Strange Cough At 3000 Rpm

[Hum@nzee]

Hello - I'm trying to do a bit of research into the cause of this - I spoke to someone else and they said theirs does it too. It seems to be around 3000 rpm and on boost - and worse when cold (I don't rag it when cold but going uphill for example when it kicks down and the boost comes in it could do it then). It feels almost like fuel starvation - a proper throttle-off cough - wondering if its to do with the valve timing, fuel pump or transmition (basically no feckin' idea).

Engine mods so far:

GT30 Turbo (just fitted - but it did this before)

Turbosmart e-Boost2

Blitz down pipe

Trust-GReddy FMIC

HKS Fuel-Cut Defenser

HKS SuperFlow Filter

Rolling road tuned and set up

300 bhp @ 0.9 bar

TEIN Coil-overs

got to go

cheers

John

Edited October 12, 2007 by Hum@nzee

[Mr_RS4]

What have you got as far as ECU. I'm guessing since your using a fuel cut defender then you've still got the factory ECU with a piggy back like a SAFC or something. Could be many things. With just that info to go on I would guess maybe factory ecu hitting R&R, ignition break up of some sort, crook fuel pump. Whatb happens after 3000rpm and with more throttle. Does it get worse, better???

[ssshonky]

I am no expert on the matter but I wonder if its either

coilpacks breaking down ( quite common )

or

boost cut? does it do it between ( or during ) actual gear changes?

I presume from your description you have an auto?

our stagea does a strange little braap braap type hesitation / noise between shifts

and I am lead to beleive it might be boost cut ( is this the same as R&R? )

I am sure someone will come on here and give you a more definate answer.

[Hum@nzee]

Sorry guys - I kind of got half way through writing and had to go.

Running an e-Boost2 controler also - and the whole thing has been set up really well by the peeps at weston performance - in the absence of further ECU and fuelling mods. These are obviously the next step but funds won't allow just yet. Its been tuned to a reliable 300 (223 kw) at 0.9 bar - and with an appropriate ECU, fuel pump, Fcon etc it should make closer to 400+.

This cough thing seems to disappear after it is hot and has some high revs/boost - and sometimes it dosent happen at all. Just had new coilpacks so they're good and its not a misfire as such anyway - its like a very quick foot off the throtle and back on again. The other bloke who said he'd got this issue said that his seemed to do it at 3-4000 revs and then 5000, 6000, 7000 (on seperate climbs up the dial) and then it was clear for the rest of the run. Mine seems more hit and miss though. I was just wondering if anyone else had experienced the same thing - and if it was just a Stagea Auto transmition characteristic.

Cheers anyway guys - any ideas welcome.

John

[petrolfix]

mine was doing the something similar. it stutters though a bit like a miss. mine is a manual with PFC front mount exsaust running10 pound. it just starts stuttering at aboout 3500rpm under slight load when you get on off the throttle then on again seems to go away or load it up more to clear it? i just thought it was water in the petrol at first till i went looking in the tank and changed fuel filter no water. so now i just asume it's coilpacks. they went in my silvia the same. the only other thing i can tell you to try is to gap your spark plugs down to 0.7mm try that a 33 that we did a turbo converstion was cutting off at 4500 cos it was blowing out the spark .7 and it was sweet. i havn't been able to drive my stag now for 5 months so havn't changed coilpaks yet. let us now what you come up with.

[Hum@nzee]

mine was doing the something similar. it stutters though a bit like a miss. mine is a manual with PFC front mount exsaust running10 pound. it just starts stuttering at aboout 3500rpm under slight load when you get on off the throttle then on again seems to go away or load it up more to clear it? i just thought it was water in the petrol at first till i went looking in the tank and changed fuel filter no water. so now i just asume it's coilpacks. they went in my silvia the same. the only other thing i can tell you to try is to gap your spark plugs down to 0.7mm try that a 33 that we did a turbo converstion was cutting off at 4500 cos it was blowing out the spark .7 and it was sweet. i havn't been able to drive my stag now for 5 months so havn't changed coilpaks yet. let us now what you come up with.

Yeah cheers mate - the coilpacks I know are a problem on the RB25DET - (don't get them hot - I know, lets stick 'em on top of a 2.5 litre turbo charged engine and stick a lid on top with no vents!) Even the Japanese make mistakes I guess. I had your miss too - new coilpacks solved it - had them dipped in epoxy first - helped a bit but no cure. I swaped mine for a new set of standard packs and the miss-fire is gone. This 'cough' is different however - it is like a sudden one-off miss - but stronger somehow - seems almost as if the turbo stops spooling and then resumes really fast - there is a slight sound of air/pressure escaping during the event too - as if something is choked - still got the standared centre section on the exhaust - do you reckon that might be part of the problem? Failing that I think its got to be the ECU/fuel management or something.

If I blip the throttle so it kicks down and shoots past the 3000-4000 mark it seems to by pass the problem. Makes you look like an aggressive driver though and pisses my wife off!

Cheers

John

[Tangles]

bov could be dodgy ?