Causes of hunting?

[Automania]

Ok I've asked about a problem I'm having on another forum but haven't solved the problem yet so thought I'd try some fresh people to see if I can solve it.

First up engine spec, 4.6 heads were very lightly skimmed and have been ported a little too, new crower cam, running 3.9 Hotwire, but using Megasquirt.
Also using the old 3.5 rocker covers.

I ran the engine in its original p38.

So the problem is when it gets hot it hunts at idle quite badly, from about 550 to about 850 or so it only does it when it's hot.

The only thing that is still to be connected up is the drivers rocker breather mainly because I need to sort a way of connecting it to the other breather. The other breathe is connected up using the proper pipe setup for the original 3.9.

Hopefully I've put all the facts there that could be needed

So what could be causing the hunting? It was suggested that there was an air leak somewhere on the intake, but I've stripped the inlet off, new gaskets etc even used a bit of sealant but its no different.

I did think it could be the ms settings but now I'm not sure, so what else could be causing it? Any ideas please? Thanks mike

[Quagmire]

Ok so I'm assuming that your second rocker breather is blocked off, or thats gonna be an air leak right there!

Have you checked your idle AFRs when hot? You might be getting heatsoak on the IAT sensor and MS then leaning stuff out and making it unhappy.

Are you using any kind of idle control valve? If so, blank that off for now until you have sorted a stable idle as from what I have read it'll only make things worse on an engine that is already hunting a little.

*edited to correct my poo English!

[Automania]

Hi mate thanks for the reply.

The other breather is just at atmosphere at the minute but I've tried putting my finger over it and it makes no difference.

Pwm us disconnected and pipes are blanked.

Idle afrs not checked those, but the rear O2 bank voltage guage is up and down like a yo yo I put a vid of that an lr4x4

[Quagmire]

Thinking about it I suppose that having one connected to the plenum and the other open is actually how it is designed anyway, with the passenger side rocker normally having the little foam filter on it and air being drawn in through it.

Your video is showing your pulsewidths dropping right off to 1.2ms when the o2 gauge goes nuts. You don't have any kind of o2 correction turned on do you?

My idle pulsewidth is around 2.3ms I think?

If no o2 correction is on then try setting the block of cells around your idle to all the same value and tweaking them all up and down in unison until your idle is happy.

[Automania]

Have ego correction authority turned down to 20% which I believe means its off?

What exactly is the pulsewidths? Ill have a google but no doubt I still won't understand it

Ill try changing the cells, it only uses four so shouldn't be too difficult.

Still open to other ideas regarding the rest of the engine too

Cheers mike

[Ian Anderson]

Exhaust leak upstream of the O2 sensor?

Look for soot around joints. If exhaust escapes it can also draw in air. So the O2 sensor sees lean, tells it to add fuel, sees rich, turns fuel off etc

Ian

[Quagmire]

To turn of O2 correction I believe you change the "Controller step size (%)" to 0 and that should disable it.

Your pulsewidth is the time in milliseconds that the injectors are being earthed by the MS in order for them to open and inject fuel. This is a total of the injector "deadtime" and the time needed to inject the correct amount of fuel - this is calculated at any given moment by the MS based on engine temp, air temp, load, rpm etc etc.

The injector "deadtime" is a fixed value in milliseconds that it takes the injector to do anything. Imagine for a second you have a big electric motor on the bench and you apply a current, you will probably find that it does nothing for a split second whilst it comes out of stall and begins to turn.

Same idea with an injector, there is a time where current is being applied but the injector is in the transition between closed and open and is not (in theory anyway) injecting any fuel.

So say you have an injector with a 1ms deadtime and you need to inject 1ms worth of fuel. You actually need to apply a pulsewidth of 2ms to the injector - that is 1ms to cover the deadtime and get the thing open, and then 1ms to actually inject fuel.

If you needed to inject 2ms worth of fuel with that same injector the pulsewidth would be 3ms total.

100ms of fuel would be a 101ms pulsewidth... you get the idea

[Automania]

Exhaust leak upstream of the O2 sensor?

Look for soot around joints. If exhaust escapes it can also draw in air. So the O2 sensor sees lean, tells it to add fuel, sees rich, turns fuel off etc

Ian

I've thought about that as it does sound like its got a leak, but can't see any soot or feel anything with my hand, but I think, though I may be wrong, that the ego correction authority set as it is stops it from doing that.

[Automania]

To turn of O2 correction I believe you change the "Controller step size (%)" to 0 and that should disable it.

Your pulsewidth is the time in milliseconds that the injectors are being earthed by the MS in order for them to open and inject fuel. This is a total of the injector "deadtime" and the time needed to inject the correct amount of fuel - this is calculated at any given moment by the MS based on engine temp, air temp, load, rpm etc etc.

The injector "deadtime" is a fixed value in milliseconds that it takes the injector to do anything. Imagine for a second you have a big electric motor on the bench and you apply a current, you will probably find that it does nothing for a split second whilst it comes out of stall and begins to turn.

Same idea with an injector, there is a time where current is being applied but the injector is in the transition between closed and open and is not (in theory anyway) injecting any fuel.

So say you have an injector with a 1ms deadtime and you need to inject 1ms worth of fuel. You actually need to apply a pulsewidth of 2ms to the injector - that is 1ms to cover the deadtime and get the thing open, and then 1ms to actually inject fuel.

If you needed to inject 2ms worth of fuel with that same injector the pulsewidth would be 3ms total.

100ms of fuel would be a 101ms pulsewidth... you get the idea

Ah ok didn't see this post as we posted at the same time, I get that now.

Tried changing the ve table values on ms, changed four that it was jumping around in at idle and it SEEMS to have cured it, fingers crossed on this as I've done things before that seemed to have fixed it then the problem has come back, but gonna try it again tomos and see

Cheers mike