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Today I was coasting up part of a steep incline. When I hit the gas again to excellerate, I noticed a dieseling sound coming from under the hood. The sound only lasted for a second or two but it did it several other times during my trip under the same conditions. The sound in question is coming from a 5.0 olds in my 87 Brougham. The only thing I could come up with is that maybe it's the cylinder heads overheating or the timing chain needs to be replaced. If anyone has any insight to this sound please help me out here. I don't have much experience with these cars or engines. Thanks......
 

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Sounds like you might be hearing pinging. What grade of gas do you use? Is the timing set right? If it is pinging those are usually the 2 biggest causes.
 

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brougham said:
Sounds like you might be hearing pinging. What grade of gas do you use? Is the timing set right? If it is pinging those are usually the 2 biggest causes.
I agree. It's pre-ignition, brought on by a heavy load. Sometimes, a little bit of this can be normal. But if it's bad, you can really cause some damage.

The first thing I would do, is put in a higher quality fuel. Then, I would find a nice, steep, freeway incline. If you live in Kansas, just find a good stretch of highway. Then, at 50 mph, in TOP GEAR (do not allow the car to downshift) apply slow stead throttle until the car is going 80 or 90. No school zones, okay?

Once you're at speed, let off the gas and let the car engine brake (coast) back down to 50. Do it again. Then again.

What you are trying to accomplish with this, is blow the carbon out of the combustion chambers. When this carbon is present, it can glow like an ember, and it can create an environment where the fuel is combusting before the piston arrives at top dead center. The fuel and air mixture combusts, and the piston continues up, forcing its way against the detonation. This is very stressful on the piston and rods, and its the cause of the noise you are hearing. Clearing out the carbon is the first step towards fixing this.

If it continues, check your timing. There may be too much advance dialed in. Your vacuum advance cannister could also be malfunctioning. This too is easy, and cheap, to address.
 
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