Cold start/Running Issue

Hi all, wondered if you could give me some guidance. Last year having completing the HPA stand alone tuning course (amongst others) I have successfully mapped my VR6 Turbo Golf drag car using a EMU Black. All the mapping was done at the track using logged data. I'm happy to say that for the most part its been really successful, I've made good consistent passes, but the only issue I have is a bit of a cold start/cold running anomaly.

Cold start aside, the real curious issue is that before I hit around 80 degree water temp, the car stutters, hesitates or even cuts out whenever you touch the throttle with anything other than the lightest touch. However if you do very gently bring the rpm up to say 3k, then give it a good rev it behaves as you would expect. Once above 80 degrees it behaves much better and will make a solid 1/4 mile pass at WOT without issue.

I mention the cold start as well, as sometimes it can take a while to start, especially in colder temperatures, and I wondered if it could be linked.

So far I've tried changing cold start values, cranking values, fuel tables (up and down), accel enrichment, timing (in case I needed to add to assist the tip in) but to be honest I've not felt that any of that had made the slightest difference. I've added a copy of the map and some logs from earlier today when I gave it the first run up of the year to try and provide a fuller picture. The odd thing on the logs and live data is when you touch the throttle when cold you can see the lambda just reads full lean immediately. Which obviously would explain it, but I can't correct it whatever I do with the fuelling?

Am I even looking in the right place or is this perhaps not a tuning issue but mechanical/plumbing related perhaps? I've had a good look for air leaks and the like and all the plumbing seems correct and I haven't found anything amiss? I'd love to know what you all think, and any addvice you have for what I should be looking/testing for?

Thanks,

Ed

Ed,

If everything is great when the engine is warm, that narrows it down a lot.

If you're running a high ethanol content, the window of acceptable fueling becomes a lot smaller than on gas, so far greater precision is required.

Also, while an engine is cold it's far more likely to misfire during a brief lean condition, so any areas of the main fuel table or accel enrichment which aren't quite optimized, will be far more likely to induce a hiccup when the engine isn't warmed up.

Since this is a drag car, I would consider targeting a bit richer lambda target during warmup than at hot idle if you aren't already. Additional tip in enrichment is also required while the engine is cold. Either too little or too much accel enrichment can cause a hiccup, and wideband data isn't always completely clear in a brief transient. Over time you may find over rich tip in and over lean tip in sound differently though. Lean sounds a bit more like a dry cough, over rich sounds a bit more like a gurgle. Again, if you're on a high ethanol fuel, the window of correct fueling is much smaller and less tolerant than on gas until the engine is warmed up.

This will take some tinkering, but I hope that helps and please let us know how it goes.

Hi Mike,

Sorry for not replying sooner and thanks for the advise! I finally took the car out for an event and definitely found some areas of the fuel table that needed optimisation, but solving my issue turned out to be a lot more straight forward. I was looking through the accel enrichment settings, as you suggested, and toggled on the 'Enable Full Group inj.' setting, which as I understand it batch fires the injectors during accel enrichment. This has completely removed the issue I was seeing when cold. I assume there's no real downside to this?

FYI car is run on 99ron pump fuel with an additive.

I thought i should update the thread in case this helps someone else.

Thanks again for the help.

I'm glad to hear things are going well!

When it comes to acceleration enrichment, if the engine stops misfiring and seems smoother and happier, you've probably made the right choice. By enabling that setting, it sounds like you caused an increase in total accel enrichment and gave the engine the extra fuel it needed.