95 LT-1 Idle Cell Comparison - Humidity?

[spfautsch]

We generally don't see lows near 5C from about mid May to mid October. I'm guessing your average monthly temp (i.e. several hundred samples per day averaged over 30 days) is a solid 3-6C lower. That doesn't sound like much but in terms of air density it is.

Whatever the case, I think a case of mistaken identity has been a major contributing factor. I won't be able to test until later tonight, possibly even tomorrow but I think the combination of all of the aforementioned factors have stacked up to cause me the severe cold start problems.

This, boys and girls is the part of the show where Scott eats his hat in front of you all. :-) Anyone have any ketchup?

After a bit of research it seems like this coil, which is what I have:



Is not one of the supposed "hot" or "truck" LS coils. Seems it's electrically similar to the common LS coils and needs a target dwell of 6ms.

Whereas this coil which looks quite similar:



Is a "hot" or "truck" LS coil and needs a target dwell of 4.5ms.

Anyone want to guess what target dwell I was using?

[Terminal_Crazy]

Not the one you thought! ��

Would anyone consider opening the manifold idle air passages up any bigger?....

Went to the track on Saturday. (1/8) Had a fantastic day but traction was diabolical.
Spun all through first even feathering the throttle and clutch. It’s never that bad on the road.
Best 9.18 @81. 60’ 2.399 so more mods over the winter.
However the rear seal on the manifold needs resealing after I blew it out arsing about with pcv so I’ve just ordered manifold gaskets and need to pull it off again.

Mitch

[spfautsch]

Oh no, it was exactly what I'd intended it to be. I'd just labored through the whole diy-ltcc project under the assumption the coils I have were the 4ms "hot" ones. I wish there were datasheets available for these items like injectors.

Unfortunately bumping dwell up didn't miraculously solve any problems. Cold start (albeit from 33C and ~50% RH) was pretty much the same. IAC was pegged until about 4 minutes in. O2s hovered around 460-560mv and the ecu dropped out of CL for a frame or two numerous times during the 5-1/2 minute log. So I guess I'm back to the drawing board.

I think I'll try a SD flash and see what happens.

When / if I ever get this figured out I intend to experiment with different sized bypass orifices to answer the question of whether enlarging the port feed holes is in any way necessary / beneficial. In fact at this point I have nothing to lose by removing my 1/4" npt orifice plug (leaving a 1/2" bypass hole) and see if it doesn't let the engine run away when started.

[vilefly]

Well, I was going to say, "unplug the MAF, tune for speed density", but you beat me to it.

All this talk about humidity being a major factor reminds me of when I determined the exact nature of the MAF sensor. A typical sensor heats an element 100 deg C above ambient temp to determine the specific heat of the airflow. This crudely compensates for humidity as well, but not in an exacting way. So technically, the output of the sensor is less sensitive when it is humid out, since the cooling effect of humid air is less (and also less o2 by way of water vapor displacing the usable oxygen). Crude, but effective for the emissions at the time of manufacture.
I just hope the MAF is accurate at low RPM with a choppy idle, but I suspect not. Tinkering with the MAF calibration might be viable, only if the sensor is still good. I say clean the MAF sensor, just in case. I suspect the MAF sensor won't be used to a 383 sucking on it as opposed to a 350. Best to eliminate it for now, then come back to it.

[spfautsch]

Hey vilefly - have any plans this Saturday? Care to make a trip to central misery? I'll pay for your fuel. I could use some help measuring dwell time and led and coil igniter current draws with my circa 1984 CRT oscilloscope.

I'm nearly tempted to ask the mods to delete this thread. There's enough inaccurate information in it regarding the nature of mass air flow sensor operation that it's quite rudely reminded me why I hate asking for help.

All I was hoping for is someone who perhaps

a) also has a MAF enabled 383 gen 2 LT-1

and

b) lives in a similarly hot and humid climate

to chime in with any thoughts about the idle airflow numbers I'm seeing and IAC bypass size so I can assess how much effort I should exert looking for a consistent misfire / weak spark situation.

MAFs aren't evil. I can't believe there aren't thousands of cammed up 6.0, 6.2, and 7.0L LS based cars running around still using the airflow sensor for it's intended purpose. However, those guys all have the benefit of ETC to control idle air, so there's no need for an IAC motor, or a bypass. I can however believe no-one is doing the same with a 6.3L gen 2 LT-1, because most of the tuning "experts" encourage disabling the MAF and using speed density only. Things like this are what drive me to drink.

[kur4o]

I should say you are running really lean on startup.
Don`t forget you are spraying cold fuel straight in the cylinder, There is not enough time to evaporate and it should be extra rich to run smooth.
The engine doesn`t make enough power and wants to stall, drawing more unused air, making things worse, that`s why you are seeing 160 iac and high map and low rpm. The engine is fighting to run.
It gets a liitle better when the 02s start to climb.

Compare that with high humidity and possible weak spark not having enough energy to ignite the lean humid mixture.


Engine is not making enough power to stay running.

Maf doesn`t play at engine starting at all it is the crank VE table that matters.

And that 02s are like frozen they should be jumping like mad from rich to lean. There is something very bad happening there. Load the stock CL settings and see if there is some improvements.
If you still can`t dial the idle closed loop, I have a remedy called Open loop idle patch.

You should also investigate the controversial readings between narrowband 02s and wideband readings.

[spfautsch]

I should say you are running really lean on startup.
...
The engine doesn`t make enough power and wants to stall, drawing more unused air, making things worse, that`s why you are seeing 160 iac and high map and low rpm. The engine is fighting to run.
It gets a liitle better when the 02s start to climb.

Compare that with high humidity and possible weak spark not having enough energy to ignite the lean humid mixture.

Engine is not making enough power to stay running.

Now you're making sense. I'll give it a try.

Maf doesn`t play at engine starting at all it is the crank VE table that matters.

I understand that - the startup / cranking fueling tables are well out of the picture after the first 8-12 logged frames of startup. But immediately after those initial frames the MAF and Injector constant pretty much run the whole show. Agreed?

And that 02s are like frozen they should be jumping like mad from rich to lean. There is something very bad happening there.

As I mentioned previously, I think I've raised the injector constant enough to cause this. In the first post, both frames (43kpa and 48kpa) were taken with 42.036 for the injector constant. It's currently at 43.547. I suppose it's possible the injectors flow less than 42, or my dwell problem was wholly to blame and I've moved it from rich (or ideal) to lean fighting what I believed to be a problem of too much fuel and not enough air.

Load the stock CL settings and see if there is some improvements.
If you still can`t dial the idle closed loop, I have a remedy called Open loop idle patch.

If you would, take a look at these logs and critique the closed loop behavior. The 43kpa idle frame was taken from one of these logs, and the only closed loop setting I've changed since is the Stoich AFR Target.

You should also investigate the controversial readings between narrowband 02s and wideband readings.

I'll worry about that another time. As discussed in other threads it's using the D27 analog input with the default ADC output settings. It's also mounted about 18" downstream from the narrowbands in the X pipe. It doesn't get hot enough from idling alone for me to use for calibration purposes.

Edit: Acutally the x pipe is more like 24" downstream of the header collectors.

[Rocko350]

MAF sensors work on a heated wire principal. The wire is heated and then the resistance is checked, then the wire is pulsed to return i to a "known" resistance. The amount of pulses it takes to return that wire to the known or base resistance is reported to the ecm as a Hz signal. Hence the lookup table is referenced in Hz. MAF sensor performance is based on is internal processor, the supply voltage and ground.

As for humidity, if BARO is not reading within 3 of reported actual baro, the air density calc can be off. The humidity flowing over the MAF wire cools the wire, misreporting actual airflow. We are trying to calibrate a sensor table to report a mass of air that happens to include oxygen. Temperature (iat), mass flow(MAF) BARO (key on MAP) reading and engine vacuum (VE) determine the air density being delivered to the cylinder. So the actual humidity is not that big a problem. Its impact the actual combustion process in the chamber not so much the calibration of the engine. The stfts are fast enough to handle the humidity.

The enlarging the idle passages is for allowing the air passages to do their jobs. There is not a "closed loop idle" like there is in a GEN3 engine. If opening the idle bypass does nothing, but opening the throttle blades does, the passages need to be larger. Air in the main intake chamber (non idle passages of intake manifold) can be robbed from cylinder to cylinder if your just gonna open the throttle blades. Cylinder to cylinder fueling will need to be redone either way you choose. If you haven't adjusted the eoit i would visit that as well. Maybe stick a set of injectors in that you have excellent data for, then swap back the the njectors you need for power and adjust the injector data around the idle data from the known injectors.

Chris

[vilefly]

I just remembered something from my obd-I days that really screwed with me at the time. Narrowband O2 sensors sometimes go nuts and put out NEGATIVE voltage on the output wire. This really made things crazy, since each computer brand reacted differently to this. The OBD-1 ecms could only see voltage differential, did not ignore the O2 sensor like they should have, skewing everything backwards. Lean became leaner and rich became richer.
Not that this might help, but one should always check for positive voltage output from the O2 sensors on OBD-1 setups if suspicions are raised.

I have an old injector flow tester that tests the injectors on the vehicle (with some temporary fuel line rerouting). Let me see if I can find it and check to see if the display works still. It has a faded lcd display that may or may not work.