just for fun lets force your IAC into operating range. crack the throttle plates open until cold start yeilds iac counts <160 and see if things improve. the air will be less even than a properly sized idle passage but that shouldn't affect startup too much.
it takes a lot for it to 'smell' rich. often a 'fuel' smell is a misfire due... lean will hit a misfire state more easily than richMore fuel isn't generally the direction I felt it needed to go when it smells so obscenely rich as it is.
I'll try that if things aren't improved today. I actually tapped my throttle body to take a 1/4 pipe plug that I'm drilling to make different sized bypass orifices. 1/4" is the largest orifice I can create with the hex socket drive plugs I currently have. Yesterday evening I had a fairly successful start from 38C. IAC was pegged at 160 for the first few minutes but it was at least able to make the target rpm. I was really hoping to hear from someone who's done a 383 LT-1 in a climate that sees swamp-a$$ type humidity like St Louis. Houston, TX and the Carolinas are the only other areas I've been to with comparable humidty.
I didn't want to hear the word "misfire". That points me back in the direction of the ignition controller.
I would completely drop the humidity idea if I didn't also have a problem with my daily driver - a 1.9L turbo diesel at this same time. The vane actuator pot was worn causing the ecu to lose control at higher rpm and go into limp mode where it would command minimum boost all the time. The difference between a 90hp engine trying to climb a moderate incline with little or no boost in May versus July humidity was immense. In 95F air I could very plainly feel the "boost" from drafting semis.
Last edited by spfautsch; 08-04-2019 at 05:16 PM.
so the only difference between the two snapshots above was humidity? no other engine modifications?
There were - solid lifters and larger IAC bypass holes. But this problem started as soon as it started to get hot & humid, well before any modifications. Nothing really changed with the addition of the lifters.Originally Posted by steveo
Cracking the throttle a bit made a huge difference. The MAF was actually registering slightly less airflow at the same engine speed. I'm working on checking hot valve lash so can't post too many details. Will try a cold start in the morning and post an update.
You're at the point where you need to enlarge the idle passages in the intake manifold.
Anyone have a second on this opinion? I'm thinking the same but damned if I didn't just put the manifold back on 3 weeks ago.
What would baro tell me about? I thought $EE only uses SD if the MAF stops working.
At startup the IAC are set at 144, I think that setting can be increased somewhere in the bin. The intake passage will affect only idle quality and you should eliminate every other possible reason before doing it.
Too much and you will never have a good idle again, The individual cylinder trims will get all around and will need a fresh tune from zero. Even GM made different size holes to compensate for the unequal air distribution.
Once I made the mistake to make the holes the same size and the idle was crap with constant surging. Only fine tuning ind cyl trims make it run stable.
Humidity hits the ignition system to the limit, so it will be good to take a look at that first.
the maf isn't really good with air density, im sure it uses barometric pressure to tweak fueling in some way in MAF mode (although i haven't looked at the code). either way ~1 KPA of baro difference shouldnt' do this to you. something else is going on.
Hi Scott, I know you know what you're doing.
Have you played with injector startup PW and crank VE tables.
Mine cranks right away now cold but doesn't always fire right away when warm... but is ok hot.
I can't tell whether it needs more or less fuel, Probably more.
Just played back a log starting. My IAC starts at 130 & drops to 108 as soon as the motor fires, then drops as motor warms up.
I've lowered most of the tables re IAC and nothing is set that high.
IAC keep alive :20
present motor position loaded at reset : 40
Park position crank offset vs coolant
-4 20
8 21
20 21
32 21
IAC Initial position
-4 77
8 70
20 63
32 56
So no idea where the 130 comes from
IAC relearn done with new iac several times. No change anywhere
I'm going to mix it up with a new Throttle body - yay.
How does AFR & WB compare in EEHack?
Mine sits initially at 3.30:1 at 20C
Jumps to 5.70 as the motor starts turning
Jumps to 12.1 as the motor flares up 13/1400 rpm (iac at 108 so starting to control revs)
at about 30 secs, the wideband starts recording & matching AFR at 12.6
As Rocko350 also mentioned increasing the manifold idle ports, Who would agree it's a good idea?
I've ordered 2 pair of gaskets for the manifold.
Hmm the IAC does seem to control the idle though.
It also depends on idle timing where it sits.
As I lowered idle from mid 30's to 20 I needed to re restrict the bleed hole in the throttle body.
When idle was in 30's the iac was hitting zero and my idle is set at 800.
HTH
Mitch
'95 Z28 M6 -Just the odd mod.
'80 350 A3 C3 Corvette - recent addition.
Here's a short log of a drive this afternoon. In general it's not running very impressively, but as I've mentioned the transition to closed loop was unnoticeable if that means anything. I noticed some popping in the exhaust when decelerating from a few PE "events".
I suspect that the humidity is causing the MAF to register inflated airflow #s. I say this because I've always logged less spark knock in humid conditions, and I'm presuming that's caused by the water vapor increasing the cooling effect on hot / heated parts. I haven't tried swapping to SD mode yet but will if I can get it to start and stay running reliably.
Wideband is a LC-2 on D27 using default settings. I'm not sure how meaningful any of the data is except to use for cylinder balance testing. I pay it almost no attention unless I drive the car a few minutes to get the exhaust hot. Even then, Missouri's laws on ethanol are stupid - it's considered required in some concentration but they don't have to tell you how much or that it's even present. I'm guessing the 93 octane I'm running has a stoich about 14.5:1.
By the way, with the help of a definition file I found in kur4o's build folder I found I could display the wideband units in Lambda with this in the definition.csv:
Code:54,WIDEBAND_D27,Wideband O2 @ Pin D27,^,EXTENDED,8,2,0.007874016,,0x01,0xFF,,,,,
Your phone have a baro sensor built in or have you checked local baro reading from weather bug or another trusted source and see if your within 3 kpa of reported. If it was humidity related, a smaller plug gap would yield a driveability improvement. Wide band would report a richer mix also if the MAF was over reporting due to increased air mass from the humidity. startup ve is usually about 60% of normal VE.
Your phone have a baro sensor built in or have you checked local baro reading from weather bug or another trusted source and see if your within 3 kpa of reported. If it was humidity related, a smaller plug gap would yield a driveability improvement. Wide band would report a richer mix also if the MAF was over reporting due to increased air mass from the humidity. startup ve is usually about 60% of normal VE.
That 02s and BLM reading looks weird enough. Did you mess with the closed loop settings. Does the AIR system present and functioning. 02s looks frozen at stratup and really slow moving after that. They should be pig rich at startup and I noticed blms were 120 at open loop meaning they are pulling fuel.
You can set mode4 controls before starting the engine. Like setting target afr and spark for startup.
Humidity revealed some hidden problem you already had. Is it a tune or mechanical.
Humid air takes alot more energy to ignite, You lose about 10-20% power and there is water vapor condensation inside the cylinder untill it gets warmed up, which can foul the spark plugs with water.
But that is likely to happen at much lower temperatures.
The engine gets less efficient and draws more volume for the same amount of oxygen. That can explain the maxed out IAC counts at stratup.
To elimimnate CL tune problem I will start by running Open loop and than CL SD and OL SD.
It could be also 2 different problems mixed up.
1 is hard startup, which can be the result of spark syncronisation, Crank ve table, or slower fuel pressure build up.
2 is crap runninng untill warmed up, the result of weak spark, CL setting off chart, MAf table off chart.
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