Another Rb25 Misfire Topic

[fmlycar]

Soooo, I have a s2 rb25 in a stagea. Power FC, splitfires, z32 afm, td06, nismo 550cc injectors, gtr fuel, tuned at 18psi.

Has been running fine for 6 months until yesterday it has developed a misfire under load and full boost. Seems ok at very light load and cruising.

Has constant miss when you stand on it and try and rev it out, also get a lot of black smoke out back.

Knock doesn't go above 18 with this happening.

I checked injector value in pfc and it got up to 90% just once, normally around 68-70% WOT. AFM voltage with car off is 0.42v according to the power fc and 1.72v at cruise approx.

I took plugs out (bpr7es gapped at 0.7), and swapped with some other spares I had laying around (not new but known working) and made very little difference.

I sprayed all the vac lines and hose clamps with brake cleaner but no change in idle speed. I did find 1 loose hose clamp after the turbo outlet under the air filter, but after tightening that, no change has been observed.

It was dark when I got into changing the plugs so I couldn't inspect the coil packs thoroughly. Might get around to it on the weekend.

Any suggestions.

[Ben C34]

Boost leak.

[GTSBoy]

Boost leak.

Could be. I reckon it sounds like a spark problem. Black smoke either way.

[Hadouken]

gearbox

[fmlycar]

Cleaned afm, no change. Pulled coil pack leads 1 by 1 and idle got rough with each one. Seems to be when you get close to building boost it starts and then sputters then entire time on boost. Idles like normal, doesn't stall or dive.

[Ben C34]

Cool story.

[fmlycar]

That ain't going to help.

Tps voltage is 0.44v at idle. Check power to all coil pack plugs (14.19v across all 6). Unplugged afm and car died straight away.

I'm a bit stuck as to where I should check next? I went to repco and they didn't have any bcpr6es or bcpr7es on the shelf. I would have to order out of adelaide. I'm located alice springs so I can't just duck into a workshop with a dyno and it's my daily so I really wanna get this sorted

[STATUS]

try a set of bcpr7eix gapped to 0.55mm. should fix it.

we do around 10-12 skylines a week and 9 times out of ten it will fix the really persistent misfires.

[fmlycar]

Thanks. I'll see if I can get some locally otherwise I'll order some

[Hunky]

Boost leak.

[fmlycar]

New plugs are in but only gapped at 0.8. Hesitates still coming onto boost but then clears up and revs clean through to redline. Makes the same amount of boost as normal once it gets up and goes. would pulling the gap back further make much of a difference that early in the Rev range if it clears up and revs clean after about 7psi?

Idles perfectly, and drives off boost as it did beforehand.

Also checked timing, 20deg btdc cold and fuel filter is new.

Hasn't got any leaks that I can see, no smoke from and where when it's running.

Edited July 9, 2015 by fmlycar

[fmlycar]

Pulled gap back to 0.6 and taped coil packs. Better, but still there.

Comp tested 150, 150, 150, 145, 150, 150

Still possibly coil pack if it got a little better with some tape

[Ben C34]

Yu can't see a boost leak.

[fmlycar]

I've checked all the hose clamps and vac lines and nothing seems suspect. I might try removing all the hose clamps and joiners and inspecting them all off the car

[GTSBoy]

Do a pressure test.

[Hadouken]

Yu can't see a boost leak.

Do a pressure test.

Do a smoke test

[Ben C34]

You can easily hear or find with soapy water a boost leak when pressure testing.

It's easy to make an adaptor for a compressor. I don't know anyone with a smoke machine.

[GTSBoy]

I don't know anyone with a smoke machine.

Just ask an R31 owner.

[fmlycar]

I'll duck into Reece plumbing and grab a pressure cap today then.

[iruvyouskyrine]

Just ask an R31 owner.

I don't understand. What is this. Will it fit in my RB30? just looking for a bit more power from my completely standard auto NA 1985 R31 that has 385,000 on the clock. Want to spend as little as possible thanx.