ECU "long term memory"?
09-22-2011, 03:25 AM
#1
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ECU "long term memory"?
I've never seen this discussed before but I feel it's relevant to Toyo/Scion tuning. When I started boosted ny 08 XB 2 years ago the first thing I did was install the 440cc inj's to see how well the ECU could adapt to them. The first drive was pretty dodgy. The engine bogged and stalled several times and generally ran pig rich for the first few day or two. It kept getting better as new LTFTs were set and after say 100 miles, it ran like it did with the stock 370's.
2+ years later and I've noticed on numerous occasions now that I can reset the ECU by battery disconnect and it re-adjusts to the 440s immediately. No bogging, no stalling, no 10:1 AFRs ever. I've suspected that our ECU has a long term memory for over a year now but now I am convinced. I believe that the ECU has a multi-level memory that remembers previous fuel trim conditions and quickly adapts to them. Disconnecting the battery only resets the short term memory and to truly return to the base oem tune requires a factory reset procedure other than a simple battery disconnect.
FWIW...
2+ years later and I've noticed on numerous occasions now that I can reset the ECU by battery disconnect and it re-adjusts to the 440s immediately. No bogging, no stalling, no 10:1 AFRs ever. I've suspected that our ECU has a long term memory for over a year now but now I am convinced. I believe that the ECU has a multi-level memory that remembers previous fuel trim conditions and quickly adapts to them. Disconnecting the battery only resets the short term memory and to truly return to the base oem tune requires a factory reset procedure other than a simple battery disconnect.
FWIW...
09-23-2011, 02:31 AM
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I don't know how else to explain it. This last battery disconnect was overnight and I pushed the brake pedal too (just in case it actually does anything). The car started up and ran as though it came from the factory with 440cc inj's.
Have you ever seen similar behavior?
BTW, if you haven't already, bookmark this site. Great info IMO.
http://www.autoshop101.com/techartic...larticles.html
Have you ever seen similar behavior?
BTW, if you haven't already, bookmark this site. Great info IMO.
http://www.autoshop101.com/techartic...larticles.html
Last edited by ScionFred; 09-23-2011 at 08:52 PM.
09-23-2011, 03:28 AM
#4
cant say i have seen the exact same...but just think about if there is a "extra long term fuel trim" so to speak that the ecu learns and stores as memory then why wouldnt it learn a new trim and store it after a period of time?
what i have seen is absolutly perfect fuel trims for roughly 30-40min of driving and suddenly long term fuel trims change to a large value while cruise controle is set and on level ground. stft never changed and vac was not fluctuating. ltft will stay that way no matter what engine load unless you are in open loop, that is till you shut the car off and restart. after restart, perfect fuel trims again for the rest of the day. Mind you this is weeks to months after clearing the ecu of fuel trims. It happens at random and will not happen every day.
this happens to me every so often. I thought it had something to do with the primary o2 sensor so while it happend i left the car running and jumped out to disconnect the primary o2 just to see what happens. now the ltft was sitting at -22 and afr was at roughly 14.5 before disconnecting, after afr went to 10's and car sputtered and died. that told me the primary was good but something is adding fuel when it shouldnt be. So I went through the fuel system making sure the fpr was operating properly and fuel pressure was consistent. That checked out. Then I looked at a possible short.
A couple of times stft would kick in and sort of compensate for the extreme ltft, eventually fuel trims would level off to low to perfect values.
still makes me wonder what would happen if I replaced the primary o2 anyways.
in anycase if there is some sort of hidden memory that my ecu is reverting back to it would explain the condition. I doubt it though, still is an intresting idea.
what i have seen is absolutly perfect fuel trims for roughly 30-40min of driving and suddenly long term fuel trims change to a large value while cruise controle is set and on level ground. stft never changed and vac was not fluctuating. ltft will stay that way no matter what engine load unless you are in open loop, that is till you shut the car off and restart. after restart, perfect fuel trims again for the rest of the day. Mind you this is weeks to months after clearing the ecu of fuel trims. It happens at random and will not happen every day.
this happens to me every so often. I thought it had something to do with the primary o2 sensor so while it happend i left the car running and jumped out to disconnect the primary o2 just to see what happens. now the ltft was sitting at -22 and afr was at roughly 14.5 before disconnecting, after afr went to 10's and car sputtered and died. that told me the primary was good but something is adding fuel when it shouldnt be. So I went through the fuel system making sure the fpr was operating properly and fuel pressure was consistent. That checked out. Then I looked at a possible short.
A couple of times stft would kick in and sort of compensate for the extreme ltft, eventually fuel trims would level off to low to perfect values.
still makes me wonder what would happen if I replaced the primary o2 anyways.
in anycase if there is some sort of hidden memory that my ecu is reverting back to it would explain the condition. I doubt it though, still is an intresting idea.
09-23-2011, 08:53 PM
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When this happened, was there a FIC connected? I've seen similar oddities but only with the FIC installed. Never happened with the X1 or no piggy. Extra fuel is added when the A/C is running and I've seen that reflected in the trims but not a 20% change.
When my primary O2 went bad my UEGO was reading 10:1, the engine sputtered, stalled and was undriveable but the scan tool was reading from 10:1 to 15:1 from the bad O2 sensor. The sensor output was very erratic but mostly reading leaner than actual.
When my primary O2 went bad my UEGO was reading 10:1, the engine sputtered, stalled and was undriveable but the scan tool was reading from 10:1 to 15:1 from the bad O2 sensor. The sensor output was very erratic but mostly reading leaner than actual.
09-26-2011, 05:55 PM
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FWIW, one of the most respected Scion tuners on the east coast told me that they send back an unexpectedly high percentage of new FICs for various problems. He added that AEM's usual response is to say that they didn't find any problems but they return a different FIC and the previous problems don't recur. He highly suggested that I get a GEMU instead. This was "off the record" so I'm not naming names.
Personally I have my doubts about the component and build quality of the FIC and the accuracy and reliability of the tiny watch battery sized MAP sensor. If practical, I would definately test a different FIC and see if you still have the same problems.
BTW, I think I may have figured out why the FIC causes a delay on engine startup. The ECU won't supply fuel or spark until it sees a valid crk signal and the FIC generated crk signal is weaker than the oem by about 1/2. Unfortunately there is no easy way of amplifying that crk signal. A different model FIC (1911) has been electrically modified by AEM to output a stronger crk signal but the cam signal circuitry is not compatible with the TC or XB.
Personally I have my doubts about the component and build quality of the FIC and the accuracy and reliability of the tiny watch battery sized MAP sensor. If practical, I would definately test a different FIC and see if you still have the same problems.
BTW, I think I may have figured out why the FIC causes a delay on engine startup. The ECU won't supply fuel or spark until it sees a valid crk signal and the FIC generated crk signal is weaker than the oem by about 1/2. Unfortunately there is no easy way of amplifying that crk signal. A different model FIC (1911) has been electrically modified by AEM to output a stronger crk signal but the cam signal circuitry is not compatible with the TC or XB.
09-27-2011, 12:55 AM
#8
I still havnt had a start up problem... I do have a very slight (I stress the word slight) lag in start up over stock. However I have had customers with a start up issue that I couldnt pin down, I could ease it to some degree but never gone, while others I didnt have a problem like that. Im starting to think AEM's quality control is lacking a bit. I myself am just about ready to ditch the fic.
09-27-2011, 01:43 AM
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I had 2 different FICs. One of them had fairly signifcant startup lag and the other one was slight but still annoyed me. IMO the FIC design is fantastic but it's real world operation often leaves much to be desired. If AEM modified the 1910 to better match our crk and cam sensors and improved their QC, I'd buy one. Unfortunately, I'm not impressed by the GEMU or Unichip and the very impressive but currently unavailable APR X1 simply didn't work correctly with my car for unknown reasons. There are other good piggys but I don't want to be the first to test them on a Scion. I'm surprised that no one at SL has ever tried a Map-ECU or Haltech Interceptor. The new Map-ECU3 appears to combine the best of the GEMU with the best features of the FIC. Gadget at URD is running them on boosted Toyota trucks with good success. Might be worth considering.
09-27-2011, 06:48 PM
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Which version? 1, 2, 3 or all of them? I don't have any firsthand experience with them so I can't comment other than to say that the spec's on version 3 look very good.
Seriously? That's very interesting. Unfortunately I could never get the FIC to pick up my cam sensor signal 100% so that's another potential issue. I really don't know which problems were FIC, which were the harness and it's even possible that my 3V cam sensor signal is weaker than it should be. However, if I could get a FIC working 100% on my car, it would be a nice addition.
Seriously? That's very interesting. Unfortunately I could never get the FIC to pick up my cam sensor signal 100% so that's another potential issue. I really don't know which problems were FIC, which were the harness and it's even possible that my 3V cam sensor signal is weaker than it should be. However, if I could get a FIC working 100% on my car, it would be a nice addition.
09-27-2011, 06:55 PM
#16
Im thinking about selling my EMU and going to a MS3x just for fun lol. All id really need to do is convert the car to cable throttle and it should be good to go. Dont get me wrong, I love the EMU, but there are still limitations Id like to get around, and I dont want to pay $1700 for an EMS. Or maybe I could try the EMS-4... Hmmm.... Keep in mind, these options arent for everyone. My tC is far from a daily driver and I have the electronics and automotive background to get one of these solutions to work without paying someone $1000+ to install/tune it.
09-27-2011, 07:54 PM
#17
Which version? 1, 2, 3 or all of them? I don't have any firsthand experience with them so I can't comment other than to say that the spec's on version 3 look very good.
Seriously? That's very interesting. Unfortunately I could never get the FIC to pick up my cam sensor signal 100% so that's another potential issue. I really don't know which problems were FIC, which were the harness and it's even possible that my 3V cam sensor signal is weaker than it should be. However, if I could get a FIC working 100% on my car, it would be a nice addition.
Seriously? That's very interesting. Unfortunately I could never get the FIC to pick up my cam sensor signal 100% so that's another potential issue. I really don't know which problems were FIC, which were the harness and it's even possible that my 3V cam sensor signal is weaker than it should be. However, if I could get a FIC working 100% on my car, it would be a nice addition.
Yes I can modify an AEM to work for you for full control.
Im thinking about selling my EMU and going to a MS3x just for fun lol. All id really need to do is convert the car to cable throttle and it should be good to go. Dont get me wrong, I love the EMU, but there are still limitations Id like to get around, and I dont want to pay $1700 for an EMS. Or maybe I could try the EMS-4... Hmmm.... Keep in mind, these options arent for everyone. My tC is far from a daily driver and I have the electronics and automotive background to get one of these solutions to work without paying someone $1000+ to install/tune it.
Doing custom EMS is not for the faint at heart, experience nor technical knowledge. Plenty of people think it's just create a custom harness and be done. There is plenty more to it than that. I wish it was that easy sometimes.
Not discrediting you or anyone else on here, but doing a custom EMS is a lot of work. Period.
09-27-2011, 08:30 PM
#18
That it is 
Ms3x has gotten much better than the MS2/x and MS1 - Ive personally wired up several MS1 and MS2 but still have alot to learn when it comes to tuning them. I had already planned on when I build an SC300 using an MS3x and converting to COP. Getting the MegaSquirt to work the tc I dont think would be extremely difficult, just labor intensive and alot of trial and error.
Ms3x has gotten much better than the MS2/x and MS1 - Ive personally wired up several MS1 and MS2 but still have alot to learn when it comes to tuning them. I had already planned on when I build an SC300 using an MS3x and converting to COP. Getting the MegaSquirt to work the tc I dont think would be extremely difficult, just labor intensive and alot of trial and error.
09-27-2011, 08:40 PM
#19
That it is Ms3x has gotten much better than the MS2/x and MS1 - Ive personally wired up several MS1 and MS2 but still have alot to learn when it comes to tuning them. I had already planned on when I build an SC300 using an MS3x and converting to COP. Getting the MegaSquirt to work the tc I dont think would be extremely difficult, just labor intensive and alot of trial and error.
Ms3x has gotten much better than the MS2/x and MS1 - Ive personally wired up several MS1 and MS2 but still have alot to learn when it comes to tuning them. I had already planned on when I build an SC300 using an MS3x and converting to COP. Getting the MegaSquirt to work the tc I dont think would be extremely difficult, just labor intensive and alot of trial and error.