I just hope that the code 41 doesn't make the ecm lock the ignition timing.
I have 2 more spare arduino 328P pro mini's at my disposal. I bought 5 for halloween animated eyes that I made so I could teach myself about these things. So no need to recompile.
I need to get a hold of 8 ls1 coils still.
It doesn't seem to have any effect on timing, it's just an ECM diagnostic to let ppl know their EST wire is broken / disconnected. It would be simple enough to just disable the test in the calibration (if possible) but I'm trying to work around it electrically.
I've found that a 470 ohm resistor is enough load on this pin to prevent the code, at least while cranking. Unfortunately it pulls the voltage down enough the arduino isn't seeing the pin go high. So it might require a schmitt trigger or ???
I got a bit sidetracked trying to fix this issue and got off the task of posting the sketch. Will try to get it on github in a bit.
Here are some info on dtc 41 and 42.
It is triggered during cranking when the voltage on the line exceed 4.6 volts. Normal value is between 0.5 to 4.5 volts.
On the calibration you can disable dtc 42.
For DTc 41 you can only raise the voltage threshold. It is located at byte_12037. It is set at 4.6volts. Raising it to Max value will likely disable DTC 41.
I still can`t be sure, does the PCM provides power or ground path on the IC line?
FYI (anyones) On my '95 LT1 PCM ($EE 16188051) is it set to 10.43 for the stock Z28 and the LT4 .bin i have.Originally Posted by kur4o
Mitch
'95 Z28 M6 -Just the odd mod.
'80 350 A3 C3 Corvette - recent addition.
The conversion on the xdf is wrong. It should be
x*0.019607843
The PCM drives the EST line low, or in other words its an open collector output.
I'd rather stay away from tuning requirements, and I think I can - connecting the EST line to ground through a 470 ohm resistor seems to prevent the DTC. I just need to figure out this voltage comparator circuit so the microcontroller can see the signal.
This won't increase any inherent RPM limitations, but it should give stronger spark than the opti above 4500 RPM.
Initial code commit - diy-ltcc-0.9.0
Hope to have time this week to work up a partial schematic.
Been banging my head against the wall with this EST line / DTC 41. Replacing the 10k pullup resistor with a 470 ohm pull-down allows cranking without setting the code, but with the side effect of the microcontroller not catching the falling edge (and no spark). I've tried a LM339N comparator, a 7407 buffer and a 2501 optocoupler. The optocoupler showed promise but nothing close to success. I'll have to do some bench testing on this one because it's really difficult getting useful test data cranking (but not running).
ebay has a nice deal on the arduino 328P pro mini (5v version) 5 + 1 programmer unit for $16.84
https://www.ebay.com/itm/5Pcs-Atmega...IAAOSwoAxZrwyA
What happens when you turn off the code?
Interesting - do you know what year that info pertains to? Because the code certainly triggered the MIL while this document states it won't. I immediately noticed there was a code because the fans were running on high right after startup. I was freezing my kiester off what with the garage door half open and 15 degree air coming in while the cooling fans were blasting my legs with not-so-warm air as well.
Haven't tested that yet, saving as a last resort. I'm hoping to come up with an electrical workaround so this mod remains a bolt-on affair.
I went dumpster diving in the recycling bin and located a 7414 schmitt trigger ic on an old switch card. Going to give that a shot tonight.
It's supposed to get even colder tonight - man do I hate winter. Anyone have some swamp land in Florida they'd sell me cheap?
It is from 94 f-body manual.
Whenever the voltage on the est line is higher that 4.6 volts the error will trigger.
You can monitor the ICM voltage on the eehack AD tab, hacker label ADCHANNEL_02B5.
$eb gives you 4.6volts threshold.
94 and 95 calibrations are all set with these settings.
Last edited by kur4o; 01-16-2018 at 12:31 AM.
I wonder if you could just cheat and leave the ignition module hooked up (but not to the coil) and tap into the wiring (use optoisolator only if needed). If not,
I will have to run a scope pattern to see what how much the voltage shoots up when terminal "b" on the ignition module when it is unplugged. That way, I might be able to match the impedence by wiring the EST signal through the center tap of a 10K potentiometer in which one side is tied to 5v and the other is grounded. May need to be higher in resistance, also.
est biasing idea.pnggoing to be zero degrees F tomorrow, so don't hold your breath, as I am working out in the open. Can't spare the shop room at work, too busy. But I will try sometime.
Last edited by vilefly; 01-16-2018 at 04:11 AM.
I've put 50+ hours into this project, if this electrical issue takes another 20 it's worth it simply to not have taken the easy route. This is the kind of "solution" I'd go with in an apocalypse, or if disabling the DTC wasn't an option and I wasn't opposed to using wire nuts and electrical tape on my pride and joy.
As I've mentioned about four times, my testing has shown a 470 ohm resistor from the EST line to ground gives enough load to prevent the DTC. If you look closely at the Bailey module in the upper right quandrant of the PCB there are two 1k ohm 1/2 watt resistors (thinking they're wired in parallel for net 500 ohms) very close to a 14 pin dip IC (maybe an op-amp or Schmitt trigger). But if you're going to test with a potentiometer to confirm this I would suggest you try one in the neighborhood of 1k-2k because I was getting the code with a 1k resistor to ground. A 10k pot is going to give you a very small range of adjustment once you hit the threshold. Also, you're probably going to get the code almost all the time if you connect the pot to +5v because the PCM has it's own pullup on this pin.
What happens when the ignition line is switched on is the PCM pulls the EST line low. You can confirm this with a TTL safe test light (led + current limiting resistor) by connecting the positive lead to +12v and negative to the EST circuit. When key is on the led will light solid, and pulse off when cranking starts. When it pulses off what is happening is the n-channel output transistor in the PCM is being switched off and the pin is allowed to float (presumably there is an internal pullup resistor) towards +5v. I believe the voltage threshold mentioned in the DTC description is only measured by the PCM when the line is allowed to float. When I take out the 470 ohm resistor that's simulating the load of the ignition module, I suspect the line rises up to +5v almost instantaneously after the EST transistor switches off.
What I need to figure out is how to amplify this signal on the EST side of the 470 ohm resistor to a clean TTL one that the Atmega can see the falling (or if inverted, the rising) edge of. EDIT: Unfortunately I can't see the signal to quantify what I have to work with here. The optocoupler (essentially just an optically isolated transistor) was the closest, but some of my attempts with the comparator were very sketchy at best. The 7414 Schmitt trigger also seems to be a bust.
Let me do some more experimenting in my garage. If I can't nail it down I might ask you to do some work with the scope, but let's wait until the weather is a little less stupid.
What I really need is a capture scope of my own. Unfortunately my toy budget was completely annihilated in 2017. I'm going to try kur4o's eehack definition to see what voltage the PCM is measuring here, but I have the feeling the sampling rate won't be fast enough to be useful.
Last edited by spfautsch; 01-16-2018 at 06:20 AM. Reason: added image
Just watched the videos. Looking Good.
Will this allow the motor to rev over 7K or is that limited by the PCM ?
Thanks
Mitch
'95 Z28 M6 -Just the odd mod.
'80 350 A3 C3 Corvette - recent addition.
The PCM will freak out at 7228 rpm. Beyond that the opti signal might be too corupt or the PCM too slow to read it.
Most of the tables will be maxed at 6000-6400 rpm too.
The opti signal is capped at 7228 rpm and the injectors at 7245 rpm in the code. These limits can be raised but the engine operation might become unstable.
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