 GTR and simply replacing an old cippler and cleaning the dust off the rest fixed the problem fine.

superspit Mentor

superspit

Posted
  • Author
Posted
maby you have a small slit in your pipeing and only opens up a little when on high boost and then you just have a simple boost leak. Ive had this problem before on a 32 GTR and simply replacing an old cippler and cleaning the dust off the rest fixed the problem fine.

Thanx Ceffy....when I do the plugs, and take everything apart while doing so, I will be attempting to find a leak, or loose clamp.........your explanation sounds really logical to me!...

I thank you!

Regards,

Superspit.

post-9261-1170662298.jpg

post-9261-1170662401.jpg

post-9261-1170662578.jpg

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • sunsetR33
      Unpeeling the Orange

      By sunsetR33 · Posted

      Update 3: Hi all It's been a while. Quite a lot of things happened in the meantime, among other things the car is (almost) back together and ready to be started again. Things that I fixed or changed: Full turbo removal, fitting back the OEM turbo oil hardlines. Had to do quite a bit of research and parts shopping to get every last piece that I need and make it work with the GT2860 turbos, but it does work and is not hard to do. Proves that the previous owner(s) just did not want to. While I was there I set the preload for the wastegates to 0,9bar to hopefully make it easier for the tuner to hit the 370hp I need for the legal inspections that will follow later on. Boost can always go up if necessary. Fitted a AN10 line from the catch can to the intake hose to make the catchcan and hopefully the cam covers a slight vacuum to have less restrictive oil returns from the head and not have mud build up as harshly in the lines and catch can. Removed the entire front interior just shy of the dashboard itself to clean up some of the absolutely horrendous wiring, (hopefully) fix the bumpy tacho and put in LED bulbs while I was there. Also put in bulbs where there was none before, like the airbag one. I also used that chance to remove the LED rpm gauge on the steering column, which was also wired in absolute horror show fashion. Moved the 4in1 Prosport gauge from sitting in front of the OEM oil pressure gauge to the center console vents, I used a 3D printed vent piece to hold that gauge there. The HKB steering wheel boss was likely on incorrectly as I sometimes noticed the indicator reset being uneven for left vs. right. In the meantime also installed an airbag delete resistor, as one should. Installed Cube Speed premium short shifter. Feels pretty nice, hope it'll work great too when I actually get to drive. Also put on a fancy Dragon Ball shift knob, cause why not. My buddy was kind enough to weld the rust hole in the back, it was basically rusted through in the lowermost corner of the passenger side trunk area where the wheel arch, trunk panel and rear quarter all meet. Obviously there is still a lot of crustiness in various areas but as long as it's not rusted out I'll just treat and isolate the corrosion and pretend it's not there. Also had to put down a new ground wire for the rear subframe as the original one was BARELY there. Probably a bit controversial depending on who you ask about this... but I ended up just covering the crack in the side of the engine block, the one above the oil feed, with JB Weld. I used a generous amount and roughed up the whole area with a Dremel before, so I hope this will hold the coolant where it should be for the foreseeable future. Did a cam cover gasket job as the half moons were a bit leaky, and there too one could see the people who worked on this car before me were absolute tools. The same half moons were probably used like 3 times without even cleaning the old RTV off. Dremeled out the inside of the flange where the turbine housing mates onto the exhaust manifolds so the diameter matches, as the OEM exhaust manifolds are even narrower than the turbine housings as we all know. Even if this doesn't do much, I had them out anyways, so can't harm. Ideally one would port-match both the turbo and the manifold to the gasket size but I really didn't feel up to disassembling the turbine housings. Wrapped turbo outlet dumps in heat wrap band. Will do the frontpipe again as well as now the oil leak which promted me to tear apart half the engine in the first place is hopefully fixed. Fitted an ATI super damper to get rid of the worn old harmonic balancer. Surely one of the easiest and most worth to do mods. But torquing that ARP bolt to spec was a bitch without being able to lock the flywheel. Did some minor adjustments in the ECU tables to change some things I didn't like, like the launch control that was ALWAYS active. Treated rusty spots and surface corrosion on places I could get to and on many spots under the car, not pretty or ideal but good enough for now. Removed the N1 rear spats and the carbon surrounding for the tailpipe to put them back on with new adhesive as the old one was lifting in many spots, not pretty. Took out the passenger rear lamp housing... what do you know. Amateur work screwed me again here as they were glued in hard and removing it took a lot of force, so I broke one of the housing bolts off. And when removing the adhesive from the chassis the paint came right off too. Thankfully all the damaged area won't be visible later, but whoever did the very limited bodywork on this car needs to have their limbs chopped off piece by piece.   Quite a list if I do say so myself, but a lot of time was spent just discovering new shit that is wrong with the car and finding a solution or parts to fix it. My last problem that I now have the headache of dealing with is that the exhaust studs on the turbo outlets are M10x1.25 threaded, but the previous owner already put on regular M10 nuts so the threads are... weird. I only found this out the hard way. So now I will just try if I can in any way fit the front pipe regardless, if not I'll have to redo the studs with the turbos installed. Lesson learned for the future: Redo ALL studs you put your hands on, especially if they are old and the previous owners were inept maniacs. Thanks for reading if you did, will update when the engine runs again. Hope nothing breaks or leaks and I can do a test drive.
    • Kapr
      What brakes on R34 GTT(Europe)

      By Kapr · Posted

      No those pads are DBA too  but they have colors too. I look at the and imo the green "street" are the best.
    • wizlb
      Who has a Infiniti Q60, Q50 (V37)?

      By wizlb · Posted

      I’m not sure what happened I told them about sonic tunes free OTS tune and the next the I know .. I was booted..   To funny 
    • Kinkstaah
      Starting again

      By Kinkstaah · Posted

      Yea - I mean I've seen my fuel pump which is decades old and uh, while I'm not saying this with real knowledge... but I sure get the ick at using anything in the fuel system that produced the state of that pump. Many years ago I went through multiple pumps (and strainers) before I dropped the tank to clean it out with extreme violence. I'm talking the car would do maybe 50km before coming to a halt, which resulted in me cleaning out the filter with some brake cleaner and going on my way. None of my stuff ever looked like what came out of your fuel tank. I don't think I'd be happy with it unless every single component was replaced (or at least checked/cleaned/confirmed to be clean here).
    • GTSBoy
      What brakes on R34 GTT(Europe)

      By GTSBoy · Posted

      I'm not going to recommend an EBC pad. I don't like them. Just about anything else would suit me better. I've been using Intima pads for a while now.
×
×
  • Create New...