House style Diagnosis- SC400 random stalling
03-20-10, 02:34 PM
#1
House style Diagnosis- SC400 start and immediate stall
Could use CLs help pinning this down! Oh yeah and it's not lupus!
Patient:
16 year old white lexus sc400, 250k miles
Overall in great health- interior is flawless, engine is all original everything on car is bone stock. I’m the 3rd owner and the first owner under 40. Dealer serviced it’s whole life.
Recent procedures:
Serpentine belt, fuel filter, battery, heater VSV
Dash indicator lights:
Airbag light (minor) Radiator light (bad coolant level sensor)
CEL Codes using TE1 E1 jumper:
Code 15: ?
Code 24: Intake Air Temperature Sensor signal
Symptoms:
Car starts hits about 400-500RPM and immediately dies.
5-16 Update- Got car to idle for about 60 seconds then it died. Started it back up and was able to rev it then it died. Now back to immediate stalling. Tach needle goes back down as fast as it comes up, it never actually idles. Holding down the throttle does not keep it idling.
Used to have Intermitent stalling.EFI Relay is white hot after the car has reached operating temp.
When car is running engine pulls hard, transmissions shifts smooth, and no vibrations are felt.
Fuel pump does turn on when engine is cranked even when it dies. FP ECU seems to function properly without bypass, turning on the FP when engine is cranking and turning off FP when engine dies.
Potential diagnoses:
Ruled out- Bad fuel pump ECU. Bypassed fuel pump using B+ to FP in diag port. FP turns on when key switched to ON.
Ruled out- Bad 02 sensors. Seems to happen regardless of if ECU is in open or closed loop
Ruled out- Bad EFI relay- swapped with no change. All issues present, still gets very hot to the touch
Ruled out- Bad ECU- replaced ECU with no luck
Ruled out- Bad MAF - The IAT code would indicate a bad MAF, but with the MAF unplugged nothing changes. Checked resistance of MAF and resistance is normal indicating it's still functional. (Updated 3/29)
Bad fuel pump? - Fuel pump starts properly and I can hear it running with FPECU bypass with key to ON (Updated 3/23)
What else should I add to this list? Getting desperate...
Patient:
16 year old white lexus sc400, 250k miles
Overall in great health- interior is flawless, engine is all original everything on car is bone stock. I’m the 3rd owner and the first owner under 40. Dealer serviced it’s whole life.
Recent procedures:
Serpentine belt, fuel filter, battery, heater VSV
Dash indicator lights:
Airbag light (minor) Radiator light (bad coolant level sensor)
CEL Codes using TE1 E1 jumper:
Code 15: ?
Code 24: Intake Air Temperature Sensor signal
Symptoms:
Car starts hits about 400-500RPM and immediately dies.
5-16 Update- Got car to idle for about 60 seconds then it died. Started it back up and was able to rev it then it died. Now back to immediate stalling. Tach needle goes back down as fast as it comes up, it never actually idles. Holding down the throttle does not keep it idling.
Used to have Intermitent stalling.
- Engine will lose all power and turn off. All electronics stay on, CEL comes on briefly and then disappears.
- Sometimes car will cut power and then reengage and keep driving without issue.
- Sometimes will cut then reengage several times.
- Sometimes will cut and then shut off entirely.
- When it’s entirely shut off sometimes it restarts right away and drives fine.
- Sometimes it will restart and then die immediately (start, 8-900 RPM, die). This happens regardless of throttle position (holding throttle will not keep car on). It will keep doing this several times, and then eventually it starts up and runs perfect.
- Eventually car will restart and keep driving.
- This has happened when the car is cold, and when the car is at full operating temp.
When car is running engine pulls hard, transmissions shifts smooth, and no vibrations are felt.
Fuel pump does turn on when engine is cranked even when it dies. FP ECU seems to function properly without bypass, turning on the FP when engine is cranking and turning off FP when engine dies.
Potential diagnoses:
Ruled out- Bad fuel pump ECU. Bypassed fuel pump using B+ to FP in diag port. FP turns on when key switched to ON.
Ruled out- Bad 02 sensors. Seems to happen regardless of if ECU is in open or closed loop
Ruled out- Bad EFI relay- swapped with no change. All issues present, still gets very hot to the touch
Ruled out- Bad ECU- replaced ECU with no luck
Ruled out- Bad MAF - The IAT code would indicate a bad MAF, but with the MAF unplugged nothing changes. Checked resistance of MAF and resistance is normal indicating it's still functional. (Updated 3/29)
Bad fuel pump? - Fuel pump starts properly and I can hear it running with FPECU bypass with key to ON (Updated 3/23)
What else should I add to this list? Getting desperate...
Last edited by Klaus; 05-16-10 at 02:08 PM.
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03-20-10, 03:42 PM
#4
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Hmmm...maybe a progressive neurodegenerative genetic disorder (Huntington's)....OR
is it possible that there's a short in the circuitry in and around the relay? If the relay is that hot, it's got to be saturating with current flowing somewhere.
is it possible that there's a short in the circuitry in and around the relay? If the relay is that hot, it's got to be saturating with current flowing somewhere.
03-20-10, 06:27 PM
#7
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I don't have a schematic in front of me, so just throwing it out there, I'd look to see what all is driven on the secondary side of the relay. Potentially, anything downstream that's sourcing power through it could be suspect for being the bad apple. The thing that's troubling me though, is why doesn't the fuse blow if the relay is truly getting "white" hot?
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03-20-10, 07:04 PM
#8
Very true- you would think something would pop. When I say white hot, it's not literally turning white obviously but I couldn't grasp it with a bare hand without severly burning myself. Yesterday the car at least started and idled for about 30 seconds then died. Now it's will not stay started at all. Starts, hits about 500RPM then dies. Will keep doing this. Tried 3 starts in a row, tried letting it sit for a few hours, nothing. So whatever the problem is the system causing the issues has now completely failed...
03-20-10, 07:44 PM
#9
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I wonder if whatever it is, is taking out the relays. Do you still have the second one in, or are you back onto the first one? I'd pop the other one in and see if it changes the consistent symptoms you're having right now; maybe one problem is causing collateral damage. Relays don't like to run hot, they can get a bit twitchy and die, but you still need to know what is sourcing all that power through it in the first place.
03-29-10, 08:07 PM
#15
Tested MAF per instructions:
I measured the resistance as instructed and came up with 1.9K at room temperature which seems about right (my house is at 73* right now). So I guess that rules out MAF.... hmmm what now? Could use the help, I'm getting stuck!
I measured the resistance as instructed and came up with 1.9K at room temperature which seems about right (my house is at 73* right now). So I guess that rules out MAF.... hmmm what now? Could use the help, I'm getting stuck!