*********************UPDATE/ISSUE FIXED*********************
i will keep the OG post below, under the line... but so you dont have to go find the solution it is placed up here.

pretty simple actually. the positive battery cable was no large enough to handle the power once the engine was warm. that, and it was hose clamped to the original fuse box main wire and the alternator wire....

replaced with big 0 gauge wire, it cranks over 2x fast now, hot or cold, and fires right up. the engine *seems* to even run better, but that could be in my head.







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AEM V1 - tuned by JK tuning so i dont think i have a tuning issue..

after i drive, especially after aggressive driving, if you shut down the engine and try to restart it it cranks very slowly and wont start. you must either bump start it or wait until it cools down.

john said it may be an issue with the fuel trim on heat soaked startup, but i dont think thats the case because i stalled it yesterday at a stop sign and it wouldn't fire back up, and it only sat for about 5 seconds before i tried.

"sometimes" it will fire up if i go 100%throttle on startup (to shut down injectors) but i honestly think its just coincidence.

also.. battery is in the trunk... dont know if mabye a new battery cable or grounds could be the issue.. i think theres a $250 battery in there its def. no walmart.

lastly, it happens in summer and in winter, so ambient temp is not affecting it.


thanks,

Matt

 

This is a common problem with this ecu it seems. I believe its the coil drivers. Not sure what the remedy is, maybe someone with more direct experience on this one can chime in.

 

It has to do with how the ecu is designed. There is a main board and a daughter board with pins that is pressed into the main board. It is not a good design for something that is subjected a lot of vibration. I fixed one not too long ago by simply unseating the daughter board and reseating it. I did a full checkout on my work bench and didn't find anything wrong with it. Sent it back to the guy and he said it's working perfectly now. I wasn't impressed with the design.

 

so, the daughter board is inside the main ecu???

maybe over my head, but can anyone explain why and how it happens? like, what changes when the car sits and cools down?

thanks.


also actively looking for someone to help with the fix. if i stall this stage 5 clutch with the 6lb flywheel on a busy road im SOL

i

 

I'm not quite saying that. I'm saying that the design of the ECU allows the daughter board that has about 60 independent pins on it to come lose. For most there is no relationship between a warm car and cold start. For most it simply wont start sometimes but knowing it's the aem v1 and knowing that I've fixed it before by simply unscrewing it, sliding out the whole board with the daughter board, separating the daughter board carefully essentially unseating all of those 60 pins and then reconnecting them and pushing down on the pins to ensure they are seated and making good contact. That fixes the issue. I'm saying I wouldn't want to chase a cold /hot start rabbit hole issue before doing the easy thing and reseating the board.

edit:
also be careful doing it yourself. their method to keep the pins seated was to force oversize pins into one size smaller holders it seems like so the daughter board doesnt separate easily by any means, it almost feels like you can snap the daughter board off trying to safely remove it. and make sure you do it somewhere where you wont cause a lot of static. obviously dont do it on carpet or anything. be careful.

 

^^ Sounds like a separate issue from what I was talking about which is a fairly common one with the coil drivers (I think) that do act up when the car is warm.

I had a friend with a V1 ( coincidentally also batt relocate to trunk, not sure if any correlation) would 5/10 not be able to get his car started after turning it off from drive within 15-30min after parking it, like clockwork. I believe there was some hardware update AEM provided to owners with the issue which made an improvement, but not 100% fix to my recollection. But again, I never ran one myself, in part because of hearing about these issues from others on s2ki many years ago when this unit was new. So let some others chime in, or possibly do some searches on this issues with the v1 and see if its something you want to continue deal with and potentially fix, or move to another ems.

 

"or move to another ems.", haha reminds me of about 12 years ago, my buddy stalled at a light in his s2k with the aem v1. missed 2 lights and had to run around to my side to switch back to the stock ECU. hahaha. good times.

 

yeah im doing my research... seems to be many different opinions on what is happening...

a lot of people are saying that the starter needs replaced... but that makes absolutely no sense to me... its still turning over... just slower...

but then, how could the aem make the engine turn over slower? that part doesnt make any sense either.

my car is 10/10 if you shut it off, dont even think about driving it again for about 15min.

 

ok I didnt know those details initially . that makes me think battery or battery cables. i dont want to go back and forth on why it could or couldnt be batteries but hopefully you have someone good with electronics that could help you diagnose that part. I recommend getting a beefy battery. used to mess around with the lightweight race ones and not worth it. what guage are the cables going to the battery? and are they a consistent guage at all points? basically, a draw on the battery will generate some heat, batteries perform poorly when warm, maybe a stereo amp is putting too much of a draw on it? maybe trunk not able to help cool the battery. etc.

 

you think its possible that the hot start table is either too rich or too lean?? you think maybe its adding way too much fuel in and cant fire, ans thats why the cranking is slower?