Sorry for long title :p

 

Anyway, for those of you out there who have an exact understanding of how it works, I have a question...

 

On a coastdown with 0% throttle open, what is happening in the engine? Are the injectors applying fuel? Are the spark plugs operating?

 

I need this information to try and cure a prob i'm having.

 

Many thanks you brainy bunch :D

 

Rob.

Just to add mine is a 1990 UK TT Manual if that makes any difference.

On a coastdown with 0% throttle open, what is happening in the engine?

Inside it's going round and round ;)

 

Are the injectors applying fuel?

Yes but there are times on over run where the fuel is switched off completely from memory.

 

Are the spark plugs operating?

Yes it helps keep them clean and emissions down should the fuel come back on.

Inside it's going round and round ;)

 

Yes but there are times on over run where the fuel is switched off completely from memory.

 

Yes it helps keep them clean and emissions down should the fuel come back on.

 

 

LOL thanks, I got the roundy-roundy-uppery-downery bit figured ;)

 

 

So sometimes there is fuel being supplied on overrun? could you please clarify this as I'm getting closer to my answer now :p

 

:duffer:

Not fitting a flamer kit or something are you???? lol

not 100% sure on a zed but most cars have over-run shutoff, which stops the injectors from firing until the engine approaches idle speed again

I think I remember reading that the fuel starts again as the ECU re-enters the closed loop area of the fuel map (i.e. starts to run using the exhaust gas sensors). Don't quote me on it as there has been a lot of information come and go over the years.

Why don't you post up the specific problem you are having. People might know the answer.

 

Certainly from the above it would seem that it depends on what the ecu detects from various sensors as o what happens.

 

Darrell

Correct Coopers - many variables

not 100% sure on a zed but most cars have over-run shutoff, which stops the injectors from firing until the engine approaches idle speed again

 

 

Yes, I think this too, as a fuel economy increaser...

 

OK so as to tell you guys what the problem is, smoke.

 

I get NO SMOKE on startup at all.

 

After driving a bit I get white smoke on a closed throttle overrun, then when I open the throttle it goes blue for a short while until it clears completely. It smokes out of the RH pipe more than LH

 

Ticking over hot or cold=no smoke.

 

I have just done PCV valves ~80 miles ago, VERY little difference. Both tubs were done ~300 miles ago?

 

Why I was asking about overrun fueling is I'm thinking valve stem seals have gone. When you take your foot off the throttle the intake goes into vacuum right? Sucking oil from wherever it can do. Now as there is no petrol in the cylinders burning, the compression ratio is not enough to ignite the oil/air mix...hence white smoke

 

When I open the throttle the injectors fire up again and will burn off all the remaining oil on the inlet valves etc etc hence blue smoke.

 

How does this theory sound?

 

Has anyone had their valve stem seals deteriorate on a Z32?

 

Thanks peeps!! :cool:

I get NO SMOKE on startup at all.

And you're complaining ??? :)

 

I have just done PCV valves ~80 miles ago, VERY little difference. Both tubs were done ~300 miles ago?

Things could still be clearing after these short distances. There is a lot of intake piping and a lot of it will be up hill.

 

Why I was asking about overrun fueling is I'm thinking valve stem seals have gone.

Quite possibly but give it a couple of thousand miles before jumping to conclusions

 

How does this theory sound?

Interesting, very interesting :)

>> On a coastdown with 0% throttle open, what is happening in the engine? Are the injectors applying fuel? Are the spark plugs operating?

 

It depends on engine temperature, speed and on automatics on other variables as well, but basically if the ECU detects the throttle is at 0% (this is determined by the closed throttle switch) it will cut fuel until rpms have dropped to 1900 rpm.

 

>> How does this theory sound?

 

possible, but more likely on a Zed it's due to worn rings.

Have you done a compression test yet ?

 

-Eric

I get white smoke on a closed throttle overrun, then when I open the throttle it goes blue for a short while until it clears completely. It smokes out of the RH pipe more than LH

 

 

Sound's like turbo seal failure

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but i'm crap at this stuff so i'm prob wrong lol

 

 

 

 

 

 

Neil

And you're complaining ??? :)

 

Things could still be clearing after these short distances. There is a lot of intake piping and a lot of it will be up hill.

 

Quite possibly but give it a couple of thousand miles before jumping to conclusions

 

Interesting, very interesting :)

 

 

LOL thanks. Will see if it gets better or worse with more usage then I guess :duffer:

>> On a coastdown with 0% throttle open, what is happening in the engine? Are the injectors applying fuel? Are the spark plugs operating?

 

It depends on engine temperature, speed and on automatics on other variables as well, but basically if the ECU detects the throttle is at 0% (this is determined by the closed throttle switch) it will cut fuel until rpms have dropped to 1900 rpm.

 

>> How does this theory sound?

 

possible, but more likely on a Zed it's due to worn rings.

Have you done a compression test yet ?

 

-Eric

 

Eric thanks, I've just been talking to my Father about this and he suggested rings too :mad: . But we did a compression test a while ago and he said the results were fine for a 105k mile car. IIRC all were in tolerance except 1 which was 2psi below minimum. Max difference between any 2 was 10psi.

 

But it's not blowing any smoke out the dipstick at all. :confused:

 

I shall also revise something, minimal traces of white smoke (oil) on a hot tickover.

 

This is really doing my head in now but thanks all for your advice :duffer: :duffer:

Sound's like turbo seal failure

Neil

 

 

From my experience turbo seal failiure is clouds and clouds of smoke straight from startup. (I've done about 4 turbos now) :cry:

>> IIRC all were in tolerance except 1 which was 2psi below minimum.

 

I think you have already found the problem then....

Eric thanks, I've just been talking to my Father about this and he suggested rings too :mad: . But we did a compression test a while ago and he said the results were fine for a 105k mile car. IIRC all were in tolerance except 1 which was 2psi below minimum. Max difference between any 2 was 10psi.

 

But it's not blowing any smoke out the dipstick at all. :confused:

 

I shall also revise something, minimal traces of white smoke (oil) on a hot tickover.

 

This is really doing my head in now but thanks all for your advice :duffer: :duffer:

A compression test isn't infalible!(sp)-this can tell you the bores/piston and rings are o.k. but the oil rings can still be fubar,letting to much up the bore.

I just found my compression test results....

RH LH

145 137

145 137

155 140

Front

 

 

140-160psi is acceptable range.

 

Strange thing is the RH bank (145,145,155) is the one that smokes the most. But as Manta says, compression can be ok with a busted oil ring. But would you have combustion gasses also passing and going into the crankcase?

 

Many thanks, :duffer: to all :D

Is that a hot or cold test?

Is that a hot or cold test?

 

 

Cold....

Bloody hell they're not bad! Test it hot and let us know :)

Bloody hell they're not bad! Test it hot and let us know :)

 

Will do that then!! :duffer: :duffer: :dance: Cheers mate.