mk4 Supra Starting Issue | AEM
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SupraNA-T
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Last seen: 1 year 1 month ago
Joined: 10/26/2018 - 13:51
mk4 Supra Starting Issue

94 Supra 2JZ GE NA-T

Hello currently having a very weird issue with starting my supra. The car was a GE but I have fully converted to GTE sensors and cams, (welded bung on head for cam sensor. so no distrubitor at all) I have installed a 2 way battey kill switch in the rear bumper for racing. Wired in from battery- fuse-switch-starter-fuse box under hood with the alternator on it's own wire going directly to the battery. The issue is when I go to start the car sometimes it will crank and crank without even trying to start. leave the key in the run position, walk to the back of the car and turn off my kill switch for about 5 seconds, then turn it back on and car will start up right away. Drive the car outside and leave it sit same issue. Iv tried leaving the switch on at all times when sitting/parked. Doesn't seem to effect it. Or leaving it off when its sitting/parked also doesn't matter.  I'v checked all gounds to EMS along with my powers and switched 12v's. All seem to be fine. Any help would be great!

On a side note. When the car was only a GE with a bolt on turbo kit. the car use to give me issues starting in the morning or when it was warm. Also would crank tell the battery was dead. never found that fix because the next year it was converted to GTE parts. Not sure if this is related or not.

So im just wondering if this was an issue with the box or am i mising something?

Also my tuner was having issues connecting at random times to the box as he would make a change and power cycle the box from the key it would loose connection untell I cycled my kill switch ...

AEM_SB
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Last seen: 1 month 3 weeks ago
Joined: 06/07/2014 - 14:29
Based on your description,

Based on your description, the first thing I would do is check if the laptop can stay connected to the ECU while you are cranking the engine. Add the channel 'Run Time' to the channels list and watch for it to continue counting while the power is on. Run time should not reset back to zero or low numbers when cranking, that would indicate the 12V power to the ECU dropped too low and the ECU reset.  Some production cars that were designed to have a rear-mounted battery run a separate power wire from the battery to the ECU, so the ECU power is not affected by the starter engaging.

 

If the ECU is connected, watch for the channel Stat Sync to turn on when the engine is spinning. If the ECU doesn't see the crank & cam signals as expected, Stat Sync will remain off and the ECU will never activate fuel or spark.

 

If Stat Sync is on and the ECU is remaining connected while you crank the engine, it's likely just fuel or idle position or spark timing that needs to be adjusted to make the engine start better.

 

Hope that helps,

SB

SupraNA-T
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Last seen: 1 year 1 month ago
Joined: 10/26/2018 - 13:51
Thanks for the reply. I have

Thanks for the reply. I have the car currently doing the issue. I jumped battery12v's to pin 33a (permanent 12v's). Car still would just crank.  Tried to connect with laptop and couldn't connect (ver 3.2) power cycled from the ignition key and nothing changed. went and power cycled from kill switch and the car started and laptop connected.... any ideads? Is there a switched 12v's im forgetting to check?

AEM_SB
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Last seen: 1 month 3 weeks ago
Joined: 06/07/2014 - 14:29
Thanks for the additional

Thanks for the additional explanation, I think I'm starting to understand what's happening. Many of the Lowside output pins have a circuit that will prevent the ECU from powering down properly if they are receiving 12V power when the ignition key is off, for instance if they are triggering a relay that is getting its 12V from permanent battery power. My notes say the LS4-LS12 outputs are the most likely to cause problems. Solution is to change the wiring so the relay's coil (pins 85 or 86 using Bosch relay pin labeling) is only receiving 12V power when the ignition key is on. I realize it's pretty common to run a big power straight from the battery to the relay, you can keep that big power wire connected to pin 30 (the high-current switched power source) but make sure it's not connected to pins 85 or 86 (the coil that triggers the switched power). 

 

Hope that helps,

SB