Fine tuning the ECU to get a smooth idle when cold

[julians]

I've been driving around this problem for a while now, but its starting to bug me.

 

When I start the car from cold, it will not idle until the engine is up to temp, it runs but will stall within a few seconds. I've had a look at the engine management software (DTA 3d system if it matters, I would imagine its all the same in principal).

 

I think the two options I should be looking at at the startup enrichment map, and the water temp compensation settings. The startup enrichment map has water temp across the top (horizontal) and turns down the side (vertical), and for each cell there is a figure, I dont know what this figure is though (I guess at fueling).

 

On the water temp compensation section, I can set both the fuel compensation and the advance compensation (in terms of % of the original value) for any given water temp.

 

Could someone point me in the correct direction as to which figures to tweak to give better cold running. I would initially be inclined to alter the advance compensation on the water temp compensation section, but this really is just a guess (because it looks the simplest to do), so would appreciate some experience on this one.

 

Thanks

 

Julian

[Tony Martyr]

I have just been fine tuning my dta/QED TB kit.

The cold idle also has a mechanical setting of the butterfly bypass drillings that are fitted with bleed screws. You are correct to query the fueling map but if the air settings are too retricted at closed throttle you will have an idle problem

[julians]

I forgot to add, it idles fine at ~1000rpm when the engine is fully warmed up. It is just when its cold that it wont idle without a bit of throttle.

 

Julian

[Red SLR]

Place large brick on loud pedal!

 

X777CAT

[StewartG]

Take it back to the people that mapped it not so long ago and tell them to do it properly this time.

[julians]

I was thinking about ringing John Noble, but the less I have to do with them the better. besides it seems that it should be a fairly simple job to do, I'm just looking for a few pointers of how much to increase what figure by.

 

The more I think about it, the more I think that the water temp compensation settings should be increased by a few % (both fuelling and ignition). I guess I'll just suck it and see, I can always revert back to the original map if I cock it up (which I probably will).

 

Julian

[Roger King]

The first job that you must do is to make certain that the settings at idle are correct when the engine is warm. You say that it idles just fine, but it is still possible that the fuelling or ignition are marginal here. The point is, that there is no point in putting in corrections for temperature if the basic settings are wrong. Once you are certain on this point, you can then start experimenting.

 

Unfortunately, you will need to do an analysis on the exhaust gas for this (either with a CO meter or with one of the small lambda meters that are available from the likes of Lumenition).

[julians]

So its possible to have a rock steady idle when warmed up, but the mixture etc could still be out.

 

What are the consequences of this sort of setup, is it something I should be bothered about , or is it just something that needs to be right for the MOT.

 

Why are these things never simple?

[Roger King]

You won't get a rock steady idle if things are miles out, but as with most things in life, there will be a small range of fuel and ignition settings over which it will run OK.

 

Once upon a time in the dim and distant past, the advice was to set the fuelling in the middle of the OK range, but these days with injection and catalysts and emissions legislation you have to be more precise. If you are running a catalyst you will need to maintain the fuel/air ratio at stoichiometric (14.7:1) at idle. If you have no catalyst you have more freedom.

 

I'm simply making the point that you should make sure that the fully warm settings are correct before fiddling with correction values.

 

If the idle really is rock steady then it is unlikely that things are far out.

 

Edited by - roger king on 13 Mar 2001 11:52:16

[julians]

Ah, thats OK then, Yes the idle is rock steady when fully warmed up, and there is no cat.

 

So is it the water temp compensation I should be changing, do you have any ballpark figures for me to start with. I mean along the lines of start by increasing fuelling by x% when the water is between 10-20C. The software will let me increase the fuelling by up to 400%, but I would imagine I would need to increase it by 50% max if the water was at 0 C.

[julians]

OK, just for the record.

 

I've managed to get it so it will now idle when cold, I did this by setting the fuelling to a 45% increase when the water temp is 0 gradually decreasing to 0% at 65 degrees. This now lets it idle when cold, however it is not idling at full speed ( ie ~1000rpm) until it is fully up to temp, at coldest it idles at 500rpm and gradually increases speed until up to temp and idling at ~1000rpm.

 

Is there anything I can do to get it to idle at ~1000rpm when fully cold?

 

Julian

[Mike Bees]

You really need an ECU-controlled idle air control valve to get achieve the same idle speed across all temperatures. When the engine is cold it takes more effort to turn it over, thus it needs to make more power for a particular idle speed, thus it needs more air and more fuel. Most throttle body setups don't have provision for this, so you have to accept a lower idle when cold or a bit of foot-on-the-pedal to keep it running until it's warmed up. Some ECUs have a fine idle control which tweaks the ignition advance to achieve the desired idle speed.

 

Mike

[julians]

Thanks for that Mike, It looks like I'll just put up with a lower idle speed until up to temp.

 

Julian