Cold start enrichment advice.

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mgbloke
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Cold start enrichment advice.

Post by mgbloke »

To cut a long story short I have had a miserable time with the change from carb and dizzy to full throttle body engine management.
It turned out to be mainly wiring problems but all sorted now.
I have just fitted a new 5.0L engine with TA heads and am not confident that the guy that mapped it previously new what he was doing.
Please can you guys take a look ant my cold start settings and let me know what you think. Would like to know if they are ball park before I try and start it. The main fuel map I am pretty happy with but will need tweaking on a rolling road.
Thanks
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stevieturbo
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Post by stevieturbo »

There's a bit of a paradox with this.

ie you need to have normal operating temp mapping correct, before worrying too much about cold starts.

So anything that lets you get the engine hot to get those right first...just go with it, then tune it all when warm

Then from cold start with enrichments either low or zero and add fuel as required to make it happy and start reliably.

And obviously the engine also needs air to start, often many overlook this. Whether that air is via the main blade, some form of air bypass etc etc...entirely down to each users setup.

Never start with large enrichments, simply because you can flood the thing when then leads to non starting and you end up thinking it needs more fuel...vicious circle

Starting low, it's almost impossible to go wrong.
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DaveEFI
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Post by DaveEFI »

Dunno your software, but it it were MS, I'd say your cranking enrichment isn't enough, and your after start enrichment too much.

MS guidelines say:-

200-400% cranking when cold, 100% when hot.

For after start enrichment about 50% cold, 5 % warm.

But your software may well measure things differently, and I dunno TBs anyway - only port injection.

Are there no guidelines with your ECU instructions?

As Stevie said, get the normal temperature fuelling correct first, and start off on the weak side for any cold enrichment.
Dave
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mgbloke
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Post by mgbloke »

Thanks so much for the replies.
much appreciated.
the ECU is a Link G4 extreme (long story)

stevieturbo
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Post by stevieturbo »

Dont copy what other ecu's might do.

2-400% might work for MS....but certainly that is one motherfucking HUGE amount of increase

I've used plenty of ecu's on different engines, and never come across one needing anywhere near that for cold starts.


Again, keep it simple, start low and work upwards. Link make quite good ecu's and there is no reason it wont work great.
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http://www.youtube.com/watch?v=XgWRCDtiTQ0

Quagmire
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Post by Quagmire »

I don't quite see how the ECU being used has anything to do with it tbh - the engine needs what it needs fuelwise. How you define that whether as a percentage of warm fuelling or as a pure pulsewidth value shouldn't make any difference.

The guidelines on the MS pages are based on trying to start a generic engine, and so may not totally match your expectations as are not for anything specific engine.

Having said that in my experience the figures provided on the MS pages are usually close enough to use as a starting point.

Whats to lose? That's the joy of having a programmable ECU right? Save your current map away safe somewhere and try something different. If its doesn't work, the worst case is you have to restore your old map.

The megamanual (http://www.megamanual.com/ms2/tune.htm) says this:

Typically, the first time someone tries to start their engine with MegaSquirt® EFI Controller, it starts after about 5 minutes of alternating various cranking pulse widths numbers to get started (on the Enrichments page), and changing the:
•Cranking Pulse Widths: ◦The cranking pulse width at -40°F should be about 3 to 5 times the 170°F value.
◦If you over-estimate the correct values, you WILL flood the engine.
◦To begin, set the -40°F cranking pulse width to about 88% of your "upper" req_fuel value, and the 170°F cranking pulse width to about 23% of your req_fuel. Those should get you 'in the ball park' for starting.
◦Once you have the engine running, you can tune the cranking pulse widths with small changes, moving them up or down together, and check it over a few days worth of starts before deciding which direction to go next. Remember that the cranking pulse widths need to be with ~0.5 milliseconds of the optimal value at both -40ºF and 170º F. ◾You move them up and down together, but not by the same amount. You want to keep the cold cranking pulse width about 3 to 5 times the hot cranking pulse width.
◾For example, suppose your reg_fuel was 14. Then you might start with a cold cranking PW of 12.3 and a hot cranking pulse width of 4.0. Suppose you try this and see it is too rich, and your temperature when you tried it was 40°F. So you need to lean it out (after making sure the engine hadn't flooded, in which case you would have to clean the plugs). You might try reducing your cold cranking pulse width by 0.8 milliseconds, to 11.5. You don't want to also reduce you hot cranking pulse width by 0.8. You really want to reduce it by the proportional amount you reduced the cold pulse width, which would be 0.8*(4.0/12.3) = 0.26 = 0.3. So you would reduce it to 3.7.
This maintains a reasonable ratio between the pulse widths. You don't have to calculate it each time though, just adjust the hot number by about 1/3 of the cold number, and you should stay 'in the ballpark'. Conversely, if you had to richen the pulse widths, you might add 0.8, and 0.3, etc.

◦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.
◦It is very easy to flood the engine, especially when cold, without realizing it, and this can confuse your start tuning quite a lot. So it's better to start with low pulse widths and work your way up in small steps (lean cranking is much easier to recover from),
◦As you get closer to optimal cranking pulse widths, you can adjust just one of the hot or cold pulse widths a bit to fix particular starting issues - for example, if you have hot start issues, warm the engine up fully (ideally by driving, not idling) then shut it off and adjust only the hot pulse width slightly to get the best starting. You can do the same with cold start, but you can only do it on 'true' cold starts, which means that: a) you have to wait for a cold day, and b) you only get one test per day (starting it and shutting it off right away still warms the combustion chamber, etc, and basing your tuning on that will throw you off).
◦If your engine doesn't respond while cranking at all, try disconnecting the serial cable to the laptop from your MegaSquirt® controller. The power supply from the laptop may interfere with your MegaSquirt® controller at times, making the engine impossible to start. If you try to datalog a cranking attempt, and the datalog is blank, or you are getting resets (secL keeps dropping back to zero before reaching 255), then you likely need to disconnect the laptop while cranking. You should be able to reconnect after the engine is started, and tune/datalog normally, without any issues.
◦Most engines are quite sensitive to the cranking pulse widths, so you may need both pulse widths to be within about 0.5 milliseconds to start well under all conditions.
◦Make sure you have power while cranking, otherwise you are starting on your prime pulse, and will go crazy trying to tune it,
◦Keep the prime pulse short, less than 4.0, and ideally around 2.0, while tuning the cranking pulse widths.
◦Make sure you are not in flood clear mode while cranking,
◦Datalog your starting attempts using TunerStudioMS, and study them carefully, you will learn a lot,
◦Don't use EGO feedback to guide you on cranking pulse widths, it won't help you at all, and may confuse you a lot. Instead, use your subjective sense of how long it takes the engine to start at any temperature (you are seeking to minimize this, obviously)

•Afterstart Enrichment: If the engine tries to start, but dies right away, you need to adjust the after start enrichment. Generally this should be between 25-45% for 100 to 250 cycles,
•Warmup Enrichment: If the engine starts but dies after a several seconds or minutes, then you need to adjust your warm-up enrichment. Use up to 15% greater than the defaults if that seems to help.
•VE Table: Adjust the values at the idle kPa and rpm to get it to idle. You want to change the VE table entries while watching the engine MAP (in kPa) to try and lower the MAP as much as possible. Do this after the engine has warmed up. As you do this, the engine rpm will rise, and you may have to adjust the throttle stop on the throttle body to lower the rpm back to the desired idle speed. Once the idle VE are tuned, you will have to retune the afterstart and warmup enrichments.
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