Offroad-Express

Hi, I'm hoping someone on this forum may be able to help with something.. it has the mechanics stumped, but who knows someone here may have come across it.

We have a 1991 2.5 diesel delica 4x4, when sitting idling in park it will on occasion all by itself rev up till the trottle is fully open, black smoke everywhere then die away again... pulling the key out wont stop it till its gone through it "cycle".... well I pull the key out it keeps reving like its going to blow up for maybe 3 or 4 seconds before dieing back. you can restart and it idles fine... it has never happened while driving, thank goodness.

The mechanics have checked all they could.. throttle, fuel pump etc and can see nothing wrong.

any thoughts, and thanks.

perhaps a mild version of this


http://www.offroadexpress.co.nz/Forums/ ... 69&t=35064

gosh..., I have to say we are on edge waiting for this exact thing to happen..

Scenario 1...

It's called "runaway" where the engine will feed on its on oil due to a blown turbo seal or valve seal or worn piston rings until it
A. Explodes throwing conrods and pistons into space or
B. runs out of oil to burn

(more on the worn piston rings, it creates crank case pressure that is vented back to the intake pipe. this pressure is saturated with oil vapour which accumulates inside the intake manifold then is dragged down the runners into the engine when running.
Scenario 2...

The injector pump has worn out and allowing diesel to pass through to the injectors. Now you said they "checked" the injector pump. how ever knowing how high pressure these things push diesel through to the injectors it may only be .2 of a mm worn enough to allow diesel through when it is not supposed to...So unless you watched them crack out the micrometer on the work bench "checked" is a very vague term. ....the effect is like the injectors on a petrol engine squirting fuel constantly instead of pulsing.

One's a new engine...the other is a injector pump rebuild or replacement.

Crash bandicoot wrote:Scenario 1...

It's called "runaway" where the engine will feed on its on oil due to a blown turbo seal or valve seal or worn piston rings until it
A. Explodes throwing conrods and pistons into space or
B. runs out of oil to burn

(more on the worn piston rings, it creates crank case pressure that is vented back to the intake pipe. this pressure is saturated with oil vapour which accumulates inside the intake manifold then is dragged down the runners into the engine when running.
Scenario 2...

The injector pump has worn out and allowing diesel to pass through to the injectors. Now you said they "checked" the injector pump. how ever knowing how high pressure these things push diesel through to the injectors it may only be .2 of a mm worn enough to allow diesel through when it is not supposed to...So unless you watched them crack out the micrometer on the work bench "checked" is a very vague term. ....the effect is like the injectors on a petrol engine squirting fuel constantly instead of pulsing.

One's a new engine...the other is a injector pump rebuild or replacement.

Thanks for this..
I have to say my theory was close to your number two... something causing a buildup of pressure forcing the diesel past the injectors... pressure releases normal idol returns.. sort of like a diesel bomb

Most of the vids of diesel runaway where the engine is running on oil show plumes of blue smoke.

If it's belting out black smoke, seem more likely that it's running on diesel.

pjb wrote:Most of the vids of diesel runaway where the engine is running on oil show plumes of blue smoke.

If it's belting out black smoke, seem more likely that it's running on diesel.

It was black.... and lots of it