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051 - COLD START - Fuel Enrichment

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Can you explain again the warm-up enrichment at low load (idle) vs higher load (opening the throttle)?

It was at 27:30 of the (051) webinar.-"...at wide open throttle...the high air velocity, we don't need as much enrichment"

but for acceleration enrichment, I understood that the engine need more fuel enrichment as we go from low to higher load as the fuel puddle gets bigger.


Attached Files

Sorry for the late reply.

One of the key reasons why we need additional fuel enrichment (over and above the normal fuel requirements at operating temp) are because the fuel will tend to wet out on the cold intake port wall and the intake valve and the fuel doesn't make it into the engine in a finely atomised or vapour form. Under larger throttle openings though the higher air velocity tends to allow less fuel to wet out the port wall or in other words the high air velocity does a better job of drawing the fuel into the cylinder and hence we don't need as much warm up enrichment.

This is a separate issue to accel enrichment and the accel enrichment requirements are still valid and still active when the engine is cold. I'm referring more to steady state operation under large throttle openings though.

OK thanks for the explanation and highlighting the additional warm-up enrichment at higher load/throttle (on the Link G4+) is in addition to the acceleration enrichment & the acceleration enrichment is also active during warm-up; so the net impact (warm-up+accel. comps) is more fuel enrichment at higher load during warm-up - this now makes more sense to me!

Would be nice to see a warm-up webinar #2, with a throttle servo:- full warm-up cycle with the throttle held open at say 15%, tuning the load axis of the warm-up enrichment, with a few blips thrown in along the way :)

As a side note, am starting to appreciate how much time, effort & resources OEMs would devote to tuning this area!

I'll just add a couple of points here to be clear:

1. In steady state conditions you need less additional warmup enrichment at WOT than you do at low throttle openings.

2. Under transient conditions (accel enrichment) you need additional fuel enrichment when the engine is cold.

3. Transient and warmup enrichment work in conjunction with each other - ie the accel enrichment is typically based on a percentage of the main fuel table.

It's quite tricky to perform a warm up tuning webinar as the actual time when the engine is truly cold is so brief.

Because I live in coldest place than anybody-I'd like to share some numbers for a cold start tuning as a beginning point.

Engine is inline 4 (3SGTE GEN3) with stock intake plenum and valves

Injectors are ID1000, base fuel pressure = 300 kPa

Trigger is Motronic 36-2, so it takes about 3 engine revolutions to start.

ECU is Haltech PS

Because it has no cranking table you should add "cranking" cell in base fuel table with VE~95% and AFR=13 in Target AFR table

For -10°C outside temp numbers are:

Prime pulse time = 43 ms

Cooliant temperature correction = 25%

Post start enrichment (2s, 3s, 4s, 5s, 7s, 10s, 20s, 140s) 70%, 65%, 65%, 55%, 45%, 22%, 5%, 5%

If we have some more days with outside temp around -20, surely I'll share)

Here is a log for -10C, a little bit richer than perfect 0.9 Lambda.

Attached Files

Thanks for sharing. It definitely gets harder to get perfect results when you have a very large swing in local ambient temperatures. Moving from our old base where winter temps would seldom be below 5-10 deg C to Queenstown where we are regularly seeing -5 to -10 has required a lot more work to get clean starting.

Believe me that -20° is a total nightmare. Even if the engine starts perfectly with primer = x, it dies on 4 second with post start = 90% before 4s with Lambda=1.5. I have to increase primer > x, because it's the one right way to evaporate fuel till 4s.

I don't know how should I handle with -30 or -40°C, sometimes we see these temperatures on thermometers)))

I like going over OEM information just for stuff like this.

here is two screenshots of how its deal with on a GM vehicle that I'm currently working on.

Look at the units carefully to see what they repersent, the first one is for factor likely a multipler, the other is lambda

This first one shows how much more fuel they add in based on map vs IVT ( inlet valve temp )

This next one is the open loop table ( when in open loop, generally right after it starts up it will be in open loop for a few seconds before going closed loop ), there is one for ethanol and no ethanol and p\n and D\R

You can see they are targetting a lot more fuel at cold in OL, combine that fact with the table up top so when throttle opens they have to add even mroe fuel at the various map areas, and still have to think there is also the traisent enrichments going on ( dynamics )

Hey guys,

The webinars on Cold Start Enrichment were great! Do you have any advice about additional ignition timing when the engine is cold?

Cheers, Dean

What engine, what ECU?

ECU is Haltech Elite 1500.

Engine is an aircooled VW Type 4 2827cc turbo. Using flex fuel but mostly e85.

Do you have a datalog of your current cold starts? Is this sequential injection? Does it have an idle air valve?

No the car has not even been tuned yet, it has just been started. It is sequential injection. It has a drive by wire throttle so it does have idle control. I am watching these Webinars and they have great information for the cold start fuel tuning but there just seems to be no information regarding ignition advancing or if it's even required. The Haltech has a few degrees of ignition advance by default for cold coolant temperatures and low load, however as I have a fairly large cam, my engine does not reach these low load cells at idle and therefore does not advance the ignition when cold. I basically want to know if I should be adding a degree or 2 at the idle zones when the engine is cold or if there is no point as I have idle control anyway. Does MBT change when the engine is cold? Thanks

Hey Dean,

I don't typically add ignition timing during cold start although this is quite common, particularly in OE applications. A little advance during cold start will have the effect of increasing engine torque (assuming your base ignition timing in the idle areas are below MBT to start with), which can help the engine idle after a cold start. In general I find that the base idle bypass vs ECT coupled with an increased idle target during cold start operation, and idle ignition control is sufficient to get OE-like cold start performance.

Thanks Andre!

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