Drftn280zxt Posted June 27, 2004 Share Posted June 27, 2004 Can a non-turbo engine have a detonation problem? Occasionally when I turn my car off, it chugs, continues to cycle for a second or two, on its own after turning the ignition off. Could my exhuast system cause this, because it is much larger than the stock unit? Is this bad? Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted June 27, 2004 Share Posted June 27, 2004 That's not detonation that's run on or dieseling. But to answer your question, yes any motor can have detonation problems. Run on can be caused by a LOT of things, depending on who you ask. My old SU L28 motor used to diesel all the time. From what I gathered it can be caused by: Timing too retarded Timing too advanced Car running too hot Idle set too high "Hot spots" in the combustion chamber Crappy fuel Wrong heat range spark plugs Vacuum leaks Cam timing being off Misadjusted valves No or bad vacuum advance on the distributor Dont think you're exhaust would have anything to do with it. After trying to fix all these things, I never did solve the problem in my Z. I believe there were more possible causes that I"m forgetting as well. Good luck dude Quote Link to comment Share on other sites More sharing options...
Guest BigWhyteDude Posted June 28, 2004 Share Posted June 28, 2004 "The most common cause of that is the failure of the anti dieseling mechanism, sometimes an "anti dieseling solenoid", found on most late model carbureted cars. What is happening is that the throttle is remaining partially open when the engine is shut down, which gives the hot engine sufficient fuel to run without a spark from the spark plugs. Most hot engines have sufficient carbon build-up that remains glowing red hot and acts as an igniter for the fuel. The solution is to make sure that the throttle closes completely when you turn off the ignition switch. Check the throttle stop and make sure that the fast idle on the choke or the "bottom stop" isn't what is stopping the throttle from closing. It must be the anti-dieseling mechanism and that mechanism must be functional. Some motors (Olds for example in 85) used an actual servo motor for this function. The motor drives a worm gear which advances or retracts the idle speed control rod depending on what the computer tells it to do. When it is in the "closed throttle" position and the key is killed it retracts completely to allow the throttle plate to close completely thus preventing the "dieseling" that so many cars are experiencing." "DIESELING, also called after-running or run- on, is a problem when the engine keeps running after the key is turned off. A knocking, coughing, or fluttering noise may be heard, as the fuel ignites and the crankshaft spins. When dieseling, the engine ignites the fuel from heat and pressure, somewhat like a diesel engine. With the key off, the engine runs without voltage to the spark plugs. The most common causes of dieseling are high idle speed, carbon deposits in the combustion chambers, low octane fuel, overheated engine, or spark plugs with too high of a heat range" There you go, 20 seconds on google Andrew Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted June 28, 2004 Share Posted June 28, 2004 SU's dont have any valve closing solenoid like that for when you shut the car off... the butterflies always stay slightly open, and given the nature of how they work, it's very easy for the motor to keep sucking fuel in from them as well... So I would think it's easier to end up with dieseling in an SU'd Z. Quote Link to comment Share on other sites More sharing options...
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