02 GT at full Throttle issue?

DKVL · Jan 10, 2009

I noticed that while in gear 4 and gear 5 and with the accelerator fully pressed down there is a slight,faint sound that resembled marble in a can. When this occured my gt continues to accelerate.

Is this normal in all 02 GT's?
If this is not normal, what can be causing this and how do you fix it?

Will this cause any long term damages?

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DKVL · Jan 11, 2009

I apologize for the double post. I had done this on my blackberry and didnt know it was double posted.

But can anyone help?

98COBRA281 · Jan 11, 2009

i have heard a few times before, that spun rod bearings can sound like marbles in a can........

trinity_gt · Jan 11, 2009

"Marbles in a can" is almost certainly detonation. The car was tuned from the factory to run on 87 octane and should be able to to that without detonation setting in. If you're really lugging it and have 87 in the tank you might still hear some.

If you've got a tune and are running a lower grade of fuel, you'll likely get detonation too. Regardless, try using a 91 or higher octane fuel on you next fill (or whatever your tune calls for if you're not stock.)

If you can, stop doing this. That sound you hear is the piston crown and cylinder walls ringing acoustically as if they'd been hit by a hammer, which is about what detonation is like to engine parts, and brittle hypereutectic pistons don't like being hit with a hammer. Go down a gear to accelerate or use less throttle in the upper gears and/or run better gas.

MaxedGT · Jan 11, 2009

Good info from trinity.
Also might suggest putting your stock air intake setup back in. Some cold air kits cause you to run lean, and will cause detonation too.

DKVL · Jan 11, 2009

I am currently running octane 87 and I dont know if the car has ever been tuned. I am actually the second owner. Is there a way to tell without getting it tuned myself?

As for the concern with Spung Rod Bearing, what is it (sorry for being auto ignorant)?

I will try a higher octane level and see if it occurs.

Thanks!

trinity_gt · Jan 11, 2009

DKVL said:
As for the concern with Spung Rod Bearing, what is it (sorry for being auto ignorant)?

The lower ("big") end connecting rod bearings come in two pieces that fit snugly in the upper and lower connecting rod and cap. In fact, the bearings sit proud of the mating surface ever so slightly so that when the cap is torqued in place, the bearing is subject to a "crush" force and really held solidly inside the connecting rod.

However, if the bearing surface grabs the journal (due to oil starvation, for example), or the crush is insufficient, the resulting torque can actually cause the bearing shells to spin inside the connecting rod. When this happens, the bearing has "spun" and the bearing, the rod and the journal are all damaged very severely, very quickly. The result is a nasty, hard knock and an engine in need of a rebuild.

98COBRA281 · Jan 11, 2009

its probably just detonation from cheap/low octane gas, but there was a member on here, that had described a "marble in a tin can sound", and it ended up being a rod bearing...

DKVL · Jan 11, 2009

I saw that post about the other post. In his case, he had indicated that the sound increased progressively with increased in RPM. In my case, i only hear it at or near full throttle. So i am guessing this is not the worse case scenario. At least I hope not.

Can you please describe what hard knock sound like or how I would know?

Chili · Jan 12, 2009

DKVL said:
I saw that post about the other post. In his case, he had indicated that the sound increased progressively with increased in RPM. In my case, i only hear it at or near full throttle. So i am guessing this is not the worse case scenario. At least I hope not.

Can you please describe what hard knock sound like or how I would know?

It's detonation.. You are only hearing at WOT. So either you are running lean, there is a tune on the car or there is a manual timing adjuster on the car. Just throw some higher octane gas in it and try to get a dyno pull with air/fuel ratio to make sure you are not dangerously lean. if your air fuel is good and the premium gas gets rid of the pinging then you should be good to go. In the mean time keep it off of WOT so you don't go boom.

DKVL · Jan 14, 2009

Okay, so I did some more further observation and I wanted to see what you guys think about the problem.

I am planning to take my 02GT into the mechanic this Saturday and I want to make sure I give a better description.

This is what I observed about the marble in a cup sound during less then full throttle and during full throttle. These observation are based on which gear the car was in, the rpm and the speed of the car.

Gear 1: No sound at all at all RPM.
Gear 2: No sound at all at all RPM.
Gear 3: No sound at all at all RPM.
Gear 4: Faint sound at 3500RPM at 45 miles per hour. The sound is on and off.

Gear 5: Audible sound at full throttle, 3000RPM at 70+miles when shifted to 5th at 55mph from 4th gear.

Gear 5: Sound is very obvious and audiable when shifted to 5th gear from 4th at 45mph. The sound remains audible all the way from 45-55 (sometimes 60)mph and then it becomes faint, but still audible. The sound becomes audible if I go into full throttle at this point.

The Marble in can sound sounds a lot like when I miss shift and go into 4th or 5th gear when my GT is traveling at 25-30 mph.

Now do this still sounds like Detonation? What is the difference betweening a "ping" and a "Detonation"?

Possibly spark plugs gone bad?

I am waiting for my tank to empty and fill it with a higher octane gas.

2000GTdriver · Jan 14, 2009

It surely sounds like a detonation issue. Putting a heavy load on the engine by trying to accelerate in too high of a gear on low octane gas is a classic trigger for detonation. Get some Premium gas in it ASAP, should fix it but your driving style is also a contributor. Go easy on it for now those pistons are not very strong.

DKVL · Jan 14, 2009

Ok, I will try to empty the tank and fill it up with the highest octane gas and see if this fixes the problem.

Also, talking about driving habits.

This is what I do:

Gear 1: 0-15mph
Gear 2: 15-25 mph
Gear 3: 25-35mph
Gear 4: 35-45mph
Gear5: 45+

Am i shiffting too early then? Where do you guys shift at when daily driving your mustang?

2000GTdriver · Jan 14, 2009

I shift about the same speeds as you if the car is not pulling a load (like going up a hill) and I am being light on the gas peddle, like half throttle at most. I would delay shifting 3 to4 and 4 to 5 by 10mph or more under harder acceleration and I almost always downshift if I need to floor it. Still all of my driving is at high altitude where detonation is less likely so take it for what it's worth.

Tazzy · Jan 15, 2009

My 04 makes the sound I think your talking about but only in 5th gear while pulling in mid rpm's, it is definately in the trans or shifter area. Don't thik mine is the shifter though as it made the noise with the stock shifter and the MJW shifter that is currently installed. It is a faint sound but it does sound like marbles bouncing around in a can.

02 GT at full Throttle issue?

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