Oh God Not Again... Strange Hesitation

[rsmithdrift]

And when I say strange I mean it... Car info first though for those who don't know.

93 240sx SE Fastback 5sp KA24DE with 248/232 cam swap intake and stock exhaust
NO EMISSIONS AT ALL
NO PS
NO AC
New MAF, O2, CTS, Injectors, FPR, Fuel filter, fuel pump (walbro), spark plugs, cap, rotor, wires, coil as of 6 months ago

I have the MAF control wire and CTS control wire run with a wire directly from the connector to the ECU to improve continuity and retain the proper signal to the ECU.

Runs consistently 12:1 on A/F gauge.

The last 6 months this car has run like a champion... then today something felt wierd. Made me get out of the throttle wierd. I heard and felt something at 4k rpm in 4th gear at WOT like the car jumped back on me. Like The fuel cut out momentarily, sounded and felt like a rev limiter.

Turns out after testing it all day long it's consistant as the day was long. Everytime at 4k rpm under acceleration the car hesitates badly. The wierd thing is that it only does it for a split second and then goes back to normal with full power, then does it again around 5k rpm. EVERY SINGLE TIME. I have no power loss at all. It just feels like I'm hitting a rev limiter for a split second almost. Like I'm totally loosing spark momentarily. My A/F ratio never changes from 12:1 during all of this either. No smoke or smells coming from exhaust either. Oil is perfect.

I don't have a clue what to think. Could something cause the ignition to cut out momentarily??

[rsmithdrift]

Ok... so an update since things have changed a tad bit. It no longer cuts out consistently, or completely. It now just feels like a very unstable power band where power comes and goes seemingly randomly throughout the powerband and feels like something is holding it back greatly. Even at low throttle it almost feels like I'm riding the brakes a little bit, like thiers a ton of friction in the drivetrain somewhere. Just to see how much power I was down I redid my 0-60 testing in the same road the same way I did before.

My 0-60 times have risen from 6.3 to 6.5 consistently to 7.1 to 7.4 and are much less consistent.

My A/f ratio has remained unaffected by all of this btw. It's still at ~12.1 no smoke no unusual smells no backfiring or missing at idle. It's very odd. Maybe ignition problem of sometype?? IDK and if so why??
I have no clue what it's problem is.

[ghx407]

Cheap fixes first - check for vacuum/exhaust leaks and spark blowout (close the spark plug gap to .028 and see if that helps).

[MyKAkillsV8s]

thats exactly what i would have said spark plug gap bro. use a bkr7e ngk plug .028

[rsmithdrift]

that's exactly the plug I use... but I thought the NGK already came pre-gapped to the proper spec which is like .044 or something??

[Pyrosynjection]

The only plugs that come pre-gapped are the Iridium's and Platinum's. Copper or Resister type plugs need to be gapped.

[rsmithdrift]

well turns out my plugs are the bkr5e 11 not the 7e. (they are NGK's OEM replacement plugs)

But at any rate I changed the gap from .044 to .028 and it really helped my top end. Power comes on smooth and hard. Maybe a little more sluggish at bottom end and a little more peppy at top end than it used to be if anything.

But ofcourse, a side effect of this is that now I have a random missfire at idle because the plug gap is too small and that is something you CAN see having an affect on the A/F gauge. But I'd much rather have a miss at idle than a uneven, sluggish power band any day.

0-60 times are in the mid to high 6's now. And considering my tires are two sizes bigger than they were when I put in the 6.3 average, that seems about right, since my gear ratio's are longer now.

So THANX FOR THE HELP GUYS

[ghx407]

If you're running a NA KA with stock compression and use your car for mostly daily driving, you should try to stick with the OEM plug and gap spec. Colder plugs are not as good at burning off carbon deposits on their tips, so they tend to foul up quicker and should be used only if the driving conditions or engine modifications (higher compression/forced induction) require them to prevent detonation. As for the gap, larger gap = bigger spark = better power/efficiency. So the ideal gap is factory spec or the biggest one you can run without getting spark blowout.

The fact that your situation improved with a smaller gap shows that your ignition system probably needs some maintenance. In other words, the current reaching the spark plug tip is no longer enough to arc accross the stock gap, but it's enough to arc accross the smaller gap you just dialed in.

[rsmithdrift]

my cap and rotor suck. They are new factory replacements from autozone within the last 6 months but they still suck.

the power coming from the coil is enough to knock you on your a**. the power reacing the plugs is barely enough to arc from the plug wire to a valve cover bolt when disconected and pressed close to it.

I'm going to get an MSD 6al ignition and blaster 2 coil and some pulse spark plugs asap which will be in a month or so. That should hopefully solve the problem.

[Adam240sx]

auto zone sucks!! replace that junk with new better parts...

[rsmithdrift]

What do you recomend as far as a cap and rotor go?? I can't find a decent one anywhere. I guess MSD doesn't make one for our cars.

[Adam240sx]

Well I would just stay away from Auto-zone/crap for mechanical pieces on your 240sx. Speaking from personal experience with their crap parts and countless friends and there parts failing. I would recommend the OEM cap and rotor from a better supplier. Napa is good!! Or purchase online from a reputable dealer.