ANOTHER misfire issue...

[Hcr32typem]

So my 92 Type M has a strange misfire issue that happens when the car hits .55 to .68 bar. RPM doesnt seem to matter nor does what gear im in.

Car has 108k on it, stock except for a BOV and coilovers.

Keeps telling me all clear on the CEL so im sort of at a loss. The car idles perfectly fine and under normal acceleration but as soon as the boost hits about .55 bar and it starts to stumble.

Hope someone can help before i lose my mind haha

Edited December 4, 2018 by Hcr32typem

[GTSBoy]

Have you eliminated ignition system failure (plugs & coils)?  Weak sparks will not work once the boost rises.

Have you checked the fuel pressure under load?  Going lean and detonating can and will feel like a misfire - although if you're familiar with it you should be able to tell the difference.

If your AFM has a problem (reading too high, essentially) then your ECU could be doing the old "boost cut" routine.  They don't normally do that until higher boost levels - but might if the sensors are lying to it.

[Hcr32typem]

I just put a set of oem plugs in the car and the coils appear fine although i havent actually replaced them or not.

I also just put a new fuel pump and checked pressure on the system.

I replaced the MAF last year as well with a new unit.

[SeanR32GtSt]

Try replacing coil packs and also the loom to the coils. 

[Hcr32typem]

2 hours ago, SeanR32GtSt said:

Try replacing coil packs and also the loom to the coils. 

You think it could manifest only at high boost? Idle and normal accel is rock solid

[GTSBoy]

20 minutes ago, Hcr32typem said:

You think it could manifest only at high boost? Idle and normal accel is rock solid

Weak coils ALWAYS show up under boost.  If the loom is sufficiently shit that there is horrible voltage drop, then the coils might not charge properly and so give the same symptoms.  It's usually coils before anything else though.

[Hcr32typem]

16 minutes ago, GTSBoy said:

Weak coils ALWAYS show up under boost.  If the loom is sufficiently shit that there is horrible voltage drop, then the coils might not charge properly and so give the same symptoms.  It's usually coils before anything else though.

Fair.

Still it only happens as it approaches .68 bar which i find a bit odd since it boosts perfectly up until that point

Now to find coils that arent 500 USD a set...

Edited December 5, 2018 by Hcr32typem

[GTSBoy]

Splitfires are ~AU$550 at JustJap, similar pricing on eBay.  OEM coils are also available, for similar pricing.

But I must point out a couple of things.

1) DO NOT, under any circumstances, buy cheap coils.  The various other rainbow shades of coilpacks available will always lead to tears.  They have poor reliability (compared to Splitfire & original).

2) Just taking the easy option and installing Splitfires (or any other same-format coil) these days is stupid.  There are kits available to install Yaris (or other equivalent Toyota-Denso coils), Audi R8 coils, R35 GTR coils, etc etc.  These are ALL modern pencil coils with much much more spark energy than the shitty old ones that use the original RB format.  Some, like the Denso ones, are very cheap, but won't fit under the coil cover.  Others, like the GTR coils, may fit under the coil cover, but will cost some more.

If I had to replace my (Splitfires) - I would most certainly be doing pencil coils.  Guaranteed.  2JZs use them and they don't need coilpack upgrades to support stupid power.

[iruvyouskyrine]

It's almost always shitty coils and shitty loom as gtsboy said. If I was you I would jam in RB25 S2 splitfires and delete the igniter and enjoy much more reliability.

[Hcr32typem]

1 hour ago, iruvyouskyrine said:

It's almost always shitty coils and shitty loom as gtsboy said. If I was you I would jam in RB25 S2 splitfires and delete the igniter and enjoy much more reliability.

Heres a question, are those a direct replacement or do you need a special harness or stand alone ecu to run them?

[GTSBoy]

Splitfires are direct swap, as I said in earlier post.  You can get the right model for S1 RB25 (ie, needs and uses the igniter module on the back end of the head) or you can get the right model for the S2 RB25 (igniters are built into each coil).  As the old Nissan igniter pack is old and prone to failure, it is worthwhile to consider using the S2 type even on an S1, but you would have to do some re-wiring - which is well documented on the interballs.

None of those options requires an ECU change.  However, running a standard RB25 ECU is dumb, so it should be changed just as a matter of principle.

The pencil coil options I described are all available as kits with wiring adapters that just let you plug them in.  I think they are all "with igniter", so wouldn't necessarily work on an S1 or RB20 or early 26 without deleting the original igniter.  Again, no need to change the ECU for this, subject to what I said in above paragraph!

[Hcr32typem]

6 hours ago, GTSBoy said:

Splitfires are direct swap, as I said in earlier post.  You can get the right model for S1 RB25 (ie, needs and uses the igniter module on the back end of the head) or you can get the right model for the S2 RB25 (igniters are built into each coil).  As the old Nissan igniter pack is old and prone to failure, it is worthwhile to consider using the S2 type even on an S1, but you would have to do some re-wiring - which is well documented on the interballs.

None of those options requires an ECU change.  However, running a standard RB25 ECU is dumb, so it should be changed just as a matter of principle.

The pencil coil options I described are all available as kits with wiring adapters that just let you plug them in.  I think they are all "with igniter", so wouldn't necessarily work on an S1 or RB20 or early 26 without deleting the original igniter.  Again, no need to change the ECU for this, subject to what I said in above paragraph!

I am running an upgraded ignitor not that makes an enormous difference but worth noting.

[GTSBoy]

If it were mine, I'd pitch the "uprated" ignitor along with the coils and just go Yaris (or any similar Denso) coil - so long as I was willing to go without the coil cover.....or just space the coil cover up perhaps.  Or, if I were a bit more flush for cash, the R35 coil kit is the smartest move.

[SeanR32GtSt]

Go with splitfire. I did few months ago. Spendy yes but it’s direct and works. Just don’t ever go the cheap route. 

[iruvyouskyrine]

Very very minor wiring change needs to be done to run RB25 S2 'smart' coils. Will work with any standard or aftermarket ECU. Personally I much prefer splitfires over Yaris, but R35 coils are a clear winner, but twice the price and unnecessary if you just want a milt street car.

[GTSBoy]

R35 coils are actually not that much more exxy than Yaris/et al in themselves.  It's the kit that winds the cost up.

[Hcr32typem]

This car will probably never make more than 220kw at the wheels so im not looking to go too crazy with it.

[Hcr32typem]

On 12/5/2018 at 1:37 PM, SeanR32GtSt said:

Go with splitfire. I did few months ago. Spendy yes but it’s direct and works. Just don’t ever go the cheap route. 

Think its worth replacing the harness first or do you think the coils are probably the problem?

[GTSBoy]

Harness is cheaper.  Coils are more likely.  Take your pick.

[SeanR32GtSt]

This ^^^^^