My knock problem theory. Make sense or not?

Onefast99gsx · 08-17-2005

Ok guys, i've been fighting a knock problem since i got the car going again in May. I've had it. I've tried so many things that it became ridiculous. Even went to 75/25 alky/water injection. I still get knock in 3rd gear at almost exactly 5700rpms on every pull. I absolutely cannot run anywhere near 11:1 or i'll get really high knock in 3rd gear. If i richen it to like 9.8:1, i get minimal knock, maybe 1.1* or less but it is there. Tried, colder plugs (BR8ES), new wires, (3) MCCC treatments, different oil brand, boost leak tests. Lowering boost helps but then again that's because the demand of fuel would be less.

Ok- about the only thing i didn't change yet was the fuel filter. I talked to the orginal owner of the car today and he never did change it either. So my 99GSX has about 90k miles on the original fuel filter. Maybe my fuel filter is so dirty that it can't handle the flow demands and load of 3&4th gears. Question: Is it possible to be able to richen to like 9.5:1 on dsmlink and still have a clogged filter and be running lean all this time??? To really add something to the equation is that i can knock about 99% of the time in 3rd gear --- BUT --- about 4 out 5 times when i do a pull on a freeway on-ramp the knock is little or nothing. Get out on a flat road, KNOCK, KNOCK. Figure that one out. Bottom Line: Can i be running Lean all this time and still have a 9.8:1 a/f ratio, thinking all this time i had plenty of fuel?

Thanks

slowbubblecar · 08-17-2005

I am not sure about the A/F, but when we had a 50 trim on our 1g, it always knocked and the only way to fix it was race gas. I think it was a better when we put the 60 trim on but the fuel filter was new when we were having the problem.

**Shane@DBPerformance** · 08-17-2005

You need a real wideband. The airfuel in DSMLink is just based off of airfuel vs injector time, so it is possible for the real A/F ratio to change drastically in there is a boost leak or a fuel pressure issue. O2 volts also often do not stay linear across a whole run. I have had cars with perfect flat A/F lines on a wideband and the stock sensor's volts starts at something like .92v and goes to .98v by the top of the gear.

Are the on-ramps uphill or downhill? Downhill would be less load on the car and less likely to knock.

**JET** · 08-17-2005

Alright, I don't care what DSMlink says, that is not your A/F ratio unless you have a WB02 plugged into it. Start low and work your way up. Kill the water injection, turn the boost all the way down, check for boost leaks and tune from there.

Getting the right plugs would help too. Put some BPR6ES's in there until you get things figured out. If you have a setting in the DSMlink set wrong, it will mess up your supposed A/F ratio.

Onefast99gsx · 08-17-2005

Slowbubblecar- Well the fuel filter was a long shoot. Regardless, if it was never changed, it should be. Interesting that you had problems tuning the 50 trim on pump gas also. I have 5 galls of 114 octane. I'm just waiting for the perfect day to use it.

Shane- it's a down ramp, so yeah, probably less knock due to less rolling resistance and load on the motor.

JET- Yeah, i know, i know... i need a wideband and not to listen to what dsmlink says. About the best think i could do at this point, is turn boost down to 15psi, log a 3rd gear pull, turn boost to 16psi, log.... 17psi....etc.. The BPR6ES plugs are the ones i just took out. I still have them. I just tried 8's for the heck of it. Man i wish i lived closer to you guys so you could actually take the driver seat of my car.

Question: Are you most likely to make more HP, with 17psi, and +4 on timing sliders and running through the traps at 17-18 deg at the top of 3rd gear -- OR -- to run it at 23psi and -4 to -5 degrees on the timing and running through the traps at 13-14 deg at the top of 3rd gear?

**JET** · 08-17-2005

You will make more power with the boost. Get the thing running good on 12 psi first, then jump to 15, 18, etc.

Onefast99gsx · 08-17-2005

Thanks... Will do. You know how it is though sometimes. So and so is running a 50trim @24 psi, this much timing advance with these mods- so we sometimes tend to skip the 16,17,18,19, etc.. boost levels to try and cut to the chase.

Onefast99gsx · 08-17-2005

Well tonight i changed the fuel filter(What a f'n pain in the ass). I did on my old car and I WAS NOT looking forward to it. I put the BPR6ES plugs back in and also lowered the boost. I'm at 19psi. It felt ok for 19, of course it felt slower than 24 but i'm doing the back to the books tuning here. Log would look something like this.

Upto 5700 in 3rd gear: No knock whatsoever.

RPM Knock
5769 .4* thru
6219 .4*
6229 0
6345 0
6378 .4 thru
6567 .4
6591 0 thru
7036 0

At this point, i can either lean or richen it, OR lower the boost a pound or so and see what it does for me.

**scheides** · 08-17-2005

Turn down the boost & see what happens.

**JET** · 08-18-2005

Add 2% from 5600 on up. Then try it and if it's good, turn up the boost a bit and do it again. 24 psi is pretty damn high if you are going to be running a lot of timing. Give us a major mods list too, turbo, fmic, injectors, fuel pump, etc. I am sure it is somewhere else, but I am not going to go look it up.

Onefast99gsx · 08-18-2005

Good idea. Adding fuel should also tell me if my a/f ratios are off too i think.

Here is the mods list for the 99GSX:

PTE 50 Trim w/cut divider/Internal Gate, PTE 780 Inj, FP 3" Intake Pipe, HKS 272 cams, Griffin FMIC(24x10x2.75 core), Magnus Intake Manifold, 1g TB, 2.5" I/C Piping, DSMlink, TurboXS BOV, Hallman MBC, Rewired 255LPH F.Pump, Fidanza Flywheel, SouthBend Clutch, 3" Exhaust, Greddy A.Filter, 75/25% Alky/Water INJ, (2) 1400 cfm Fans.

Thanks... I will try it tonight.