pcmhacking.net

Hi guys, I have an interesting one

VR304 setup with standard ignition, standard NGKR plugs
286 crow cam with memcal, double valve springs, roller rockers, headers and 2 1/2 twin system, no cats

The problem is the old plugs only lasted 15months, with really only 2 months of driving. This is the second set of plugs BTW
Old plugs look clean with no visible issues but the engine hesitates and misses around 1500RPM but then goes well above 2000RPM.

I have put new plugs in it and there are no more issues

Things i have checked/changed

Checked: fuel pressure, 45psi turning on ignition, settles at 42psi once the pump stops after 2 secs and doesn't drop, idle 37-38psi, all as per spec from the manual, pressure stays around 35-38 psi when blipping the throttle
: fuel pressure reg checked ok
: base timing set at 10 degrees, goes up to 26 degrees when running
: all earthing checked ok and cleaned up
: plug gap set at 0.8mm as per the manual
: new plug leeds since motor rebuild
: coil resistance with in spec as per the manual
: ignition module changed but made no difference, put back the old unit
: new dizzy with the motor rebuild
:O2 sensor doing it dance once warmed up

Changed: found a faulty injector 7 of the 8 measure 15.8 ohms cold, 1 measured 23 ohms, these are a new set of injectors so I had to buy 1 new injector.

I'm really at a loss as to why the plugs won't last, I have full time monitoring going on, AFR starts out rich when cold then sits on 14.7:1
So at this stage she's running great with new plugs, go figure, I'm wondering is there a way to check how much spark there is as I recon something is going on with the ignition system killing the plugs

Have you tuned the ECM ?

Spark plug gap .8mm?

Mikestech0 wrote:these are a new set of injectors so I had to buy 1 new injector.

Sniffs like knockoff garbarge. Get a used set rebuilt and run with that.

Read my mind...

Me too, I always run good uses sets or fork out the 80-90 odd each for modern genuine Bosch units. Or FoMoCo USCAR type injectors if I can be bothered rewiring the loom for USCAR plugs.

I found the green 777 ones great replacements for the old leaky clunckers the VN-VR had and it saves me having to get any other non standard sets sent to The1 for calibration data generation as the data can be pulled from later MAF tunes but I found them to work fine as is too. Same with the L67 injectors, look for yellowed 2nd hand units. Pure white they are fakes 99% of the time unless you are paying said 90ish bucks each.

What brand and part number spark plugs?

Well i think i have sorted the problem.
Put a MSD blaster coil and no more missing. Plug gaps are still at 0.8mm but i might go 1mm

bigger spark might be hinding a real fueling problem. injectors or tuning.

The symptoms you described tells me it was a weak spark problem. When you think about it theres little more than a coil that could have caused the problem.