How does the ECU work in open loop?

[zach44102]

My car pulls hard as shit, and the AFR is right at 12.5:1 at wot @7000 rpm in open loop. Once the car is warm and running closed loop it runs really rich and looses top end power. 10.2:1 AFR by 6500rpm.

So how does our ecu work in open loop? What signals does it ignore? The Maf and o2's? And explanations?

 

[yamahaSHO]

WOT is ALWAYS Open Loop and has nothing to do with cold vs. hot.

Closed Loop is idle and cruise, that's it. It uses the MAF and O2 sensors to hit a target of 14.7:1. Open Loop just uses the MAF to calculate load and look up commanded AFR's.

 

[Toolman]

You MAF is always being monitored and used, it is the primary source of information for the engine.

In OL, your MAF and your commanded fuel are the main things looked at, and assuming your injector parameters are close to where they need to be, you should be okay. It is in CL that the O2's are used to compensate. in OL, the O2's are ignored. My track car does not have O2 sensors. It is in OL at all times.

 

[Toolman]

Again, I am a slow typer.

 

[zach44102]

So at WOT its not using o2 sensors to calculate the target AFR, just the MAF? So if im hearing this right o2 sensors should have no effect On WOT AFR's?

 

[zach44102]

Ok so with me changing 2 maf's and still getting the same AFR's at WOT sounds like the rich problem is just a tuning problem. Unless im having ignition problems correct?

 

[yamahaSHO]

O2's have NO effect on WOT.

We have no idea what you have a for a current tune.

 

[zach44102]

O2's have NO effect on WOT.

We have no idea what you have a for a current tune.

Well its a stock tune is the problem. Im just trying to figure out why the ECU would all of a suddon command 10:1 AFR's out of nowhere.

 

[yamahaSHO]

Stock tune, modified car...


Here's your sign.

 

[SHOspazz92]

Stock tune, modified car...


Here's your sign.

The problem is it never did it before. All of a sudden the car is commanding 10:1 @ WOT. So again, I say something is amiss with the car, not necessary the tune.

 

[yamahaSHO]

How do we know the car is commanding that AFR?

 

[zach44102]

If the car uses the MAF as at WOT and not the o2 sensors then im not going to touch the o2 sensors. But i have tried 2 MAF's and cleaned both with nothing changed. Im going to pull the plugs tomorrow to see how they look. Maybe im having ignition problems.

 

[zach44102]

How do we know the car is commanding that AFR?

Why would a stock X2j command 10:1?

 

[yamahaSHO]

We don't know what it is commanding. What is learned from CL is applied, to an extent, to OL.

When you do a log, you'll see the correction factor in CL as well as what the ECU is actually commanding to hit what is in your table. The stock X2J commands in the 11's. If the car is modified and the MAF is completely calibrated [for your car], it can be very easy to hit AFR's like that, especially as the environment around you changes.

At some point, you're going to need to start data logging.

 

[zach44102]

I should be able to datalog in 2 weeks or so. Maybe shorter.

 

[SHOspazz92]

How do we know the car is commanding that AFR?

Commanding was a not what I meant. oops.

-Sam

 

[rubydist]

the pcm 'learns' how the injectors do their job by monitoring how it has to command fuel compared to what it nominally has to command, based on the 02 sensor feedback in closed loop.

it then applies that 'learning' to the fuel pulsewidth commanded during open loop. for the stock pcm tune, the high load, high rpm adjustment is based on what it learned at around 50% load and around 3-4krpm.

what I deduce from your data is that the pcm is having so richen the injectors by some 10-15% in the 50% load 3-4krpm range, and is applying that to the open loop situation.

you can 'reset' that by powering down the pcm so it goes back to the baseline (no correction) situation, but it will again 'learn' to make it more rich over time.

the real solution is to figure out why the pcm has to command more fuel at ~50% load, and fix that.

 

[zach44102]

Ok well been messing with the car today. Trying to find my detonation issues (spark ping). I pulled all the plugs and everyone of them was white, or showed signs of either being too lean or the plug is to hot. And one plug, the back middle cylinder, had small pieces of porcelain missing and had carbon build up on the ring of the plug. So i changed out the old Autolite coppers for NGK platniums. Drove the car for 15 mins, and pulled them out.

While driving the ping was the same. So i pulled one front cylinder plug and the back middle plug. The front plug was white just like the previous ones, and the back middle cylinder plug was not only white but had a black spec on the porcelain which told me that cylinder has pre-ignition problems.

So what do you suggest, running a colder plug? What could cause 1 cylinder to detonate prematurely?

 

[dogstar]

Zach just crush it!

 

[Sho Amo]

Zach - Do you like to read? Im asking because if you want to know more about this I can send you this book.

http://www.amazon.com/exec/obidos/ASIN/0837603013/ref=nosim/broughsbooks/

When I was tuning, it helped me understand what the computer was actually doing. If you aren't much of a reader, then don't bother. It is not amusing and full of color pictures with lots of shiny wheels and big turbos. Let me know.