Hi guys, I was wondering what can i do to fix dieseling or engine run-on? The idle is always near 900 to 1000 when it happens, I know that the 96 idle is should be around 850. I was wondering is there anything I can do to fix this?

Could it be the spark plugs...the car is my family's and its old. I am not sure what has been replaced and what has not.

Thanks guy

 

Wow, typically dieseling is caused by carbon deposits. I am trying to think of what could do it. You would need fuel, compression and spark to make a diesel happen. With the engine off there would be no spark, but if there is carbon build up that could be still glowing hot enough to ignite fuel. Compression is there so fuel may be your culprit. Possible leaking injectors?????

 

thanks for your advice boxpin,

I have heard the theory about carbon deposits and the possibility of leaky injectors, how can I fix it thou?

 

I vote on the leaky injectors- fuel injected cars should never diesel... unless the injectors are leaking. High idle speed WILL cause a car to diesel if there's a supply of fuel. Incidentally, the leaking injectors could also- indirectly- cause the high idle! The ECU would see rich mixture at idle, and would slightly increase airflow to compensate... thus increasing idle a tiny bit. Old, carbureted engines would diesel if the idle was set too high, or if you shut off the engine with the gas pressed a little bit.

And no, you don't need spark to make a car diesel. Dieseling is when an engine runs... well, like a diesel- where the heat from compression is enough to ignite the fuel mixture. This is how excessive carbon deposits would cause dieseling- they actually increase compression.

But I don't think your problem is caused by carbon deposits. (or, at least, it's not the primary cause) the fix for leaky injectors is to replace them- to check them, pull the fuel rail off of the manifold with the injectors and fuel lines still attached. Turn the key to the on position, but don't start the car. Then, observe the injectors- does fuel drip out? Yes? Change the dripping injectors. Now, to clean carbon, usually a treatment with seafoam will do the job- basically, you VERY SLOWLY and CAREFULLY run a can of seafoam through a vacuum line while holding the throttle open slightly (2,000-3000 RPM) by hand, a little at a time- too fast, and you'll hydrolock the engine.

 

I forgot to mention in this post, that my dad was using **** fuel for the volvo as suppose to premium. So chance of carbon build up is high, but where do i put seafoam to fix this issue? Any walk through please. Thanks!

 

sorry i mean, couldn't I just put it in the crankcase? I am not very experienced with this, I don't want to screw it up

 

run it thru your intake, let it suck in thru one of the vacuum lines on the intake a half a can or so, let it it sit for 5 mins or so. then fire it back up and let it burn it off. no real need to run it in the oil

 

sounds good, I am going to try that.