I've had similar threads and questions about this sound in other forums and never get much else but "timing" suggestions. The problem is, the sound is not a ping, it sounds almost exactly like a diesel engine. This occurs less with premium fuel than regular, and less when i really retard the timing vs having it at 0 or a couple degrees advanced. The engine is definitely stumbling and if i continue at the same throttle level once it starts with the diesel sound, the entire car will start to shake and the engine will start to die out.

The only way to fix the problem is to let off the gas and then give it more throttle than it had before, this seems to shift it to a lower gear and thus produce higher rpms.

I think the fuel and timing effects are masking or revealing a deeper issue, as my timing is no where near extreme to the point where i would have predetonation issues.

So does anyone know what causes this type of sound? It starts off as just a dieseling type of sound and gradually the car starts shaking worse and worse as the engine lopes worse and worse until it sounds like it's about to die. It only happens at low rpm under load... like up any slight incline. Once rpms are pushed over some threshhold, the sound completely dies away.

 

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deposits cause that to happen? So i should see an improvement if i do some heavy duty multi-step cleaning or something like seafoam ?

I used to run premium when gas had a reasonable price and i made a decent amount of money. Now, years later, i make more as far as dollar amount, but that money buys me much less than it used to so no premium fuel is in this car's future anytime soon.

 

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Is there a reason why it only happens at very low rpm at part throttle under load but at no other time? if it's something like carbon buildup, wouldn't it not care what the rpms are in the car? Just seems weird that it wouldn't cause predetonation in more than one narrow instance.

 

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Ok, so basically i have two main ways of using seafoam. Add it to the gas tank or directly to the tbi via the brake booster or pcv. If i add a can to the tank, will it still smoke the entire tank of gas or will it be much less smoke than the direct to tbi method? Will the tank method not clean as well as the vacuum method?