View Full Version : High Knock CEL light when warm

06-08-2003, 12:53 PM
OK.. I am having a slightly funny <not so funny> problem.
First I have a JDM S14 Silvia with minor mods
PFC / Z32 airflow / FMIC .. EVC small stuff..

2 days before my last track event I put in the Z32 airflow
and have it correctly set in the PFC.. I was not getting
this Problem with the normal MAF
At my last track day.. on the way to the track my car was
fine. even with some spirited driving car was still doing
at the track about my 3rd heat.. my engine is about 90c
and I start getting a really HIGH knock reading
at around 5000RPM ... CEL light flashes..
when this happened the car lunged forward and back.
I did not HEAR any knock.. but not sure if that was due
to my exhaust being too loud or not..

So.. i went in and took a look at my car.. right after
the heat car still quite warm.. step on gas.. same RPM
the knock on the pfc is really high.. but still hear NO

ok.. let my engine cool down.. for about hour.. and then get
back in for heat 4.. is fine until about halfway when the
same thing starts to happen..

Now.. the day after the track.. cold engine.. about 5000
RPM the CEL flashes ...

Now.. I have thought it could have been .. bad gas / oil what not.. but those would have caused me to hear it..

SO.. I thought.. maybe knock sensor.. but changed and working fine..Could the air flow have caused a strain on already poor parts.. like fuel pump/ injectors.. that have caused it to run lean but could nto hear any knock?? http://forums.freshalloy.com/images/graemlins/confused.gif

the PFC has been initialzed with same results

All help is greatly welcome.. I don't see any sense in doing
anymore to my car until this problem is fixed.. thanks guys

oh yea.. this is on.. .8psi of boost..and the pfc has not maxed out the injector cycle

06-08-2003, 02:03 PM
For some reason if we are going to get knock we get it at 5000rpm. I assume you are running your stock T28. If you are running above 13 or so psi with the stock injectors and fuel pump, you could be leaning out. I have have a sneaky feeling that on our cars at 5500rpm when VTC takes the retard off the cam, we get a sudden in rush of air in the engine and can easily go lean at that point. I have run a wideband on my car and always find a little spike in air fuel ratios right around that point. BTW what is your max injector duty cycle?

So this is what I would do. try pulling back on your timing and or add fuel with the ign/inj adjustment screen.
Upgrade to 550cc or 740cc injectors and get a bigger fuel pump, walbro 255 high pressure is fine and inexpensive.

Garage Battle
06-08-2003, 06:12 PM
no exp with PFC but id be willing to venture that something is wrong with the MAF settings.

also, and this is taking a wild guess, are there limiting factors on the ECU to MAF readings ranges?

in all honesty it sounds like the MAF isnt getting along with ur PFC &/or ECU.

06-08-2003, 08:10 PM
yeh, i would look at inj duty cycle if you still have stock injectors. Not sure how the boost goes on the t28, but on the t25 it seems like around 5-5500 is where you have the most boost at the highest rpm before it falls off. After that you get down to 10.5 psi or so. So I think that might make sense for running lean there?

over 90% duty cycle would be a bit sketchy. I also think 550s+/fuel pump would be a wise investment. After that, if it does it, you can really start to narrow it down. Remember, higher temps will make everything more prone to detonate, so it could be knocking...especially with high duty cycle/crap pump.

btw, you try bumping fuel in those cells and maybe retarding timing 2 degrees or so?