The definitive guide to fixing SC400 hesitation issues
07-21-11, 12:12 PM
#46
I also have another question. What is the valve with the throttle plate in the throttle body closest to right side of vehicle? When removing the intake duct, my buddy and I noticed that this specific valve is wide open, whereas the throttle body stayed closed while engine was off. This is on a 93 sc400
Thanks
Charley
Thanks
Charley
10-17-11, 06:27 AM
#48
I also have another question. What is the valve with the throttle plate in the throttle body closest to right side of vehicle? When removing the intake duct, my buddy and I noticed that this specific valve is wide open, whereas the throttle body stayed closed while engine was off. This is on a 93 sc400
Thanks
Charley
Thanks
Charley
10-23-11, 07:35 PM
#49
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Possible MAF ground issue
Wow, very helpful post. Many thanks Brad.
I have a '94 SC400 throwing code 31 (low MAF voltage). Dies when idling, coughs at freeway speed accelerations. Runs much better with MAF unplugged. Swapped with two other MAFs with no change to symptoms. Problem started on second drive after a major repair including timing chain, valve replacements, head gasket, etc., making me want to believe it is more than coincidence.
My MAF connector has exactly the same 5 wire colors as your photo on page one of this thread. Is it really true that pin 5 (the brown wire next to the light blue one) is ground? If so, I have a bad ground -- I get 1V with key on, and a voltage varying between 1.1 and 1.6V when engine is running.
Should I splice this wire and connect it to chassis ground? Before hacking in such a connection, I'd like to ask whether I risk damaging anything? If that really is supposed to be a ground, it would seem that I would be safe.
Thanks for listening,
Lonnie
I have a '94 SC400 throwing code 31 (low MAF voltage). Dies when idling, coughs at freeway speed accelerations. Runs much better with MAF unplugged. Swapped with two other MAFs with no change to symptoms. Problem started on second drive after a major repair including timing chain, valve replacements, head gasket, etc., making me want to believe it is more than coincidence.
My MAF connector has exactly the same 5 wire colors as your photo on page one of this thread. Is it really true that pin 5 (the brown wire next to the light blue one) is ground? If so, I have a bad ground -- I get 1V with key on, and a voltage varying between 1.1 and 1.6V when engine is running.
Should I splice this wire and connect it to chassis ground? Before hacking in such a connection, I'd like to ask whether I risk damaging anything? If that really is supposed to be a ground, it would seem that I would be safe.
Thanks for listening,
Lonnie
12-09-11, 06:55 AM
#50
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Amazing post. Lord knows I hope one of these fix my baby. As over the length of about 5 months I have done:
First the Starter went out at the walmart down the street not bad as I was only a 2 miles from home towed her home and change the starter, while doing the starter I also change the Air filter, plugs, new value cover gaskets. Happy again.
Then about a month later driver from a friends place and the Alternator dies. Was able to drive her home under battery power. Changed the Alternator and Engine belt.
Then about month and a half later one I had start her and walked back in the house she had been undering for about 25-30 before I came back out and got in and notice my temp needle was on the way up. Ok time to do the water pump. So new Water Pump, Timing Belt, Caps and rotors. After this she ran like a new car strong with a noticeable different in power. I was loving her.
Then about 3 weeks later had to fix the A/C is was just getting unbearable driver her with no A/C a conversion kit and some new o-ring and a charge and BAMMM I had A/C. Compressor needs to be replace as it as a nice little whine to it, but it blows cold as Ice.
About a month later me and my son was coming from BrandsMart USA and without warning my steering wheel just turns about 1/4 of a full turn to the right, but the car was still going straight. I was like what the H***. Came on good ol trusty Club Lexus once more found out the issue and replaced the rack/steering bushing with the all metal ones. Great steering was better then ever.
Now the two days before thanksgiving I let my oldest son used the car. I told him he needs to but gas in. So he brought it back to me with around half a tank. So the day before thanksgiving she was going strong as every and I was loving her as usual. So it was little cool out on Thanksgiving morning so I remote started her to let her warm up a bit. Stuck my head out the door to make sure she was running and it was. Don't use remote start offend.
So me and my youngest son was ready to go down to my moms for some Thanksgiving grubbing and when we walked out i notice it was idling rough. hmmm I got in and pulled out the drive way and press the accelerator and she just had no power hesitated bad. What the H*** she drove like a million bucks just last night what could have happen from the time I park her to the time i started her that morning. Called my son and ask what gas did you put in the car a couple days ago. He said QT, no son what grade. 87 he said I said no no no no no no son 93 only. I read on here that some run 87 with no issues, but I never want to take the chance. So now I thinking Lord know what the issues could be.
I got out and the exhaust smell was very strong, to the point it made my eyes water. The car was on empty so I drove it to the gas stations and add some 93 from Shell and some Lucas fuel treatment to it. It seem to clean the smell up, but as I drove it the RPM gauge would go up to about 2000 and drop back down. So changed out my plugs, it got a little better. So I had some extra parts around I had got from a friend who did a swap on a low mileage 93 SC400 like mine. If i remember correctly it only had like 65,000 miles on it. So change out the injectors i got from him as I was going to do it anyway. Idle was great then it went back a little rough.
Now after reading all this and already having test a few of the above I thinking it is the coil. As it is going thru gas pretty fast. No power at low rpm, but was the rpm now go up the power starts to kick in.
Sorry guys for the long post, But this have been driving my crazy for since Thanksgiving had to get it off my chest. I'm just luck I do all my work myself of I would be even broker then I current am. LOL
Thanks once more for amazing post. I'm sure the Coil or ECU is my issue now.
First the Starter went out at the walmart down the street not bad as I was only a 2 miles from home towed her home and change the starter, while doing the starter I also change the Air filter, plugs, new value cover gaskets. Happy again.
Then about a month later driver from a friends place and the Alternator dies. Was able to drive her home under battery power. Changed the Alternator and Engine belt.
Then about month and a half later one I had start her and walked back in the house she had been undering for about 25-30 before I came back out and got in and notice my temp needle was on the way up. Ok time to do the water pump. So new Water Pump, Timing Belt, Caps and rotors. After this she ran like a new car strong with a noticeable different in power. I was loving her.
Then about 3 weeks later had to fix the A/C is was just getting unbearable driver her with no A/C a conversion kit and some new o-ring and a charge and BAMMM I had A/C. Compressor needs to be replace as it as a nice little whine to it, but it blows cold as Ice.
About a month later me and my son was coming from BrandsMart USA and without warning my steering wheel just turns about 1/4 of a full turn to the right, but the car was still going straight. I was like what the H***. Came on good ol trusty Club Lexus once more found out the issue and replaced the rack/steering bushing with the all metal ones. Great steering was better then ever.
Now the two days before thanksgiving I let my oldest son used the car. I told him he needs to but gas in. So he brought it back to me with around half a tank. So the day before thanksgiving she was going strong as every and I was loving her as usual. So it was little cool out on Thanksgiving morning so I remote started her to let her warm up a bit. Stuck my head out the door to make sure she was running and it was. Don't use remote start offend.
So me and my youngest son was ready to go down to my moms for some Thanksgiving grubbing and when we walked out i notice it was idling rough. hmmm I got in and pulled out the drive way and press the accelerator and she just had no power hesitated bad. What the H*** she drove like a million bucks just last night what could have happen from the time I park her to the time i started her that morning. Called my son and ask what gas did you put in the car a couple days ago. He said QT, no son what grade. 87 he said I said no no no no no no son 93 only. I read on here that some run 87 with no issues, but I never want to take the chance. So now I thinking Lord know what the issues could be.
I got out and the exhaust smell was very strong, to the point it made my eyes water. The car was on empty so I drove it to the gas stations and add some 93 from Shell and some Lucas fuel treatment to it. It seem to clean the smell up, but as I drove it the RPM gauge would go up to about 2000 and drop back down. So changed out my plugs, it got a little better. So I had some extra parts around I had got from a friend who did a swap on a low mileage 93 SC400 like mine. If i remember correctly it only had like 65,000 miles on it. So change out the injectors i got from him as I was going to do it anyway. Idle was great then it went back a little rough.
Now after reading all this and already having test a few of the above I thinking it is the coil. As it is going thru gas pretty fast. No power at low rpm, but was the rpm now go up the power starts to kick in.
Sorry guys for the long post, But this have been driving my crazy for since Thanksgiving had to get it off my chest. I'm just luck I do all my work myself of I would be even broker then I current am. LOL
Thanks once more for amazing post. I'm sure the Coil or ECU is my issue now.
Last edited by SQ400; 12-09-11 at 05:03 PM.
12-29-11, 05:11 AM
#52
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Ok guys i got a 92 sc400 with 170k and was running fine fow a few weeks now when i accelerate sometimes it doesnt want to go i let off and floor it again and sometimes it fixes te problem an sometimes it doesnt is getting horrible gas mileage about 10/gallon and not smoking or shaking or any fuel smell...wth is goin on? please help
01-05-12, 06:47 PM
#53
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UPDATE-
got some lucas fuel system cleaner from walmart put half of it in with my 1/3 tank of gas drove it for a bit...nothing happened...slowy its started to feel less sluggish...car sat for a few days...started up yesterday and noticed white smoke and kept revving it up...drove it today and BAM.Not one hesitation and no more white smoke and feels much peppier....I'm so happy
and I still have half the bottle left...woot!
got some lucas fuel system cleaner from walmart put half of it in with my 1/3 tank of gas drove it for a bit...nothing happened...slowy its started to feel less sluggish...car sat for a few days...started up yesterday and noticed white smoke and kept revving it up...drove it today and BAM.Not one hesitation and no more white smoke and feels much peppier....I'm so happy
and I still have half the bottle left...woot!
02-10-12, 04:40 PM
#54
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Update on my hesitation issue. Checked everything and it was all OK. My mechanic had me describe exactly how it happened. I was going for as quick a start as I could, floored first gear to 6250 rpm. Slammed it into second And it hesitated until the revs got up. That was the beginning. The mech said ah ha, I bet your timing belt skipped. I never went there because I only have 45,000 miles. Turns out the passenger side cam skipped one tooth. All good now .
.
06-10-12, 03:17 PM
#56
Fuel injector cleaner
I went through a month where my hesitation was fueling my insanity.
It would feel like it was missing a cylinder, bogging under light or medium throttle, under wide open throttle it wasn't noticeable.
I replaced my coils, spark plugs, and wires, O2 sensors, MAF sensor, coolant temp sensor.
The sensors did test having bad voltages. That's why I replaced them.
None of this really fixed the problem.
I ran seafoam through, which fixed it for a month or two, right around the time I seafoamed it I also drove to LA and back, so maybe the drive had something to do with it.
After a month or two it came back, now throwing engine code for rich and lean.
Checked the O2 sensors again, they were OK, the MAF OK, scan showed nothing else wrong.
So I seafomed it again, no help
What finally worked
--------------------------------------------------------->
Ran three tanks of gas with fuel injector cleaner and drove it hard.
Problem has been gone three months.
It would feel like it was missing a cylinder, bogging under light or medium throttle, under wide open throttle it wasn't noticeable.
I replaced my coils, spark plugs, and wires, O2 sensors, MAF sensor, coolant temp sensor.
The sensors did test having bad voltages. That's why I replaced them.
None of this really fixed the problem.
I ran seafoam through, which fixed it for a month or two, right around the time I seafoamed it I also drove to LA and back, so maybe the drive had something to do with it.
After a month or two it came back, now throwing engine code for rich and lean.
Checked the O2 sensors again, they were OK, the MAF OK, scan showed nothing else wrong.
So I seafomed it again, no help
What finally worked
--------------------------------------------------------->
Ran three tanks of gas with fuel injector cleaner and drove it hard.
Problem has been gone three months.
08-15-12, 12:33 PM
#57
TPS is f+cking up my mood ...
Well guys tribute to this forum and of course the users that ake and make the affort to wright tutorials. So i want to add my experience with a LS400 1991 European model.
I bought it and it had the problem with the gaspedal. Whenever i hit the pedal good and deep the LS falls away into a gap of nothing. In the beginning i didnt know because the LS is an impresive piece of art. But sinde this Maserati left me behind at a stoplight i had it:
I changed the TPS for a new one
i opend the engine ECU to seek for cola and burnmarks
i cleaned the throttle house and manifold
i renewed the cables and sparks
i renewed al filters
i checked everysensor possible
i checked the AT lever
i checked the valves ( they were on the edge)
i flushed and drained the AT
i renewed al liquids
i read the engine multiple times and not once a code 41
but it didn't help totally baffered and depressed i went back to the internet and found topics with the same kind of problems, all related to the TPS.
I took it off again and checked everything the resistance the ECU input en output everything seemed ok ....
Then i removed the rubber and plastic zo i could see the wires, because it surprised me but whenever i wiggelt the wires something happened to the engine.
So when i saw the wires i got hope they looked o so bad, have a look yourself.
i fixed this problem by cutting the wire and solder them again, and it helped pretty good.
I also had to adjust the connectors because on the new TPS the size was a bit smaller.
Greetings from Amsterdam
I bought it and it had the problem with the gaspedal. Whenever i hit the pedal good and deep the LS falls away into a gap of nothing. In the beginning i didnt know because the LS is an impresive piece of art. But sinde this Maserati left me behind at a stoplight i had it:
I changed the TPS for a new one
i opend the engine ECU to seek for cola and burnmarks
i cleaned the throttle house and manifold
i renewed the cables and sparks
i renewed al filters
i checked everysensor possible
i checked the AT lever
i checked the valves ( they were on the edge)
i flushed and drained the AT
i renewed al liquids
i read the engine multiple times and not once a code 41
but it didn't help totally baffered and depressed i went back to the internet and found topics with the same kind of problems, all related to the TPS.
I took it off again and checked everything the resistance the ECU input en output everything seemed ok ....
Then i removed the rubber and plastic zo i could see the wires, because it surprised me but whenever i wiggelt the wires something happened to the engine.
So when i saw the wires i got hope they looked o so bad, have a look yourself.
i fixed this problem by cutting the wire and solder them again, and it helped pretty good.
I also had to adjust the connectors because on the new TPS the size was a bit smaller.
Greetings from Amsterdam
Last edited by LexterLS40; 08-15-12 at 02:18 PM.
08-16-12, 03:09 PM
#58
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I went through a month where my hesitation was fueling my insanity.
It would feel like it was missing a cylinder, bogging under light or medium throttle, under wide open throttle it wasn't noticeable.
I replaced my coils, spark plugs, and wires, O2 sensors, MAF sensor, coolant temp sensor.
The sensors did test having bad voltages. That's why I replaced them.
None of this really fixed the problem.
I ran seafoam through, which fixed it for a month or two, right around the time I seafoamed it I also drove to LA and back, so maybe the drive had something to do with it.
After a month or two it came back, now throwing engine code for rich and lean.
Checked the O2 sensors again, they were OK, the MAF OK, scan showed nothing else wrong.
So I seafomed it again, no help
What finally worked
--------------------------------------------------------->
Ran three tanks of gas with fuel injector cleaner and drove it hard.
Problem has been gone three months.
It would feel like it was missing a cylinder, bogging under light or medium throttle, under wide open throttle it wasn't noticeable.
I replaced my coils, spark plugs, and wires, O2 sensors, MAF sensor, coolant temp sensor.
The sensors did test having bad voltages. That's why I replaced them.
None of this really fixed the problem.
I ran seafoam through, which fixed it for a month or two, right around the time I seafoamed it I also drove to LA and back, so maybe the drive had something to do with it.
After a month or two it came back, now throwing engine code for rich and lean.
Checked the O2 sensors again, they were OK, the MAF OK, scan showed nothing else wrong.
So I seafomed it again, no help
What finally worked
--------------------------------------------------------->
Ran three tanks of gas with fuel injector cleaner and drove it hard.
Problem has been gone three months.
10-24-12, 08:14 PM
#60
Confused on ISC Resistance Check
Going thru troubleshooting for acceleration hesitation & I'm checking resistance of ISC valve as indicated in 1st posting. The ISC has only 4 terminals, yet they discuss testing B1-S1 & S3 and B2-S2 & S4. Does that mean B1 & S1 are same terminal & B2 & S2 are same?
If so, how do I do next steps of applying 12V to B1 & B2 & repeatedly ground S1-S2-S3-S4-S1 in sequence? If I have 12V on B1 & B2, I don't think I should be then grounding the same terminals S1 & S2. I must be missing something here. Can someone that's done this before clarify this for me. Thanks.
If so, how do I do next steps of applying 12V to B1 & B2 & repeatedly ground S1-S2-S3-S4-S1 in sequence? If I have 12V on B1 & B2, I don't think I should be then grounding the same terminals S1 & S2. I must be missing something here. Can someone that's done this before clarify this for me. Thanks.