Rpm / Boost Issue

[Excuses]

The car

Stock R33 1996 S2 skyline,

I have talked to a few people about the possible issue, thought i might make a post. Gears 3,4,5 at 3-4k rpm will hesistate or die down.

Example 1,

I can get to 4,000 RPM then it would drop down to 3-3.5k, with my foot on the accelerator still.

It will hold at 3-4k rpm for a few seconds before going any further beyond,

hopefully thats enough information, i just changed my spark plugs, coilpacks look fine.

any ideas?

[STATUS]

intake pipe? or plug gap

[tridentt150v]

^^^agree sounds like sucking pipe or cleaner in

[lachlanw]

bahahaha "coil packs look fine "

they might require further attention

the whole car "looks fine" from the outside

[Excuses]

retarded replies goes in the retarded section, if we have one, thanks lachlan.

[Room42]

retarded replies goes in the retarded section, if we have one, thanks lachlan.

Agreed

[Shazza24]

How much boost are you running?

[lachlanw]

ffs

as if the intake pipe could suck shut on a stock car . then magically open up again above 4krpm .

did you gap the plugs ?

[paulr33]

I can get to 4,000 RPM then it would drop down to 3-3.5k, with my foot on the accelerator still.

this is what a clutch does when it is warn out and slips

it free revs higher then slips and so forth

baby it around and get a new clutch

if you keep pushing it, it will fail, and take the flywheel with it

the stock clutch is pretty basic and not geared up for heavy use

[LeCoq]

is it missfiring?

[t4t4nk4]

does the boost feel like its spiking the revs down? and it could most probably be spark plugs i had a similiar p[roblem recently but got it fixed quick and cheap.

If you want any help or info on how i fixed it just message. cheers mate,

[_x_FiReStOrM_x_]

Either spark breaking down, or AFM fault.. by the sounds of it. Hard to do internet diagnosis' though lol, as most will agree.

[paulr33]

how on earth do you reach that conclusion?

if the AFM is a fault, rev cut is 2500rpm and the ecu does hard fuel cut, thus you cannot rev past 2500rpm

if spark is breaking down the engine misfires its ass off but the rev needle doesn't slip

if the clutch is slipping or worn the engine revs until peak torque, around 3500rpm (on boost) and slips and then re-grips when past peak torque

so i have no idea how you believe its afm or spark

but good luck

[_x_FiReStOrM_x_]

how on earth do you reach that conclusion?

if the AFM is a fault, rev cut is 2500rpm and the ecu does hard fuel cut, thus you cannot rev past 2500rpm

if spark is breaking down the engine misfires its ass off but the rev needle doesn't slip

if the clutch is slipping or worn the engine revs until peak torque, around 3500rpm (on boost) and slips and then re-grips when past peak torque

so i have no idea how you believe its afm or spark

but good luck

Apologies, i didn't read correctly/understand it wasn't actually a misfire, i just read hesitation and assumed. As for AFM i've seen a few give bad readings at certain outputs, but still within what the ECU sees as 'acceptable'. The 2500cut will only happen if the voltage is either missing, or way out of range.

Edited August 21, 2011 by _x_FiReStOrM_x_

[paulr33]

even if the afm is mangled under certian conditions

the worst it woudl do is give incorrect load reading, either lean out or richen up (smoke or pinging)

it doesnt explain the RPM needle going from 4000 down to 3,500 or 3,000 with the accel pedal still pressed

nothing matches the symptom with the problem other than a clutch slipping or auto box toast (if its auto), which is still a clutch

no afm, map sensor, intake pipe, external wastegate, blah blah would make the needle slip like that

[_x_FiReStOrM_x_]

even if the afm is mangled under certian conditions

the worst it woudl do is give incorrect load reading, either lean out or richen up (smoke or pinging)

it doesnt explain the RPM needle going from 4000 down to 3,500 or 3,000 with the accel pedal still pressed

It seems out opinions may differ .

Nevertheless it may be a clutch at fault, i'm not ruling that out at all. From what i've seen with clutches though, generally once the grip is overcome and it begins to slip it heats up rapidly and then continues to slip until you release load from it and it cools. - instead of slip-slip then suddenly grip. The OP needs to describe things a little more i think.

[STATUS]

ignition, if the needles dropping out.

[SargeRX8]

Doesn't sound like a clutch slipping.... He said it feels like its dieing down and revs drop, rather than rapidly increase. It takes that little moment for it to kick back in and move again. You need to describe the problem further.. What it happens, do you get any popping or machine gun sounds?

I had this issue twice, once it was misfire, the second time it was lean popping(failing fuel pump) and with the lean popping there was no way in shit stick I could get it past 4k.

[_x_FiReStOrM_x_]

From what i can gather from the OP.. he can eventually rev it out further. Or am i reading it wrong?

[Rolls]

What about 4.5-5k does it do it then as well? Or specifically 3-4k ?

Are you running more boost than stock? Aftermarket intercooler? bigger exhaust? If yes then it is probably combination of bad spark and running way too rich, check plugs, plug gap (should be 0.8mm), and check coils for cracks and scalding marks.

If it is completely stock then it is probably a different issue as the above tends to cause a misfire at peak torque, not lower in the rev range.

Also is it those revs regardless of load, or with minimal throttle will it rev out cleanly and it is only on WOT that it happens? Does the engine completely die or does it msifire (eg pop pop pop and lots of black smoke) ?

Need more information.

Edited August 22, 2011 by Rolls