spark knock or something else?

4.6boy · Mar 17, 2010

i got an 02 gt with a sct tune on it. i have it set for 87 and only added 1 thing of fuel to even out my cai. the car runs good but when under load or if i go wot i get a rattle/knock sound. it does not do it at idle(only if i hit the trottle. the car was sitting for like 3 weeks and i went to get gas i put 87 from da same mobil i always use and it started doing it. also i dont know if there related but the car has been dieing out after i start it but it always starts back up

trinity_gt · Mar 17, 2010

It's possible you've got a bad tank of gas but all the same I'd use higher octane fuel. Take it easy on it 'til this tank is done, then fill up with one-grade higher octane.

The other thing is that the CAI may be causing a lean condition. Did you keep the screen that was in front of the MAF when the CAI was installed?

4.6boy · Mar 18, 2010

nope the only screen thats on it right now is behind the maf also its a roush cai. i am aready using 89 in it but i will go up to 93. is it safe to use 93 with the sct set at 87 and i only add fuel and 2 d of time to it (it made the nosie before i added the timing) and the cai is been on the car for 2 yrs now

4.6boy · Mar 18, 2010

also yesrtday i was sitting outside were i work and 3 towncars and 2 f150s made this same sound i think mobil had some bad gas or something

trinity_gt · Mar 18, 2010

4.6boy said:
nope the only screen thats on it right now is behind the maf also its a roush cai.

I've never heard of a screen after the MAF. The OE screen that was placed before the MAF helps to even out the flow through the MAF so it accurately measures total airflow. Without the screen, it's possible that you could have more air entering than the MAF reports which can cause a lean condition. In closed loop, the PCM will compensate but it can cause issues during transients like throttle tip-in and WOT runs.

i am aready using 89 in it but i will go up to 93. is it safe to use 93 with the sct set at 87

Absolutely. Octane is simply a measure of a fuel's resistance to auto-ignition (i.e. detonation.) Higher octane fuel is just more resistant than lower octane fuels. You can always go from a lower to a higher grade of fuel. It when you're tuned for 93 and you can only get 89 that you might have an issue as the 89 will be more prone to detonation. I keep a couple of cans of octane booster in my trunk for this eventuality.

and i only add fuel and 2 d of time to it (it made the nosie before i added the timing) and the cai is been on the car for 2 yrs now

Assuming it's detonation you're hearing, you might want to take those 2o of timing back out until you can identify and rectify the problem. You say you've heard other cars making the same sound so maybe the bad-gas angle has legs. There are other possibilities though that can cause detonation, including even a malfunction in the EGR system...

4.6boy · Mar 18, 2010

would the egr set off a mil cause i dont have any codes

4.6boy · Mar 18, 2010

YouTube - Spark Knock this is what it sounds like

trombonedemon · Mar 18, 2010

Hey, did you try octane booster, or something that improves the performance of gas.

4.6boy · Mar 18, 2010

i tryed some stp gas treatment and some stp fuel inj cleaner just the two bottles it werid casue it only happens above 2,000rpm and at wot. but at idle it runs fine.

trinity_gt · Mar 18, 2010

4.6boy said:
i tryed some stp gas treatment and some stp fuel inj cleaner just the two bottles it werid casue it only happens above 2,000rpm and at wot. but at idle it runs fine.

I don't believe "gas treatment" nor "fuel injector cleaner" boost octane any degree.

Try something like the NOS racing formula:

4.6boy · Mar 18, 2010

i am going to try it tomorrow and see what happens but it is safe to put all this stuff in at once?

trinity_gt · Mar 19, 2010

4.6boy said:
i am going to try it tomorrow and see what happens but it is safe to put all this stuff in at once?

Yes.

4.6boy · Mar 20, 2010

filled it with 93 shell today it still makes the nosie but not as bad. but i keep hearing a lot of towncars makeing this sound.

4.6boy · Apr 10, 2010

bump still got this rattle

twogts4us · Apr 10, 2010

Remove the SCT Tune! Does that resolve the issue? If not, remove the CAI. Does that resolve the issue?

4.6boy · Apr 13, 2010

removed the sct tune and no more nosie i am guessing the tune + cai made it run way to lean. so now i just need to adjust for my 373s but i will not be using the sct tuner casue i dont like how the trans feels(plus the how lean thing) has anyone used this Hypertech 742000 - Hypertech Speedometer Calibrators - Application - SummitRacing.com i have heard that hypertech is not as good as sct but i just want to adjust for the gears sct doent do that for what ever reason

Stark77 · Apr 13, 2010

Change out your speedometer gear, it's easy and CHEAP.

trombonedemon · Apr 13, 2010

Hmmm, another tune bites the Dust.

4.6boy · Apr 13, 2010

Stark77 said:
Change out your speedometer gear, it's easy and CHEAP.

its a 02 gt auto i tot u could only do it through the ecu

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