Rattling while accelerating

Deleted member 38176 · Aug 23, 2011

I've noticed a rattle recently that is originating from, what sounds like, the rear portion of the engine bay to directly under me. It only happens when I accelerate. When I took my foot off the gas it is immediately gone......and immediately returns when I put m foot back on the gas. It sounds like dropping a pebble into an empty soda can and shaking it vigorously.

Im going on about 6 months or so since completely re-doing my exhaust (LT's and mid-pipe). Could something be coming loose (ie. a leak)? Does it sound more like spark knock? I already have leaking valve guides so could this be related to something more serious in that area?

Thanks.

Stumbaugh · Aug 23, 2011

If you are being really easy on the car, does it do it? Or does it only do it under hard excelleration?

Deleted member 38176 · Aug 23, 2011

Both. As soon as the pedal is touched, the rattling commences.

Lugnuts · Aug 23, 2011

What does it sound like from outside the car and where does it sound like it is coming from? with the car running and the hood up, operate the throttle and see if you can discern the location. let us know.

40oz · Aug 23, 2011

It's either an exhaust leak/related issue, or detonation. I'd check the exhaust, but you could try 93 octane or higher to see if it is detonation.

Jhunter · Aug 23, 2011

If the 93 fixes it or at least helps it you should probably get new plugs and wires.

Stumbaugh · Aug 24, 2011

Jhunter said:
If the 93 fixes it or at least helps it you should probably get new plugs and wires.

99-04 2v's do not have wires, they are a coil on plug system.

Deleted member 38176 · Aug 24, 2011

Stumbaugh said:
99-04 2v's do not have wires, they are a coil on plug system.

I was just about point that out along with saying that just had my plugs changed.

I payed a little more attention to it today. I only hear it when I am completely off the throttle then hit it aggressively. It doesn't last long but as soon as I get into it hard from a coast, it's pretty loud.

Im thinking it's exhaust related.

Rick 91GT · Aug 24, 2011

It sounds like it is tip in spark knock unless you find a clearance issue with the exhaust.

trinity_gt · Aug 24, 2011

Nightfire said:
I only hear it when I am completely off the throttle then hit it aggressively. It doesn't last long but as soon as I get into it hard from a coast, it's pretty loud. ...

Rick 91GT said:
It sounds like it is tip in spark knock unless you find a clearance issue with the exhaust.

Agreed. A classic way to describe the sound of detonation to a lay person is to say it sounds like "marbles in a can" which sound a lot like Nightfire's description of it being like "dropping a pebble into an empty soda can and shaking it vigorously."

Bad fuel (incorrect octane for your tune), malfunctioning EGR, too much spark advance (e.g. handheld tuner), low fuel pressure, excessive intake air or coolant temps, a dirty MAF etc can all contribute.

Detonation can damage these engines as the piston crowns above the top ring are very thin brittle and can snap off under the hammering of detonation pressure shockwaves. The sound you're hearing it actually the metal bits of the engine ringing audibly in response to these shockwave hammer blows. I'd avoid sharp tip-ins until you sort it out to reduce the risk of breaking something.

03_TrueBlue_GT · Aug 24, 2011

I was having Detonation problems with my car about 3 weeks ago similar to what you are describing. I think I just had a bad tank of gas because I ran two tanks of 93 through it and it doesn't do it anymore. Of course I changed the plugs, added seafoam, and used injector cleaner, but you said you just had the plugs changed so that shouldnt be the issue, unless you arent running motorcraft or autolite plugs. It could also be the dang 100* plus weather we have been having out here in Tx.

Jhunter · Aug 24, 2011

My bad, I knew they have the coil system, I'm just used to saying wires. They may need replaced also or rebuilt. I had a spark knock come on in my maxima. I changed the plug and not the coils. It helped but did not fix. I could run 93 and it would not do it, but go back to th e87 and it would. I finally replaced the coils. Problem went away. Car had 150,000 approx miles on it. If your over 100,000 they made need replaced or you may be able to just replace the guts in the boots. That option was available for the maxima.

Deleted member 38176 · Aug 24, 2011

I lowered the oct rating in my tune. I was running a 93 tune with 91 fuel (best we have here). I changed it to the 87 tune and will continue running 91. The sound has decreased drastically but isn't gone completely. Maybe after a few more miles on the tune change will get rid of it. I'll clean my MAF too.

2002BLGT · Aug 29, 2011

Nightfire said:
I lowered the oct rating in my tune. I was running a 93 tune with 91 fuel (best we have here). I changed it to the 87 tune and will continue running 91. The sound has decreased drastically but isn't gone completely. Maybe after a few more miles on the tune change will get rid of it. I'll clean my MAF too.

You may want to take it somewhere to get an in person tune since you are having issues that seem to be tune related

Deleted member 38176 · Sep 16, 2011

2002BLGT said:
You may want to take it somewhere to get an in person tune since you are having issues that seem to be tune related

I don't have that option where I live. It seem to come and go. I have been running the correct octane fuel for my tune.....and it's a BAMA tune (from what I've heard, BAMA is on top of their ****). I am not smelling any exhaust gases whatsoever but I have had some major clearance issues. No matter how carefully/slowly I take speeds bumps and the like, I bang the exhaust occasionally. Oh, I have also cleaned the MAF and the plugs were changed a few months ago.

JoeDaddy · Sep 16, 2011

Not sure if you buy your gas at the same station all the time or not, but if you do, you could try switching gas stations. I have notcied where I usually buy my gas (A grocery store gas station, across the street from my house..) that if I go out rompin on it durring the weekend, I'll get detonation under hard acceleration. If I buy my gas somewheres else, it does not do that. Just a thought.

LastCallRacing · Sep 16, 2011

You can take a datalog and see where your timing is on throttle tip in. Then send it to BAMA and have them adjust the tune so you don't get the spark knock. I'm sure they will adjust your tune for you.

Fabbed4d88 · Sep 16, 2011

I run the same exhaust set-up as you and in my case the exhaust had shifted just enough to rattle ever so slightly against the frame... May want to check that before going to far into unneeded repairs.

Rattling while accelerating

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