Tuning question - cold start & decel

[TurboRA28]

Hi all, got a couple of tuning questions for those in the know..

Firstly, with cold start.. Hard to explain my thinking here, but i'll try...

Are you making the mixtures richer in order for a richer than normal mixture, or are you doing it in order to keep the mixture at a normal level.

So lets say for argument sake that I aim for a 14:1 ratio at idle with a warm engine. Now when it's cold, do I am for 13.5:1, or do I still aim for the 14:1 ratio knowing that it'll need more fuel to be at this point?

Now the decel or close to decel question.. I find it hard to tune the point where you are 'almost' on decel and injectors cut. So like a few % of throttle and 20 " mercury. I find to keep a reasonable air fuel ratio at this point it needs a lot of extra fuel. I don't know if this is really required. It gets pretty poppy on the exhaust around this point also, but then also a slight surge which I find indicates a lean mixture. I would have thought at this point I could lean the mixtures right out.

Cheers
Joel

[JP]

On my car I've got the smoothest warm idle with an AFR of 14:1, my cold start is about 12.9-13:1. On my old ECU and tune from a "reputable" Woollongong workshop had the cold start at 10.5:1 and warm idle used to bounce around anywhere from 13-14:1. I believe the extra fuel from cold helps the engine to get up to temp quicker.

For Overrun fuel cut, I tuned my new ECU with overrun fuel cut disabled first, then enabled the fuel cut with a TPS Threshold of 1.3%, Activation delay of 1sec, igntion retard of 10deg and Deactivation rpm of 1500rpm from a coolant temp of 80deg onwards, higher from the lower temps.

[KARNAGE]

my tune had a cold start of around 11 to 12:1 on my 20 valve turbo that was the final set up that we had they had a much richer set up to start with and it was horrible then they went lean and it was really hard to start the car when it was cold it seamed ot work well when the set it up properly

[JZA70 R]

the extra fuel for cold start is required because of the cold head/ports condense the fuel vapour before it gets to the cylinder... so your basically adding more fuel to increase the odds of a proper burn.

i tried to tune for stoich on cold start but it just doesnt happen, it will miss and your afr's will spike all over the place. i think it ended up cold starting smooth around 12:1

[JZA70 R]

if your almost on liftoff (borderline closed throttle) and its surging chances are wont hurt anything even if it is lean because of the lack of load.

why dont you turn the injectors off until just over idle? ...that will rid the popping and save fuel but makes tuning (my car a bitch). i turn the injectors off until 1000rpm after tuning is finished. mmm smooth quiet decel, car doesnt sound like a untuned bucket haha.

[3BarSuperstar]

Be careful it's not too rich for too long or you can risk fowling the plugs. It helps if you have a idle motor to idle it up when it's cold as well and that way you can run it a little leaner.
Also depends on your ecu of choice some are better at cold start than others. More stable mixtures.

[oldcorollas]

1. Are you making the mixtures richer in order for a richer than normal mixture, or are you doing it in order to keep the mixture at a normal level.

2.Now the decel or close to decel question.. I find it hard to tune the point where you are 'almost' on decel and injectors cut. So like a few % of throttle and 20 " mercury. I find to keep a reasonable air fuel ratio at this point it needs a lot of extra fuel. I don't know if this is really required. It gets pretty poppy on the exhaust around this point also, but then also a slight surge which I find indicates a lean mixture. I would have thought at this point I could lean the mixtures right out.

I am not sure of the AFR numbers, but i found the same emprically as you when playing with MS.

1. both i think. fuel wetting, plus larger fuel drops etc etc.. i think during warmup (initial while O2 sensor might be warming up and not 100% accurate) it is ok to have a fixed % enrichment (which obviously varies with temp) rather than AFR targetting. tune it lean enough to have a tolerably smooth idle/warmup and call ti good.

2. i thought similar. that on decel it would be good to cut fuel, but.. if you cut too much fuel, then it either lean cuts, or pops on decel, or when you go to re-enegage throttle, it kicks.. i found it had to be richer than i expected, to get smooth transitions. this is with playing around with TPS based enrichments (which i think only 0.5s was enough to smooth the throttle movement issues)

for me, on the throttle transitions, i would just tune for smoothness.. as i hate jerky tuning . on full decel no throttle, tune for no cut, no popping, and a smooth transition to throttle when you hit pedal again...

is all fun (and maybe i haven't added anything )

[YLD-16L]

Mine runs around 12.5 on cold start and doesn't like it any leaner than that for warm up idle. From what I've found though if you have a good ECU then getting close to stoich is possible, as I've found when I run the meter in factory cars on cold start they get to stoich within a very short period of time.

So for your question yes your only richening the mixture to maintain an ideal mixture in an ideal world (eg what new factory cars can obtain) but in the real world of aftermarket ECU's there seem to only be a few with the ability to have correction maps and idle control ability of a high enough standard to get close to stoich on a cold start idle.

As for decel, I run full fuel cut at 0% throttle 26" vaccuum and above 2000rpm. Works perfect, no jerkiness if you get back on it, no crackling or popping, no hesitation at any point on accel, just nice smooth throttle response . Interesting thing is my KE25 shits all over my bog stock 07 Subie for throttle transition and accelleration smoothness. The KE is everything I'd expect from a factory car and the Subie is worse than a $2 tuned shitbox under some situations

[andrew_mx83]

why dont any of u like the popping lol


thats the best part of decel


SNAP CRACKLE POP BURBLE BURBLE POP

[oldcorollas]

why dont any of u like the popping lol


thats the best part of decel


SNAP CRACKLE POP BURBLE BURBLE POP

because you sound like a fuckwit with an untuned car??

[TurboRA28]

Thanks all for your feedback.. Gives me more knowledge on what I am and should be doing

[jeffro ra28]

Joel, yours is autronic isnt it? Would be interested to know how you go with cold start as it is regarded as a "better" ecu. And the "better" ecu's are better at controlling cold start . allegedly....

[oldcorollas]

hmm, i never realyl played with having 100% cut of injectors on decel.. partly because with the cam overlap i didn't develop that much vacuum. (30kpa max?, ie 70kpa absolute.. or maybe 60?)

what vacuum do you have on decel?

[TurboRA28]

Yeah autronic, the cold start is working sweet. It's just I more wanted to check what I 'should' be doing with it. I have it around 20% enrichment at 20deg coolant and slowly taper that down to 0% at 50 deg.

[thechuckster]

i have 100% fuel cut on decel in my msefi setup. I have it wait 1 sec before cutting fuel.

Unlike stu's experience, mine doesn't kick too hard when the fuel comes back on. I think I have tried with no delay and apart from the odd zorst pop (taking a roundabout too fast and doing lots of pedal work) it was quite managable.

The fuel comes back on at about ~1700rpm (could be lower as I have a high idle and tweaks in the fuel map to stop the motor stumbling at low rpms), MAP has to be lower than 28kpa (e.g. throttle very shut), TPS has to be ~1 unit above the known 'closed' position (this is just in-case the return spring doesn't quite pull the throttle shut) and fuel cut will only happen once Coolant is >60 degrees.