SC400 turn over no start.

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blackdemon_tt

Member
Messages
53
Hello All,

I have a 93 SC400 pristine condition and 132k on the clock, dealer maintained with records. Ok I've been trying to work on some issues. for example a bouncy idle or surge idle. An extremely low idle at initial cold start and as well as hot start. I started my journey by bypassing the fuel ECU as I was stalling below 40mph. If I let it coast at speed the RPM would drop like a rock and would stall shortly after, but would come back to life if I hit the gas, but this was intermittent or 50/50. So, this led me to bypass it.. About a month passed by and the stalling was pretty much gone, but the low idle was now more common as it would often idle so low it would just stall out. So, I gave it the benefit of the doubt and continued driving it, until it stalled out 3 times in a half mile. At this point I replaced the fuel pump relay and it appeared to be good to go for about 2 months. No stalling, no hard start, no low idle. Yesterday driving home from work, I made a stop to run an errand and it would start. It would turn over, but would not start whatsoever.... So I popped the hood and started looking at the engine like a monkey would a wrench. I disconnected the battery, pushed in connectors, went over spark plug wires and pulled and reseated on each spark., and replaced the big green relay while I was there.. Not really knowing what was up I reconnected the battery and tried starting it.. and it started, but with a very low idle... so I'm looking for guidance at this point and time... I haven't probed the power from the ECM to the fuel pump yet, but I will likely do that this week, as my schedule is slightly crammed...

TLDR:
low idle and multiple stalls,
Replaced, fuel relay, Green relay, bypassed fuel ECU,
No apparent issues after a month, but then after a 30 minute drive, car refuses to start. Disconnected the battery and reconnected it 15 minutes later, started fine, but low idle continues.... pondering probing power from the ECM to Fuel pump and vice versa... any guidance is appreciated.
 

Zuffen

Super Moderator
Staff member
Messages
5,518
Location
Sydney, Australia
Low idle is common after disconnecting power to ECU.

IT usually sorts itself out after a bit of running. Minutes not hours.
 

blackdemon_tt

Member
Messages
53
Car has been running fine. Gave it a day break and have been running quick errands, has shown no issues. Starts fine hot and cold, has normal idle. I'm starting to suspect an ECM/ ECU issue.. will send it to get it inspected next month and repaired as necessary.
 

blackdemon_tt

Member
Messages
53
Well, it happened again today. Got some gas, but left the key in the ignition this time in accessory. Done fueling and went to turn it on, nothing. For context, I filled 15 gallons so it wasn't empty.

So long crank no start. Popped the hood, pulled the negative terminal for about 1 minute. Reconnected the terminal and and it turned right on. I think the ECM is my issue at this point.
 

blackdemon_tt

Member
Messages
53
Guess I'll have to purchase a new ECM... since the resistors aren't available until at least 6 months from now.. ooor research for a standalone..
 
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