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

[superspit]

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.

[Adriano]

Fuel pump, spark plugs, fuel filter, cracked coils, blocked catalytic converter. Most likely one of these

[superspit]

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 February 4, 2007 by superspit

[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.

[superspit]

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 February 4, 2007 by superspit

[Adriano]

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]

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]

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]

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]

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...

[superspit]

Bumpy bump!

[RB30 Ceffy]

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]

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.