Tomei Poncams - RB26 - HELP!

[Amaru]

Topic pretty much sums it up quite nicely. We installed some Tomei Poncams (260in/ex) into RB26 and have run into some problems, and I just cant work out what it might be and were runnning out of ideas, fast.

Basically, when you start the car from stone cold, when the car comes up to temperature and you put your foot down it starts missfiring. It does this for a while then when the car gets even warmer, stops missfiring and will run perfectly, until you start and warm it up from stone cold again. This only started happening since putting the camshafts and camgears in. The camgears are set to +2 inlet and -4 exhaust.

Its not coil packs, all have been checked, and we also used a known good set from another GTR, same goes for ignitor pack. Its not running overly rich, as I pulled the plugs just after it started missfiring and they're clean.

There is a wierd thing happening we have noticed however, in the power fc under the 'etc' menu you can check the status of sensors whilst the car is running. While the car is cold it doesnt have a "lumpy" idle and both AFM's on idle read around 1.1v. When the car warms up it gets a lumpy idle and the AFM readings get erratic and are not even across both, e.g AFM-1 is 1.2v and AFM-2 is 0.7v, then they will switch around so AFM-2 is 1.2v and AFM-1 is 0.7v. When driving however AFM-1 always reads a higher value than AFM-2. Car has apexi pods and both should be getting equal amounts of air. This was never a problem before the camshafts were installed, airflow across both was always pretty even. We have also tried another set of Z32 AFM's and had the same problem.

If anyone can help as to what it might be, would be most appreciated!!!

[cameron]

Could be your Crank angle sensor, might have been droped or just could be faulty. If it gets wrose and only miss fire's at a certain rpm its your CAS.

Had the same problem on one of our 33's were it would always miss at 3k and would never go over - due to the timing being advanced to much as the rpm goes up and the ecu would put it in a sort of home limp mode. this is at full operating temp though. but when it was still cool it would work fine. the timing was way advanced because it was faulty so the new cas makes it feel like a slug.

Could be spark plugs - common thing.

Fuel related ?

Afm's dirty wire ?

AAC valve sticky

What RPM is it missing at ?

As for the afm's spray them both with brake cleaner to un-dirty any dirty wires.

other than that its hard to tell with out seeing the car myself.

Jun

[Amaru]

Could be your Crank angle sensor, might have been droped or just could be faulty. If it gets wrose and only miss fire's at a certain rpm its your CAS.

Missfires at certain RPM, but when I start the car stone cold I putt around changing at 2500rpm until water temp is ~80deg and oil temp ~70deg and oil pressure has dropped to stable 2bar on idle. Then when I put my foot down, around 5500-6000rpm it starts missfiring. When the oil temp rises up to ~90deg (no oil cooler) the car usually starts driving fine.

Could be spark plugs - common thing.

Plugs seem ok, as said, car isnt running overly rich and fouling the plugs etc.

Fuel related ?

Fuel is ok, car has Sard 700cc injectors with GTR pump in tank lifting to 2L surge tank and Bosch 044 main pump from surge tank. Will get fuel rail pressures if you think it would help?

Afm's dirty wire ?

I cleaned inside the AFM (sparyed using carby cleaner) on the weekend to no avail. What should I use to clean the electrical contacts on the plugs?

AAC valve sticky

Havnt checked this yet, thanks

What RPM is it missing at ?

Around 5500-6000rpm (making 1.25bar boost at this rpm, HKS 2530's).

Also driven it so it missfires with some "ears" on the engine and it is not detonating at all.

[Abo Bob]

Just a suggestion but have you tried setting the cam gears back to zero and pulling base timing? If the second part worked you may just have to slowly wind it back in the usual way.

[cameron]

Does it go past 6000rpm or just stop their and hesitate ? and does it missfire when free reving or only under load/boost.

Have you tried turning the boost down to see if it goes away. As your coils could be arking the spark out the side of the rubber boot. - their was a recent thread about lighting from his coils at night. - from arking out spark you could check that.

Yep the timing might be out set it back to standard 15º with timing light and go from there. And same as what Abo Bob said.

Jun

[magic1]

gap your spark plugs down further?

[Amaru]

It will slowly go past, the car doesnt hesitate as such, just goes "brrrrrrrrrrrrrr" as if its hit a rev limiter. Doesnt miss when free revving, only when under load.

Before the camshafts were installed the car was running 1.5 bar boost (has all forged internals) and since the camshafts were installed we've brought this back down to 1.25 bar.

The coils seem ok and never had a problem on the higher boost level, theres no cracks in them etc, they look like brand new. We also tried another set of coils with the same problem.

So set the camgears to 0/0 and the timing should be 15 degrees when on they're set on 0?

Will give it a go tonight. I would have thought if it was a timing problem it would be happening all the time though?

[cameron]

Did you check over everything you disconnected in the engine bay.

You'll need a timing light to set the timing back to standard.

Jun

[rev210]

Hi there,

Got the same issue with the factory ecu and modest boost (boost restrictor pulled). Although it initially didn't carry on like that all the time.

I suspect the plugs. Plug gap and heat range in my case. Bottom line is the fuel and ignition maps need to be reworked to suit but, I've been lazy. I've got a PFC pro just sitting around waiting to go in.

I'm changing them today so I'll let you know if it fixes the problem. It sounds exactly the same down to the oil temp.

[Abo Bob]

Maybe this is too obvious, but has it been retuned with the new cams in. I mean could there be something in the previous tune that doesn't sit right with the cams?

You've got us all hanging to find out now

[Amaru]

Maybe this is too obvious, but has it been retuned with the new cams in. I mean could there be something in the previous tune that doesn't sit right with the cams?

 

You've got us all hanging to find out now

It has been re-tuned, when the cams were put in and car started on old tune, it was running EXTREMELY rich (just touch the throttle and there was mountains of black smoke).

After it stops is missfiring escapade, it runs beautifully and AFR's are nice and clean.

Will fiddle with the timing tonight and try a new CAS, see if that makes any difference.

Will let you know of the outcome, and Im still open to more suggestions of things to try

[pnblight]

try water sensor circuit back to ecu sounds a bit like your not getting cold temp compensation and i believe the sensors right where you would have been working

pete

[raist60]

Have you checked your actual ignition timing properly? If you just marked and re-installed then it will be wrong. They keys get whacked in pretty roughly by tomei.

[raist60]

pnblight its the other way round. If the signal from watertemp goes missing the car keeps enrichment on at all times and runs like a pig at idle as well.

[rev210]

I should have added that in my experience with knackered plugs, as I think mine are, they can be fine untill you stick them under load. This is with plugs that have been too rich. They get muck in them all over the place.Although you might pull them out after sorting the mixtures they are still fouled inside and around the electrode even though they look sort of clean. In this state an ultrasonic bath can clean them but, with copper plugs who cares just chuck them in a bin.

Since I drove around for quite some time with crappy rich rough idle I did enough fouling to permanently root the plugs up. I found out last night when against my better judgement I thought a trip to the drags would clean them by the second run...wrong! They went from bad to worse. two runs and I went home knowing I sould have changed the plugs. For those interested in how bad the plugs were I only ran a 13.2 @ 102mph. The plugs wouldn't let me past 5,000rpm without carry on, let alone a good launch 1.9 60ft (bog down under load thanks to the plugs).

Bottom line is if you run too rich for too long the plugs become rooted, no matter how clean you get them afterwards they just never work as well again. Yet another reason for using cheaper copper plugs when tuning things up for the first time.

[Amaru]

Thanks for the suggestions everyone.

We have changed the plugs in it several times since the car ran overly rich on idle to no avail. We are using BCPR6ES gapped at 0.8mm.

Will take the timing back to stock tonight and see how we go and get back to everyone

[rev210]

Amaru,

6's are a bit hot for higher rpms and boost I reckon. Go for BCPR7ES.

[rev210]

you should be able to tune out the lumpy idle. When I bolted in my PFC pro for a quick muck around I was able to take out the lump within a few minutes with some timing and fuel map changes, you need to raise the idle rpm a little as well. The AFM voltage difference is not suprising since the ecu averages them out it's not a problem. The position and pipe shape differences will always introduce different flows through each AFM.

If it has a lumpy idle and associated poor combustion it will foul the plugs pretty quickly, these aren't really big cams so a lumpy idle is not something you need to live with nor do you want to given the plugs last a day of driving around before their high load capabillities are shot.

[Amaru]

Ok since my last post we have changed some things on the car.

Changed the CAS, no dice, still missfired.

Timing was played with and the more the exhaust was advanced the better the car ran. It now seems to be running pretty decently on -2 inlet +6 exhaust. Now the thing is this goes against what everyone told me reccomended settings were to start with of +2 inlet -4 exhaust. I guess every car is different and needs different settings, but these are way off from what people told me, unless I got it mixed up and was -2 inlet +4 exhaust as optimal settings to begin with?

[Emre]

Rightio... This makes you the second person who had a positive result by advancing the exhaust cam on Tomei poncams.

As their Gts-t cams, if the profile is quite different to factory spec and already have a lot of retardation built into the cam, it's quite understandable.

Who else is running poncams on an RB26...?