JasonZ

iTrader: (1)

I try to start my car everyday because I have another daily driver but if I dont start it for a couple days when it starts up theres a quick rattle noise. Anyone know what that is? Is it normal? Thanks.

Jason

julwal

I GET THAT TOO....If I have not driven for about 2 days, and the weather is cold, upon ignition, there is a loud grind/rattle sound...
Must be something to do with the automatic fuel pump?....I hope it is normal....

s9am_me

iTrader: (1)

yup same here... scared the crap outta me one time... i had my door open while i was starting the car in the garage. i guess the sound bounced off the walls and made it seem louder.. hehe.. but yeah

mark350

Same here...I thought it may be the release bearing with the clutch. If you are experiencing this noise also is your car a manual or auto trans?

tcn75

iTrader: (1)

same here... i got the enthu. 6MT .. after a trip of 4 days from calif, I start the car and I hear the sound really loud from engine,
it seems like something break. what's wrong ?

JasonZ

iTrader: (1)

I have a 6MT. You guys pretty much described exactly how it sounds. It happens most often if the car sits unstarted for a couple days. Anyone out there know what this is? And most importantly....is it abnormal. Thanks.

Jason

N74DV

it's nothing to be too concerned about..... it's the valvetrain making all that racket. It does that for just a second until everything is lubed up. If it lasts for more than a second I'd take it in but less than that is perfectly fine.

kgb

I don't believe one bit this rattling noise is do to lack of lubrication. My car makes this noise too sometimes at startup, and I'm detecting pinging along with the rattle. It's subtle but detectable.

It's my opinion, something's off; it could be a sensor, or maybe the ECU code needs tweaking--I don't know. But I suspect we may be getting some detonation at startup. Detonation, as some of you may know, can be cause by improper timing too.

My basis for saying this is that I've had this noise since my car was new -- 13K miles ago -- and whenever I'd add gas the noise would go away for a while before returning. My experience has been ECU's perform some sort of reset after adding gasoline. So it’s using different timing & fuel maps for a short time before reverting back.

I'm going to have my car checked out; detonation is not a good thing.


"Detonation:
Detonation also known as pinging or engine knock occurs simply when fuel pre-ignites before the piston reaches top dead center. This means that a powerful explosion is trying to expand a cylinder chamber that is shrinking in size, attempting to reverse the direction of the piston and the engine. When detonation occurs, the internal forces can actually exceed 10x the normal forces acting upon a properly operating high performance engine. Detonation is generally caused by excessive heat, excessive boost pressure, improper ignition timing, inadequate fuel octane, too lean of an air/fuel ratio, or a combination of these. Usually excessive boost and/or too lean of an air/fuel mixture is usually the culprit. "

N74DV

i can guarantee you it is not detonation. detonation does not occur at idle rpms. it happens under load.

also your description of detonation is not entirely accurate. detonation and pre-ignition are two entirely different animals

detonation is when the air/fuel mixture explodes rather than burning evenly. detonation can induce pre-ignition due to the increase in CHT during detonation.

it's definately valvetrain noise.

Boomer

This is a new deal for me except for right after I got the car. I noticed it on startup and have never heard it since until a couple of days ago when the weather was under freezing temperatures. I never thought of it as detonation before, I use Mobile 1 just for its better cold start lubrication. I certainly hope you're wrong, the last thing we need is another major defect with this car.

kgb

The noise doesn't happen at idle regardless of the idle speed when the engine is cold. It happens as the engine revs rise and fall between 1500 & 2000rpm after the turn of the ignition key. It's usually fairly brief but can easily be heard.


Is there valvetrain noise involved? Possibly, but not because of lack of lubrication. My car makes this noise maybe 1 in 4 starts; add gas and this drops to 1 in 10 -- for a while. Reset the ecu and the results are about the same-- about 1 in 10.
In any case, I believe there's improper ignition timing taking place at start-up.

kgb

...not my description, but even if it's not entirely correct, we are experiencing some type of advanced ignition during start-up. And the fact that it's severe enough to cause the valvetrain to rattle and the engine to ping, suggest to me that if the problem is allowed to persist some part/s in the engine are going to fail prematurely.

N74DV

i think we are talking about two different noises.... the noise I'm talking about is valvetrain rattle upon startup that lasts for about 1 second. you're talking about something else.

JasonZ

iTrader: (1)

N74DV thanks for the info. I can finally sleep at night. What you described is exactly what my car is doing and it makes sense. Especially if the car has been sitting for a while, all that oil has to get distributed from sitting on the bottom. BTW i love your wheels. Thanks again.

Jason

kgb

I suspect we're talking about the same noise. It’s just our opinions differ in what's causing it. Like I said, I've determined what affects how frequently this noise occurs. I’m going to have the dealer check it out over the holidays.

One other note: I had the Crawford cats installed a couple a weeks ago and my car has rattled once on start-up since; it was this past Friday and it was relatively cold.

N74DV

KGB,

your car is not detonating on startup. that's ridiculous. I don't think you really know what detonation is.

your right about one thing... timing is advanced on engines during startup. that's simply because the engine is turning slower and the spark needs to ignite closer to TDC to make starting easier. As the RPM's increase, timing is retarded. It's been that was for MANY MANY years.... older cars did it with points/distributor ignitions using vacuum advance. we do it through the ecm.

Advanced timing at low rpms does not cause detonation. It's impossible to have detonation at low rpm. If the air/fuel mixture did detonate while at low rpm the engine would just die as there is not enough rotational energy/momentum to sustain rotation through a detonation explosion. It's high rpm/under load conditions that cause detonation.

the noise we are talking about in this thread is not ignition related. it's a physical/mechanical noise created by the valvetrain or some other rotating part due to no oil in the system at the first moment of startup.

You of course may have other noises that are being caused by something else but I think for the most part everyone else is talking about the same noise I am.

kgb

"your car is not detonating on startup. that's ridiculous. I don't think you really know what detonation is. "

"the noise we are talking about in this thread is not ignition related. it's a physical/mechanical noise created by the valvetrain"

Thanks for info on detonation, but I concede that I may not know what detonation sounds like, although I'm more clear about the definition. But I do know how pinging sounds, and it's VERY subtle when the rattle happens. I have no pinging at any other time.


Why I suspect this is timing related:
When you reset the ECU or make intake and exhaust modifications, the ECU adapts by making changes to the timing and fuel maps. The rattling DOES NOT happen for a time after I reset my ecu; and did not happen for a time after: the installation of the Borla exhaust; the installation of the JWT Popcharger; and the installation of the Crawford cats. Why would doing any of these things cause this mechanical valvetrain noise to go away?

You can't convince me that the cause of the noise is not ignition timing related because you simple don't know what abnormal sound this particular engine might make if let's say the timing too advanced when the engine revs fall after start-up.

I think we all would agree here that this noise is not NORMAL. At least, not in my experience, and I have owned several cars.

It's not my intention to scare anyone with my comments, but to be safe, take your car to the dealer and have them check it over.

khagen

I made a trip to Minnesota this weekend and put some Shell gas in my car. I have never used it before but think that it is all right for my Z. Previously the only gasoline put in my car was BP, Texaco, or Mobile 1; all in my opinion great gasolines. However, after my trip to Minn. I started it up the next day and it didn't "pop" off right away but took a couple of cranks to get going and I also heard a noise I wasn't accustom to in the Z. Could it be caused by crappy gas? I tell you one think is certain, NO MORE SHELL GAS!!!!

BROKE

Some of these buzzing/rattling noises coming from under the car can be caused by small pebbles and other junk getting trapped in and around the exhaust & cat converter shields under your car. Especially if you drive on roads that are sanded and salted for ice. Once my car threw a lead tire weight that got trapped in the exhaust shields and it drove me crazy until a guy at midas found and removed it.

Under acceleration this trapped junk can rattle & hum and make noises like pinging and drive you nuts.

BROKE

I have noticed an occasional "thump" upon starting when the engine is cold. Should I worry?