EFI Puzzler

[parsonsj]

iac position

Hmm. I can't say I've done very much with iac. That's a good idea of something to play with that I haven't done much. I'll check it out. Thanks.

jp

[camcojb]

Originally Posted by parsonsj

Hmm. I can't say I've done very much with iac. That's a good idea of something to play with that I haven't done much. I'll check it out. Thanks.

jp

it's critical to get that right. Where it parks determines how much bypassed air is happening while it's cranking. The balance between that and cranking fuel determines how hard it is to start at all temps. Of course cold starts need more fuel and more iac.

If you find it starts easier with the throttle cracked a bit, open the iac start position more at that temp.

Good luck.

Jody

[parsonsj]

Here's the current IAC vs Coolant Temp values. Look reasonable?

jp

[camcojb]

Originally Posted by parsonsj

Here's the current IAC vs Coolant Temp values. Look reasonable?

jp

looks reasonable. How much have you bumped the cranking fuel in the colder areas?

[parsonsj]

The cranking fuel is up about 20% at 70, though it is closer to 15% at 85-90 degrees.

jp

[sacarguy]

lower you iac at crank for cold temps and raise your low temp cranking fuel up ..


also is your pump wired up to prime when you key on or is it just constant after sitting for a decent amount of time without a priming pump this can happen as you lose fuel preasure in the rail.

leaning out

2 things
1 do you have the wide band setup so you are in closed loop .. your raising the fuel preasure and can be fatenting it up causing the ecu to start corecting the other way.
2 are you sure your fuel pump can handle the load of the higher preasure without losing a ton of volume.

[parsonsj]

Originally Posted by sacarguy

lower you iac at crank for cold temps and raise your low temp cranking fuel up ..


also is your pump wired up to prime when you key on or is it just constant after sitting for a decent amount of time without a priming pump this can happen as you lose fuel preasure in the rail.

leaning out

2 things
1 do you have the wide band setup so you are in closed loop .. your raising the fuel preasure and can be fatenting it up causing the ecu to start corecting the other way.
2 are you sure your fuel pump can handle the load of the higher preasure without losing a ton of volume.

I think Mike Norris finally got the cold start figured out. And with my latest changes it starts faster than my truck! Amazing, but true.

But to answer your questions:

1. Yes, I have a priming sequence. At key "on" the pump primes for 10s, and I get fuel pressure after about 4s. I then start the car. It starts immediately now!

2. I'm using an Aeromotive A1000. I'm sure it can deal with volume at higher pressure.

3. I've got a wideband and run closed loop after the engine warms up.

jp

[ohcbird]

JP-
what are your fuel #s during cranking? You might try closing the IAC a bit more for the same amount of fuel, then see what happens to idle quality & stability. How well does it transition from cold-warm-running temp?

IRT the leaning issue w/ greater pressure- was this open-loop, or closed? The injectors are supposed to be able to handle 75 PSI before overcoming the pintle or disc, so you should have seen a fattening, given all else being equal.

[parsonsj]

The car starts after about 6 seconds ... then nearly dies (or actually dies). Then I restart it, and it nearly dies ... then catches ... and then runs fine.

Listen to how the car starts. This video captures it very well:

https://www.youtube.com/watch?v=qAZPVNMh1SU

You don't have to watch the whole thing ... but that's what the car does when starting.

Yes, the leaning at 60 psi was very odd. It was at open loop. We did another experiment: we had the car hooked to the dyno A/F meter, started the car, and slowly increased fuel pressure. As fuel pressure went up, the mixture leaned out. 14.5, 15.0, 15.5, 16, etc.

jp

[parsonsj]

Cranking fuel (pulse width in ms) vs Coolant temp

20.1 ms 55 degrees
20.1 68 degrees
18.9 85 degrees
16.8 102 degrees
15.0 119 degrees
12.2 136 and up

Was that what you were asking?