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Thread: Ecm is not sending a signal to trigger iac

  1. #46
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    Best news ever. So i went to the junkyard and got an ecm from an 89 chevy. I tried looking up the code on the ecm which is AMUT but could not find anything on it. Anyway the good news is my IAC now works again, I finally have a check engine light, and i can hook up my laptop to the ecm and view everything. YAY

  2. #47
    Fuel Injected! sturgillbd's Avatar
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    According to BCC lookup, AMUT is a 1987 5.7 liter with manual trans calibration.

  3. #48
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    I did not look very close to see if the truck had a manual trans or not I am also pretty sure it was a 1989 new body style with auto transmission but it might have been a manual. The truck was burried in snow and i only had basically that one to choose from. I never opened up the ecm to see what chip was actually in it. The junkyard put paint over the bolts on the ecm so i don't want to take the cover off for a little while in case i need to return it. If the bin is for a manual trans is it ok to run it like that for a little while? Also i thought the IAC was working but it is not. Because the truck is running so much better i assumed it was working. Is thier any value in my old ecm? How much could i sell it for or should i keep it?
    Last edited by joegreen; 02-07-2015 at 11:50 PM.

  4. #49
    Super Moderator Six_Shooter's Avatar
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    Restricting you from placing the proper PROM in the ECM is counter productive to verifying that the ECM works correctly. Swap the PROM and if there is a problem expoain to them the reasone for the easy to open PROM access plate.
    The man who says something is impossible, is usually interrupted by the man doing it.

  5. #50
    Fuel Injected! sturgillbd's Avatar
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    You will not have lockup converter control with that calibration. It may have a different chip in it than what it says on outside of the case. I wouldn't be afraid to run it as is. It would be good to know what chip it actually has in it though. Have you driven it with the ecm you got from the junkyard? If you have odd issues with tcc lockup, disconnect pin A7 from the ecm connector. What happens if you bridge pins A and B on the aldl connector? With the A and B terminal jumped and turn the key on, you should be able to listen to the IAC and hear clicking where the pintle on the IAC should be bottomed out in the passage.

  6. #51
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    Quote Originally Posted by Six_Shooter View Post
    Restricting you from placing the proper PROM in the ECM is counter productive to verifying that the ECM works correctly. Swap the PROM and if there is a problem expoain to them the reasone for the easy to open PROM access plate.
    I can actually just take the whole top cover off the ecm and swap in a chip i have from a 5.7 th400 truck. That way the access cover does not need to come off. Eventually i will take it off i just want to verify the ecm works for a little.

  7. #52
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    Quote Originally Posted by sturgillbd View Post
    You will not have lockup converter control with that calibration. It may have a different chip in it than what it says on outside of the case. I wouldn't be afraid to run it as is. It would be good to know what chip it actually has in it though. Have you driven it with the ecm you got from the junkyard? If you have odd issues with tcc lockup, disconnect pin A7 from the ecm connector. What happens if you bridge pins A and B on the aldl connector? With the A and B terminal jumped and turn the key on, you should be able to listen to the IAC and hear clicking where the pintle on the IAC should be bottomed out in the passage.
    My truck has a th400 so no lockup converter. I will pop the whole cover off the ecm and see what chip it has in it. I have driven it since i put it in. I noticed it stumbles when taking off when warm but is super precise with the throttle when cold. I think that might be because the iac is not working. Could that be? I bought a new ac delco IAC from amazon that should be here in a few days.

  8. #53
    Super Moderator Six_Shooter's Avatar
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    The calibration is different between auto and manual, and is the reason you have drivability issues. This is the entire purpose of the swappable PROMs.
    The man who says something is impossible, is usually interrupted by the man doing it.

  9. #54
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    Quote Originally Posted by Six_Shooter View Post
    The calibration is different between auto and manual, and is the reason you have drivability issues. This is the entire purpose of the swappable PROMs.
    ok, tomorrow i will verify what chip is in it currently. I am going to solder in my chip adapter after using this ecm for a while. If the chip thats in it is for a manual the only other chip i have is afbw which is for a 5.7 th400 truck which should be fine for now. Also i took my old ecm apart to unsolder the chip adapter. I tried looking for anything out of the ordinary but everything looked fine.

  10. #55
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    ok, so the chip that was in the ecm i bought was AMUT. I wish i had a better look at the truck because i don't think it was a manual. At the time i was just excited to find an ecm in a truck with with a non working motor. Anyway even though the ecm was very dirty on the outside when i got it it was very clean on the inside when i took the cover off. On the remanufactured ecm i have the clear coat on the inside is all pealing and their might be corrosion under the clear coat. So the old ecm i bought is in much better shape visually. I just swapped in my old AFBW chip and the other smaller chip (i forgot what it is called). I plugged in the ecm and the truck fired right up. I am now just waiting on my new delco IAC from amazon. It is amazing how good the truck runs with the new ecm. I had been using the broken ecm since day one so i assumed thats kind of what tbi was like. I hope my fuel mileage goes up from the current 4 mpg. I am sure it will though. Here is a pic of the inside of the new ecm. It was taken with my cell phone so it was not the best pic.

  11. #56
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    ok so some things i have noticed since the new ecm. First i noticed that the engine stays cooler. I have a 190 thermostat and before it used to idle around 200, now the thermostat keeps opening and closing to keep it at 190. The exhaust does not burn my eyes anymore. Truck starts almost instantly. i thought my IAC was not working but it turns out is was. I reset the iac and set base idle to 100-125 rpm lower than the minimum in the bin. The bin is at 600 rpm. I also checked my timing with the brown wire unplugged and it was like 6-8* btdc. I put it at zero and that seemed to help. I took it out for a little drive and it still pops through the intake if i open the throttle fast. low to mid range power is up but it has like no guts when floored. It seems to have ok power if i don't lean into the throttle to much but when i do get into it the power goes away. It has a brand new timing chain in it. I took a datalog on my short drive today. when floored i only get to 70% throttle so i will have to see what i can do with the throttle linkage. maybe someone can look at my log and let me know what you think. Its short maybe like 10 min.
    Last edited by joegreen; 02-12-2015 at 05:33 AM.

  12. #57
    Fuel Injected! sturgillbd's Avatar
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    I just played back your log file. At idle and low loads on the engine BLM's look pretty good. As soon as you start to put a load on the engine, your BLM's climb higher and higher.At one point I saw the BLM climb over 150. If this is a stock tune, you may have a plugged fuel filter or a fuel pump starting to fail. Have you replaced the fuel filter? If not, replaced the fuel filter and perform another log. You also should measure your fuel pressure to see if it is in spec after replacing the fuel filter.
    Brian

  13. #58
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    so a high blm indicates a lean condition? Could that equal a power loss? I picked up a inline metal fuel filter at autozone that was for a nissan or something so i am sure it is fine for the low tbi psi. The fuel filter is pretty new like half a year with maybe a thousand miles on it. The fuel pump is the same one that came out of the donor truck. I set fuel pressure a while ago at 14 psi and it seemed to hold steady. Should i check it again? I would hate to have to drop the tank to replace the pump but if thats what needs to be done. what could be causing the backfire through the intake when moving the pedal fast? I need to get my chip adapter soldered in so i can disable some things like the egr and whatnot. Also when the truck is cold it runs awesome. I can spin the tires and it does not backfire through the intake.
    Last edited by joegreen; 02-12-2015 at 06:22 AM.

  14. #59
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    High BLM's means lean. Use a gauge and measure fuel pressure when under load to make sure your pressure stays up. Plugged fuel filter can cause the symptoms you describe and fuel pressure may be dropping under load. You are definitely leaning out as the engine load increases. Have you made any adjustments to your VE tables? That high of BLM is about to the limit the ECM can adjust. Play your log file and watch the data. You are shooting for 128 + or minus 5. I would rather it be lower than 128 instead of above. Backfire through intake us usually a sign of a lean condition. Get your BLM's in range first and then you may have to tune Acceleration Enrichment to stop the backfire under quick opening of the throttle.
    Brian

  15. #60
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    ok sounds good. i will rent a fuel pressure tester from autozone tomorrow and see how it goes. thanks.

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