EFI Puzzler

[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?

[ohcbird]

It still sounds to me that the IAC is cranked out to far- fattening it up might get it to catch a bit better. Can you see the IAC #s fluctuating while you're starting it, or does it stay static (slaved to the ECT)?

Still weird about the leaning issue!

[parsonsj]

Can you see the IAC #s fluctuating while you're starting it, or does it stay static (slaved to the ECT)?

I don't know. I think the thing to do next is log the IAC numbers and watch what the ECM does to get the motor to the target idle speed. That might be a clue to see what is going on.

About the leaning problem, something just occurred to me: I wonder if the issue was that we didn't change the fuel calc parameter for Injector Flow Rate. At 60 psi, the injectors flow more fuel right? So the number should have been more increased quite a bit ... maybe to 55 psi or something. Perhaps the ECM got confused, and was calculating the fuel load based on the smaller number? I can't quite wrap my mind around that (it's 2 am here on the East Coast, lol).

But I know we didn't change that value.

jp

[ohcbird]

Does your XFI 'see' the extra fuel pressure, and have the ability to compensate?

I did that on my S/C toyota- I got the sweet spots golden, then forgot to tune the rest of the table! It popped like a madman...

[parsonsj]

It doesn't have a connection to any sensor. We sure didn't tell it. That's gotta be the problem.

But, as Jody says, if GM only went to higher pressures for their newer deadhead plumbing, then I don't need higher pressure. It won't resolve my slow cold start issue.

jp

[ohcbird]

Agreed- and with your manifold, I don't think it's a problem anyway.

Just pump the pedal a few times to get the choke to close!!

[parsonsj]

An update:

Yesterday, I swapped the engine over to SEFI (it was bank to bank because the original tuner couldn't get the car to start that way). Now I know why! He had put in the wrong firing order!!!!!

Anyway, now that I'm running SEFI the car seems smoother at idle and part throttle accel.

Today I increased the IAC start position about 20%, and allowed it to move faster and farther. The car started much quicker, with no sag after initial fire. Much much better.

Tomorrow, I'll increase the cranking pulse width about 10% and see if that helps too.

jp

[camcojb]

Originally Posted by parsonsj

An update:

Yesterday, I swapped the engine over to SEFI (it was bank to bank because the original tuner couldn't get the car to start that way). Now I know why! He had put in the wrong firing order!!!!!

Anyway, now that I'm running SEFI the car seems smoother at idle and part throttle accel.

Today I increased the IAC start position about 20%, and allowed it to move faster and farther. The car started much quicker, with no sag after initial fire. Much much better.

Tomorrow, I'll increase the cranking pulse width about 10% and see if that helps too.

jp

that's great John. That's how you find the balance. The IAC park has to be enough so when it does fire it doesn't try to die immediately. Then figure out what pulse width makes it happy at that opening.

Jody