Hi guys
I've a very strange problem with my nissan sunny ( pulsar ) gti-r egnn14 with sr20det redtop.
I say strange because I've tried to check everything but without solve.
I use car in autocross race with stock engine, 0.9 bar boost and direct handmade exaust, 102 octane gasoline.

After I rebuild the head gasket and valve I've notice the problem.
If I start engine it sound perfect, work fine and take revs smooth.
When I open full throttle, boost going up and after 4000-4500 rpm engine seems to work 3 cylinder!
If I open partially throttle I take rpm smooth and engine sounds good, but if I open all gas go in shit!!!
I've checked and change spark plug, all ok
check electrical parts, plug wire and distributor and all is in perfect condition
check for bad electrical contact but all ok
connect direct fuel pump because seems to work bad with original wiring, but not solve ( seems to be solved because going better but after go bad again )
check fuel pressure on rail and something make me doubt, normal at idle is 3bar and when i open gas go less???
If you think the same that i think, now i want try to test two fuel pump working in parallel for understand if problem is amount of gasoline ergo fuel pump old...
Regards to all

May the gap on the spark plugs be too wide (blowing spark under full load and idle open throttle??)??

do a fault code test and see what you get, could be the knock sensor

May the gap on the spark plugs be too wide (blowing spark under full load and idle open throttle??)??

Tried to modify but nothing... Idle perfect, loose power and sounds like a boxer only with full load and hi rpm, if work engine without pressure o with half throttle or less go fine.

do a fault code test and see what you get, could be the knock sensor

Tomorrow I want try to put in diagnostic the ECU.
But if knock sensor is in fault is possible to have this kind of problem? normally it retard ignition if engine knock but here seems to have a boxer engine...

yes a knock sensor fault will cause a misfire

knock sensors on older nissans are a joke, I don't think I've seen a 90's nissan without a knock sensor code, from what I hear they don't do anything over 3k rpm, there's a reason they don't throw a check engine light...

I was going to suggest spark gap but someone beat me to it.

You aren't running individual coil on plugs are you? A lot of time's cops will run fine at idle but under a load will misfire like crazy. Some times when you have low compression in one cylinder it'll act like that too.

It's obviously a load issue, something isn't getting enough fuel or spark.

I don't remember if 90's nissans have a misfire counter in consult. That would at least allow you to pin it down to one cylinder.

as mentioned above - first check for fault codes - but also:

vacuum leaks? (all intercooler/intake hoses/clamps/etc...)
correct timing? (20º BTDC)
correct plugs? (heat range 7 or 8)
compression? (more than 135psi, and under 14psi between cylinders)
fuel? (pressure 36psi with vacuum on, 43psi with it off - pump & fpr)
catalytic converter? (collapsed)

Tnx to all in advance :)

In the last days I've test all, fault code, sensor, throttle sensor, maf, relè, all wiring connection...

All is in perfect condition and no fault code (55)

I've put a gauge after fuel filter for take under eyes the fuel pressure...

I've notice 2,5bar at idle, 3bar running engine without turbo pressure...
It's all ok... but the strange is when turbo go in pressure, because with 1bar of boost and a 1/4 of gas pedal fuel pressure is almost 4bar ( 3bar +1bar boost) and engine work fine...

When I open all throttle the pressure go down almost 3,3bar......... and engine seems to work at 3 cylinder....

I've changed the orginal fuel pump with two pumps walbro 190Lph in parallel ( i've those in garage and i don't want buy a new one) but the problem is still present........

Now i've dismount the original fuel pressure regulator, but I don't know if i can clean something or if I can only change it.

check the voltage to the maf, check gap on plugs it should be 0.44 on a plug gapper tool, also get a new fpr and see if that help also double triple check all your intercooler pipes and cuplers for cracks holes or anythink other then the normal, u would be shocked what u could miss without a true pressure test on your ic pipes

If you havent already tried I would close the gap on plugs to .25-.28 see if the miss stops. Then if it miss stops increase gap in small increments.

Otherwise i would look at ignition timing and fuel delivery.

i've dismount the original fuel pressure regulator, but I don't know if i can clean something or if I can only change it.
it's not really a serviceable item as such...

When I open all throttle the pressure go down almost 3,3bar......... and engine seems to work at 3 cylinder....
try running a direct ground/negative from the pump to chassis,
or even powering it directly: http://www.gtiroc.com/forums/showthread.php?t=59944
(there has been a slowly-increasing number of owner reports of deteriorated wiring over the last few years)

I had a similar problem on my NXR. It turned out to be a plug lead in the head was cracked and it was shorting out in the hole in the head. If you pulled it out and looked closely, you could see the crack and you could see it sparking in the head.

I have exactly the same problem. Have you solved it or you are still trying?

most of the time when it starts bugging over 4000rpm on boost, its a air leak issue. cracked coupling, leaking blowoff valve.