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Engine Specific Info and Questions => IDI Engine => Topic started by: 96jetta on July 14, 2009, 05:52:51 pm
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the car has been running great for a long while now however this after noon i was going to go see a buddy and half way there the motor sky rocketed to 5200 rpm and i didnt touch the throtttle. i tryed to turn it off but the ignition wouldnt kill it it just kept pulling 5200 rpm. i put it into 1st gear and held the breaks and managed to kill the motor but what is wrong with her? how can it still run with the ignition off and how can it hit 5200 rpm with me not even touching the throttle? :'(
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I believe that is call "run-on" or "run away". I think what is happening is the motor is consuming its lubricating oil as fuel so your throttle will have no effect but to increase the RPM if you step on it. Also with the ingition off all you have done is cut the diesel fuel to the injectors, if it is fueling off of the motor oil it will continue to run.
Does it have excessive blowby?
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what is blowby?
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If your piston rings are badly worn, when the fuel ignites and the pressure in the cylinder increases, the rings will allow the combustion gases to pressurize the crank case, blow-by. The crank case is vented through the valve cover into the intake manifold. This is done to burn just crank case vapors. If the rings are so worn that this is blowing vapor and oil with it, I believe you can have this situation.
Other will probably chime in, I think run away can happen from crank oil being pushed past the rings into the combustion chamber as well.
Does this engine have a turbo? That may play a part in this as well.
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yea its a 1.9 turbo. it does have a tube running from the bottom of the block to the valve cover is this what your talking about?
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The crankcase vent sits on top of the valve cover, looks like a hockey puck. At least it does on the 1.6 and the tdi, I've not seen an AAZ before...
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ya that what it is. any way i have to do rings and possably re-bore out the block?
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I believe the line from the bottom of the block or more probably the oil pan goes to the turbo. I never had or worked on a turbo motor or a 1.9 but I believe that line is the return oil line from your turbo to the oil pan. Somewhere there should be a supply line to the turbo as well.
Anyway, and again, I don't have 1.9 or turbo experience, but it think if your turbo oil seals blow/break you could be pumping engine oil from your turbo into the intake and into the cylinders causing your run away.
I will continue to try to help, but when one of the more experienced guys get read this I sure they will be able to give you more details. In the meantime, take a good close look at your turbo and look to see if it is wet or dripping oil.
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ya that what it is. any way i have to do rings and possably re-bore out the block?
How many miles are on that motor?
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i appreciate all your help thanks. i know there is a return and input line to the turbo but there is another plastic line that goes from the bottom of the block to the valve cover (hockey puck lol). but i will cheack the turbo too to see if it is wet too
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Your hockey puck line is connected to the block, or just hanging next to it? I don't know why it would vent into the block ??? ; that wouldn't really be much of a vent, would it? It normally goes into the intake piping; some have disconnected it from the intake piping and just let it vent under the car.
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it goes from the the bottom of the block to the valve cover to the intake piping. the gasket on the piping however is blown off :'(. im pretty sure its the rings have gone
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the return is at the bacl or the block right?
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96Jetta, check your oil dipstick level. Is it too high? That could cause runaway. Rings does not have to be worn for runaway to occur.
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it was a little higher than it should have been how is it able to cause runaway though?
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When the level is high enough, it gets sucked through the rings into the combustion chamber. Runaway usually happens when the level rises from diesel leaking into the crankcase, which I have experienced first hand.
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If you let it runaway for too long it'll run out of oil and that'll kill it but your engine might be junk by then.
Check the intake hose between the airbox (not sure where your breather tees into the intake hose), turbo and intake mani and see where it's soaked with oil.
Depending on where in the hose you find oil it might tell you if it's blowby or the turbo that's letting too much oil into the intake.
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Are there paths for crankcase oil dilution from fuel in the VW IDI's? It was the drive shaft seal on a chain driven VE pump that leaked fuel into the crankcase on the runaway that I experienced. It was scary. I was able to stop the engine with the clutch and 1st gear + brakes. After I learned what caused it, sure enough the dipstick was way above normal and was thin and clear, not black.
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Your hockey puck line is connected to the block, or just hanging next to it? I don't know why it would vent into the block ??? ; that wouldn't really be much of a vent, would it? It normally goes into the intake piping; some have disconnected it from the intake piping and just let it vent under the car.
it doesnt vent into the crank case, but rather the crank case vents into the hockey puck also. so then the blow by doesnt have to travel up through the block and around all the valve train just to come out the hockey puck anyway. so they just make it go out the side of the block and right out the puck into the air inlet.
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If you let it runaway for too long it'll run out of oil and that'll kill it but your engine might be junk by then.
Check the intake hose between the airbox (not sure where your breather tees into the intake hose), turbo and intake mani and see where it's soaked with oil.
Depending on where in the hose you find oil it might tell you if it's blowby or the turbo that's letting too much oil into the intake.
i found oil in the intake hose from the air box to the turbo and oil in the hose going from the turbo to the intake manifold. most of the oil was in the hose going from the air box
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Maybe try pulling the breather loose from the intake hose and run it to see how much oil mist you got, or just remove the oil filler cap.