94 sc400 misfire. Running out of ideas
01-12-21, 03:21 PM
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94 sc400 misfire. Running out of ideas
Alright long story short I traded my g35 for this sc400, cars body is in amasing shape,
Now comes my problem, the guy told me it runs fine on premium but horribly bad on regular. Should have taken that as a no to trade because he told me he put in regluar,
it would bog really bad when you touched the throttle, almost die but never would, and would misfire at higher rpm, so I figured I would do a full tune up after I did it has the same problems
When it is running on all 8 cylinders it will idle really low. Almost as if it was a big beefy v8 with huge cams, so I figured alright. I'll redo the whole ignition system, it has brand new coils rotors distro, wires and plugs, now it ramodly stopped firing 4 cylinders and the tach will kinda do weird things when you rev it.
The only thing I'm shure of with it at the moment is an erg delete, for some reason the iacv was bypassed (pluged) before I had it so I corrected this and it dident change how it's running.
The ecu is sending me codes and the light does come on, so I dont think its ecu related. But I could be wrong.
Coils and plugs are ngk wires are standard. And rotors and caps are wvu (I think that's it) gotten from rock auto.
I really love this car and would love to get it working right, but I'm running out of ideas, last time I checked I got codes for maf but unplugging it dosent make it run better, have removed air filter and it runs same. Disconnecting iacv changes nothing eather. Any help would be nice. Thank you
Now comes my problem, the guy told me it runs fine on premium but horribly bad on regular. Should have taken that as a no to trade because he told me he put in regluar,
it would bog really bad when you touched the throttle, almost die but never would, and would misfire at higher rpm, so I figured I would do a full tune up after I did it has the same problems
When it is running on all 8 cylinders it will idle really low. Almost as if it was a big beefy v8 with huge cams, so I figured alright. I'll redo the whole ignition system, it has brand new coils rotors distro, wires and plugs, now it ramodly stopped firing 4 cylinders and the tach will kinda do weird things when you rev it.
The only thing I'm shure of with it at the moment is an erg delete, for some reason the iacv was bypassed (pluged) before I had it so I corrected this and it dident change how it's running.
The ecu is sending me codes and the light does come on, so I dont think its ecu related. But I could be wrong.
Coils and plugs are ngk wires are standard. And rotors and caps are wvu (I think that's it) gotten from rock auto.
I really love this car and would love to get it working right, but I'm running out of ideas, last time I checked I got codes for maf but unplugging it dosent make it run better, have removed air filter and it runs same. Disconnecting iacv changes nothing eather. Any help would be nice. Thank you
Last edited by Tempryan; 01-14-21 at 06:42 PM.
01-13-21, 02:50 PM
#2
You probably have a coil pack going out then, very common for them to fail on some point on the v8 then it runs on 4 cylinders here and there and back to 8 cylinders until it fails completely and then you have 4 cylinders.
btw when its idling low like that you are on 4 cylinders.
here is a poll I started back in the day to see what side the coil failed on, take a look there are lots of threads on failed ignition coil for the lexus v8 sc400 ls400 if you do a search.
It could also be related to the cap and rotor being too worn, but since you said those were checked/replaced then probably ok.
Just cause you see new wires though don't assume someone did the cap and rotor, because its alot more work to do that, most just slap on new wires and plugs, so if you didn't install it yourself or verify it, I would recommend taking a look there also.
https://www.clublexus.com/forums/per...ason-poll.html
btw when its idling low like that you are on 4 cylinders.
here is a poll I started back in the day to see what side the coil failed on, take a look there are lots of threads on failed ignition coil for the lexus v8 sc400 ls400 if you do a search.
It could also be related to the cap and rotor being too worn, but since you said those were checked/replaced then probably ok.
Just cause you see new wires though don't assume someone did the cap and rotor, because its alot more work to do that, most just slap on new wires and plugs, so if you didn't install it yourself or verify it, I would recommend taking a look there also.
https://www.clublexus.com/forums/per...ason-poll.html
01-13-21, 04:33 PM
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You probably have a coil pack going out then, very common for them to fail on some point on the v8 then it runs on 4 cylinders here and there and back to 8 cylinders until it fails completely and then you have 4 cylinders.
btw when its idling low like that you are on 4 cylinders.
here is a poll I started back in the day to see what side the coil failed on, take a look there are lots of threads on failed ignition coil for the lexus v8 sc400 ls400 if you do a search.
It could also be related to the cap and rotor being too worn, but since you said those were checked/replaced then probably ok.
Just cause you see new wires though don't assume someone did the cap and rotor, because its alot more work to do that, most just slap on new wires and plugs, so if you didn't install it yourself or verify it, I would recommend taking a look there also.
https://www.clublexus.com/forums/per...ason-poll.html
btw when its idling low like that you are on 4 cylinders.
here is a poll I started back in the day to see what side the coil failed on, take a look there are lots of threads on failed ignition coil for the lexus v8 sc400 ls400 if you do a search.
It could also be related to the cap and rotor being too worn, but since you said those were checked/replaced then probably ok.
Just cause you see new wires though don't assume someone did the cap and rotor, because its alot more work to do that, most just slap on new wires and plugs, so if you didn't install it yourself or verify it, I would recommend taking a look there also.
https://www.clublexus.com/forums/per...ason-poll.html
Hay thanks for the reply, I did a bit more digging and found one of my brand new coil wires was cracked and not spending spark. Have replaced it with an old one now it's running on all 8 agine. Cleaned the maf sensor aswell and that fixed the problem a lot, car will idle happily now, but new problem to figure out. It seems to be idling at about 1k, and slightly touching the gas will make it bog down and it will have a pretty hard time. After I rev it to about 3k it stablises but from idle to 3k there seems to be a slight misfire. Thoughts?
01-14-21, 01:06 PM
#4
How did you clean the maf? the older sc400's before 96 had the "karman vortex" style maf which looks like a metal rectangular thing versus the 96+ which is a plastic black round regular looking "hot-wire" style maf.
If you spray maf cleaner which is only meant for hotwire maf's into the older Karman type maf, it usually ruins it and causes lots of those issues with part throttle revving out cause the ecu is not seeing the right values, it can usually figure out idle and probably when you give it lots of throttle but not always, in my experience they always run poorly after someone does this.
basically you need to try and revive that maf which is difficult or replace it with another one. IF you want to try and revive it use a can of compressed air and try and get it completely dry inside the black plastic tube that is in the middle, but don't hold it too close to the mirror part or you can dislodge the mirror or sensor inside that plastic part and itll never work again.
the karman maf works with a sensor and a mirror on the inside of that plastic housing, and the sensor can pick up distortions in the frequency readings. when that mirror gets smudged.. or you guessed it, maf cleaner on it, it usually doesn't read right.
Normally a hotwire maf would burn off any residual cleaner cause it gets really hot, Karman maf's do not work like that it is more like an optical sensor.
you need to get that mirror that you can't really access well to be squeaky clean again, think like cleaning a regular old mirror. you could even try like a touch of like glass cleaner on a qtip, then blow it out.
No guarantees though you will be able to save it, most say that once its cleaned its done, but I have revived some before. It is really important that after you try and clean it you let it dry out completely or it won't work, id let it sit overnight at least before putting it back on the car. give the ecu a reset (pull EFI main fuse or battery terminal for 30 sec) and start it again on a cold start, like the first start of the day etc.. will give ecu best chance to sort things out.
If you look at the back of the maf cleaner, they put a disclaimer on the bottom for Karman vortex style mafs and not to use the cleaner, but no one ever reads it, myself included the first time I tried to tune up an SC.
this should help give you a visual
If you spray maf cleaner which is only meant for hotwire maf's into the older Karman type maf, it usually ruins it and causes lots of those issues with part throttle revving out cause the ecu is not seeing the right values, it can usually figure out idle and probably when you give it lots of throttle but not always, in my experience they always run poorly after someone does this.
basically you need to try and revive that maf which is difficult or replace it with another one. IF you want to try and revive it use a can of compressed air and try and get it completely dry inside the black plastic tube that is in the middle, but don't hold it too close to the mirror part or you can dislodge the mirror or sensor inside that plastic part and itll never work again.
the karman maf works with a sensor and a mirror on the inside of that plastic housing, and the sensor can pick up distortions in the frequency readings. when that mirror gets smudged.. or you guessed it, maf cleaner on it, it usually doesn't read right.
Normally a hotwire maf would burn off any residual cleaner cause it gets really hot, Karman maf's do not work like that it is more like an optical sensor.
you need to get that mirror that you can't really access well to be squeaky clean again, think like cleaning a regular old mirror. you could even try like a touch of like glass cleaner on a qtip, then blow it out.
No guarantees though you will be able to save it, most say that once its cleaned its done, but I have revived some before. It is really important that after you try and clean it you let it dry out completely or it won't work, id let it sit overnight at least before putting it back on the car. give the ecu a reset (pull EFI main fuse or battery terminal for 30 sec) and start it again on a cold start, like the first start of the day etc.. will give ecu best chance to sort things out.
If you look at the back of the maf cleaner, they put a disclaimer on the bottom for Karman vortex style mafs and not to use the cleaner, but no one ever reads it, myself included the first time I tried to tune up an SC.
this should help give you a visual
Last edited by Ali SC3; 01-14-21 at 01:15 PM.
01-14-21, 01:53 PM
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How did you clean the maf? the older sc400's before 96 had the "karman vortex" style maf which looks like a metal rectangular thing versus the 96+ which is a plastic black round regular looking "hot-wire" style maf.
If you spray maf cleaner which is only meant for hotwire maf's into the older Karman type maf, it usually ruins it and causes lots of those issues with part throttle revving out cause the ecu is not seeing the right values, it can usually figure out idle and probably when you give it lots of throttle but not always, in my experience they always run poorly after someone does this.
basically you need to try and revive that maf which is difficult or replace it with another one. IF you want to try and revive it use a can of compressed air and try and get it completely dry inside the black plastic tube that is in the middle, but don't hold it too close to the mirror part or you can dislodge the mirror or sensor inside that plastic part and itll never work again.
the karman maf works with a sensor and a mirror on the inside of that plastic housing, and the sensor can pick up distortions in the frequency readings. when that mirror gets smudged.. or you guessed it, maf cleaner on it, it usually doesn't read right.
Normally a hotwire maf would burn off any residual cleaner cause it gets really hot, Karman maf's do not work like that it is more like an optical sensor.
you need to get that mirror that you can't really access well to be squeaky clean again, think like cleaning a regular old mirror. you could even try like a touch of like glass cleaner on a qtip, then blow it out.
No guarantees though you will be able to save it, most say that once its cleaned its done, but I have revived some before. It is really important that after you try and clean it you let it dry out completely or it won't work, id let it sit overnight at least before putting it back on the car. give the ecu a reset (pull EFI main fuse or battery terminal for 30 sec) and start it again on a cold start, like the first start of the day etc.. will give ecu best chance to sort things out.
If you look at the back of the maf cleaner, they put a disclaimer on the bottom for Karman vortex style mafs and not to use the cleaner, but no one ever reads it, myself included the first time I tried to tune up an SC.
this should help give you a visual
If you spray maf cleaner which is only meant for hotwire maf's into the older Karman type maf, it usually ruins it and causes lots of those issues with part throttle revving out cause the ecu is not seeing the right values, it can usually figure out idle and probably when you give it lots of throttle but not always, in my experience they always run poorly after someone does this.
basically you need to try and revive that maf which is difficult or replace it with another one. IF you want to try and revive it use a can of compressed air and try and get it completely dry inside the black plastic tube that is in the middle, but don't hold it too close to the mirror part or you can dislodge the mirror or sensor inside that plastic part and itll never work again.
the karman maf works with a sensor and a mirror on the inside of that plastic housing, and the sensor can pick up distortions in the frequency readings. when that mirror gets smudged.. or you guessed it, maf cleaner on it, it usually doesn't read right.
Normally a hotwire maf would burn off any residual cleaner cause it gets really hot, Karman maf's do not work like that it is more like an optical sensor.
you need to get that mirror that you can't really access well to be squeaky clean again, think like cleaning a regular old mirror. you could even try like a touch of like glass cleaner on a qtip, then blow it out.
No guarantees though you will be able to save it, most say that once its cleaned its done, but I have revived some before. It is really important that after you try and clean it you let it dry out completely or it won't work, id let it sit overnight at least before putting it back on the car. give the ecu a reset (pull EFI main fuse or battery terminal for 30 sec) and start it again on a cold start, like the first start of the day etc.. will give ecu best chance to sort things out.
If you look at the back of the maf cleaner, they put a disclaimer on the bottom for Karman vortex style mafs and not to use the cleaner, but no one ever reads it, myself included the first time I tried to tune up an SC.
this should help give you a visual
01-14-21, 02:47 PM
#6
I don't have any experience with the aftermarket ones, probably have to search and see if someone has used them.
used ones can be hit or miss, best is if you can find one from a car that still starts and runs well.
maybe try and clean it out the glass cleaner and compressed air first, wont cost you anything.
its one of those issues that I see people struggle with on these cars, likely the person before you shot maf cleaner into it trying to solve another problem.
then there is the chance it could still be something else.. or that plus something else. tps out of adjustment can also cause issues, if someone played with the throtlle stop screw etc..
In fact if I had to guess what else that symptom was the tps being set wrong could also do that, if it has been adjusted or taken off and reinstalled recently it could easily be that.
on a 94 you could probably just unplug the maf, reset the ecu and start it and if it revs alot cleaner it probably is the maf.
*edit* you know I just reread it and you said the IACV was deleted? they probably bumped up the idle to compensate via the throttle stop screw then and that does throw the tps out of its happy place.
when it does that it will misfire and not rev cleanly like you said. that also sounds right with a 1k idle and no iacv.
you said you reinstalled it? you have some pics maybe I can see what is going on.
as a test, loosen the 2 screws for the tps, and turn it as much as you can in the direction where it is the least engaged, basically it needs to read close to zero when its idling or the ecu will get massively confused.
this happens when you bump up the throttle stop screw to increase the idle, cause that also turns the tps and it will get out of range.
basically fiddle with the tps and find the position that it will rev out cleanly in. you may have to even lower the idle via the set screw if it was increased to get it back in range.
when you delete the IACV the right thing to do is just give it more throttle with your foot until it warms up, and the throttle stop screw is set for a warm idle.
some guys use the stop screw to compensate for cold start being at a decent idle, and the giveaway is that when the engine is warm you end up with a really high idle instead of a normal one.
Your warm idle should not be over 800-900 ever, so it is a sign someone has messed with it.
used ones can be hit or miss, best is if you can find one from a car that still starts and runs well.
maybe try and clean it out the glass cleaner and compressed air first, wont cost you anything.
its one of those issues that I see people struggle with on these cars, likely the person before you shot maf cleaner into it trying to solve another problem.
then there is the chance it could still be something else.. or that plus something else. tps out of adjustment can also cause issues, if someone played with the throtlle stop screw etc..
In fact if I had to guess what else that symptom was the tps being set wrong could also do that, if it has been adjusted or taken off and reinstalled recently it could easily be that.
on a 94 you could probably just unplug the maf, reset the ecu and start it and if it revs alot cleaner it probably is the maf.
*edit* you know I just reread it and you said the IACV was deleted? they probably bumped up the idle to compensate via the throttle stop screw then and that does throw the tps out of its happy place.
when it does that it will misfire and not rev cleanly like you said. that also sounds right with a 1k idle and no iacv.
you said you reinstalled it? you have some pics maybe I can see what is going on.
as a test, loosen the 2 screws for the tps, and turn it as much as you can in the direction where it is the least engaged, basically it needs to read close to zero when its idling or the ecu will get massively confused.
this happens when you bump up the throttle stop screw to increase the idle, cause that also turns the tps and it will get out of range.
basically fiddle with the tps and find the position that it will rev out cleanly in. you may have to even lower the idle via the set screw if it was increased to get it back in range.
when you delete the IACV the right thing to do is just give it more throttle with your foot until it warms up, and the throttle stop screw is set for a warm idle.
some guys use the stop screw to compensate for cold start being at a decent idle, and the giveaway is that when the engine is warm you end up with a really high idle instead of a normal one.
Your warm idle should not be over 800-900 ever, so it is a sign someone has messed with it.
Last edited by Ali SC3; 01-14-21 at 03:00 PM.
01-14-21, 03:23 PM
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I don't have any experience with the aftermarket ones, probably have to search and see if someone has used them.
used ones can be hit or miss, best is if you can find one from a car that still starts and runs well.
maybe try and clean it out the glass cleaner and compressed air first, wont cost you anything.
its one of those issues that I see people struggle with on these cars, likely the person before you shot maf cleaner into it trying to solve another problem.
then there is the chance it could still be something else.. or that plus something else. tps out of adjustment can also cause issues, if someone played with the throtlle stop screw etc..
In fact if I had to guess what else that symptom was the tps being set wrong could also do that, if it has been adjusted or taken off and reinstalled recently it could easily be that.
on a 94 you could probably just unplug the maf, reset the ecu and start it and if it revs alot cleaner it probably is the maf.
*edit* you know I just reread it and you said the IACV was deleted? they probably bumped up the idle to compensate via the throttle stop screw then and that does throw the tps out of its happy place.
when it does that it will misfire and not rev cleanly like you said. that also sounds right with a 1k idle and no iacv.
you said you reinstalled it? you have some pics maybe I can see what is going on.
as a test, loosen the 2 screws for the tps, and turn it as much as you can in the direction where it is the least engaged, basically it needs to read close to zero when its idling or the ecu will get massively confused.
this happens when you bump up the throttle stop screw to increase the idle, cause that also turns the tps and it will get out of range.
basically fiddle with the tps and find the position that it will rev out cleanly in. you may have to even lower the idle via the set screw if it was increased to get it back in range.
when you delete the IACV the right thing to do is just give it more throttle with your foot until it warms up, and the throttle stop screw is set for a warm idle.
some guys use the stop screw to compensate for cold start being at a decent idle, and the giveaway is that when the engine is warm you end up with a really high idle instead of a normal one.
Your warm idle should not be over 800-900 ever, so it is a sign someone has messed with it.
used ones can be hit or miss, best is if you can find one from a car that still starts and runs well.
maybe try and clean it out the glass cleaner and compressed air first, wont cost you anything.
its one of those issues that I see people struggle with on these cars, likely the person before you shot maf cleaner into it trying to solve another problem.
then there is the chance it could still be something else.. or that plus something else. tps out of adjustment can also cause issues, if someone played with the throtlle stop screw etc..
In fact if I had to guess what else that symptom was the tps being set wrong could also do that, if it has been adjusted or taken off and reinstalled recently it could easily be that.
on a 94 you could probably just unplug the maf, reset the ecu and start it and if it revs alot cleaner it probably is the maf.
*edit* you know I just reread it and you said the IACV was deleted? they probably bumped up the idle to compensate via the throttle stop screw then and that does throw the tps out of its happy place.
when it does that it will misfire and not rev cleanly like you said. that also sounds right with a 1k idle and no iacv.
you said you reinstalled it? you have some pics maybe I can see what is going on.
as a test, loosen the 2 screws for the tps, and turn it as much as you can in the direction where it is the least engaged, basically it needs to read close to zero when its idling or the ecu will get massively confused.
this happens when you bump up the throttle stop screw to increase the idle, cause that also turns the tps and it will get out of range.
basically fiddle with the tps and find the position that it will rev out cleanly in. you may have to even lower the idle via the set screw if it was increased to get it back in range.
when you delete the IACV the right thing to do is just give it more throttle with your foot until it warms up, and the throttle stop screw is set for a warm idle.
some guys use the stop screw to compensate for cold start being at a decent idle, and the giveaway is that when the engine is warm you end up with a really high idle instead of a normal one.
Your warm idle should not be over 800-900 ever, so it is a sign someone has messed with it.
*edit* link to video https://youtu.be/xS-otMFao_E
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01-14-21, 04:03 PM
#8
definitely misfiring pretty good, you might still have a bad coil. i'd unplug them one at a time and see if it makes a difference, if not then that is the bad coil. just to rule it out since it doesn't sound like its on all 8 to me still.
I want to say it will usually idle pretty good with an unplugged maf and even run around well just will be rich mixture.
so test out the coils one at a time, see what changes. if both are good then maybe try with the tps adjustment, the stumble when you first get on the gas can be tps related but it will still usually idle alright.
what is the cel code saying? is it the maf? once you plug it in and reset it shouldn't throw the code right away... if its doing alot of wierd stuff the other thing it could be is the ecu going bad, that has been happening alot lately on the early SCs the ecu components only last so long its been almost 30 years for the early ones. Another thing I have heard of is when its been misfiring for a long time the cats can get plugged up but it takes some serious fuel dumping for a long time to make that happen.
I want to say it will usually idle pretty good with an unplugged maf and even run around well just will be rich mixture.
so test out the coils one at a time, see what changes. if both are good then maybe try with the tps adjustment, the stumble when you first get on the gas can be tps related but it will still usually idle alright.
what is the cel code saying? is it the maf? once you plug it in and reset it shouldn't throw the code right away... if its doing alot of wierd stuff the other thing it could be is the ecu going bad, that has been happening alot lately on the early SCs the ecu components only last so long its been almost 30 years for the early ones. Another thing I have heard of is when its been misfiring for a long time the cats can get plugged up but it takes some serious fuel dumping for a long time to make that happen.
01-14-21, 04:19 PM
#9
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Yah its code 31, maf sensor, sometimes when I start it the idle is nice and it is happy until I give it gas. Sometimes I start it and it sounds like that. But it always has the bog is always there. I'll do the coils tomorrow to make sure, and I'll do the tps as well I'll post more tomorrow. Thank you for your help so far.
*edit* welp I hate myself somtimes lol, i went and messed with the tps some. And low and behold the bog when I touch the peddle is gone. Completely, but I have a new problem that I'm ahure I can trouble shoot out bit I may as well ask, when I adjust the idle to a good point and give it some revs with the actual throttle body it stays fine. When I get in the car and use the peddle it gets really low and bad agine. Thoughts?
*edit* welp I hate myself somtimes lol, i went and messed with the tps some. And low and behold the bog when I touch the peddle is gone. Completely, but I have a new problem that I'm ahure I can trouble shoot out bit I may as well ask, when I adjust the idle to a good point and give it some revs with the actual throttle body it stays fine. When I get in the car and use the peddle it gets really low and bad agine. Thoughts?
Last edited by Tempryan; 01-14-21 at 06:35 PM.
01-16-21, 10:18 AM
#10
Where the throttle cable is mounted before it goes to the throttle body, there are a couple adjusting nuts. loosen them so the cable has a touch more slack.
If the cable is too tight it will hold the throttle open sometimes and always sit differnetly. usually when you back off the idle screw, you also have to loosen the throttle cable if it was adjusted with no slack before.
So everytime you touch that set screw, you have to make sure the throttle cable still has a touch of slack so its not causing the throttle body to hang, and you have to reverify your tps is still in range.
This is why when people go na-t on the tt ecu and they ask me if they should get rid of the IACV on their FFIM, or go FFIM at all, I always say to hold off till you get it running right cause its a delicate balance with the idle position, tps etc..
compensating for a missing IACV by bumping up the idle causes all of the above to happen, then someone has to go in there and troubleshoot and fix it, but alot of the time the ecu will throw an unrelated code and the car never gets fixed properly.
good luck man keep at it, just go through it all one step at a time it is very hard to actually ruin a 1uzfe, most of the times its the electronics or pickyness of the stock ecu.
If you have the budget for it and want to keep the car a long time, you could even look into running a standalone ecu off a map sensor and get rid of all that nonsense, but that comes with its own set of issues like tuning etc.. wont be as reliable of a daily compared to a happy stock ecu.
If the cable is too tight it will hold the throttle open sometimes and always sit differnetly. usually when you back off the idle screw, you also have to loosen the throttle cable if it was adjusted with no slack before.
So everytime you touch that set screw, you have to make sure the throttle cable still has a touch of slack so its not causing the throttle body to hang, and you have to reverify your tps is still in range.
This is why when people go na-t on the tt ecu and they ask me if they should get rid of the IACV on their FFIM, or go FFIM at all, I always say to hold off till you get it running right cause its a delicate balance with the idle position, tps etc..
compensating for a missing IACV by bumping up the idle causes all of the above to happen, then someone has to go in there and troubleshoot and fix it, but alot of the time the ecu will throw an unrelated code and the car never gets fixed properly.
good luck man keep at it, just go through it all one step at a time it is very hard to actually ruin a 1uzfe, most of the times its the electronics or pickyness of the stock ecu.
If you have the budget for it and want to keep the car a long time, you could even look into running a standalone ecu off a map sensor and get rid of all that nonsense, but that comes with its own set of issues like tuning etc.. wont be as reliable of a daily compared to a happy stock ecu.
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