Speed density/Open loop

[WS6FirebirdTA00]

Chris is that evap purge or?

[jimmyblue]

Is the AIR pump active in this (NTIMID8) car?
That would whack the wideband reading though
having no in-cylinder error present.

[WS6FirebirdTA00]

Here is my scan, I has 1.00 eq ratio from 60*C and up but as you can see by the comments it went WAY lean on my so I commanded 13.79 so I could get back to stoich.

[S2H]

could the change in Timing for startup till it settles in be causing it???
less/more spark does change the burn rate and can make it rich or lean...

[WS6FirebirdTA00]

Yea I was thinking about the spark as well. Even at the IAT and ECT came up and the spark was constant, it stayed lean as crap. I would think pulling SOME timing would help richen it up but to richen it 2-3 points with just timing seems like it might be hard to do, or at least the car would run shitty. Plus the timing reduction goes for 80 seconds, either that or I would have to make corrections vs ECT or IAT, and those are stock right now so I wouldnt think anything would be messed up there.

[WS6FirebirdTA00]

Here you go, I pulled 10* of timing and it only changed the AFR by about 0.4. Commanding 14.63 on 60*C start it was so lean it was off my aFR gauge, that is like 18.5:1 or so. Here is the log

[NTIMID8]

Didn't see your request till after I played a bit Chris. But I will email what I have real quick.

This is an example, no where near the worst example. But it does seem to have to sit for a few minutes to do it. I tried a few immediate restarts and it was fine. It was also lean as heck on cold (commanded 11.2ish) start but didnt log it.

Phil

[NTIMID8]

Is the AIR pump active in this (NTIMID8) car?
That would whack the wideband reading though
having no in-cylinder error present.

No air pump..Not new to this

Phil

[Chris@HPTuners]

ok guys, i reviewd your logs. I am convinced IAT heatsoak is the main issue but there is another issue as well.

If i look at the log when things are relatively steady (after the afterstart enrich has finished and RPMis back to ~750) both before and after the restart this is what i see. The first part of the log shows IAT at 43F (6C or 279K, the PCM uses degrees Kelvin), after the restart it is 55F (286K) once things steady out a bit. Comparing simlar points before and after i see a WBO2 AFR of ~12.2 before and ~12.5 after.

The calculation the PCM does to get CylAir from VE is: cylair = VE x MAP / IAT

So here we have a ratio of IAT = 286/279 or 1.025 (2.5%). Amazingly, the AFR ratio 12.2/12.5 = 1.025 as well. I'll bet once the IAT reaches what the IAT was before the restart the fuel will be equal.

Now the other problem, why is the fuel so lean after the inital restart? Again the IAT heatsoak plays a part, the IAT is 63F (290K) giving approx 1.04 (4%) ratio. Also i noticed the VE table seems to have a dip right around 45-50kpa which will be contributing to the problem as well. when you start the car it is running at ~950 rpm @ 45Kpa but g/cyl is only 0.15. compared to it being 0.18 @750rpm/50kpa. You have a 25% increase in RPM but cylair has decreased by 20% ! This would account for the extra leanness of the afterstart.

So according to me, your VE is a little low in the 45-50 kpa range and also you have an IAT heatsoak issue. Unfortunately, your code doesn't use the ECT/IAT bias function that gives you some control over this, effectively using ECT to stabilise the IAT at low airflows.

Having an accurate IAT is critical for SD tuning, and for you guys with the old code it seems it is even more critical.

Chris...

[WS6FirebirdTA00]

so you think it is IAT for the main part. Now when the car is cold, everything is cold including the IAT sensor, it matches the ambient temp here or at least really close (sure it may be sucking in warm engine bay air). It is still lean on the start up when this happens. When the car is hot and sits I woudl think the air going into the cyls would be hotter than the IAC due to it just sitting there and all engine parts are heat soaked and would make it richer?

[Chris@HPTuners]

yeah but you have tuned it lean based on a certain amount of manifold heating which doesn't occur when the engine is cold. Your VE is too lean, because when the engine is cold the IAT *is* a good representation of the cylair temp and more air is actually entering the engine than your VE table suggests.

[WS6FirebirdTA00]

so really it would be better to get an IAT reading at the intake valve lol. is there any way to work in a VE modifier based on IAT, my friend said he thinks live is comming out with something like that. kinda like the modifier in the one bar for tps except change that to IAT, that would also fix the cold/hot day issues with an SD tune.

So with the MAF on the car it knows the exact airflow comming in, with it off there is error when it is cold in the VE. Maybe a VE modifier on ECT as well? This way commanded=actual, that would kick ass.

After my 2nd log today I went down the street and instantly my AFR went to 14.6:1, is that inline with what you think it shoudl do?

[WS6FirebirdTA00]

the only issue this would leave would be a hot start at operating temp, the ECT modifier would need to be 1.00. but it would fix the majority of problem

[NTIMID8]

I have chased the Ve all around and the problem still occures regardless of engine RPM. That hole you percieve is not a hole, that area still is rich over commanded by 3-5%. The 30-40kpa area is set higher (richer)there for a slow injector response and still always logs in leaner than commanded by 3-5%.


Bottom line, if I tune the VE correctly for normal operating condition startup is adversely effected. This is NOT the case with the MAF. It purrs like a kitten.

The IAT sensor is located in the intake tract, its a Turbo car and no way around it. I see no way to speed up the Response, but my thermocouple shows IAT tracking pretty close to the actual air temp. Now, could this be the IAT fueling correction? If so its going to be a problem ALL the time when the temp changes. Is this what everyone has to deal with in the future? 10 degree temp change and have to retune?


Phil
At this point, are you telling me to continue NOT recommending SD tune for daily use to customers? Unless their is a solution I see no way to recommend it.

[WS6FirebirdTA00]

i understand why the MAF is ok, it registers the change in airflow and accounts for the more g/cyl. have you tried to adjust the VE table for a cold start? like adjust it the 15% and see if it will hit commanded or get closer? i might try that out and see how it goes. there has to be some way to fix this. cold temps are easy to "patch" but its the hot start that bothers me.

[NTIMID8]

I understand very well why the MAF works . Funny thing is low speed it not one of the MAF strong suits and the PCM factors a lot out.

Bottom line, you can patch your VE but it will be pig rich under normal operating conditions.

The only way to that I see to bandaid it is to use the afterstart enrichment correction fueling and work with the amount,delay and decay rate.

You can command more restart fuel, I have a test file that commands 10:1ish.
Then the decay delay can be set to 255 max. This buy us about 20 second for the decay to start.
Then the decay step can be cranked up as well. I believe this can add the most time as its the delay between cut in added fuel. Theoretically, you can add 20 seconds to each fuel reduction "step". This I have not done yet as well as reducing the delay mult which will add more steps

It can be "rigged", I was just hoping not to have to do it this way. Its a million dollar control system, I try to let it do its job.

Phil

Phil

[WS6FirebirdTA00]

never really thought about that, since the maf is not used exclusively, you would think there woudl be something wrong. esp wtih that low flow

[Chris@HPTuners]

i'm not suprised it is broken at all. Many things really are broken in the code and some things are "wrong" from our perspective which is probably a lot siffernt to GM's. A classic example is the LS2 bug where the MAF freq suddenly goes to 0 at high rpm... kinda depressing that we have to release patches to fix these ridiculous issues.

You are running old code, most of which was written in the mid 90's. The newer OS's don't seem to suffer from this due to the charge temp model/bias/filter. The dumb thing is a simpler version of this code is in your PCM but not used!

I think the after start enrich is probably the easiest solution.

[WS6FirebirdTA00]

maybe ill have to save up for a new OS then, i just hate to tell the car one thing and have it do another. i did play with afterstart enrich but sometimes that makes it too rich, im gonna play around with it and see if i cant get it reasonable

[WS6FirebirdTA00]

so warm idle my AFR is off by 2-3 points, warm cruise it is only off by 0-0.75.