Hi all,

I have a 93 FD with the following mods: intake, hks downpipe, tomei catless midpipe, and tomei cat back. I also have my wastegate ported on my stock twin turbos. I’m running manual boost controllers set to 8psi max at the moment. Sadly I have no wideband so I can’t tell what my AFR is

I’m currently running a power FC and studied this thread: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/how-make-your-untuned-pfc-basemap-safer-idle-better-no-datalogit-needed-841706/

Here, it’s said to retard the timing by 4 degrees in rows p16-p18 (8-11psi boost range) for rpm ranges 2800-8000.

I did that and still get some knock (60-89 count max) on my apexi.

I feel like I’m getting knock in higher rpm ranges with load ( I know not good)

So I’m thinking about also retarding row p14-15 (5.2-6.6psi boost range) above 2800 rpm by 4 degrees too. Should this help?

also I don’t know if I get knock in boost range or just in high rpm in general, but is there any harm in just retarding timing by 4 degrees in rows p1-10 above 2800 rpm? That’s the early rows where there’s no boost. I was considering doing that but wanted your guys guidance before doing that as I’m new to tuning.

also should I focus on retarding timing at lower boost levels or retard timing EVEN more in rows p16-18 (8-11psi boost range)? Maybe also rows p14/p15 is my culprit since my max boost is set to 8psi

Also, I shouldn’t be getting knock in 0 boost high rpm levels with the default map with my current mods right?

as you can see I’m at a fork in the road and would love some guidance

 

don't be so fixated on the knock value. knock is relative from car to car and especially with the stock knock sensor, it can vary. the most important thing here is to STOP and install a wideband. without an afr reading you have no reference as to what you are doing. you're just shooting in the dark with live targets. with what you have, knock shouldn't even be a factor. leave everything to your tuner and install a wideband.

 

yeah that’s how I feel. Without a wideband, it’s just a guessing game but by retarding it enough, I’m hoping it’s safer even if it runs richer (I don’t mind). I also added fuel across the PIM voltage range as suggested in that thread as well. I’ve heard that peoples knock values are all over the place so I’m not too worried but I am uncomfortable. Also, I’ve run this car with these mods on the stock ecu for a long time before (1-2 years) so I feel like if the knock was real, it would’ve blown up already by now—unless the new map for apexi is more advanced than the stock ecu map. I’ve been wanting to get a wideband setup but nobody here wants to tune a pfc. They all recommend haltech + single turbo but I just love the stock twins and think it’s a beautifully designed system from factory. I’m trying to learn as much as I can myself

 

FC Tweak, with a wideband will have the ECU hit its fuel targets, and retard the timing enough to get rid of the knock

what fuel pump and spark plugs are you running?

 

yeah I’ve been tempted to go with fc tweak but the main thing holding me back is the wideband install. I was thinking of temporarily installing wideband in stock o2 sensor location and then getting fc tweak to do its job.

im running new stock ngk plugs and afaik, the fuel pump hasn’t been upgraded or changed. It’s stock. Also my injector duty doesn’t max out. Usually reaches 50-80% max. Might be less than 80% actually

 

Ok so update.

Took the FD out today and hit 5000 rpm at 4.3psi of boost and got 87 counts of knock. Injector duty cycle was at 49.7%.

I had retarded rows p14-15 (5.2-6.6psi) above 2800 rpm by 4 degrees

going to now retard row p13 (3.79psi boost) by 4 degrees above 2800 rpm and see if it makes any difference.

if not, it could just be picking up drivetrain noise considering I’ve driven it aggressively for a while now without a blown motor.

ultimately will eventually buy a wideband and fc tweak to tune this Q4 of the year.

 

Also theoretically I shouldn’t be getting any substantial knock in 0 boost high rpm ranges right? So there’s really no need to retard timing in those 0 boost ranges? Especially with my mods (intake, full catless exhaust system, ported wastegate on turbos)

 

Also not sure how much this affects it but I don’t have my heat shield, lost it somewhere a while ago so maybe the heated air isn’t helping knock.

I took the car out again after retarding row p13 above 2800 rpm by 4 degrees and got 55 counts of knock at 5k rpm this time. Forgot to read the boost but it was probably up there. Could have just been a fluke though so will drive some more.

 

Did three more WOT and got 51 counts of knock on the first two and then 71 on the third. Around 5-6k rpm at what I think was full boost (8psi)

I also noticed I had a knock (41) reading in relatively low rpm and load (maybe 2800 ish rpm with 0 boost)

I know a little bit of knock is normal so maybe I’m getting noise (like the 41 counts of knock) plus some extra (30-40) counts? Could just all be noise and there’s no real way to tell without AFR. Maybe I’ll retard rows p1-12 by 1-3 degrees

 

the knock sensor is just a microphone so it does pickup noise.
there is something on my car that is loud when its cold and it settles down when its warm, also our roads are so bad that will sometimes do it too, lol

you might add a little fuel in those spots and see what that does, if you're on the commander there is a screen where you can add it temporarily, which would be great for testing

 

My car has always had phantom knock around 3000/3500RPM with no boost. My car has an AFR gauge that has always indicated healthy AFR even when the knock sensor has gone off.
Unplugging my chattery air pump has helped, as has refreshing some vacuum lines. All this to say that the knock sensor is really not a reliable way to tell AFR.

 

yeah it seems like pim voltage 3 corresponds almost to 3psi as 4 pim voltage does a little under 10psi. So I’ll add 2% fuel there and see what happens

 

my emissions including air pump are all deleted and blocked off. I also refreshed all my vacuum lines. I agree with you that the knock sensor doesn’t tell the AFR. it’s good to know you also experienced some phantom knock at those ranges with 0 boost. Honestly on the basemap it shouldn’t lean out on me in the 0 boost areas at those rpm ranges considering my mods are simple. I’m wondering if a heat shield will help though because right now it’s sucking in hot air. Was thinking of getting some Home Depot heat resisting hvac ducting lol. Would look ugly but hey heat shield

 

Ok so after multiple rounds of testing maybe it got better with adding fuel and retarding the timing in those rows I mentioned before?

it usually has a knock value in the 50s and that’s it. However, I see knock rise when I let off gas a lot so I’m thinking maybe there’s drivetrain noise somewhere. It also doesn’t always rise when I’m pushing boost, seems more rpm (drive train noise?) related than boost related.

I went ahead and decreased the additional fuel a bit too since I feel like I was running a little rich. Everything else is good though besides my lower OMP banjo bolt. It wasn’t fully tightened before so it was spraying oil everywhere and so I tightened it by hand until it started becoming righty-loosey (oops). So it leaks a little now and not sure what to do. Praying I stripped the thread on the bolt and not inside the OMP. It’s not even that righty-loosey so maybe the copper washers just didn’t seat properly?

 

knock when you let off the gas is kind of common, not every car does it, but if you searched for like high knock in the PFC section, you'd see threads about it.
you could go under the car and look for loose stuff, exhaust hitting things, loose bolts etc.

its hard to separate engine knock from other noises sometimes too.

 

Timing chain whip