ECMlink Common Questions and Answers

[Calan]

The following are questions/statements that have been posted in past threads, along with responses provided by various members here.




***** This is a work in progress *****

If you would like to contribute, or if you come across something that you think should be added to this thread, PM us.

 

[Calan]

Is it worth it trying to get AFRatioEst and my logged WB to match?

Absolutely. If ECMLink isn't showing the correct measured AFR, you have no point of reference for tuning while reviewing logs. It's also a good idea to compare your wideband gauge and logged value to a known calibrated wideband at a dyno or speed shop.

Calibration is everything...whether you are talking about wideband sensors, boost gauges/sensors, expected airflow to actual airflow, amount of fuel delivered (measure how much fuel the pump can flow, get the injectors tested, etc). Anything that isn't a known value adds some amount of guesswork into the tune, and getting a solid repeatable tune is difficult enough even when you are working with known values for everything possible.

 

[Calan]

My goals today are to try and get my BoostEst and boost gauge to be the same. Also my wideband and AFRest to be closer.

To keep it simple, pick one method or the other. You'll pull your hair out trying to get your wideband to match AFRatioEst, while also trying to get BoostEst to match actual boost. Just take my word on this.

My suggestion - Ignore BoostEst and focus on getting your fuel trims (CombinedFT) to be as close to 0 as possible during closed loop, using ECMLink's MAFComp adjust tool. Then work on getting your wideband to match AFRatioEst in the open loop areas. This page will help, if you haven't seen it: MAFComp Adjust (CombinedFT)

 

[Calan]

When I was dialing in my CombinedFT trying to get it close to 0 as I could at idle, I was adjusting the injector deadtime.

So are you telling me that by adjusting the MAFcomp, that will be changing my CombinedFT?

AFR is a result of both airflow and fuel delivery. When you adjust injector deadtime, you are changing fuel delivery; when you adjust MAFComp, you are changing the ECU's idea of airflow.

So both of these will affect CombinedFT, which is just the AFR error as measured by the front O2 sensor.

WBFactor = AFR error, obtained by comparing a logged wideband to AFRatioEst.
CombinedFT = AFR error, obtained by the ECU monitoring the front O2 sensor and keeping track of corrections it has to make while in closed loop.

It's a balancing act between adjusting injector deadtime and the MAFComp sliders. Deadtime has much more effect at short pulse widths (low fuel flow, idle, light cruising). The ECU is only briefly firing the injector, so the mechanical delay of the injector has more of an effect. When the injectors are open for long periods of time (WOT, high fuel flow), the deadtime isn't as much of a factor. So you have to find a balance between injector deadtime and airflow calibration at different operating points. It's a PITA, but manageable after you get the hang of it.

So either way, CombinedFT should be at 0, also deadtime and MAFComp affect CombinedFT?

Correct.

 

[Calan]

What about this huge spike in my MAFComp table? It shouldn't spike as it does? Why would DSMlink suggest such a spike?

You must be logged in to view this image or video.

Because something in that area is causing a big change in airflow. Dips and peaks are normal; large changes and spikes usually point to something mechanical going on, like a boost leak, MAF issue, etc.

That 50hz spike looks pretty typical for a GM MAF, a hacked stock MAF, or a setup where the PCV breather is being vented to atmosphere (no longer connected to the turbo inlet after the MAF). This is a sign of un-metered air entering the engine, causing the ECU to fight a lean condition at low airflows.

The PCV breather hose is NOT connected to the intake, but rather has a breather filter on the nipple right off of the valve cover.

There is your vac leak.

During off-boost (idle and cruise), air is being sucked into the IM from that breather and through the VC and PCV valve. Since that air isn't coming through the MAF, more air is entering the engine than the ECU thinks there is, so it's running lean. It's most noticeable at low airflow, which is why you are having to crank up the 50hz slider so much to compensate for it.

 

[Calan]

The injector deadtime/latency has less of an effect as the duty cycle increases. It becomes less and less of the total time the injector is told to be open, so it's effect decreases.

'Tis true. For general reference, we tend to tell people that you can expect a change in deadtime to have twice the effect on mixture at idle that it would have at cruise because effective pulsewidth at idle is half that of cruise. This effect certainly decreases as effective pulsewidth increases. More airflow results in higher effective pulsewidth and less relative effect from deadtime.

One (perhaps non obvious) way to use this in tuning is to check combined fuel trim at idle and compare to cruise. If idle fuel trim is more positive than cruise fuel trim, then increase deadtime. If idle is less positive than cruise, decrease deadtime. Because the effect of changing deadtime is greater at idle than cruise, this general rule tends to bring the two fuel trims together. Once they are matched (non-zero, but equal), you can then adjust global fuel to bring them both down to zero together.

This only works with well-matched injectors with linear flow rate curves between idle and cruise. With non-matched injectors and/or non-linear flow, you have a bigger problem of course.

Thomas Dorris
ECMTuning, Inc.

 

[Calan]

What do you mean "I shouldn't use the sliders to tune with"? People have been using the sliders in Link for years.

The fuel and timing sliders in ECMLink are a holdover from earlier versions. While they are useful for making quick, temporary changes on the fly, it's much better to keep the sliders zero'd and use the new DA tables to change target AFR and timing.

The DA tables have much more resolution than the sliders, since they allow you to adjust fuel and timing based on both load and RPM.

 

[Calan]

I have a mtxl wideband in the front o2 position and use nb sim through that. My question is why when it is logged does it look so square? Like it jumps directly from .8v to .2v. There is no in-between like I've seen in so many other logs. Is there something wrong with this?

This is normal. The narrowband O2 signal is switched; meaning it changes state when the AFR goes above or below a certain point, which is normally 14.7:1. The actual values it switches between are somewhat irrelevant, as long as they are above or below the threshold that the ECU is watching for.

Factory NB O2 sensors produce an analog 0-1v signal, so they usually have more noise and somewhat inconsistent waveforms. Simulated NB signals are digitally created from an analog 0-5v wideband signal, so their waveforms are much more well-defined and almost perfectly square.

What is going on with my afr when I let off the throttle? It goes really lean, all the way up (22.4), when I let off. Is it supposed to do that?

It's normal. When you let completely off the gas while cruising in gear, the ECU cuts off the injectors, so your WB will go max lean. Once RPM and load drop below a certain point and the idle switch is closed, the ECU will resume firing the injectors to maintain idle.

 

[Ludachris]

Test...