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.
I'll have to dig up where I read this, but the word "mass" is used in the name because it's designed to measure air mass through the sensor. This implies it compensates for temperature and pressure by design. I'm going to have to dig but I believe this was the same source that mentioned humidity being the only thing a maf can't compensate for, only the O2s could do that. It might have been a Jeff Hartmann book or it might have been something I found online.
I'm going to work with the throttle blades to give it more air at startup and try to tune around that b/c it responded very well there. I suspect most of my other problems stem from moving the injector constant too far.
I'm also going to bump up the dwell in my controller to see if anything improves because I'm not sure where I came up with the dwell figure I used for these coils. I'm 99% confident there are no other issues with the ignition system. When the air was cooler and drier it was firing immediately every time and idling better than it ever did with the mechanical distributor. When I first saw 42-43kpa at idle I had to double-take on it because the last I recall seeing that good of idle vacuum was when it was stock.
Thanks for all the ideas guys.
I'd really like to know about the BLMs question two posts back. If no-one is sure I'll have to dig into the disassembly.
I’ve lowered my IAC values at startup around 40 i think.
Thereseems to be startup values in tables but it usualy starts as 160 ish.
I also reduced the air bleed size in the throttle body after reducing the idle timing as the iac valve couldn’t go lower.
'95 Z28 M6 -Just the odd mod.
'80 350 A3 C3 Corvette - recent addition.
Mitch am I mis-remembering, or did I read somewhere that you'd also drilled out your port orifices (the holes pointing at the injector tips)?
It sounds like there might be some misunderstanding and confusion on the subject - the how-to I've seen about setting a base bypass hole size and adjusting the throttle blades fails to mention that it should be done at maximum air density for the climate you drive in. For example if you're in a cold weather season and consequently high air density, you want lower IAC counts - say in the 20s at hot idle. This is the point where the engine needs the least amount of idle airflow.
I'm at the other extreme of the spectrum. In minimum air density situations you want enough bypass air to reach your idle target speed during a cold start without maxing out the IAC motor (160). This is when the engine needs the maximum amount of idle airflow.
If you're logging 160 IAC counts during cold starts it's an indication that the engine speed is below your idle target and the ecu has opened the IAC as far as it can trying to correct the situation with more airflow.
All this of course assumes your IAC position has been learned by the ecu. There's no feedback mechanism for the pintle position. The ecu has a relearn procedure it uses to extrapolate when the pintle is fully closed and then stores that position (not sure where or how) and tracks it whenever it commands a change in IAC position. But if you replace your IAC motor or the position is otherwise lost by the ecu, the counts aren't going to be very meaningful until the relearn routine runs. I other words, if your ecu thinks the IAC motor is at 50 and it's actually fully open, there's no way for it to know and it will continue to command it open in steps until the ecu's tracking variable is also at 160.
Last edited by spfautsch; 08-05-2019 at 07:14 PM.
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.
Extensively. That's really a subject for a completely different discussion - the point of this discussion is to make it stay running once it fires. But since all my threads eventually turn into into free-for-alls here's what I've learned.
I had the same problem after my injector swap, before the stroker kit. It would flood when restarting warm. I spent a lot of time fiddling back then and got it "pretty good" restarting warm. Then when I looked at these tables again a couple weeks ago I realized I'd scaled the prime pulse tables in the wrong direction (made them bigger) and then compensated by removing fuel from the cranking VE tables. Totally wrong way to go about it, but it worked.
Look at the prime pulse width tables - this is a raw pulsewidth that does not reference the injector constant. The ecu fires the injectors for this period in batch mode (I believe all 8 at once) when it sees the first low res pulse from the opti. This is to re-establish wall film in the intake ports. So you'll want to scale this table by the relative difference between your stock injector constant and your current injector size. I started with about 25% (42 / 24 = 1.75) or multiplying by 0.75, but I also factored in the additional displacement so ended up around 0.82 as the multiplier. The warm and hot cells of this table will need to be massaged by hand in hex because the stock values are like 0x02, 0x03 and 0x04 and there is very limited resolution for removing an accurate amount of fueling. You'll have to settle for "close".
Then move on to the cranking VE table and use this to add / subtract fuel based on how it behaves in those first few firing events. The fueling calculations behind this table do reference the injector constant so you shouldn't need to factor that in. Just changes in pumping efficiency caused by cam & displacement.
Lastly, the Crank AFR vs Low Res Pulse vs Coolant Temp can be tweaked. This is the target AFR the calculations are using with the cranking VE table for. Notice the first two cranking pulses are much leaner than the rest. I assume this is because the first and second prime pulses aren't factored into the fueling and wall film modeling. I've no idea however if this then adds to the prime pulse or what.
Mine is far from perfect, but I'm not trying to get it perfect yet. This can be a slow & tedious process b/c you have to let it cool down to test.
That's a question kur4o might be able to answer - he mentioned it a few posts back as being set to 144 but not the address for the table / constant. But long story short the ecu uses IAC for coarse idle speed control, and spark timing for fine control. So it will move the IAC as the ecu sees the need (there's a RPM Variation pid you can monitor / graph in eehack).
My WB controller pulls the analog pin to ground until the warmup timer has expired (30 or 60 seconds). So it reads 0 (in units of lambda).
Once it starts reporting AFR it's all over the place. Sometimes showing rich of the narrowbands in OL and then usually 20% lean in closed loop. I'm really not paying it much attention because at cold start, or in any other instances where you have unburned fuel getting in the exhaust the effect is lean output from the O2. For example one of the Banish tuning guides I talked to you about says at cold start you should see the widebands showing stoich because the unburned fuel isn't seen by the sensor. Only the concentration of oxygen in comparison to other gases. Bear in mind his wideband probably costs more than my car, so I doubt we'll be able to use this method to favorable results with a $200 instrument.
I didn't get in a hurry to pull my intake off to try that, and I don't intend to unless nothing else gives results. I'd like to see some quasi-scientific data that compels me towards that before I jump out of that airplane. I already had a plan to fix my IAC bypass before I decided to drill it. Doing the same with the port feeds is a whole different animal.
Last edited by spfautsch; 08-08-2019 at 12:47 AM.
It looks like the 02s you have are dead shot. Not swinging enough in either direction. They can crack from moisture but yours are completely dead, if something else is not going on.
Get a good afs75 delco ones.
Here are some logs i made showing good voltage swing. The car is perfectly untuned but you can get the idea. There is a cold start and some idle showing the IAC in stock form can easily support 15 AFGS. It has a midlength SLP headers and some tweeks in the delay times. The wideband is set at 0v-11.4 5v-16.5 at d27.
The way you modified the injector scalar can lean the mixture alot. For the sake of experiments set it at 41 and see how it goes.
I will have to dig out the iac tables. Sure there is one for startup counts vs iat or coolant.
Are you saying that based solely on analyzing the two big logs from 5/31?
Trust me, there's the possibility of a great many other "somethings" going on. Not least of which is that this is the entirety of the calibration data I received with my injectors. Be sure you zoom in because it's hard to see. At the very least I'd like to determine the main injector slope within reason through extrapolation. I know this isn't the way to do this, but hear me out.
In a couple weeks I'll be in a state where I can buy ethanol free gas. I intend to bring 10 gallons back. I'm already braced for my wife's response when she finds out why I'm bringing two empty gas cans along for our 25th anniversary trip.
Assuming I can tweak the ADC output and get my wideband to a spot where I feel it can be trusted to report stoich, I believe I can extrapolate injector flow in a manner more objective than guessing. Obviously I'll want to be forcing OL and AFR to 14.7:1 during this experiment, and running at a load that yields a pulsewidth above the slope knee (aka low pulse adder).
This theory is based on the (relatively huge) assumption that my MAF transfer curve is accurate. But assuming it's in the ballpark, you should now be able to more completely understand my fascination with the effect of humidity on the MAF function. Adjusting for humidity, and assuming I have healthy enough spark for complete combustion, it should be realistic to be able to scale my injector constant based on however rich or lean of stoich the results are.
When I get to fine tuning closed loop I'll likely create a new discussion. I might even break down and buy some new ACD O2s. I would be honored and grateful if you'd contribute to it. But that's not my goal for today.
Based on my faulty assumptions, that was my intention. I've discovered through experience that trying to improve on the factory MAF transfer function isn't a terribly productive exercise.
I'm getting ready to test a cold start with 41.92 for the injector constant. Fingers (and plug wires) crossed...
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.
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