(32 Gtr) Odd Missfiring At Low Revs (idle To 3k)

[Wobbz]

Hey peoples...

Long story short, bought a GTR a while back, missing an engine. Got that sorted, with a rebuilt 26 (basic rebuild... head cleaned with new stem seals, re-honed bores, new bearings, rings etc etc.).

Anyhow, that's gone in, but now some nasty problem seems to have reared it's head... the damn thing misfires at low/medium throttle, at revs below about 3 grand. Now, the last owner must have had some type of nasty race gas in the tank, or some additive, as it sat in the driveway for about a year and half before the new engine just recently went in. Basically, whatever was in the tank, completely f*cked the bosch 044 that was in there (it was seized, and covered in yellow flakes... almost looked like sulphur?), and turned most of the rubber lines into a gooey mess.

Needless to say, the tank copped a clean out, and a new pump (small Walbro) and rubber lines were installed, along with trying to flush any possible crap out of the steel lines, if it was in there.

So, now i'm stuck with the missfiring issue... after installing fresh plugs, it'll start missfiring shortly after on one or two cylinders at low rpm (ie. idle till about 3 thousand revs). The missfiring seems to disappear as the car comes onto boost (~2800-3000rpm), and it'll pull hard to redline with no real issues at all.

We've been pulling off the new fuel filter, and cleaning it out with air compressor, and sometimes *really really* fine black particles will come out, almost like fine bits of vaporised rubber which may have been still left in the tank/steel lines?

Anyhow, after going through a couple sets of plugs today, I've found that it's cylinders 1 & 2 that are running pig rich, coming out completely sooted up after only 5 minutes of going for a spin... so this leads me to believe it's more likely to be an ignition issue, with plugs not being the answer. I've tried cleaning the original platinum's that were in there (NGK, 7's), tried my mates NGK iridiums (5's), and then tried the current NGK coppers (BCPR7ES). All were gapped to 0.7mm.

So, I'm guessing its one of the following:

Knock Sensors

Coils

Crank angle sensor

Ignitor module

I'm going to test the coils, CAS, and ignitor tommorow, as I've got a spare set in my 32 GTS-t to play with... but does anyone else have any ideas?!

I've had coils die in the past, but it appears that usually when they die, they missfire under boost/higher RPM? This is basically the inverse of that...

Oh, and I can rule out the airflow meters, well, at least for now... I borrowed a set of very good condition ones, which are known to work flawlessly. While they made the car run *slightly* better, it didn't fix the issue... i guess they're just slightly better condition

Another mechanic suggested i try running this green fuel additive called "Fuel Set" to try and clear any shit out of my tank/lines? anyone have any experience with this?

Sorry for the long read peoples, cheers in advance for any suggestions...

Edited August 23, 2010 by Wobbz

[DVS JEZ]

take the injectors out and get them flow tested and cleaned, if there is crap in them they might not be spraying correctly

[Wobbz]

Cheers for the advice mate, worked out what it was though! The diaphragm in the fuel pressure reg must be split, as fuel is making it's way down the vacuum line, which connects to the manifold near cylinders 1 & 2... so i'll be changing that out in the morning, should be right then! Obviously during off-boost it's under vacuum, drawing fuel into the manifold, then while it's pressurised under boost, it's keeping most of the fuel out!