Setup is a AMC 304 V8 with Chevy TBI and sensors. I was able to get an idle the first two times I test fired the engine. Now it just dies as soon as the throttle plates close. I've read the section really carefully about how to calibrate the IAC. I'm getting strange results compared to what the manual is telling me I should see. I've tried the full range of AfterstartIAC settings and the engine still performs the same. Real time readings on the laptop show the same settings too.
MT Ver MegaSquirt Signature
3.00 MSII Rev 2.10000
During calibration I pulled out the IAC to watch the plunger. What I noticed is that sometimes when I power up the fuel injection system that the plunger cycles like the manual says. Other times it doesn't. Seems to cycle if I leave the system powered down for few minutes. I've gone in to MegaTune 2.25, settings, idle control, under time-based after start adjusted the cold position steps. Is this the correct location to adjust the IAC? The manual needs to be updated since it refers to older MegaTune versions. I've tried settings thoughout the entire range of 0-255. Nothing changes.
I've double checked the wiring to the IAC. Confidence is high that it is hooked up correctly. Although I almost think the IAC is operating backwards from what the manual says. But I do have it wired the way I'm supposed to. Since I can't get the engine to respond to changes I can't confirm if it's operating backwards. I'm hoping someone can look at the log and tell me.
Can someone look at my log file and let me know if they see anything unusal?
New setup won't idle possible IAC problem.
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Forum rules
Read the manual to see if your question is answered there before posting. If you have questions about MS1/Extra or MS2/Extra or other non-B&G code configuration or tuning, please post them at http://www.msextra.com The full forum rules are here: Forum Rules, be sure to read them all regularly.
Forum rules
Read the manual to see if your question is answered there before posting. If you have questions about MS1/Extra or MS2/Extra or other non-B&G code configuration or tuning, please post them at http://www.msextra.com The full forum rules are here: Forum Rules, be sure to read them all regularly.
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jonfx4com
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It loks in the software like your IAC is moving the right way. It closes as the engine warms up which is correct.
Start value is a number bigger than the total number of steps the IAC is able to move. this makes sure the IAC pintle is at a known wide open position before we start counting outwards. 250 on mine
Cranking position is how many steps to move forward from the start (wide open) value for cranking, that is a number a little further out to give it loads of air while cranking but not wide open like the start value position. 120 on mine
Time based after start is a wider IAC opening for a period of time when temp is at or below the number in "cold temperature" it is not used if it is above this temp. I just leave it at the default, may be usefull in siberia but not england. 0 on mine
Cold position steps and cold taper time are only used if the time based after start is in play (ie its VVV cold) 120 on mine
In the IAC steps table you want a low number in the cold temperatures and a higher number in the warmer parts (higher number of steps outward = less air) on mine 100 at -40F and 216 at 190F
Hysterisis is how much the coolant temp must change before the IAC moves. This prevents it jiggling about for small temp changes and potentially losing its position. 5F on mine
On turning on MS the IAC it should go to the fully retracted position and if the that is less steps than the number you set in start value it will buzz a little as it hits its limit. It will then move out to the cranking value. If this works you are not far wrong in your setup.
You may want to set the throttles open just enough for a very slow idle and then use the IAC to trim it to where you want it, that works for me.
Jon
Start value is a number bigger than the total number of steps the IAC is able to move. this makes sure the IAC pintle is at a known wide open position before we start counting outwards. 250 on mine
Cranking position is how many steps to move forward from the start (wide open) value for cranking, that is a number a little further out to give it loads of air while cranking but not wide open like the start value position. 120 on mine
Time based after start is a wider IAC opening for a period of time when temp is at or below the number in "cold temperature" it is not used if it is above this temp. I just leave it at the default, may be usefull in siberia but not england. 0 on mine
Cold position steps and cold taper time are only used if the time based after start is in play (ie its VVV cold) 120 on mine
In the IAC steps table you want a low number in the cold temperatures and a higher number in the warmer parts (higher number of steps outward = less air) on mine 100 at -40F and 216 at 190F
Hysterisis is how much the coolant temp must change before the IAC moves. This prevents it jiggling about for small temp changes and potentially losing its position. 5F on mine
On turning on MS the IAC it should go to the fully retracted position and if the that is less steps than the number you set in start value it will buzz a little as it hits its limit. It will then move out to the cranking value. If this works you are not far wrong in your setup.
You may want to set the throttles open just enough for a very slow idle and then use the IAC to trim it to where you want it, that works for me.
Jon
I have no throttle stop on this TBI. GM used the IAC to control all idle control(I believe). Otherwise I would cheat and set the the set screw for now and work on the other issues I'm having.
When you stay retract(like the manual says) does that mean fully closed or fully open? I think of it as pulling the pin into the motor housing causing the valve to open wide. That would work for me to bring the throttle high during start. What I'm finding is that the IAC is going fully out and closing the valve. This is what I see when I have the IAC out of the throttle body. What I see on the laptop realtime screen is 0 during power up and 109-135 after engine starts. I see it very slowly climb as engine warms.
Conclusion in my mind is that the software is doing the right thing but the IAC is not acting correctly. Should I buy a new IAC? I'll probably try that tonight unless you guys have other ideas. Thanks for checking this out and supplying such a detailed response. That was a big help.
Here's some pictures of what I'm building if you are curious.
http://www.trailrigoutfitters.com/Proje ... /index.htm
Pete
When you stay retract(like the manual says) does that mean fully closed or fully open? I think of it as pulling the pin into the motor housing causing the valve to open wide. That would work for me to bring the throttle high during start. What I'm finding is that the IAC is going fully out and closing the valve. This is what I see when I have the IAC out of the throttle body. What I see on the laptop realtime screen is 0 during power up and 109-135 after engine starts. I see it very slowly climb as engine warms.
Conclusion in my mind is that the software is doing the right thing but the IAC is not acting correctly. Should I buy a new IAC? I'll probably try that tonight unless you guys have other ideas. Thanks for checking this out and supplying such a detailed response. That was a big help.
Here's some pictures of what I'm building if you are curious.
http://www.trailrigoutfitters.com/Proje ... /index.htm
Pete
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jonfx4com
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by retract I mean fully open or as you say, "pulling the pin into the motor housing", if its pushing the pintle out fully on MS power up it is wired up wrong.
If you have it this way the idle speed would go up as the engine warms but that does not fit your symptoms either. If this was the case it would be a biatch to start and then idle way too fast as it warms up. All a bit weird but for sure if it pushes the pin all the way out when you power up there is a wiring problem not an IAC problem so save your money, if it moves it works.
The MS sequence is pull it all the way in so you have a known reference point then push it out to "cranking value"
I had to play with this for hours to get it moving the right way. It seems there is one correct wiring combination and lots of wrong ones that either just buzz or spit the pintle out of the end.
Jon
If you have it this way the idle speed would go up as the engine warms but that does not fit your symptoms either. If this was the case it would be a biatch to start and then idle way too fast as it warms up. All a bit weird but for sure if it pushes the pin all the way out when you power up there is a wiring problem not an IAC problem so save your money, if it moves it works.
The MS sequence is pull it all the way in so you have a known reference point then push it out to "cranking value"
I had to play with this for hours to get it moving the right way. It seems there is one correct wiring combination and lots of wrong ones that either just buzz or spit the pintle out of the end.
Jon
This is making sense. I think it is working backwards then. It fired the pintle across the garage twice on me last night when I powered up the system. I never once saw it suck the pintle in and keep it keep it in a somewhat retracted position. I'll try changing some wires tonight and see what the results are. Thanks for the help.
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69 1/2 Six Pack Bee
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jonfx4com
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Its worth the hassle, once you get the wires right it works very well. No stalling or holding the throttle open when its cold. If you go through it logically you will get there. If all else fails draw a chart of all the ways you can connect 4 wires to 4 wire, one will work. Thats what i did in the end and it took me a while to check each one until it worked.
Jon
Jon
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69 1/2 Six Pack Bee
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Hey. Jon.
I am right with you there, buddy.
My IAC does operate as intended except that it is very inconsistent. The wiring was one of the first things that I sorted out. I jumpered the resistors on the chip as well. It goes through all of the correct motions but it will not repeat. I have tried 4 different IAC's and all are just alike in operation. As I had first stated in one of my numerous posts about this (and thanx alot to those who added their support
) it goes through the motion like it is slowing down the idle and it does....a little bit...yet the pintle will NEVER completely close from a first-in-the-morning startup. If it is warmed up and I shut off the engine and re-start THEN it will close. I have played with step settings, closed steps, hysterisys, motor speed, temperature curves, yada, yada, yada, and it will never close from a dead start up...ever...ever. The steps indicate correctly in MT but the motor just "shudders" like it is moving but nothing like it should.
I have just run out of ideas and things to try that I know of.
I've got bigger fish to fry than spending any more effort on something that I know not how to fix.
I will carry on fine tuning the system and just leave the IAC in as a "vacuum leak plug" for the time being.
I have considered sending back the chip to Glen for a swap in case I have one of the "one-in-a-million" duds. That's my luck .
BTW..what type of IAC are you using and if you don't mind, what setting do you have in yours to make it work?
Thanx,
Bud
I am right with you there, buddy.
My IAC does operate as intended except that it is very inconsistent. The wiring was one of the first things that I sorted out. I jumpered the resistors on the chip as well. It goes through all of the correct motions but it will not repeat. I have tried 4 different IAC's and all are just alike in operation. As I had first stated in one of my numerous posts about this (and thanx alot to those who added their support
) it goes through the motion like it is slowing down the idle and it does....a little bit...yet the pintle will NEVER completely close from a first-in-the-morning startup. If it is warmed up and I shut off the engine and re-start THEN it will close. I have played with step settings, closed steps, hysterisys, motor speed, temperature curves, yada, yada, yada, and it will never close from a dead start up...ever...ever. The steps indicate correctly in MT but the motor just "shudders" like it is moving but nothing like it should.I have just run out of ideas and things to try that I know of.
I've got bigger fish to fry than spending any more effort on something that I know not how to fix.
I will carry on fine tuning the system and just leave the IAC in as a "vacuum leak plug" for the time being.
I have considered sending back the chip to Glen for a swap in case I have one of the "one-in-a-million" duds. That's my luck .
BTW..what type of IAC are you using and if you don't mind, what setting do you have in yours to make it work?
Thanx,
Bud
My problem was stupidity. I found 3 of the 4 wires that I labeled were mislabeled. Once I confirmed which IAC pins belonged to what coil I then determined polarity. I figured out how to make the IAC make it's steps by alternating power to the coils. Then I traced the wires completely from IAC to relay board and labeled them correctly this time. Baby steps and troubleshooting. One systematic change at a time. The engine came to life but it doesn't seem to be consistent... yet. Same performance as above. I have more tuning to do. I just needed it to hold an idle for now.
I'm running this on a Jeep that must crawl large rocks. I need the idle to be extremely reliable. It's the most important aspect. I'm getting a bad feeling about this. I'm a little disappointed the software doesn't have an easier way to control idle. You would think they could make a slider bar that would work the IAC. Slider bar could be used to troubleshoot and make sure the direction is correct and that you have the correct range of movement. Maybe next version??? PLEASE!
I think your IAC won't close completely because of it's in warm-up mode. If you fooled your temp sensor I'll be it closes all the way. I would think you could take the warmup table and make adjustments to fool it there too.
I'm running this on a Jeep that must crawl large rocks. I need the idle to be extremely reliable. It's the most important aspect. I'm getting a bad feeling about this. I'm a little disappointed the software doesn't have an easier way to control idle. You would think they could make a slider bar that would work the IAC. Slider bar could be used to troubleshoot and make sure the direction is correct and that you have the correct range of movement. Maybe next version??? PLEASE!
I think your IAC won't close completely because of it's in warm-up mode. If you fooled your temp sensor I'll be it closes all the way. I would think you could take the warmup table and make adjustments to fool it there too.