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Old 12-05-2011
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Pre-detonation and transmission srvce question

Ok, so I've heard this issue could possibly be pre-detonation of which I have no experience whatsoever. When I get on it or just accelerate a little hard say getting on the fwy, the engine rattles. Like a bad gas ping. On idle at a stop light, engine is not smooth. Almost like timing is off maybe. Could this be a vacuum leak somewhere causing this? I have new plugs and wires, new fuel filter, new air filter. Cleaned the mass flow sensor.

2nd question is I bought my Ranger used with 111K on it. It belonged to a young woman (20's) so I doubt transmission has ever been serviced or been awhile if ever. Whats better, flush or complete service? Fluid looks good last time I checked.

Thanks!
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Old 12-05-2011
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You actually mixed two terms:
Preignition- Ignition of the mixture due to glowing carbon deposits in the chamber. This occurs independently of the spark, usually prior to the plug firing, as the piston is nearing top dead center. Often accompanied by dieseling (engine continues to run after turning the ignition off)
Detonation- occurs due to fuel with an octane rating too low for the demands of the engine. Occurs after the spark plug fires, but an area ahead of the advancing flame front ignites and the two flame fronts collide.
Both conditions produce a ping, a sound like bb's dropping on sheet metal. The full sound of the explosion is muffled by the surrounding engine parts (Out in the open it sounds like an M80 going off, as was demonstrated to me back in automotive school many years ago.), but either condition is very hazardous to your engine. It can knock a hole right through a piston, I've personally had it happen.
Yours appears to be detonation. It can be due to excessive carbon in the chamber raising the compression beyond what regular fuel can deal with, or a mixture that's too lean. Check thoroughly for vacuum leaks. Timing and fuel air mixture are a bit more complicated to alter on these new vehicles.
Regarding the tranny, a fluid change would be cheap insurance against unnecessary wear. I wouldn't have it flushed, just a fluid and filter change.

Last edited by shovelmike; 12-05-2011 at 08:03 PM.
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Old 12-05-2011
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Quote:
Originally Posted by shovelmike View Post
You actually mixed two terms:
Preignition- Ignition of the mixture due to glowing carbon deposits in the chamber. This occurs independently of the spark, usually prior to the plug firing, as the piston is nearing top dead center. Often accompanied by dieseling (engine continues to run after turning the ignition off)
Detonation- occurs due to fuel with an octane rating too low for the demands of the engine. Occurs after the spark plug fires, but an area ahead of the advancing flame front ignites and the two flame fronts collide.
Both conditions produce a ping, a sound like bb's dropping on sheet metal. The full sound of the explosion is muffled by the surrounding engine parts (Out in the open it sounds like an M80 going off, as was demonstrated to me back in automotive school many years ago.), but either condition is very hazardous to your engine. It can knock a hole right through a piston, I've personally had it happen.
Yours appears to be detonation. It can be due to excessive carbon in the chamber raising the compression beyond what regular fuel can deal with, or a mixture that's too lean. Check thoroughly for vacuum leaks. Timing and fuel air mixture are a bit more complicated to alter on these new vehicles.
Regarding the tranny, a fluid change would be cheap insurance against unnecessary wear. I wouldn't have it flushed, just a fluid and filter change.
Regarding the vacuum leaks, yes I will definitely check into that if you believe that's the possible culprit. It isn't too bad or loud but enough I can hear it. Same for tranny thanks.
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