Difficult to tune cold start - Advice needed

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shauer
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Difficult to tune cold start - Advice needed

Post by shauer »

This question is more of a general knowledge type of question than a question about a specific tuning parameter. I've been using various configurations of MS on the same engine for almost 10 years and this is a first for me. I'm hoping someone else has had similar experiences and might have a few ideas.

I updated the induction system on my engine over the winter and installed Bosch EV12 type injectors with the long extensions on them and have them mounted in the stock kjet injector location on my engine. This means that the injectors are spraying almost on top of the intake valves, very little air path from the injector to the combustion chamber. This is on a common plenum intake manifold.

My problem is with trying to tune cold start. I set the cranking pulse and ASE the same as my previous intake where the injectors were a few inches from the combustion chamber and the start acts like it's not getting enough fuel (cranking with no firing). I increase the cranking pulse about 5% to 10% and the engine will briefly catch and sputter but never really get going. If I do this two or three times the engine will catch and idle but I manage to foul a spark plug and need to burn off the carbon on the plug to get all cylinders firing again.

Having the injectors so close to the intake valves appears to make for a very difficult and sensitive cold start tune that I cannot seem to get right. I suspect the short air path does not give much time for the fuel to vaporize in the cold air? Has anyone else run into this problem, and how did you resolve it? There appears to be an extremely fine line between getting enough fuel vapor to start combustion and having so much residual fuel that you foul a plug...

I'm beginning to understand why the kjet injection systems had a cold start injector feeding into the plenum, that would give time for the fuel to vaporize. Unfortunately that really is not an option I want to explore if possible.

Any suggestions are welcome.

thanks
Steve Hauer
http://www.77e21.info
1977 BMW 320i with MAF, COP, IAC, Sequential fuel and spark, MS3 knock sensing
MS3 / MS3X / V3 mainboard, MS3 V1.5 a4
subwoofer
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Re: Difficult to tune cold start - Advice needed

Post by subwoofer »

Drop me an email to remind me if I forget to do it, but you can have a look at my setup, also plenum and stock injector position.
I have found that a solid shot of fuel for just a very few cycles gives clean starting, the crank taper curve is your friend.
Joachim
1974 Jensen-Healey
1990 VW Caravelle Syncro - running MS3+X
2014 Ford Fiesta EcoBoost
shauer
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Posts: 364
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Location: Rochester, NY USA
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Re: Difficult to tune cold start - Advice needed

Post by shauer »

Thanks, I will also try enabling the cranking pulse taper for my drive home today. I will be interested to see what starting percentage you use and how quickly you taper it down while cranking. I have not been following feature development for few months while I took a break during the winter.

I also discovered that my priming pulsewidth was very small. I increased that to approximately what the ASE pulse width is immediately after cranking in an attempt to wet down the walls and maybe get things more stable during cranking.
Steve Hauer
http://www.77e21.info
1977 BMW 320i with MAF, COP, IAC, Sequential fuel and spark, MS3 knock sensing
MS3 / MS3X / V3 mainboard, MS3 V1.5 a4
subwoofer
Super MS/Extra'er
Posts: 884
Joined: Sat Apr 30, 2011 12:34 pm
Location: Sandefjord, Norway

Re: Difficult to tune cold start - Advice needed

Post by subwoofer »

Back at a computer I can post attachments from...

There may be better ways of doing this, but this way works for me. It starts just fine with a very short priming pulse, but adding the priming pulse makes it faster. The idea is to have an initial very rich condition, tapering off to something that will not flood the engine too badly if start doesn't happen immediately. If you ever see very cold weather, adding the setting "batch injection while cranking" and setting number of squirts to 4 simultaneous will effectively remove the 65ms maximum pulse length that may cause slow starting if you don't have huge injectors or you run on corn.
Joachim
1974 Jensen-Healey
1990 VW Caravelle Syncro - running MS3+X
2014 Ford Fiesta EcoBoost
subwoofer
Super MS/Extra'er
Posts: 884
Joined: Sat Apr 30, 2011 12:34 pm
Location: Sandefjord, Norway

Re: Difficult to tune cold start - Advice needed

Post by subwoofer »

I too would be interested to know what other people are doing for cold starts, I now get consistent starts in 3 to 6 compressions (< 1.5 cycles), but I would like to get it down to OEM like "bump the key and it starts" territory, without too high risk of flooding if it for some reason does not fire on the first cycle. So suggestions for improvements to my tune are welcome!
Joachim
1974 Jensen-Healey
1990 VW Caravelle Syncro - running MS3+X
2014 Ford Fiesta EcoBoost
subwoofer
Super MS/Extra'er
Posts: 884
Joined: Sat Apr 30, 2011 12:34 pm
Location: Sandefjord, Norway

Re: Difficult to tune cold start - Advice needed

Post by subwoofer »

Anything to report on this, Steve? Have you experimented with it?
Joachim
1974 Jensen-Healey
1990 VW Caravelle Syncro - running MS3+X
2014 Ford Fiesta EcoBoost
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