Extreme breakup upper RPMS
 

Hello guys, I am having a MAJOR problem at upper rpms

i have always had a minor breakup where the car stutters above 7k to 8k

today i...

- changed plugs from ngk 9's to br10eix's all the way around (didnt change their gap)

- routed my profec b II to setup number 2

- added 2.25in restrictor plate to my exhaust

I took the car out for a test run after warmimg up to 180F

- car pulled EXTREMELY hard like never ever ever before on hte first turbo..with a hard but snappy transition and super duper hard 2nd turbo up to 6k rpms

after 6k rpms the car hits a brick wall...its almost like an RPM Limiter...i CANNOT push the car past 6-7k RPMS and it gets worse the higher i try to push it...the boost drops off considerably as well

i tried turning up the gain to 25% on the boost controller NOTHING helped....same issues with boost controller off....when the 2nd turbo comes on pulling past 6-7k yeilds major breakup with what soudns like very suddle quick backfiring

HELP!...how can htis possibly be the spark plugs as these are higher cold stepped plugs to fight this issue up high...and i'm only pushing 10-11lbs of boost i have my PFS set for 12lbs for fuel safety

HELP!!!!!

ive done some research on gapping

is it possible that leaving the out of the box gap of .028 is too large causing breakup on the stock igition at high rpm?

should i pull them out and reduce the gap down to .022?

These plugs don't have any way to adjust gap.

You might want to check your ignition coil harness. Sometimes they ground out and there is an updated version available from Mazda.

Dave

dgeesaman, he's not using stock plugs.


Monsterbox, changing the gap might help a little bit, but I suspect there is something else wrong. Personally, I would measure your spark plug wires and ignition coils as well. The specs can be found in the service manual. I remember posting measurements after replacing spark plug wires a couple years back, you might find it by searching under my username.


edit: found the thread. A few people offered help on how to test ignition coils, there's some great info in there.
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/testing-ignition-coils-spark-plug-wire-corroded-408014/

-s-

If you are using the Peter Farrell ECU, some people experienced fuel cut in the upper rpms. This was due to the ECU being overly sensitive to the knock readings. To combat this, they would relocate the stock knock sensor to the rear rotor housing.

I'm not saying this is 'exactly' what you are experiencing, but this is something to take a look at as its fairly common with that ECU.

Two more comments then I'm done:

1.) A fellow racer was having trouble tracking down a misfire that would happen at different RPMs, especially when the engine was under a lot of load. After double-checking a LOT of igntion-related things, including relocating his ECU further away from the coils (gutted interior, aftermarket coils, and this wasn't an RX-7 by the way), he eventually found a clogged fuel filter. Replacing that solved everything. This is a guy who has been racing for years, and has a very good reputation for knowing his way around an engine bay. In the end, it was a very simple problem that seemed more complex because we all were assuming that misfires are always ignition related.


2.) I'd like to hear how long your plugs last, I've never run anything colder than 8's leading. Another tip: The BR_EIX iridium plugs are nice, but I've since switched to BKR_EIX plugs, which use the smaller ( 5/8" I think) spark plug socket so you don't need any special tools to install them. I haven't found them in heat ranges past 9, however.


-s-

well i shaved the socket on a lathe it looks like it was made as a thin-wall as it is shiny and perfectly even...ill be selling them soon

anyways,

I can't see how this could be anything other than the plugs...i was driving it up to 8k rpms the other night on some 0-120 times not to shabby of breakup...i think the plugs are just incorrectly gapped at .028 and my ignition system was weak to begin with...

ill change the wires ASAP as they feel really dry andd they are hard to "clip" onto the plug tips

here are some other symptoms i have had the past few weeks that may narrow this down

- hot starts, when i start the car it will start up very fast idle perfectly for 2 secs and die down very smoothly until it stalls out (no shaking or anything) sometimes i have to hold the throttle in to keep it alive until it "catches"

- with the new plugs in ill be driving and feel it randomly buck at a steady rpm out of no where..feels like i'm riding a camel

May be the fuel pump or restriction in fuel supply.
Do a fuel pump volume test or scope the pump waveform with an ocilloscope.

Warm your car up to 200-210 degrees, and try it again. It may be that your ECU "thinks" the car is not warmed up, and will not allow full power at higher rpms.

Get some Autolite AR-3933 or 34 and try them. These are racing plugs, obtained at your local Advance Auto. I run 3933 all around.

tom

Post more info about your setup, ecu, etc. What battery are you running?

Anthony

dude he totally went hard core!!:):)

ok i think i may have found it

im running some advance auto battery

but anyways..

- changed to .22 gap (little better)
changed back to 9eq's same as b4


took it for a drive...breakup moved to 7k and above...and if i keep the throttle at 4k i hear surging mixture of backfires


- switched my boost controller back to 10lbs and my fuel system back to 1 on PFS...NO BREAKUP to 8k rpms, if i switch the fuel system back over to 2 for 12lbs/boost worth of fuel it breaks up high again....if i turn the boost up to 12 and run it on setting 1 for 10lbs it runs 12lbs with no breakup and fast as shit...so im thinking this is a running rich up high problem... how is this possible that i am running too rich up high? for assurance i set profec at 10lbs and flipped the PFS over to 3 which is pre-programmed for 15lbs...the car misfires all the way up the rpm range past 4k

i need to get on a wideband and check the a/f ratio? i am running stock injectors and pump how the hell am i running RICH at 12.8psi on the middle setting of my ecu...i thought the car cant pump enough for 13lbs

Did you warm it up to 200-210 before trying this?

I think a wideband would be extremely useful at this point.

So would a PFC, but that's another discussion.

Dave

it wont warm over 190...its too cold outside...i may need to let it idle for a long time to heatsoak the coolant system then try

Then warm it up while it is parked. Shouldn't take very long. It's really easy to do, and definitely worth trying.