Missfire Boost@4500-5500 RPM - The Answer! (for me at least!)

[Bazelinez]

Woop de doo, Problem is back, just like before. Barely lasted a week.

I think mine may be air flow metre related. It seems to happen every time the it rains here in Perth which at the moment is a lot. I think the HKS filter lets through too much moisture.

I'll clean the afm and get back to you.....

[noise]

OK so my mate helps me take out the coils on my GTT. We look at all of them and can not find a single crack or blemish, they all look new.

We tape them up anyway and go for a drive, problem is still there.

So we decide to gap the plugs at .8, SO FAR THE PROBLEM IS FIXED!!!

He reckons it will be fine from now on, I hope he is right.

[SECURITY]

has anyone tried urethane? im going to give it a go tomorrow.

[mad34]

hi guys i had the same problem that you all discribe the misfire after 4000rpm.

i have a r34gtt tiptronic i checked my coils they were fine no cracks because at first i thought that was it, it seemed likely seeing as i had gapped my plugs down to .75 from 1.1 and that didn't fix the problem. when i checked the coils i was surprised to find them all perfect. Someone told me at first when i was having the problem to gap the plugs to .6 i was reluctant seeing as everyone else recommended gapping to .75. So just out of interest and out of desperation i pulled the plugs out and gapped em to 0.6 and what do you know it works perfect now the car boots no probs all the way through the rev range.

so before you invest in some new splitfires as i was about to check to see if gapping the plugs right down works. IT DID FOR ME!!

anyways guys hope i have helped becuase i hate when my car isn't running perfect it drives me nuts.

now i just have to sort out a problem with my front head lights they have tampered with the originals to get them through regency apparently. so if anyone knows how to fix them or who can turn them back to how they were originally any help would be good

[benl1981]

What boost are you running madr34?

I would have though if you have to gap them down to 0.6 then there is something amiss with your coils.

I only notice a problem at 9psi in temps where the air temps are low. I don't think it is the coils, rather the ECU doing Rich and retard to protect the engine. I'm going to build a jaycar fuel asjuster and get it tuned to hopefully smoothen up the power delivery.

[mad34]

standard boost

but i have an exhaust airfilter and intercooler so maybe slightly higher than standard also i think auto run slightly higher boost anyway

you reckon its the ecu??

thats interesting

how do you know this???

mine was doing it all weather didn't matter just as soon as it was under full boost bang it would misfire.

[benl1981]

Ive read a bit on here about how the standard ECU has a fit when you run a bit higher boost. I actually had what felt like a harsh rev limit at about 3k rpm when I ran 10psi. I have a full exhaust and slightly bigger intercooler. With the extra airflow and a cold night I think it may have been the ECU cutting the fun..to do this safely it richens up the mixture and retards the timing heaps. Apparently if it were coils I wouldn't really get this feel as you would have to have more thatn 3 coils misfire at the same time...

Still not sure but swapped over to another set of good coils and still the same. If cold night and 8-9psi in the higher gears it isn't that smooth.

Will fit a SAFC style device and see if I can get that to help tidy up the ignition/fueling issues.

[mad34]

that sounds likely also

mine sometimes does it still aswell, but only rarely now

well it looks like i will have to get safc2 aswell. ah well atleast its not my coils

[Scooby_Steve]

Hi,

Had my coils taped up and it seems to have fixed the problem but if i'm in 4th and decide to give it some, the car will cut out, then all of a sudden pick up again. Apart from that and flat spots all is good. Currently running 10psi with a 3" turbo back exhuast and fmic, and pod filter.

So i have bought a pack of "DynaGrip" plastic weld but it says on the back that this product is not suitable for polyethelyne or another poly plastic but not polyutherane. So is this product suitable to be used on the coils? the reason why i ask is that it has a temp resistance up to 160 Deg so i thought that should last a little longer than tape etc.

Any help would be great. Thanks

Steve

[Zahos]

Hi,

Had my coils taped up and it seems to have fixed the problem but if i'm in 4th and decide to give it some, the car will cut out, then all of a sudden pick up again. Apart from that and flat spots all is good. Currently running 10psi with a 3" turbo back exhuast and fmic, and pod filter.

So i have bought a pack of "DynaGrip" plastic weld but it says on the back that this product is not suitable for polyethelyne or another poly plastic but not polyutherane. So is this product suitable to be used on the coils? the reason why i ask is that it has a temp resistance up to 160 Deg so i thought that should last a  little longer than tape etc.

Any help would be great. Thanks

Steve

http://www.skylinesaustralia.com/forums/sh...ead.php?t=51046

Thermal plastics cannot be welded.

The back of the coil is covered in epoxy during production, so an epoxy like araldite is fine for the temperatures the coils see.

[5hift]

ok hello everyone, my first post...I drive a '90 Gts-t and I've been suffering from the same problem (havent checked my coils yet, tomorrow) but i think its also due largely to the airflow meter as there seems to be a short in the wiring. Now, the engine of the car was swapped just before i bought it and i havent even gotten to service the car yet. I thought i would try restting the ECU first to see if maybe the problem lessened any. Went for the fast reset, disconnected the battery and pressed the brake to discharge the car, reconnected the battery and then.... there's now a clicking noise coming from the fusebox and lights in the car are flashing (glovebox, behind headlamp). the car also does not start, no turnover at all. I checked the service manual but it makes no mention of this, any ideas?

[DOUGMO]

i have a miss also with ces split dump and full 3"

exhaust wirh apex hybrid front mount and bmc

air filter in standard air box, fitted splitfires and

it made it idle better but still runs soft alot of

the time, still holds full boost and sounds ok

just running at about 40% power output,

running boost @ 0.85 bar 0.8 plug gap with coppers,

also seems worse in the wet or very cold

anybody??????

[Cubes]

i have a miss also with ces split dump and full 3"

exhaust wirh apex hybrid front mount and bmc

air filter in standard air box, fitted splitfires and

it made it idle better but still runs soft alot of

the time, still holds full boost and sounds ok

just running at about 40% power output,

running boost @ 0.85 bar 0.8 plug gap with coppers,

also seems worse in the wet or very cold

anybody??????

If its worse in the cold that would suggest its possibly leaning out.

Cold air = denser air that requires more fuel.

Have you had it on the dyno?

[DOUGMO]

no dyno run yet,

trying to eliminate as many

things as possible at the moment,

do you think faulty a/f meter could

cause it to run lean?

[SECURITY]

hey guys.. someone mentioned using a dremil drill to sand away a light layer of the inside of the coil away, i did this 4 weeks ago and i havent gotten a miss since. the car feels brand new!

it seems as the problem was a crappy connection between the coil and the spring.

im going to re-gap my spark plugs to around 1.0 or 1.1 and maybe scavenge some more kw.

[Zahos]

i have a miss also with ces split dump and full 3"

exhaust wirh apex hybrid front mount and bmc

air filter in standard air box, fitted splitfires and

it made it idle better but still runs soft alot of

the time, still holds full boost and sounds ok

just running at about 40% power output,

running boost @ 0.85 bar 0.8 plug gap with coppers,

also seems worse in the wet or very cold

anybody??????

<{POST_SNAPBACK}>

With those mods, and that level of boost, the increased airflow on colder days (due to low temps -> denser air), would probably make the car run rich. (ECU detects more airflow and increases fuel to compensate).

Don't know how the RB20 ECU behaves, but when the S1 RB25 ECU detects increased airflow, it over compensates in fuel, making it increadible rich and misfire/splutter in the mid/high rev range.

A piggy back fuel computer or replacement ECU can sort this out.

Either way, you will need to get it on a dyno to monitor your A/F ratio's...

[maccaz_gts25t]

hahaha noob question...whats SAFC?

[Zahos]

hahaha noob question...whats SAFC?

<{POST_SNAPBACK}>

I think it stands for Super Air Flow Controller.

It intercepts the signal from the air flow meter, and alters it before it gets to the ECU.

This tricks the ECU into thinking there is less or more airflow, which dynamically alters your A/F ratio at any given RPM.

People use these when their air flow ratio's get really rich (or lean) after a few modifications, to get their air flow ratios in the desired range.

It is NOT a full ECU, it just plugs in before your ECU, and modifies 1 signal before it gets to your ECU.

Below I attached a dyno graph before and after a SAFC tune. The green lines are before and black after..

You can see the initial A/F ratio plot (botton green line) is all over the place. Now this one appears to be lean, but initially the sensor that took the reading was stuffed, so we changed it for a new one. The plot was similar with the new sensor, but sat lower, meaning the A/F mixtures were very rich.

After adjusting the air flow meter signal accross the rev range with the SAFC, a flat 12:1 A/F ratio was obtained, giving very smooth and consistent power delivery. (black lines)

[YTRI]

I have an auto R34 GT-t that seems to be doing this. Starting at roughly 4500, it starts to misfire heaps. The car is completely stock. I replaced the plugs and checked the coil packs but they look fine. It happens a lot more on colder nights. Any ideas?

[LodDog]

Had exactly the same problem missing after 4000rpm. Used an old plastic card and smeared a thin (1-2mm thick) layer of gasket silicon around the area of the crack and underneath the coil. Now the car is running 100% It has always been a bit lagy and now the laginess is gone along with the missing. It wasnt really a crack that i found it seemed more like where the plastic was joined together in production but i saw burn marks on the joins as if it was arcing from there. Great Fix!

Edited September 12, 2005 by LodDog