Engine Rattle during acceleration?

[cekeys]

Car: 2001 Saturn SC2 DOHC Engine, 122,500 miles.

There is a rattle during harder acceleration (highway speeds going from 65 to 70). It goes away if you ease up on the gas. The sound is similar to shaking a spray paint can.

If on cruise control and I go over an overpass it will occur again when the engine pushes itself harder to maintain speed.

Thoughts?

[junker]

mine has an exhaust leak and heat shield rattle that sound similar to what you describe.

[cekeys]

I thought I'd post a resolution to this problem I was having. I was chatting with my boss at work and he said, "It sounds like engine knock." He suggested bumping up to 89 octane on my next tank and see if it goes away.

So I ran the engine down to the refill light and filled up with 89 octane, the second tier gas. Within 5 minutes of driving the rattle went away! I haven't been able to get it to make the noise again. I've been trying. I push the engine hard and it sounds great.

I've been filling up with Shell gasoline 87 octane since that is the majority gas station around my area in Houston. I don't know if that means their gas is cheap or my engine is just older or what. I'm lead to believe its just my engine because my wife's civic has no issues with the regular. The 89 octane I used was Shell as well to keep the experiment conditions the same.

Anyway, I just thought I'd share fix. Thanks for listening.

[fredsfix]

You may need to have the anti-knock sensor replaced - probably save the cost in the fuel price difference in a little while. If it really was a pre-ignition knock that you were hearing - that sensor is supposed to detect the knock and make fuel adjustments to prevent it. Off chance that the 2001 has something different but according to my haynes manual they all have one even though I've never heard of one going bad. Wire may have come off it would be and even cheaper fix!

[samsr]

First question, Does you saturn burn oil?
second question, Have you let it get low on oil?
Third question. Does it rattle when you rev it at an idle.

Hopefully is has not been low on oil. I am rebuilding an engine that did the same thing as yours. Except it rattled when I would rev it in neutral. It spun two bearings.
Get an accurate oil pressure reading and post it up.

If it has not been low on oil then I would look toward the engine mounts and exhaust for your rattle.

[BarnOwl]

fredsfix has probably got it. Back in the old days, we used to call the noise you are describing valve clatter. It's really detonation. It can be caused by advancing the spark timing too much for the grade of gas you're using. The thing is that the farther advanced the timing is, the better your mileage. Cars today have a knock sensor that serves to tell the PCM when it's advanced the timing too much. When the knock sensor senses detonation, the PCM retards the timing a bit. It sounds like yours isn't working. One test I've heard about but, not tried is to give the manifold a good whack (not hard enough to break anything) with a hammer at idle. If the sensor's working, you should here the idle change as the PCM retards the timing.

That said, I'll save 97coupe the trouble of posting and say that some people believe that you will get better mileage and performance, if you use a better grade of gas. So, you may choose to continue with what you're doing. I'd still replace that sensor.