What are your ambient temps like this time of year?
What are your ambient temps like this time of year?
Had to play used car salesman tonight so no progress on any front of interest. Thought I'd share this tidbit I found - not the source I recall finding years ago, but makes me feel better knowing I'm not hallucinating memories / facts / whatever.
From this page talking about some newer humidity sensor equipped MAFs being used on the newest Duramax engines.
https://gearsmagazine.com/magazine/a...rflow-sensors/
Originally Posted by gearsmagazine_pleasedontsueme
Last edited by spfautsch; 08-06-2019 at 05:45 AM.
Anywhere from 5C to 35C. Generally it’s very cloudy so in 20’s. 30 ish when the sun comes out.
'95 Z28 M6 -Just the odd mod.
'80 350 A3 C3 Corvette - recent addition.
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?
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
'95 Z28 M6 -Just the odd mod.
'80 350 A3 C3 Corvette - recent addition.
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.
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.
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.
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