Weird Missfire Problem!

[Hakai]

Hey guys,

First off I have a 1990 R32 GTS-T. Mods include.

FMIC, K&N Pod, GFB Vent/Plumback BOV, 2.5" Catback Exhaust (Was there when I bought it, I didn't do that). After having the intercooler fitted, then going over the pipework, because the guys who did it were slack, I noticed the boost increase to ~11psi, or so says my boost gauge.

Anyway on to the problem.

About 2 weeks ago I noticed it missfiring when booting it after about 4500rpm. It would miss a few times between 4500 and about 5500 then be ok to redline most of the time. I pulled out all my coil packs after every bit of advice I got pointed to them, and presto, #5 had the carbon shim or whatever you call it, burnt completely in half and fallen out of the spring. Yesterday I finally got a new coilpack, after driving the car around limping under 4000rpm (Yes it hurt ). I completely cleaned out and taped up the new (2nd hand) coilpack before putting it in, as well I removed the other 5 coil packs and gave them a clean and tape up too. However they looked almost new.

Anyway, once that was done, about 5:30pm, I took her for a spin after really letting her warm up. Ran unbelievably, boost built faster than I remembered it doing before, pulled hard all the way to redline, every time, no hiccups at all. I was stoked as you can imagine. Then last night I went to the movies, movie finished about 11:15pm, it was bloody cold. I thought ooh nice, cold air, time for some fun, so I warmed the car up then belted it down the highway on the way home. It started missfiring again, almost identically.... I could have cried.

I thought it might just have been that the fuel system or ignition system wasn't up to it, the air being so cold (And obviously dense), running higher than standard boost without an ECU remap or aftermaket ECU, is this a possibility?

This morning I took out the old culprit coilpack #5, the coilpack is in good working condition still, or I'd take it back, but there is black buildup on it already, like it's fouling up. I'm really confused, seems to be just #5 doing it as the missfire is exactly the same? What could possibly cause this? Faulty igniter? Faulty leads to the coilpacks? The cold air + extra boost + stock ecu not coping with fuelling (But why only #5 and not all of them)????

Any help would be greatly appreciated guys. Sorry for the long post, didn't want to leave anything out.

Cheers,

Ben.

*UPDATE*

Took the car for a drive this morning. Seems that it only missfires when under boost over ~9Psi (Which is what it ran when I got it, it runs about ~11Psi now, after installing the FMIC etc). Anything less and it revs out perfectly.

Could this be a fuelling problem, injectors need cleaning? As I said before, faulty igniter? I'm using NGK Iridium plugs, with the code -11 on the end, which I assume means 1.1mm gap. Would gapping the plugs to 0.8mm help? Remembering this is only seeming to missfire on cyl #5. I was thinking more along the lines of a fuelling problem, but I really don't know, any help would be appreciated once again.

Cheers.

Edited May 20, 2006 by Hakai

[DVS JEZ]

try replacing your plugs and gapping them to .8mm or even just try gapping the plugs that are in there to .8mm.

its very common for skylines running higher boost to blow out the spark.

also by gapping them to .8mm instead of the stock 1.1mm it takes some strain off the coils.

hope this helps.

[Hakai]

try replacing your plugs and gapping them to .8mm or even just try gapping the plugs that are in there to .8mm.

its very common for skylines running higher boost to blow out the spark.

also by gapping them to .8mm instead of the stock 1.1mm it takes some strain off the coils.

hope this helps.

Is there any reason it would only be missfiring on cylinder #5? I've read numerous places that the further back from the plenum you go the leaner the cylinder runs, is this true, could this be why it's doing it to only #5, but if #5, wouldn't #6 be missing too?

The reason I am assuming it's #5 still is because even though I've replaced the coilpack, the carbon shim that contacts the tip of the plug, and the tip of the plug itself seem to be fouling up (With like a black dust type substance) and the other cylinders aren't doing it.

I'll give the 0.8mm gapping a shot, what is the best way to crimp down the bit that overhangs the tip safely without damaging it, is there a set proceedure?

Cheers,

Ben.

Edited May 20, 2006 by Hakai

[The Mafia]

Gap the plugs man, the coil pack on number 5 might be a little weaker than the rest, and can't fire the plug under boost.

The Resistance will be less when the gap is at 0.8mm, and then it will fire much easier.

Don't panic.

[iandawsonwa]

when was your fuel filter last changed

[m.i.c]

Mine did exactly this, was the stock fuel pump, try a high flow one. Worked for me!

[CATKICKER]

is there a correct way to gap the plugs other than smack them on the bentch?

[Hakai]

Gap the plugs man, the coil pack on number 5 might be a little weaker than the rest, and can't fire the plug under boost.

The Resistance will be less when the gap is at 0.8mm, and then it will fire much easier.

Don't panic.

Will do man, thanks. Can't help but panic sometimes though, when the pride and joy is playing up and I don't have all the knowledge on my own to fix it up nice and quick Any special way I should gap them, or just put the spacer in and squash it down?

As for the fuel filter, I don't honestly know. Aren't they legally supposed to change all filters/oils/coolants when the car is first imported from japan? If that is the case then march last year, if not, then I have no clue and will change it as soon as I get the cash to buy a new one New fuel pump would probably be on the cards too I'd imagine.

Thanks for the help fellas,

Cheers,

Ben.

*EDIT*

Oh and lsatly, the coil pack on #5 is a 2nd hand one and even after cleaning it out with de-rust, wd40 and fine grit sand paper it's still not as clean as the other 5, they look like they're brand new, so you're probably right on that one, however, could it be the ignition pack (If that's what you call that square box that feeds the leads to the coil packs) being faulty?

Edited May 20, 2006 by Hakai

[The Mafia]

Will do man, thanks. Can't help but panic sometimes though, when the pride and joy is playing up and I don't have all the knowledge on my own to fix it up nice and quick Any special way I should gap them, or just put the spacer in and squash it down?

Just go and get a new set of plugs. I used Copper bkr6eya's and they were perfect. Not sure if they are the same for the RB20's though. I would assume so, but check anyway.

Will cost you about $18. They come standard at 0.8mm gap. (unless it has a -1 on the end)

[chrissso]

Hey Mate,

You can get a misfire when ECU picks up detonation from the knock sensors because it adds fuel and retards timing. You could have detonation from leaning out. Cold air is denser and requires more fuel. Furthermore your fuel system might not be coping with the extra demand.

I would get the air/fuel checked on the dyno, and maybe your fuel rail pressure.

As stated above, you might need a new fuel pump. The stock ones are old (16 years in your case) and don't pump much more than needed in a gtst. So with 11lbs of boost, it could be your problem.

Infact, the best thing to do IMO is replace the fuel pump anyway and get the standard ECU remapped.

If you already have a new fuel pump,then you might be running to rich! either way, a ECU remap will fix it.

If the a/f ratios are good, then at least if you still have the misfire, you know that the engine isn't going to blow up!!! Misfire issues from here are then resolved with things like sparkplug gapped to .8mm new/repaired coil packs and injector cleaner etc.

[blind_elk]

Was the spark plug in tight? I've often noticed that the plugs seem to be loose when I go the remove them for what ever reason.

If you swap the #5 coil to another spot, say swap with #2 coil, does the problem still happen at #5, or does it then happen at the new location, ie is it the cylinder or is it the coil that is misfiring?

[Hakai]

Hey Mate,

You can get a misfire when ECU picks up detonation from the knock sensors because it adds fuel and retards timing. You could have detonation from leaning out. Cold air is denser and requires more fuel. Furthermore your fuel system might not be coping with the extra demand.

I would get the air/fuel checked on the dyno, and maybe your fuel rail pressure.

As stated above, you might need a new fuel pump. The stock ones are old (16 years in your case) and don't pump much more than needed in a gtst. So with 11lbs of boost, it could be your problem.

Infact, the best thing to do IMO is replace the fuel pump anyway and get the standard ECU remapped.

If you already have a new fuel pump,then you might be running to rich! either way, a ECU remap will fix it.

If the a/f ratios are good, then at least if you still have the misfire, you know that the engine isn't going to blow up!!! Misfire issues from here are then resolved with things like sparkplug gapped to .8mm new/repaired coil packs and injector cleaner etc.

Fuel pump is original I think, as the fuel filter might be too, who knows. I will replace fuel filter as soon as I can and pump when I have the money.

If it was fuel though and I was leaning out, wouldn't it be sensible that it would be not just the one cylinder? Not trying to say I won't upgrade the fuel system, I fully intend on doing it, just a question, trying to get the knowledge into my head heh.

As for a dyno, you live on the coast, same as me, where is a reputable place to go, and what should I expect to pay for a checkup like that? What should I go in and ask them to do? I was considering getting a remap done, should I just wait for that then get it checked, since they recommend getting the A/F ratios checked after you plug in the new ROM anyway?

I already thought of the fact it might be the plug itself although there was no sign of wear or damage on it, so I swapped plugs #1 and #5. I also thought about swapping the coils, but I figure doing it one step at a time is the best way, if you do two things at once and the problem moves to the new location or disappears, you don't know which of the two it was for sure, so I'm about to pull all my plugs out, regap them to 0.8mm and swap coilpack #5 with #1, assuming it's not the plug, which I'll know soon enough.

I don't particularly think the plugs need replacing, they are only 8000kms old, (Same as my oil, I know it's bad, don't shoot me, it's getting done as soon as I get the $90 for a bottle of oil heh, moving house = no money) and they're iridiums, aren't they supposed to last ~25,000kms?

Sorry for all the continued questions, thanks for the advice and insight, every bit helps

Cheers,

Ben.

*EDIT*

This is the ECU remap I was thinking of going with [link]http://grapevine.com.au/~marzenna/[/link].

Unless you can tell me of a better one, possibly one that's done in house on the gold coast, obviously I'd prefer that to a mail order one. And also I hear alot of people saying copper plugs are better in the RB engines than iridiums, true or false, what brand and part number am I asking for if I get coppers for an RB20?

Edited May 21, 2006 by Hakai

[Hakai]

Well I habe some updates, good ones!

I pulled out the coilpacks after I wrote my previous post, and remembering that I'd swapped the spark plug from #5 and #1 around. It seems the fouling on the top of the plug, followed the plug! So #5 was no longer fouling at all and the top of plug #1 was fouled up. Conclusion, maybe the coil pack when it was faulty and arcing, or whatever it did that caused the carbon to burn away and wreck the coilpack, damaged the plug as well and reduced its integrity under load?

Either way I took out all 6 plugs, regapped them to 0.8mm and took it for a spin. After a few 2nd through 3rd 6000rpm runs with no missfire I was smiling Did my shopping and retested on the way home, still no missfire, I'll give it another test tonight in the really cold to see how she goes then. Either way it's not missfiring now, and it feels a little bit smoother to drive too and the exhaust note seems to have changed ever so slightly, but my exhaust is so quiet I might be imagining it, just sounds a -tiny- bit throatier. Maybe I just wish it was

Thanks to everyone for the advice/help, it's much appreciated. I still plan on replacing the fuel filter and pump, and the plugs/oil, it's all just a matter of money isn't it

Anyone know anyone on the Gold Coast looking to hire a casual for some 6-12pm shifts monday to friday? Need a 2nd job, afford make car go fast hah

Cheers all,

Ben.

Edited May 21, 2006 by Hakai

[NewKleer]

did u replace that plug then? (the one that was in 5 and now 1)

[Benno31]

I had a similar problem, i have since found a dud o-ring seal on injector 6 which could be to blame.

I will post if i have success.

[Hakai]

did u replace that plug then? (the one that was in 5 and now 1)

Not yet. As I said, moving house and getting screwed out of $2,000 severence pay from old job = bad finances at the moment, I'll be replacing all 6 plugs with 0.8mm factory gapped coppers as soon as I can afford it.

That said, with the plug gapped to 0.8mm it's running fine for now, which is good