1UZ gurus please help.
04-14-13, 03:51 PM
#1
1UZ gurus please help.
Alright guys. here is the story, please read carefully as every single detail I can list will be explained:
Background on car:
1992 SC400 all stock. Car had CEL codes for both main O2 sensors, O2 sensors were replaced, codes remained. Car runs pretty rich. Timing belt, water pump replaced almost a year ago. PS pump, alternator replaced 2 months ago. Battery doesn't hold charge for crap. New K&N Air filter (OEM replacement).
Two days ago:
Got rear ended lightly. Damage to rear was minimal except for the exhaust tubing on drivers side was pushed forward about 2-3 inches causing kinks in the tubing where it curves around the rear wheels. After inspection, no visible damage to any components in front of where the exhaust splits.
That night:
Car started running a little rough, felt like a random miss every now and then. Like a hiccup. Parked and waited for next day.
Yesterday:
Started car in morning, same problem. Idled fine except for a slight "miss". Somewhat more frequent than night before. Inspected battery terminals and noticed negative connector was loose from negligence after replacing alternator 1 month ago. After tightening, the car immediately ran like ****. No high idle when cold like normal, went straight to 500 rpm and sounded like a 4 banger. No power at all, no acceleration.
I thought the kinks in the exhaust may have been causing too much backpressure because I noticed the driver side cat was glowing after 3-5 minutes of running as stated above. I removed the exhaust from right before it splits into two, removing all the kinked sections. Still ran like garbage, albeit much louder.
Was suggested that ECU might have gone out, and upon inspection of ECU, noticed burnt out capacitor with others leaking very badly.
Today:
Replaced ECU with a used one in much better condition. Only one slightly leaking capacitor (same one that was burnt out in my old ECU). Still running like garbage, except now the car refused to start unless I maintained an open throttle while cranking.
Checked all ignition components, wires, distributor, rotors were all good.
Replaced afm with identical unit off the Supra, same issue. Checked timing, all good. Was told it would not be fuel pump related if I could keep the car running with gas applied. The car indeed is able to run as long as I need as long as I keep the gas pedal depressed even a little. I also don't think it is limp mode because the engine WILL rev to whatever I want it to. But as soon as I let off the gas, the car dies immediately.
I am at a loss. My questions are:
- Anyone have any more ideas as to what could be causing this?
- Are ruined catalytic converters a viable cause for my issues?
- Could the ruined cats be throwing O2 readings off that bad?
- If anything exhaust related is the culprit, then what's the deal with the throttle, why does the car only run with gas applied?
- Will a bad IACV cause the car to run poorly?
Thanks for any help guys. I've checked and double checked so many times, all sensors are good and connected, no damage to exhaust manifolds, everything LOOKS fine.
Background on car:
1992 SC400 all stock. Car had CEL codes for both main O2 sensors, O2 sensors were replaced, codes remained. Car runs pretty rich. Timing belt, water pump replaced almost a year ago. PS pump, alternator replaced 2 months ago. Battery doesn't hold charge for crap. New K&N Air filter (OEM replacement).
Two days ago:
Got rear ended lightly. Damage to rear was minimal except for the exhaust tubing on drivers side was pushed forward about 2-3 inches causing kinks in the tubing where it curves around the rear wheels. After inspection, no visible damage to any components in front of where the exhaust splits.
That night:
Car started running a little rough, felt like a random miss every now and then. Like a hiccup. Parked and waited for next day.
Yesterday:
Started car in morning, same problem. Idled fine except for a slight "miss". Somewhat more frequent than night before. Inspected battery terminals and noticed negative connector was loose from negligence after replacing alternator 1 month ago. After tightening, the car immediately ran like ****. No high idle when cold like normal, went straight to 500 rpm and sounded like a 4 banger. No power at all, no acceleration.
I thought the kinks in the exhaust may have been causing too much backpressure because I noticed the driver side cat was glowing after 3-5 minutes of running as stated above. I removed the exhaust from right before it splits into two, removing all the kinked sections. Still ran like garbage, albeit much louder.
Was suggested that ECU might have gone out, and upon inspection of ECU, noticed burnt out capacitor with others leaking very badly.
Today:
Replaced ECU with a used one in much better condition. Only one slightly leaking capacitor (same one that was burnt out in my old ECU). Still running like garbage, except now the car refused to start unless I maintained an open throttle while cranking.
Checked all ignition components, wires, distributor, rotors were all good.
Replaced afm with identical unit off the Supra, same issue. Checked timing, all good. Was told it would not be fuel pump related if I could keep the car running with gas applied. The car indeed is able to run as long as I need as long as I keep the gas pedal depressed even a little. I also don't think it is limp mode because the engine WILL rev to whatever I want it to. But as soon as I let off the gas, the car dies immediately.
I am at a loss. My questions are:
- Anyone have any more ideas as to what could be causing this?
- Are ruined catalytic converters a viable cause for my issues?
- Could the ruined cats be throwing O2 readings off that bad?
- If anything exhaust related is the culprit, then what's the deal with the throttle, why does the car only run with gas applied?
- Will a bad IACV cause the car to run poorly?
Thanks for any help guys. I've checked and double checked so many times, all sensors are good and connected, no damage to exhaust manifolds, everything LOOKS fine.
Last edited by lithium14; 04-14-13 at 04:09 PM.
04-14-13, 04:38 PM
#4
relevant photos
Exhaust pushed in
Burnt Capacitor
Leaking
Mud dauber nest inside afm. Cleaned it out easily
Removed exhaust section. You can see the kinks
Only bad capacitor on new ECU
Spark plug 1
Spark plug 3
Spark plug 5
Spark plug 7
Spark plug 2
Spark plug 4
Spark plug 6
Spark plug 8
Exhaust pushed in
Burnt Capacitor
Leaking
Mud dauber nest inside afm. Cleaned it out easily
Removed exhaust section. You can see the kinks
Only bad capacitor on new ECU
Spark plug 1
Spark plug 3
Spark plug 5
Spark plug 7
Spark plug 2
Spark plug 4
Spark plug 6
Spark plug 8
Last edited by lithium14; 04-14-13 at 04:42 PM.
04-15-13, 12:35 AM
#5
Lead Lap
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Heres a thread for the best SC4 hesitation issues, saved me twice.
I would say either clean the iacv, very easy besides the corroded bolts to take it off or bypass the fuel pump ecu, very easy as well. Both are in the thread.
Other than that i would say maf, clogged fuel filter, or the coils.
Good luck!
I would say either clean the iacv, very easy besides the corroded bolts to take it off or bypass the fuel pump ecu, very easy as well. Both are in the thread.
Other than that i would say maf, clogged fuel filter, or the coils.
Good luck!
04-15-13, 12:39 AM
#6
Lead Lap
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Clean your throttle body too! And if nothing works then adjust your tps a bit by loosening both bolts and tilting it either side in small increments. I would save this for last but its up to you since its also the easiest and can solve your problem.
04-15-13, 08:27 AM
#7
OLT had a recent thread about the resonator box in the intake hose coming loose and causing a bad idle. Check that!
Also, look into buying a truly reman ECU vs just another used one. All the ones on the market are just too old to use as they are.
Jumper the fuel pump connector under the hood and see if that helps. It can't hurt and it's quick and free to try.
The IAC may have finally bit the dust. This is one thing you can't really buy new unless you've got $700+ burning a hole in your pocket. I bought a used one with good results but I know it's only a matter of time.
Also, look into buying a truly reman ECU vs just another used one. All the ones on the market are just too old to use as they are.
Jumper the fuel pump connector under the hood and see if that helps. It can't hurt and it's quick and free to try.
The IAC may have finally bit the dust. This is one thing you can't really buy new unless you've got $700+ burning a hole in your pocket. I bought a used one with good results but I know it's only a matter of time.
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04-15-13, 11:45 AM
#10
OK. I just jumped the diag terminal under the hood. Pins Fp and +b as per what I found in another thread, Nothing changed. I finally got a response from AutoECU, so I will be sending my old ECU out asap to get rebuilt. in the meantime... I'm going to clean the IACV as best I can, and maybe replace the cats as well, just in case.
04-15-13, 01:59 PM
#11
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https://www.clublexus.com/forums/sho...d.php?t=551125
Whoops idk what happened to the link lol but I'll try again
Whoops idk what happened to the link lol but I'll try again
04-16-13, 05:40 PM
#14
I have confirmed that my ISC valve is dead. Tested it as per the manual and the motor did nothing but jerk slightly. No actual moving of the piston. SO. Anyone know of one I can get that is in good condition or know of a place to get a replacement without costing me an arm and a leg?
04-16-13, 06:13 PM
#15
Andrew, that cap on your "new"ecu leaked bad and did a number on the board as well. Try getting some high grade isopropyl alcohol and get a tooth brush slightly wet with it, lightly scrub away the bs, blow dry with keyboard duster. You don't wanna saturate the brush or it'll saturate the board. Also, the pick and pull in delvalle was chock full of 400s last time I went, cap city on congress had a few too. Prob cost you ten bucks. By the way, this is the guy with the 1j cressida/sc that gave your friend the 1uz. PS: I also fix ecu's from time to time.