Ok This Is A Weird "flat Spot' Thread, No Missfire, Std Boost Etc

[TUF250]

Ok I need the SAU guru's to help out on this one.

My car is an R33 gts-t with very low milage in good condition. The following mods/work have been carried out:

- Std Turbo with std boost (5/7 as confirmed by a boost gauge)

- R34 gt-t intercooler (cleaned out)

- 3inch bellmouth dump pipe

- high flow cat (apparently xforce, came with car)

- 3inch stainless system with two big mufflers (also came with car)

- new timing belt (timing reset)

- full fluid service (inc. AFM clean)

- new iridium ngk standard spec plugs (5 heat range, 1.1 gap)

Now the cars runs really well, really stong.

The car has developed the typical br25 flat spot on some nights (keep in mind it is extreamly cold in melbourne at the moment)

The car takes off hard, then flatens out, then feels strong again. This matches up with what I have searched in relation to two things. Not there is no obvious missfire (ie spluttering, coughing)

1. R&R

2. Coils/plugs

Now R&R seems unlikely given the car is running std boost? Is it possible to get R&R is the air is cold/dense enough?

Second I took the coil cover off in the dark and the not one missfire is obvious at any RPM. The car only has 80,000ks and is in exception cond so its not impossible that the coils are ok, Cant find any cracks...

So im confused??? Is it my heat range 5, 1.1 mm gap plugs? Is it R&R?

I must have read 50 threads on the topic but everytime R&R appears is on higher boost and the coils show missfires and actually missfire (ie splutte where mine dosnt?)

Thoughts?

[Moodles2]

Was the problem there before the timing belt change?

[Spurdo]

if anything, the cold air is far more likely to help your engines output , not hinder it.

[TUF250]

no its developed recently. Car has the symptoms of the threads I have read on here but only std boost and no lightning show from the coils.

[BenSm]

im not the smartest of the bunch but just throwing ideas out, i havent read up on this problem either. lol.

maybe try putting it on a dyno? do a self diagnostics on the computer to see if it results come up with anything, i have read somewhere that a TPS can cause this?

[GTScotT]

Have you cleaned the engine bay lately?

Perhaps you have water down the plug gaps, sounds typical of this.

[TUF250]

no I havnt, it is something im planning to do though but not as yet

[mickey]

worth testing some known to be working coilpacks I think, despite your belief the existing ones are fine.

[Tangles]

get a proper boost guage, with free-flowing exhaust and cooler intake (weather) your boost would be more like 10psi

Id suggest a SAFC to fix the issue, setup correctly on a dyno

[TUF250]

well I took it for a drive today, being slightly warmer compared to at night and perfect. pulls strong all the way through. Slight dip at around 4500 but some have told me thats to do with the VVT? is that the case?

Was worried about my spark plugs too, heat range 5, gap 1.1 but given im only running the standard boost I think they should be ok?

PS still only getting 7psi on the gauge (digital) with these mods

[paulr33]

RB25 Doesnt have VVT, it has VCT and the default kick off is at 4700rpm

it comes on early in the RPM range and off at 4700rpm

if VCT was dead/disabled your car would be sluggish always until 4700rpm

when it feels flat does the RPM tacho slip to a higher rev range? aka clutch slip

when you light cruise do you notice any different behaviour? aka 02 sensor

[tridentt150v]

I'd also try setting your plug gap to say 0.9 and see if that works - a long shot, but if cold dense air is the culprit it could be affecting the spark?

[TUF250]

thanks for the replies.

Ok would you be able to feel the vct change at 4700? definately no 'flick' of the tacho indicating broad minded personch slip, it is all very smooth, no pops, crrackles or anything odd. Just that 'flat spot'

No problems in cruise. Not I have also replaced the O2 sensor as part of my service and cleaned out the AAC valve.

I have considered the plugs, coils do seem fine and 9 times out of 10 there is not an issue. Didnt want to bring the gap down from 1.1 if I didnt have to but might be required

[lachlanw]

how cold it very cold?

do you have a real boost gauge ? or the factory waste of space on the dash that happens to resemble a boost gauge?

its gonna make the ecu see more air/denser charge and send it into slack timing look at this picture and youll see what and why .

it runs something around 20-17 then chops it back to like 6 then back up to 14 ish

[TUF250]

probably less than 10 degrees each time, maybe as low as 5. hard to say eactly but faily cold.

Yeah replaced it with a digital boost gauge. reads 7 under full noise.

[TUF250]

interesting, the car didnt do it today but tonight the colder it god (to the point of fog) the worse it got. Its definately temp related. wonder if gapping plugs to less than 1.1 will fix it

[TUF250]

how cold it very cold?

do you have a real boost gauge ? or the factory waste of space on the dash that happens to resemble a boost gauge?

its gonna make the ecu see more air/denser charge and send it into slack timing look at this picture and youll see what and why .

it runs something around 20-17 then chops it back to like 6 then back up to 14 ish

interesting graph, that certainly wouldnt be helping, wonder why they were so aggressive at that rpm range?

[gotRICE?]

interesting graph, that certainly wouldnt be helping, wonder why they were so aggressive at that rpm range?

I think its relatively normal on the stock ECU with the mods you have.

This is mine:

Before, and after an SAFC2 tune. Managed to improve the dip as you can see. But its impossible to eliminate without timing adjustments!

And, just so all you "veteran" SAU posters dont get excited, hub dyno, different country.. so dont fret about the "happy numbers" The peak isnt what i was looking at in this instance. More the gain and improvements.

[R3N3]

Ok I need the SAU guru's to help out on this one.

My car is an R33 gts-t with very low milage in good condition. The following mods/work have been carried out:

- Std Turbo with std boost (5/7 as confirmed by a boost gauge)

- R34 gt-t intercooler (cleaned out)

- 3inch bellmouth dump pipe

- high flow cat (apparently xforce, came with car)

- 3inch stainless system with two big mufflers (also came with car)

- new timing belt (timing reset)

- full fluid service (inc. AFM clean)

- new iridium ngk standard spec plugs (5 heat range, 1.1 gap)

Now the cars runs really well, really stong.

The car has developed the typical br25 flat spot on some nights (keep in mind it is extreamly cold in melbourne at the moment)

The car takes off hard, then flatens out, then feels strong again. This matches up with what I have searched in relation to two things. Not there is no obvious missfire (ie spluttering, coughing)

1. R&R

2. Coils/plugs

Now R&R seems unlikely given the car is running std boost? Is it possible to get R&R is the air is cold/dense enough?

Second I took the coil cover off in the dark and the not one missfire is obvious at any RPM. The car only has 80,000ks and is in exception cond so its not impossible that the coils are ok, Cant find any cracks...

So im confused??? Is it my heat range 5, 1.1 mm gap plugs? Is it R&R?

I must have read 50 threads on the topic but everytime R&R appears is on higher boost and the coils show missfires and actually missfire (ie splutte where mine dosnt?)

Thoughts?

i had a similar issue, im in hamilton, NZ and we get thick as fog and the temps have gotten down to -4 deg a couple of times so far this winter. my car also has similar mods to you and my car has done around 82000ks. i recently changed my plugs to bcpr6es (i think) with .8mm gap. and it mostly got rid of the problem, so i suspect it could be a combination of plugs and coils (even though my coils look fine). so i am looking at getting some new coils soon. i run high boost all the time, and its around 9psi because of the mods. im suprised that your car still sits an 7psi at full noise, and my exhaust is the factory one with the mid muffler and cat removed.

Edited July 20, 2010 by R3N3

[TUF250]

great replies thanks. I think I will invest in some new plugs and go from there. Pity because I only just bought my platinums... fell for the marketing...

Thanks