Cutting In And Out Of Power At High Rpms - What's Up?

[benro2]

Hi guys, done some searching on here already and can't seem to find anything that matches exactly with what's happening to my car. Might be best to tell the whole story just in case I've missed something...

It's an R33 GTS-T and it started misfiring at idle at about 80,000 km's, which is about 30,000 km's after I bought it. I was messing around with a boost controller which was making the car R&R so I naturally thought I'd just clogged the spark plugs or something. It wasn't too bad to drive, just a bit annoying when it was idling as sometimes it would misfire when the A/C compressor turned on, or at random times.

Then very recently I took it in for its 100,000 km service, and the spark plugs were replaced with platinum plugs (I think - they were damn expensive anyway!). I expected this to fix the misfiring problem, but instead, it came out 10x worse! It now felt like about 2 or 3 cylinders misfiring and sometimes the car would nearly stall at idle. This only seemed to happen after the car had warmed up and had been driven for a bit and could be improved slightly by raising the idle speed by about 100 rpm. However, at full throttle and high rpm - say at about 4500-6000 rpm - it would cut in and out of power, as though several cylinders weren't firing at all. I didn't get any pops or anything, just a complete loss of power, randomly, for a split second.

I took it back to the servicing place and they said it was a faulty crank angle sensor, but I'd have to take it somewhere else as they didn't have the equipment. Took it to the other place and they got a specialist in and he said I needed new coilpacks, so I replaced the factory items with Splitfire ones. Now the car seems to have slightly more power, however I still have the high rpm cutout problem. It seems to be pretty random in whether or not it cuts out, and by how much. The other day it seemed to be almost back to normal, but tonight it was really bad.

I'm currently only running 5 psi boost so it's definitely not R&R. Any ideas? Could it be the crank angle sensor, and if so, how much are these and how hard are they to replace?

[trel]

Try changing the coil pack loom, check that theyre plugged in properly. Maybe even clean the contacts with some crc and check for fraying and damage to loom, after that could be ignitor. The problem with this is it could be many different things, just a process of elimination now. What else can I think of? Try running a diagnostic too see if any error codes appear that might help you diagnose it.

Good luck.

[benro2]

Thanks for the help - I'll check all that out. I think I'll probably get my mechanic to run a diagnostic on it because the original workshop seemed to think the symptoms (misfiring at both low and high rpms) are consistent with a faulty crank angle sensor. If that fails, I'll try all the other stuff.

Oh yeah, tried another WOT run today, worked like a charm! Dammit I hate inconsistent problems!

[NZM.031]

im with you mate, currentlyt having dramas with a 32 i just bought.

have you checked your coilpacks?? at 80000kms is about when they let go... and if you upped the boost, they would have been struggling to manage, and if youve replaced the plugs with iridiums then again... they will be working that bit harder. also, sometimes if you get the problem quick enough and then wind the boost down... it can be a temporary fix... but if it does damage and they crack the silicon stuff around them then they are just about dead... you can eleco tape them up to get around but not a good fix either. also try gapping the plug down a bit. 0.8 is a good point as standard skylines run 1.1mm, means the coils dont have to build up as much spark to cross the gap.

also it could be an air leak. heck, it could be lots of things, but start with the simple and obvious is always good.

cheers

Linton

[benro2]

Yep, I've just replaced the coilpacks, and that fixed the misfiring at idle. Now I've just got the high rpm power problem. I think I must have had two separate problems - so I've fixed half now, and I'm hoping it actually is the crank angle sensor for the second half.

As for the boost, I've been running on the stock wastegate pressure (~5 psi?) for several months now - basically because I was messing around with the solenoid before and can't be bothered returning it to normal Well, actually I have tried to get it back to normal but it doesn't appear to be working... but I'll figure that out later - not much point in going for *more* boost when there's clearly a problem!