OPEC

Okay here is the scenario, I have had this problem on and off for a little while now. Under 3/4 or full throttle I am hearing what I am to assume is detonation. I really only hear it in 4th gear, everyonce in awhile in 3rd. I will be cruising in 4th at about 3000-3300 rpm and then punch it. I started getting in the habit of doing this for tuning purposes so I could lessen the notice of the transition from primaries to secondaries. I know that if i really wanted to get the car up and moving, I should shift to 3rd, but even then it will happen sometimes. I have never heard it the noise, which sounds like something metal hitting together, above say 5500 rpm or so. It always seems to happen between 3800-4500 rpm, which is about the time or shortly there after the turbo has hit full boost 12psi. It doesn't seem to matter if it is cold outside or hot. I never see anymore than 10.5 lamda on the wideband when it is happening. I have had it tuned out leaner 11.2 or so and never heard a thing. The EGT temps never get above 670 Celcius when I hear it.

The first time it happened, I thought that I had gotten some bad gas, I always use 93 Octane and only buy the same brand of gas. So I put some octane booster in and new gas and the problem seemed to go away. But it has come and gone a few times since then, during about a 4 month period. The car never feels like it stumbles or looses power when it happens. I back off the throttle immediately. Other than that the car runs awesome, the only other things is that sometimes I will get a stumble around 5500-6000 rpm this will happen in 2nd, sometimes 3rd., but this is never associated with the noise and has been happening basically ever since I put the new engine in the car a year ago. So i am pretty sure that they are not related.

The car is in the same basic state of tune as when I dyno'ed the car. the boost is the same the fuel map is the same, maybe minor, and I mean minor adjustments have been done. If anything right now, I have the car running richer across the board, low and high throttle. The car hold an awesome idle dead on 750-780 rpm, and pulls 15-17psi of vacuum. Same amount of vacuum it has since the engine first ran. Here are a list of concerened mods and parts.

full 3" exhaust
stock turbo 12psi
4 720cc injectors. less than a year old
Apex SAFC (they are tuning the injectors way down)
HKS Front Mount
Mazdacomp 3" radiator
Manual boost controller
Paul Stokes FCD
4 NGK Platinum BUR9EQ plugs (less than 4000 miles)

I think that is the list of the concerened mods, I may be leaving out something small though. I am stumped on this one.

RETed

Where is the EGT probe mounted?
Just by the EGT numbers, you're running overly rich.&nbsp What you could be hearing is a rich misfire - try and back down the fuel even more.&nbsp What's your settings on the S-AFC?



-Ted

OPEC

The EGT probe is mounted about 2" from the turbo on the DP, that is the exact same place where I have the sensor for the wideband tapped in. Here are the settings for the SAFC

Throttle Points
LO 20% HI 60%

LO rpm x 1000
1 2 3 4 5 6 7 8
-17% -3% +2% +2% +2% +2% +2% +2%

HI rpm x 1000
1 2 3 4 5 6 7 8
0% -6% 0% +8% -11% -16% -21% -14%

I hope this helps. If you need more info Ted let me know.. Thanks man

RETed

WOT, shoot for 780C EGT temps.
Are you using the stock fuel pressure regulator?
Do you have an upgrade fuel pump in your car?



-Ted

OPEC

Yeah.. I do have a stock regulator, but I have a walbro fuel pump in the car. If I take the car full throttle all the way through 4th gear, it will get pretty close to 780. But I have never heard the noise when i am really close to redline, only around 4500 rpm or so, when the EGT are much lower

RETed

Is that a +8% at 3kRPM?&nbsp Try leaning that out back to "0" or going negative...



-Ted

OPEC

it is actually +8 at 4k rpm.. sorry about it being hard to read, I tried to format it some, but it was lost when i posted it. I will give that a shot if you think that i should lower it at 4k also

RETed

You'll need to "linearize" the adjustment points...
No need to format them, I know how the S-AFC operates, so you can just dump the raw numbers left to right.

Remember, the rotary revs so fast, that you'll need to look at adjustments a bit earlier than you're having at a certain RPM band.&nbsp The +8% looks a little suspicious.&nbsp I run almost the same set-up as you with 4x720's, but I use a Field SFC-HyperR for fuel adjustment.


-Ted

OPEC

Thanks man.. I will give this a shot and let you know what happens. Thanks for some insight. Off to tune, back soon

RETed

Yeah, it makes more sense that the +8% is actually at 4kRPM rather than 3kRPM...



-Ted

OPEC

Okay back from adjusting the maps a bit. Here are the new settings

Throttle Points
LO 20% HI 60%

LO rpm x 1000
1 -17%
2 +4%
3 +4%
4 +4%
5 +2%
6 +2%
7 +2%
8 +2%

HI rpm x 1000
1 0%
2 -7%
3 -7%
4 -7%
5 -8%
6 -15%
7 -21%
8 -14%

Here is what happens now. I am not hearing anything in 3rd gear at all, and the whole time I was out I never had that bog happen at around 5500rpm or so like I was talking about, so that is good.

However I am still hearing the same noise in 4th gear, right at about 3800-4000 rpm or so. This is just shortly after I am hitting full boost. I am getting the same amount of boost in 3rd and 4th 12psi. I had the problem of the car going really lean at this point when I had 550cc injectors in the primaries. That is why I put the 720cc injectors in and that problem was cleared up. EGT's under WOT look dead on 780C. If I am in 4th above 4000rpm and I go WOT, no noise. I have also never heard it doing 2nd-4th WOT pulls. At this point I am completely stumped as to what could be the cause of it just happening in 4th.

The car pulls a lot harder now with the new HI map settings. I do have a under the hood manual boost controller that is tucked in between the turbo and the shock tower of the engine compartment. I am almost starting to wonder if that much sudden air flow going to the turbo is flexing the lines going to the controller and it is moving and tapping something metal. I don't think this is the case, cause I am pretty sure that I have it zip tied pretty well. But I am going to check that.

snoopster76

hey i don't have a metal sound, but just about 6000 rpms at full 11-12psi boost the car acts like someone plugged my intake.

RETed

3800 is the magic number for the fuel injector crossover.&nbsp It sounds like you might have grounding problems...

Try this for now...jack down the 3, 4, 5 positions -2% at a time, and see if the sound changes.&nbsp If it ges LOUDER, readjust back to the original settings - this confirms it's leaning due to the fuel injector crossover.&nbsp If the sound starts to disappear, jack those ranges another -2% and run again...if the sound lessens, then it's still rich misfiring in the midranges.&nbsp The car likes to run about -5% leaner from 3kRPM to 5kRPM, so you might be still too rich in the middle...


-Ted

OPEC

I will give that a shot and let you know what happens. I think that you might be right on with it being to rich still, cause as soon as I go WOT all I see are 10.0 on the wideband for about what seems like a second.

OPEC

Well I wasn't able to test it a whole lot, but I did take away fuel from 3000-5000 rpm like you said, and I still heard it. I can't say if it was louder or not seemed about the same. So I richened it up just a bit in the 3000-4000 rpm range and did a couple runs and it didn't happen, and I got quite excited. I did one or two more test runs and it came back. I think that I have the fuel adjusted much better cause I did notice this time that wideband measured about 11.2 for just a split second right at about 4000 rpm and that is when I noticed the sound.

I didn't get another chance to adjust stuff cause I was almost out of gas and was on my way home from the office. It would seem that I am not able to get enough fuel for that split second. I could try and richen it up a bit more in the 3000-4000 range. In order to see if I am maybe running out of the ability to feed the car more fuel I could try and hold the car at about 3500 rpm and richen the mixture up and see if I a change on the wideband. The only problem that I could see in that is that I wouldn't be under boost and I wouldn't be under the HI map.

If you have anymore ideas, let me know. I think that we are getting much closer.

RETed

I really think it's the 3800RPM hesitation you're trying to tune out.&nbsp Check here for detailed info...
http://fc3s-pro.com/TECH/FAQ/3800.htm

Adding grounds would be the easiest way to fix this...



-Ted