Weird sound coming from under the car :(

2003_GT · Nov 5, 2008

I have a 2003 Mustang GT automatic my mods include:ACCUFAB 70mm throttle body and plenum combo, BBK CAI, flowmaster 40's, perdetor tune, motive 3.90 gears

My car started to make a weird sound coming from under the car somewhere (so it seems lik) when i am just cruisuing and i lightly step on the gas pedal it sounds like if i was dragging cans under the car, since this started the car has lost power and is really sluggish on accelaration, the sound got even louder after the CAI and ACCUFAB TB and plenum... Im kinda new to the tunig world and dont know much about cars but this sound doesnt sound like it could be too good for my car.. some say it is running lean, others say its a detonation problem but i cant get a cleat answer, can anybody help me and give me any info on what is wrong with my car and how do i fix it ASAP.

BTW im new to stang.net so please bare with me

Any input would be HIGHLY appreciated!!!!

Thank you

96SCstang · Nov 5, 2008

that sound could very well be what is called detonation or preignition. when you are cruising and just barely step on the gas you are putting the most load on your engine causing cylinder pressure and temp. to be very high. if your not tuned right and dont have the right amount of fuel going into the cylinders you will have spark knock. this is very bad for your engine and could cause catistrophic piston failures. that being said there is a few other things it could be and i would check these first. catylitic converter could be plugged, or and exhaust rattle. take a hammer and lightly tap on the exhaust to see if you get a rattle. in the cat is rattleing than you have a bad cat. since you say you feel lose of power i would check cat and spark knock possibilities

2003_GT · Nov 5, 2008

well i have a flowmaster O/R h pipe so i doubt cats are the problem (since i have none) i am going to remove my CAI as some say it causes a lean condition since it is in the fender well and has the MAF after the bend, ill clean the MAF check my plugs and replace if neccesary. Im running diablo sport 91 octane tune should i change that as well??? this is my DD and my only means of transportation, so by driving it around how much damage am i looking at??? its been like this for about a month and a half so how bad do you think the damage is already, is it BAD??? i want to fix this as soon as possible so any help would be GREAT

thank you

H What 4.6 · Nov 5, 2008

2003_GT said:
Im running diablo sport 91 octane tune should i change that as well???
thank you

When was the tune loaded? An improper tune is what would most likely cause the pinging...

And i assume you are definately running 91 octane gas?

2003_GT · Nov 5, 2008

the tune was only loaded about 2 weeks ago, and yes i only run 91 octane, should i go lower in octane or just remove the tune completly???

2003_GT · Nov 5, 2008

ok so heres wat i did... i removed my BBK CAI and reinstalled the factory air box, cleaned the MAF, removed the predetor tune and reinstalled the stock one, my gas tank was on its last drop so i pumped 86 octane into it to see if that might help, after all this NO CHANGE, that F****** sound is still there. i drove around for a while logging a couple of things with the predetor. i noiticed that the DEG SPRKADV would change a lot, when cruising without even touching the gas it would stay at 20 DEG, when i would accel a little it would jump up to 34-36 DEG, one time it went to like 46 or 56 cant quite remeber, i would let go of the gas pedal and it would rapidly drop back down to 20 DEG, and when i would floor it the DEG would drop down to like 10 or 12 DEG, i think the lowest was like 8 or 9... my question is, is this normal for any car??? also forgot to mention that i checked my plugs and they looked pretty bad, i wont be able to replace them until friday (PAY DAY), does this sound like detonation, will replacing the plugs fix my problem or would i have to do something else aswell???

if you need more info let me know

thanks

spederman · Nov 5, 2008

why are u putting in even lower octane fuel? If i had detonation, i would be putting in a higher octane fuel.

2003_GT · Nov 5, 2008

somebody on another forum told me to try it, something about the octane being too high for my tune or car something like that... i only put enough gas to test it see if it would work... im back to 91 octane... should i try some octane boost or something????

BurningRubber · Nov 5, 2008

2003_GT said:
somebody on another forum told me to try it, something about the octane being too high for my tune or car something like that... i only put enough gas to test it see if it would work... im back to 91 octane... should i try some octane boost or something????

No no no... that person is dead wrong.

Throw some 91 or 93 in the tank WITHOUT the Predator tune and see what happens. The only downside to this is that your speedometer will be off because it won't be calibrated for the gears. I don't reccomend driving like this for more than just a short period of time, because it also adds "ghost miles" to the odometer due to the gear ratio not reading right.

Your timing jumping around is normal, 10* at WOT is stock timing if I am correct, 12* is a 2 degree advance, nothing significant. At normal and part throttle driving, it will be much higher.

When is the last time you changed your fuel filter and spark plugs? If you are comfortable with changing your spark plugs, pull each one, one at a time and see how they look. Do this when the engine is COMPLETLEY COLD and be careful not to over-tighten the plugs upon re-install if you do it.

The plugs should be a light brown color. Black is too much fuel, white is lean. Anything mangled, damaged, heat scored, is bad. If there is some red on the plugs, no concern as that is from fuel additives.

2003_GT · Nov 5, 2008

before i put the tune in i was running 91 octane, iv been running 91 since i got the car and nothing lower, and the problem started while using 91 and the car was completly stock... other than the odometer, what other problems am i looking at... i will remind you that it is the only way for me to get around so i must drive it everyday, so what do i need to do to fix it ASAP!!!!

BurningRubber · Nov 5, 2008

Nothing other than the odometer and speedometer being off if you switch back to the stock tune.

If you have ran it on 91 BEFORE the tune though, and it was the same problem I doubt it would make much of a difference.

I'd suggest changing your fuel filter and checking, and replacing the spark plugs if needed. Fuel filter is around $9 bucks for a Motorcraft filter, and $5 for the fuel line seperation tool. Takes about 20-30mins to change depending on how quick you work.

2003_GT · Nov 5, 2008

Iv already done the filter change.. and i changed the plugs about 2 weeks after i got it, i checked them earlier and they were REALLY BAD, so im guessing my problem is deffenetly detonation, i should be able to change the plugs tommorrow, will this finally be the answer to my problem???

96SCstang · Nov 6, 2008

listen bro....since you really dont know what you are hearing for sure and you are throwing money at this thing that you really dont know is goin to fix it maybe you should consider bringing it to a qualified mechanic so it can be fixed before you do some serious damage. i am a mechanic myself and is sounds like you have spark knock and pretty bad spark knock if you hear it all the time. this is very bad for your motor and doesnt take that long before it could cause some real damage. it may end up being something really really stupid and easy too. its just hard to help when we cant drive or hear the car you know. good luck!!

2003_GT · Nov 6, 2008

just thought that if it was "something really really stupid and easy" i could fix it myself without having to pay a mechic to fix that "really really stupid and easy" thing.. i know i said i wasnt that good with cars, but i am pretty mechanicaly inclined, just the things i have never heard of are the one that stump the hell out of me... but ill probably just take it to a shop tomorrow and just get it fixed already

Weird sound coming from under the car :(

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