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Playing with reqfuel is a quick way to see if you need more or less fuel. But the better way to do it is to calculate the approximate reqfuel value and then adjust the VE table cells to get your actual AFR in line with the target AFR.
Your car may run happier at 0.9-0.95 lambda warm; it might not be as happy at 1.0. It helps to turn off/unplug your IAC valve and adaptive idle timing setting too while trying to get a stable idle. The engine should be able to idle stably just with the air coming leaking around the throttle blade, with fixed timing and a good AFR. The adaptive timing and IAC are add-one to help with extra load from AC or electric fans kicking on.
This is the proper way. Calculate req_fuel, then adjust VE tables until they meet your target AFR. When reaching warm running temps, warm up enrichment should be at 100% (no warm up enrichment).
Idle speed RPM is controlled by the IACV. Once warm, get your RPM target speed set (IACV duty cycle curve controls this) in open loop idle mode then adjust your fuel to where the engine runs best. My car likes to idle around 12-13 AFR (ie: richer than stoich) when warm. If you have an idle adjustment screw on the Throttle Body then you should set warm idle using the screw. In this case, the IACV then opens only when the engine is cold to allow extra air needed for a richer warm up. Side note: 16V cars do not have and idle adjustment screw so the IACV is open slightly all the time, more when cold, less when warm, but still open all the time. I *think* all 8V cars have an idle adjustment screw, but if not, you may need to run the IACV somewhat open in order for it to idle when warm.
When you unplugged your stock ECU and plugged in VEMS did you set base timing? (At least in Megasquirt) This is the first thing you need to do to match the engine timing and VEMS. It requires a timing light and there should be documentation walking through how to do this.
Last edited by walfreyydo; 07-31-2023 at 10:38 AM.
Let the IAC plugged. Set it to 100 Hz and adjust the warm up enrichment curve.
I set IAC to 100Hz and adjusted Warm-up enrichment curve as suggested. The car runs a little bit smoother, but not significantly and still super rich (I left Req Fuel on 16).
I let it to warm up up to 78-80C to try use VE Live Analyzer, but it's still giving me "Filter Error!" when collecting data. I don't understand why and what does it even mean?
This is the proper way. Calculate req_fuel, then adjust VE tables until they meet your target AFR. When reaching warm running temps, warm up enrichment should be at 100% (no warm up enrichment).
Idle speed RPM is controlled by the IACV. Once warm, get your RPM target speed set (IACV duty cycle curve controls this) in open loop idle mode then adjust your fuel to where the engine runs best. My car likes to idle around 12-13 AFR (ie: richer than stoich) when warm. If you have an idle adjustment screw on the Throttle Body then you should set warm idle using the screw. In this case, the IACV then opens only when the engine is cold to allow extra air needed for a richer warm up. Side note: 16V cars do not have and idle adjustment screw so the IACV is open slightly all the time, more when cold, less when warm, but still open all the time. I *think* all 8V cars have an idle adjustment screw, but if not, you may need to run the IACV somewhat open in order for it to idle when warm.
When you unplugged your stock ECU and plugged in VEMS did you set base timing? (At least in Megasquirt) This is the first thing you need to do to match the engine timing and VEMS. It requires a timing light and there should be documentation walking through how to do this.
No, I didn't do the base timing... I don't think VEMS requires it.
1) I believe there are small differences between each engine that requires a slight adjustment to your "trigger wheel angle" (this is what its called in MS) - at least this is the case with Megasquirt. Ive not used VEMS. After I installed MS, I needed to adjust the trigger wheel angle based on my timing light to get the engine and ECU in sync. It only required a few degrees of adjustment to get the timing light to match the mark on my cam. You can very easily check this if you set your timing in VEMS to a standard 10 degrees (a safe advance for idle), then adjust your timing light to have 10 degrees of advance, start the car and see if the timing light shows the mark on your cam lined up with the mark on the housing. You can also do 0 degrees advance if your timing light doesnt have adjustment.
2A) Target Lambda/MAP table: your lambda values at idle are at 1.0 (700 RPM and approx 20 MAP) - which is approx 14.7:1 - this is too lean. They need to be at around 12-13 AFR (0.82-0.88 lambda) since these cars are batch fire. AFR/Lambda targets wont influence the VE table values (where fuel is actually controlled) unless you run autotune. I recommend adjusting the VE table values at warm idle so your wideband is showing approximately 12-13 AFR. Changing your target lambda table to match would be good after the fact.
2B) Look at your Target RPM/MAP Fuel VE Table. Your VE values at idle (700-1200RPM, MAP below 30 kpa) are much higher than those around it (they are 51-55 where everything else is much lower). Those really need to be the lowest VE values in your entire table (because you are at idle). I dont know what you should set them at but you need to look at your wideband and adjust in real time (while the car is warmed up). I would perhaps start down in the 40 range, but your wideband will tell you - again, adjust until you get to 12-13 AFR. Turn off closed loop idle (see #3 below)
3) Idle control PID settings - this is closed loop idle. Its recommended you get the car running in open loop idle (Assymetric PID Conf setting under "Idle Control PID settings" to be disabled I think), where idle is controlled by your VE table values (fuel/afr) and your IACV (Idle air reference position settings) OR Idle control screw on the TB. Idle speed RPM is controlled through the IACV opening OR if you have an idle control screw, and fuel in the VE table. Again, if your car has an idle control screw on the TB, then you should set RPM based on that, and have the IACV 100% closed at warm temp. If your car does not have an idle control screw (like most 16V cars) then the IACV will be partly open at idle.
4) Before doing any of the above, verify your req_fuel is calculated correctly. Everything related to fueling is dependent upon this variable. If req_fuel is way off then all of your fueling will be way off. I would do some forum searching here in rennlist and elsewhere to see what others who are running VEMS might be using for req_fuel. Verify your value against what others are running. Run the calculator in VEMS (assuming there is one).
-A bunch of technical jargon I dont understand: http://www.megamanual.com/v22manual/mfuel.htm
-There is a calculator in MS Tuner Studio, I assume there is one in VEMS. If not, I can try plugging some values into my Tuner Studio for you if that helps.
-Here is a bunch of documentation for MS/TunerStudio that may directionally help you understand VEMS - many of the settings and interface seem similar: https://www.diyautotune.com/support/tech/
Last edited by walfreyydo; 08-01-2023 at 11:42 AM.
Ok, idle surge indicates, that your IAC is working. So there is an interference between Idle air valve reference position and your idle control screw. Turn your screw down until the idle stops surging. Try it and let us know.
Apart from that. Vems can control you idle via the IAC completely, so you can even turn down your idle screw until it's closed. That's what I did. The IAC does ist better than the idle screw. In case it doesn't work, just adapt the values of your Idle air valve reference position. But always just a little bit up or down.
Then the next step. The next step should be to adjust the mixture.
1) I believe there are small differences between each engine that requires a slight adjustment to your "trigger wheel angle" (this is what its called in MS) - at least this is the case with Megasquirt. Ive not used VEMS. After I installed MS, I needed to adjust the trigger wheel angle based on my timing light to get the engine and ECU in sync. It only required a few degrees of adjustment to get the timing light to match the mark on my cam. You can very easily check this if you set your timing in VEMS to a standard 10 degrees (a safe advance for idle), then adjust your timing light to have 10 degrees of advance, start the car and see if the timing light shows the mark on your cam lined up with the mark on the housing. You can also do 0 degrees advance if your timing light doesnt have adjustment.
2A) Target Lambda/MAP table: your lambda values at idle are at 1.0 (700 RPM and approx 20 MAP) - which is approx 14.7:1 - this is too lean. They need to be at around 12-13 AFR (0.82-0.88 lambda) since these cars are batch fire. AFR/Lambda targets wont influence the VE table values (where fuel is actually controlled) unless you run autotune. I recommend adjusting the VE table values at warm idle so your wideband is showing approximately 12-13 AFR. Changing your target lambda table to match would be good after the fact.
2B) Look at your Target RPM/MAP Fuel VE Table. Your VE values at idle (700-1200RPM, MAP below 30 kpa) are much higher than those around it (they are 51-55 where everything else is much lower). Those really need to be the lowest VE values in your entire table (because you are at idle). I dont know what you should set them at but you need to look at your wideband and adjust in real time (while the car is warmed up). I would perhaps start down in the 40 range, but your wideband will tell you - again, adjust until you get to 12-13 AFR. Turn off closed loop idle (see #3 below)
3) Idle control PID settings - this is closed loop idle. Its recommended you get the car running in open loop idle (Assymetric PID Conf setting under "Idle Control PID settings" to be disabled I think), where idle is controlled by your VE table values (fuel/afr) and your IACV (Idle air reference position settings) OR Idle control screw on the TB. Idle speed RPM is controlled through the IACV opening OR if you have an idle control screw, and fuel in the VE table. Again, if your car has an idle control screw on the TB, then you should set RPM based on that, and have the IACV 100% closed at warm temp. If your car does not have an idle control screw (like most 16V cars) then the IACV will be partly open at idle.
4) Before doing any of the above, verify your req_fuel is calculated correctly. Everything related to fueling is dependent upon this variable. If req_fuel is way off then all of your fueling will be way off. I would do some forum searching here in rennlist and elsewhere to see what others who are running VEMS might be using for req_fuel. Verify your value against what others are running. Run the calculator in VEMS (assuming there is one).
-A bunch of technical jargon I dont understand: http://www.megamanual.com/v22manual/mfuel.htm
-There is a calculator in MS Tuner Studio, I assume there is one in VEMS. If not, I can try plugging some values into my Tuner Studio for you if that helps.
-Here is a bunch of documentation for MS/TunerStudio that may directionally help you understand VEMS - many of the settings and interface seem similar: https://www.diyautotune.com/support/tech/
According to the VEMS formula and MS calculator, the Req Fuel values are very close... The slight difference is because of the metric and "freedom" numbers LOL:
VEMS: 6.49 * (2479 / 4 / 252) = 15.96
MS:
So, I left Req Fuel 16.
Does this look like a trigger angle/timing adjustment settings?
But after shutting down the car and restarting it the idle was way lower than before and the software was showing "Warming up On", which is odd with the temperature over 75C:
Video: https://www.dropbox.com/scl/fi/h8jef...02i6lcnbg&dl=0
At the end of this session I felt heat coming from the bottom and I've noticed the glowing red hot cat again - I'm very scared of catching fire and burning alive LOL.
FYI - ignore the rattling sound - it's my muffler rattling the bottom of the car, because the hanger needs to be adjusted.
Also, when I'm restarting the car the software reconnects with VEMS ECU just fine, but when making changes it crashes very frequently. The only way to prevent it to close the program and restart it as well.
Video: https://www.dropbox.com/scl/fi/q5dum...wlifw066r&dl=0
Ok, idle surge indicates, that your IAC is working. So there is an interference between Idle air valve reference position and your idle control screw. Turn your screw down until the idle stops surging. Try it and let us know.
Apart from that. Vems can control you idle via the IAC completely, so you can even turn down your idle screw until it's closed. That's what I did. The IAC does ist better than the idle screw. In case it doesn't work, just adapt the values of your Idle air valve reference position. But always just a little bit up or down.
Then the next step. The next step should be to adjust the mixture.
Nope, what happens, when you close your idle screw?
This is your idle reference position. If it's too high AND your idle screw is open too much, your idle will surge. So either close the idle screw (what I recommend) or lower the settings of your IAC reference position.
Nope, what happens, when you close your idle screw?
This is your idle reference position. If it's too high AND your idle screw is open too much, your idle will surge. So either close the idle screw (what I recommend) or lower the settings of your IAC reference position.
Oh, got it! I will play with it tomorrow.
I adjusted idle screw all the way in before setting target lambda and VE table and car was idling around 400-500rpm. Then I changed RPM/MAP lambda target values to 0.82 - 0.89 to achieve current lambda readings 0.92 - 1.0 , but car was idling 1050 - 1100rpm.
Then I shut down the car and restarted it. It was idling around 500 again. I shared a few videos a few posts before.
Also, the glowing red cat says that there is too much air... So, I'm confused.
FYI I have no experience with VEMS just using what I know from MS and trying to apply the same principals. I would defer to HFB as it seems they have more direct knowledge on VEMS. That said, here are my thoughts:
Sounds like you have req_fuel determined, so next thing is to move on to idle.
Idle needs to be configured first. Based on the fact you have an idle adjustment screw, the way that I have read to do this is to:
1) Make sure the IACV is completely closed when engine is fully warm (adjust "idle air reference position" table or turn off "PWM" in your "idle settings control type")
2) Adjust idle screw to get to desired RPM (important)
3) Adjust VE table to get AFR to read between 12-13 at desired idle RPM (important)
4) Shut down car, let it cool down and then start configuring your warm up fuel enrichment table (this is percent fuel added during cold starts) and configure your "idle air reference position" table, making sure the RefDC drops to a point where IACV is closed (try anywhere from 0%-30% down in the 85C column).
The above is what is basically considered "Open Loop" idle. Open loop is static and does not change based on outside factors, making it much less flexible than closed loop. Closed loop is a bit more advanced and essentially dynamically controls idle RPM through dynamic control of the IACV (basically opens/closes it as needed) to counter act drops in idle RPM such as turning on the AC, turning on headlights, etc. This is how most modern cars work, however you must get open loop configured well before moving to closed loop. Me personally, I am still working through closed loop on my own car... open loop once configured correctly can function pretty well.
Also keep in mind that you should not be configuring your idle VE settings using autotune.... its not really needed and again, you have your target lambda currently at way to lean for this range (again you have it at 1.0 where it should be in that 0.8 range). Its better just to adjust the VE table manually, while the car is running, and watch your wideband, again shooting for that 800-1000 RPM range (30 kpa MAP and lower) and a AFR of around 12-13. Youll adjust the whole block of VE cells so they are set all the same probably a 3x4 group in that idle range. Another cause of surging is that you have two VE cells close to each other in the idle zone with different fuel values, causing the idle to sort of jump between the cells back and forth and give a rich/lean pattern on the wideband as well as surging. Its important that all of the VE cells in your idle zone are similar values (as well as timing advance but theres a bit more nuance there). This is why its important to set that entire block of VE cells in the idle range to basically the same number as you dont want this fluctuation/surging.
Autotune is used to basically configure the rest of your VE table outside of idle zone. Once you get your target Lambda table correctly setup (currently it needs some work) you can take your car for a drive and slowly bring it through all of the cells - autotune will adjust the VE values to get them as close as your target lambda as possible. This means taking the car through different rpm and load zones, part throttle, full throttle, cruising, etc. While autotuning, work your way through as many of the table cells as possible, as slowly as possible (to give autotune the chance to make adjustments and get good readings). This is a good way to get your VE tables "close" but will still require some small adjustments and smoothing as you continue to iron out all the little rich and lean spots that will likely remain even after autotune.
Your cat is glowing red hot because you are running way too rich and the fuel is burning inside the cat, a quick google search confirms this... Highly recommend not driving it this way until you can get your VE tables adjusted.
Last edited by walfreyydo; 08-02-2023 at 10:45 AM.
07-31-2023, 10:30 AM
