R34 GTT can't get over 3.500RPM

[Lenny64]

Hi there!

I have got a problem with my R34 GTT and before i try to do anything, i wanted to ask you guys if you have an idea what the problem could be:

So - my Skyline R34 GTT drives quite normally up until 3000/3500RPM. However, I can't get over said RPM because as soon as I hit that, the car just puts in a limiter (at least it feels like a limiter). It also begins to stutter and it is misfiring after i step out of the gas. There's no difference in the engine being hot or cold, the problem persists. In Idle the car runs not drastically smooth, but also not really rough. When i try to go "gently" (I'd say < 50% throttle), I sometimes manage to get over 3500RPM, but even then the car starts to stutter.
There is no check engine light on.

I have looked around and saw some people saying, that the spark plugs/coil packs or the MAF could be faulty. 

What do you think?

Thanks and regards,

Lenny.

Edited February 21, 2022 by Lenny64

[Duncan]

That is a pretty good description of a misfire, they most commonly happen as you come onto full boost.  

What mods does the car have and what boost does it run?

The best place to start it for a spark problem is the coil packs; check each connector to the wiring loom is tight/seated properly, then remove them and check each one for cracks or scorch marks that might show a short, then remove/check/replace the spark plugs too (you could gap the plugs done to 0.8mm if everything else looked good).

For a fuel problem start by changing the filter, also could be the pump itself dying.

[Lenny64]

The car currently has a OGS boost controller, which it came with when I imported the car from Japan. It is running on about 11-12psi.

It also has an aftermarket intercooler and an aftermarket APEXI air filter.

[Duncan]

Right, so higher than standard boost on standard ecu is probably pushing things. Are you in summer or winter (no location on your profile), in winter the cooler air can cause problems too.

I'd say most likely it is a spark breakdown problem. Go with the steps above (check wiring connections, coil packs for signs of failure and new plugs with 0.8mm gaps) as first steps

[GTSBoy]

On 2/22/2022 at 4:38 AM, Lenny64 said:

It is running on about 11-12psi.

On 2/22/2022 at 6:05 AM, Duncan said:

Right, so higher than standard boost on standard ecu is probably pushing things.

Per Duncan, you shouldn't run more than about 10 psi on a Neo with stock ECU, because all it ends up doing is using more fuel AND GOES NO FASTER.

Backing it off to 10 or less might help, and might expose the problem, although it could still be either misfire or low fuel pressure.

It is easier to diagnose fuel pressure under load than ignition. Simply connect a fuel pressure gauge in between the fuel filter in the engine bay and the inlet of the fuel rail. Then note the fuel pressure behaviour as you drive. It should increase with decreasing manifold vacuum/increasing boost. Any drop or failure to increase as you add load is a bad thing.

[Lenny64]

Yeah currently we have about 8°C but I don't think the temperature itself is a problem.

Ok then I guess I am going to check all the coil packs and spark plugs and hopefully find something suspicious.

Should the coil packs have an issue: do you have any recommendations which one I should get or should I just go with the OEM ones?

Thanks!

[GTSBoy]

OEM or Splitfire.

Or, upgrade to R35...but this entails a lot more work....and probably an ECU.

[BK]

On 22/02/2022 at 9:22 PM, Lenny64 said:

Yeah currently we have about 8°C but I don't think the temperature itself is a problem.

Ok then I guess I am going to check all the coil packs and spark plugs and hopefully find something suspicious.

Should the coil packs have an issue: do you have any recommendations which one I should get or should I just go with the OEM ones?

Thanks!

 

On 22/02/2022 at 9:56 PM, GTSBoy said:

OEM or Splitfire.

Or, upgrade to R35...but this entails a lot more work....and probably an ECU.

Personally I don't see splitfires as an upgrade over OEM coils at all. R35 coils will work fine at factory dwell settings too. OEM or jump straight to VR38 coils.

FYI we run oem, splitfire and VR38 R35 coilpacks across 3 GTRs. On the 33 we actually removed the splitfire coils and went back to OEM as their was no improvement at all.

[Duncan]

I don't think most cars need an upgrade over the standard ignition system, if it is in good working order it can handle a pretty wide power range. Of course if you are running significant boost (say 20psi+) you might need stronger spark than the factory system

In my experience the splitfires are as good as OEM but a fraction of the price, that's what I run in the race car.  Otherwise there are other aftermarket coil pack makers but since quality has varied over the years it is a bit of a lottery, I stay clear

[GTSBoy]

Splitfire are indistinguishable from new proper OEM coils (in performance, not appearance). The only reason they were an "upgrade" originally (20 years ago) is that it was hard and expensive to get hold of new OEM coils. Then it became possible to get OEM coils at a reasonable price and it was an each way bet. Then the fake OEM coils started to f**k that situation up and it was safer to stick to Splitfire if you couldn't be sure about the OEMs.

That's why I say "OEM or Splitfire" (and usually say to stay away from the other rainbow parade aftermarket coils).

[BK]

On 23/02/2022 at 10:12 AM, GTSBoy said:

Splitfire are indistinguishable from new proper OEM coils (in performance, not appearance). The only reason they were an "upgrade" originally (20 years ago) is that it was hard and expensive to get hold of new OEM coils. Then it became possible to get OEM coils at a reasonable price and it was an each way bet. Then the fake OEM coils started to f**k that situation up and it was safer to stick to Splitfire if you couldn't be sure about the OEMs.

That's why I say "OEM or Splitfire" (and usually say to stay away from the other rainbow parade aftermarket coils).

Yeah stockers can be found at a half ok price nowadays. Funny that Amayama still want about $230 a coilpack, which is just silly.

http://www.kudosmotorsports.com/catalog/coil-pack-individual-suit-nissan-skyline-gts25-gts25-gts25-p-1150.html