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My mother has a 1995 Sedan Deville. The last year it has been making noise under the hood that we just can't explain. We thought it was gas related and tried both medium and high test grade fuels and fuel/engine cleaners. We have tried mechanics who don't have a clue. At this point, I think it actually is something under the hood. I realize this is the hardest thing to figure out over the net, but I'm willing to give it a try if any of you will.

The sound is only when we give it gas. It reminds me of a head sticking...like a tap-it. Don't know if that's how it's spelled. Does this sound familiar to anyone?

Thanks to anyone who might have a clue.

Thomas
 

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1995 FWB 128,*** miles
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My mother has a 1995 Sedan Deville. The last year it has been making noise under the hood that we just can't explain. We thought it was gas related and tried both medium and high test grade fuels and fuel/engine cleaners. We have tried mechanics who don't have a clue. At this point, I think it actually is something under the hood. I realize this is the hardest thing to figure out over the net, but I'm willing to give it a try if any of you will.

The sound is only when we give it gas. It reminds me of a head sticking...like a tap-it. Don't know if that's how it's spelled. Does this sound familiar to anyone?

Thanks to anyone who might have a clue.

Thomas
Probably spark knock because of EGR system fault or #1 main bearing knock. The both are harmless.

1. Is the noise is more pronounced when engine is hot and at light throttle. Say, while driving around a block (10-20 MPH) with hot engine (180F plus) ? If so it is most likely plugged with carbon EGR tubes inside of throttle body, a bad EGR valve or/and a bad EGR solenoid, or vacuum leak caused with cracked vacuum tubes (most likely ones around the throttle body).

2. To eliminate the bearing knock decrease the tension on the serpentine belt by turning the belt tensioner with a 1/2" wrench or a bar while engine is running (be careful). If the noise goes away it is the bearing knock. If you use a thicker oil say Rotella 15W-40 the noise will be reduced.

3. Another possibility is lifters.
 

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Discussion Starter #3
I've taken the car to the same mechanic twice with the information from HUF. He has blown the carbon out twice now, but the rattle keeps coming back. It definitely occurs at any speed but only while giving the car a little gas. Even depressing the peddle half way can get rid of the sound at higher speeds. If I really lay on it, the sound goes away no matter the starting speed. I almost want to say something is either sticking, or it's not getting enough gas, even though it accelerates fine.
 

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1991 Cadillac Fleetwood
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What about an exhaust leak where the manifolds connect to the front pipe or the manifold itself? My Father had a 2000 Tundra V8 that had a cracked manifold and it ticked just like a bad lifter. :banghead:
 
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