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Best way to tune a cold crank 

 

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 Post subject: Best way to tune a cold crank
Posted: Sun Aug 28, 2005 6:56 pm 
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Hey all

Im having issues with cold start (EMS 8860)
Mostly the initial cold crank

Is there any theroys on tuning a cold start/crank?

what amount of fuel (compared to idle maby?)
what amount of timing
and cold crank percentage

eeek!

thanks :)

 

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Posted: Mon Aug 29, 2005 1:40 pm 
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John,

Might pay to have a look at the megasquirt section on this.

Covers the theory and gives some 'rules - o -thumb'

http://www.megasquirt.info/ms2/tune.htm

Quote:
Setting the Cold Start and Warm-Up Enrichments

If it is cold out, you may have to figure out the cold start enrichments/warm up enrichments right away to keep the engine running until it warms up. If it is reasonably warm out, the default values may be sufficient and you may be able leave the cold start enrichments until you have the VE table and other parameters in a reasonable state of tune.

During cranking mode (defined as when the RPM is less than 400), MegaSquirt produces cranking pulse widths that are calculated by a linear interpolation of two end-point values defined by the user, one at -40°F and one at 170°F. these are set in the warm-up wizard under 'Tuning' in MegaTune. They are called Pulsewidth at -40°F (ms) (CWU) and Pulsewidth at -40°F (ms) (CWH).

A typical setting for a Chevrolet small block V8 with a Tuned Port Injection set-up and 30 lb/hr injectors is 2.0 milliseconds at 170°F and 10.0 milliseconds at -40°F. The optimal values for your combination are likely different, though generally should follow a similar pattern.

During cranking, MegaSquirt-II injects one pulse for every ignition event, so for an 8-cylinder it shoots out 8 times for 720 degrees crankshaft, with all injectors squirting. So with the above values, at 170 degrees, the effective amount of fuel per cylinder is 8 × 2 = 16 milliseconds. For -40°F it is 10 × 8 = 80 milliseconds.

Note that even in a 'piggy-back' application, do not set MegaSquirt's cranking pulse widths to zero. This will cause unpredictable pulse widths up to 13 milliseconds. Instead, set them to 0.1 milliseconds in that application. This allows very little fuel to flow.

Once the engine fires up (defined by engine RPM greater than 300 RPM), the engine goes into after start enrichment (ASE). The after start enrichment starts out at a user-defined percentage enrichment value (typically around 20%), and ramps down to 0% after so many ignition trigger events, which is user-defined (use about 200 for this number to start). This is an enrichment above the normal warm-up enrichment, which is temperature dependent.



You're a smart lad, i'm sure you can convert this into "ems - speak"

Pretty sure it's a fuel thing... spark advance shouldnt be too different to the usual cranking settings..

 

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Posted: Tue Aug 30, 2005 12:09 am 
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I'm having a little trouble with my wolf, I find it starts after about 4 seconds of cranking, but about ever second time I start it from cold, it will have a backfire, sometimes small, sometime bloodly loud.. I'm thinking to much fuel, but havent played with it yet.
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Posted: Tue Aug 30, 2005 12:12 am 
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mine takes about 4-6 sec's to start when cold, its fine when warm tho :?

btw, that mega squirt thing is a good read, cleared up a few questions i had. Thanks :)

 

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Posted: Tue Aug 30, 2005 1:35 am 
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tjb45 wrote:
I'm having a little trouble with my wolf, I find it starts after about 4 seconds of cranking, but about ever second time I start it from cold, it will have a backfire, sometimes small, sometime bloodly loud.. I'm thinking to much fuel, but havent played with it yet.


I'm still in the process of getting my Megasquirt into the car but from what I've read Backfiring and stuttering are actually LEAN conditions as I found out recently when my O2 sensor started to go lean, It got to around 19-20:1 AFR then started to backfire.. So sounds like it needs richening up???

 

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Posted: Tue Aug 30, 2005 2:02 am 
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bloody hell jonno still having dramas with the cold start?

time for that new car you want me thinks...

 

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Posted: Tue Aug 30, 2005 12:18 pm 
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shh frank, dont tempt me


I also think it may be because ive changed my injectors to fire 720* from 360*...?

 

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Posted: Tue Aug 30, 2005 12:25 pm 
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I cut a bit of fuel from mine this morning, and it seemed to start better, no back fire. What timing are you running during starting?
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Posted: Tue Aug 30, 2005 1:55 pm 
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SVO XR6 wrote:
shh frank, dont tempt me



DOUBLE dare!

 

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Posted: Tue Aug 30, 2005 10:24 pm 
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prob about 10% less fuel then idle, 18* timing

But there is a "cold crank" setting which is the amount of fuel on cranking. Ive set it at 65% now, but ive tried 0% and 100% but doesnt seem to make sfa difference

 

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Posted: Tue Aug 30, 2005 11:21 pm 
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SVO XR6 wrote:
prob about 10% less fuel then idle, 18* timing

But there is a "cold crank" setting which is the amount of fuel on cranking. Ive set it at 65% now, but ive tried 0% and 100% but doesnt seem to make sfa difference


Try greater than 100%... ?

 

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Posted: Tue Aug 30, 2005 11:37 pm 
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ya cant. it goes from 0-100%

i think its a % more then "X" fuel....f**k knows what x is :D

 

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Posted: Wed Aug 31, 2005 1:42 pm 
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SVO XR6 wrote:
....f**k knows what x is :D

It marks the spot

 

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Posted: Wed Aug 31, 2005 9:46 pm 
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ahh, now it seems so much more easy!!!

thanks kurt

xxoo


PS: i added a lil more fuel (2%ish) and 2* more iming and it seems to start better... But i worrie too much fuel @ start could not get burnt and be pushed past the rings or dry up the cylinders and f**k my rings.. possible?

 

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Posted: Wed Aug 31, 2005 9:53 pm 
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Ive mucked around with my Wolf, starts perfect now, all temps. It always takes 3 turns of the motor to start, but thats normal and most will take a few turns as the ecu needs to find TDC befor it will inject fuel.

Does the EMS have cold start enrichement and cranking fuel rate?

if its starting ok when warm then you only need to adjust the cold start enrichment... this feature on the Wolf just add fuel to YOUR set level and slowly decreases it until it gets to 70deg... wolf say to set this to 50%

When setting up your base tune you would have had to set the cranking rate... turning the motor over and slowly adding fuel until it starts cleanly then dies. Then, you set the idle rate, but when cold you need to statr the cold enrichment at 50 and work up or down until its idles ok...
Get that all right and she will fire any time
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