rwyatt365

Environment:

• '99 1.8L, newly rebuilt engine;
  • forged bottom end
  • BP4W head
  • Flat top manifold
  • Skunk2 TB
  • Exhintake swap
  • Degreed cams (nothing radical...yet)
  • Kraken high-mount manifold
  • BW 6758
  • 3-in exhaust (homebuilt)
• MS3PNP (tune attached)

Problem; from a "cold" start, after the RPMs settle down (there's a pretty bad oscillation at first, but that's not the issue here), the AFR is full-lean and the idle valve is open to 52.1% - which is where the idle cranking value is set (more or less) for the CLT. My crank-to-run taper is set for 11 seconds, but it takes approx 3.5 minutes for the idle PWM to drop down to the target. Until then the AFR stay full-lean. See picture.

This behavior is kind of consistent when driving as well. When I'm cruising and the CLT are "normal" (i.e. in the 175-185 range) the AFRs at idle are bordeline too lean. But if I hammer it and the temps rise beyond the 190s, the idle AFRs drop richer. This is telling me that I have some kind of temperature-dependent actuation of the ICV, which...okay. What I'm wondering is if there is a setting where I can "tune" the ICV actuation -based on temperature?

Picture, or it didn't happen;

redursidae

Yes, there is a coolant based IACV position table under Startup/Idle > Closed Loop Idle Initial Value. As your tune is configured, the Y axis is coolant temperature, and X axis is Idle Target RPM.

Rrrracer

True, but that is not causing his valve to hang open. OP, post the log as well when you get a chance so we can see what's driving the high IAC value for so long after the engine is started.

oreo

I think his idle valve is wide open because the MS is trying to reach target idle rpm value, with a very lean AFR.

The OP needs to tune warmup additional fuel under startup/idle -warmup enrichment.
Once he maintains an healthy AFR during warmup, other tuning can be done.

Having said that, if the AFR at hot idle is not correct/ideal, then don't spend too much time perfectly setting up the warmup enrichment.
You will need to redo that, after the mixture is dialed in when the engine is at normal running temp.

Ted75zcar

iTrader: (2)

There is some turkey on FB that insists idle AFR doesn't matter. He actually takes people's money to "toon".

SMH

If you are lean at idle, the engine requires way more air (higher load - 55kpa for 975 rpm!) in order to deliver the necessary fuel to produce the hp needed to achieve a target engine speed. More fuel (richer) equals more power, which equals faster engine, iac closes to reduce air (load).

rwyatt365

Here's the log (attached).

I had an epiphany last night while sleeping. Tell me if I'm off-base here...Maybe it's not the CLT that is hanging the ICV open for so long. MAYBE it the IAT that's the culprit. MAYBE it's the Air Density equation that is causing the valve to "stick" open for so long. MAYBE the engine is trying to compensate for a colder intake charge by pulling fuel at lower temps and putting it back in when the intake air is hotter. That would explain why the AFRs are so lean after first start (even after WUE has ended) but gradually richens up as the IAT warms up (not the CLT).

I'm okay with being wrong.

Ted75zcar

iTrader: (2)

I don't look at logs/tunes much anymore, but there are key details just in the picture you posted. Your IAC is most likely open because you are targeting an RPM at this time that is greater than 975. The ECU is opening the valve to allow more air to increase the RPM, but you are making so little power due to a lean/poor burn that you can't hit your target. To put things into perspective ... my engine requires roughly 15-25hp to idle at 975 RPM. This is full cold, while driving a 1L PD supercharger. With efficient combustion, I need between 25kpa and 32kpa of air to achieve this power. At 55kpa I will be producing somewhere between 65 and 75hp, which with no drivetrain load would redline the engine very quickly.

Many of the widebands out there initiate a heater reset on power cycle and read full lean for a period of time. Innovate is the worst on this front in my experience, I will sometimes install an older AEM for cold-start tuning on vehicles with Innovate. When tuning a car that has a WB that does this, I will power it from a separate source so it doesn't do this reset during cranking. The point here is that you can't look at your AFRs during this reset period and interpret what is going on with the engine. You have to get all of the other factors setup well such that during this time the ECU is close in open loop to hitting your targets. This is the point Oreo is trying to make. Get idle tuned perfectly at whatever you consider to be your normal operating conditions. You then work back to the cold start conditions in a way that your open loop parameters (WUE, ASE, IAC cranking, IAC initial, EGO delays, VE, timing, ...) are close enough to get a stable and predictable response while in open-loop-after-start.

The appropriate normal condition idle AFR is somewhat subjective, and I won't go into detail here as to why. The old tried-and-true method of setting a reasonable fixed timing of say 14 degrees and adjusting the AFR to achieve the lowest required manifold pressure to maintain target RPM is a good start. Turn off any idle timing correction features while doing this test, and your VE table/IAC PID/EGO PID need to be tuned well in the idle areas to do this. Turn off all accessories and disconnect your cooling fans. Don't get bent out of shape if you end on a value richer than stoich here. Reality is that if you are slightly richer than stoich, your load will be reduced which in-turn causes the fueling equation to reduce the absolute amount of fuel. If you ~ really ~ want it to idle at stoich, you use the above procedure but then have to tune it secondarily in the timing domain such that the combination of fixed timing and stoich AFR result in the lowest manifold pressure. A fascinating experiment on this front is to compare the actual injector pw (indiciative of absolute fuel volume delivered) and the resultant manifold pressure of these two optimized operating points. I suspect you will see that with stoich your load is higher, but the injector pw for the two remains largely unchanged (same fuel for both AFRs).

It has been years now since I have really been deep into tuning, but I believe there is an option to use CLT only during start-up.

rwyatt365

Ted, I'm going to have to take a few minutes (hours?) to absorb this, but it sounds like you are on the right track...I'll report back when my brain catches up with my eyes.

I can say that I use an AFR500 (from Ballenger Motorsports) and it does indeed go through a warmup/calibration cycle on key-on. I always wait for that the complete before starting the car and DEFINITELY before doing a datalog.

poormxdad

A tangential comment... I'm curious. I was not aware the "Exhintake swap" was something done with the BP4W head. I went with the MSM intake cam for my NB1.

Rrrracer

Oreo and Ted nailed it; the car is not achieving CL Idle target RPM, so the valve and adaptive spark advance are maxed out trying to hit it.



The question is why are we idling so low with the massive amount of IAC duty cycle? This engine should be running 3000 RPM or more LOL... it's likely lean.

All the advice here is solid; you absolutely need to have your fully-warm idle squared away 100% before you can tackle any of the cold start stuff, as it is the foundation upon which all the other settings and modifiers are built.

I'm absolutely not trying to be mean, quite the opposite, but there's a lot wrong with this tune. The big ones:
- I question your req fuel, deadtime and voltage curve settings, and if you really do have 1050cc injectors I would hope you would also have some sort of small pulsewidth data
- MAT air density table never goes below 102.9% at 200* F
- Cranking RPM far too high at 700 RPM, should be around 400

There's more, but you need to focus on getting your injector characterization correct, then your warm idle, and go from there. HTH!