misfires on 1998 LS
12-11-12, 06:57 PM
#1
Driver School Candidate
Thread Starter
Join Date: Dec 2012
Location: MO
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
misfires on 1998 LS
CODES p0300 random misfires detected
P0305 cylinder 5 misfire detected
P0306 cylinder 6 misfire detected
P0307 cylinder 7 misfire detected
Car is sometimes hard to start cold and idles rough when it does this. have some hesitation and power issues maintainig speed in 50 to 60 mph range but runs perfect at higher speeds or when pushed to accelerate. Need advice on how to remedy this/these problems. Thank you.
P0305 cylinder 5 misfire detected
P0306 cylinder 6 misfire detected
P0307 cylinder 7 misfire detected
Car is sometimes hard to start cold and idles rough when it does this. have some hesitation and power issues maintainig speed in 50 to 60 mph range but runs perfect at higher speeds or when pushed to accelerate. Need advice on how to remedy this/these problems. Thank you.
Last edited by CMinner; 12-11-12 at 07:08 PM.
12-11-12, 07:47 PM
#2
Lexus Champion
12-11-12, 11:07 PM
#4
Lexus Champion
When LScowboyLS had anything go wrong on his '96, it turned out to be leaking ECU capacitors
12-12-12, 06:05 AM
#5
likely to be ECU capacitors
btw i have a 92 with 185,000
a friend of mine has a 90 with 325,000
2 customers who come in both have over 250,000 on their first gens and neither have had caps go out.
i had a random misfire issue awhile back..guess what, turned out to be the coils
1 customer has a 95..had intermittant misfire issues and stumbling at acceleration..i told him to have the ecm checked because its a known problem...guess what, that was the problem and it was fixed.
Last edited by python; 12-12-12 at 06:11 AM.
12-12-12, 08:11 AM
#6
how about a little info from the op..like,how many miles? when was the last time u had a tune up? ohm out the coils...do your basic tests first. starting at the ecu and working backwards is ridiculous
btw i have a 92 with 185,000
a friend of mine has a 90 with 325,000
2 customers who come in both have over 250,000 on their first gens and neither have had caps go out.
i had a random misfire issue awhile back..guess what, turned out to be the coils
1 customer has a 95..had intermittant misfire issues and stumbling at acceleration..i told him to have the ecm checked because its a known problem...guess what, that was the problem and it was fixed.
btw i have a 92 with 185,000
a friend of mine has a 90 with 325,000
2 customers who come in both have over 250,000 on their first gens and neither have had caps go out.
i had a random misfire issue awhile back..guess what, turned out to be the coils
1 customer has a 95..had intermittant misfire issues and stumbling at acceleration..i told him to have the ecm checked because its a known problem...guess what, that was the problem and it was fixed.
12-12-12, 12:06 PM
#7
Yes!!!
Smart diagnosis always starts with ruling out each item along the diagnostic path BEFORE you jump to conclusions about something.
This is the sign of a true master drivability tech!
Even if you have had a recent tune up and all maintenance is up to spec, that does not preclude you from getting a bad part or parts going out on you since then. Nor does it mean that the work was perfectly performed and something like a ground was left loose or even a spark plug boot missed the tip of a plug.
Something as simple as a loose or corroded ground on the wiring harness can give you all sorts of problems and are often little places you never look.
The ECU caps are something you should be aware of and even check them out, some people seem to suggest them for EVERYTHING while ignoring the more common and obvious places to start looking, they most likely are not the solution to your problem!
Doing them as preventative maintenance would not be ill advised.
Smart diagnosis always starts with ruling out each item along the diagnostic path BEFORE you jump to conclusions about something.
This is the sign of a true master drivability tech!
Even if you have had a recent tune up and all maintenance is up to spec, that does not preclude you from getting a bad part or parts going out on you since then. Nor does it mean that the work was perfectly performed and something like a ground was left loose or even a spark plug boot missed the tip of a plug.
Something as simple as a loose or corroded ground on the wiring harness can give you all sorts of problems and are often little places you never look.
The ECU caps are something you should be aware of and even check them out, some people seem to suggest them for EVERYTHING while ignoring the more common and obvious places to start looking, they most likely are not the solution to your problem!
Doing them as preventative maintenance would not be ill advised.
Trending Topics
12-12-12, 01:19 PM
#8
Lexus Champion
the ECU capacitor problem affects ALL LS400's eventually, especially the 90-97 models. - it is a known design defect.
it is something every LS400 owner would be smart to do or have done by a competent solderer! - and it costs less than $10 if you do it yourself!!
it is not a question of whether these capacitors will fail, but when!
analogy: - you could possibly drive around with a 12 year old battery in your car, but you are just asking to get stranded and for grief you don't need, just replace it and quit whining!
it is something every LS400 owner would be smart to do or have done by a competent solderer! - and it costs less than $10 if you do it yourself!!
it is not a question of whether these capacitors will fail, but when!
analogy: - you could possibly drive around with a 12 year old battery in your car, but you are just asking to get stranded and for grief you don't need, just replace it and quit whining!
12-12-12, 11:44 PM
#11
Moderator
Hi CMinner,
I think I'd better to write some as RA40 is suggesting "on point" and "a systematic approach".
Below is a rather technical approach for a professional and it needs some basic knowledge and some equipments but I dare write the detail for you although my English is limited.
I suggest you to check the DC 12V supply line to ignition coils and “IGF" lines. One of the functions to detect misfire by the ECU is to check 2 different loops. One is by the feedback loop signal "IGF1" from cylinders 1,4,6 and 7. The other "IGF2" from cylinders 2,3,5 and 8. Look at the diagram below.
The green line is the "IGF1" and yellow line "IGF2". The red line is the DC 12V from the battery via the ignition switch2 and the ignition fuse.
There are 8 ignition coils but there are only 2 feed back signals "IGF1" and "IGF2" because they are mixed 4 each. Each “IGF” signal is picked up from the primary winding of the ignition coils via a resistor and it is checked by the ECU together with the drive signal. Each cylinder has its own ignition timing and when abnormal signal is detected at the IGF1 or IGF2, the ECU can distinguish the particular cylinder.
According to your initial post, misfires are at cylinder 5, 6 and 7. The 5 is related to IGF2, 6 and 7 to IGF1. So you have problems at both IGF1 and IGF2 lines. This simply means that the DC 12V supply is not sufficient or the drive signals from the ECU are not OK or the ECU is malfunctioning. Of course there must be the possibility of failed ignition coils, but judging from the randomness, they are not causing the problem except a nearly short circuited coil.
To summarize the checking procedure,
1, Measure the voltage. It should be higher than 11.5V. If less than this, check the ignition switch, the fuse, and connections or a nearly short circuited coil.
2, Check IGF1 and IGF2 using an oscilloscope. Should be good solid pulses as similar to ignition pulses.
3, Check the drive signals indicated by pink lines. Should be good solid pulses.
If pulses of 2 and 3 not solid, check the ECU.
Another item you'd better to check is the GND ( ground lines.) connections. All the pin 4 of ignition coils should be less than 0.05 Ohm of resistance to the engine body.
I think I'd better to write some as RA40 is suggesting "on point" and "a systematic approach".
Below is a rather technical approach for a professional and it needs some basic knowledge and some equipments but I dare write the detail for you although my English is limited.
I suggest you to check the DC 12V supply line to ignition coils and “IGF" lines. One of the functions to detect misfire by the ECU is to check 2 different loops. One is by the feedback loop signal "IGF1" from cylinders 1,4,6 and 7. The other "IGF2" from cylinders 2,3,5 and 8. Look at the diagram below.
The green line is the "IGF1" and yellow line "IGF2". The red line is the DC 12V from the battery via the ignition switch2 and the ignition fuse.
There are 8 ignition coils but there are only 2 feed back signals "IGF1" and "IGF2" because they are mixed 4 each. Each “IGF” signal is picked up from the primary winding of the ignition coils via a resistor and it is checked by the ECU together with the drive signal. Each cylinder has its own ignition timing and when abnormal signal is detected at the IGF1 or IGF2, the ECU can distinguish the particular cylinder.
According to your initial post, misfires are at cylinder 5, 6 and 7. The 5 is related to IGF2, 6 and 7 to IGF1. So you have problems at both IGF1 and IGF2 lines. This simply means that the DC 12V supply is not sufficient or the drive signals from the ECU are not OK or the ECU is malfunctioning. Of course there must be the possibility of failed ignition coils, but judging from the randomness, they are not causing the problem except a nearly short circuited coil.
To summarize the checking procedure,
1, Measure the voltage. It should be higher than 11.5V. If less than this, check the ignition switch, the fuse, and connections or a nearly short circuited coil.
2, Check IGF1 and IGF2 using an oscilloscope. Should be good solid pulses as similar to ignition pulses.
3, Check the drive signals indicated by pink lines. Should be good solid pulses.
If pulses of 2 and 3 not solid, check the ECU.
Another item you'd better to check is the GND ( ground lines.) connections. All the pin 4 of ignition coils should be less than 0.05 Ohm of resistance to the engine body.
The following users liked this post:
400fanboy (07-02-23)
12-13-12, 08:31 AM
#12
u have no info on the maint. of this car and ur directing straight to the ecu as a diag...lmfao! you and cowboy do this on every thread regarding misfire issues, theres a chance ur right..but until the information is revealed, u suggesting people start at the ecu is a misdirected line of diagnosis...
12-13-12, 01:21 PM
#14
Lexus Champion
it's because on the LS400, when the car is hard to start, running rough, loss of power, etc. - the ECU capacitors are a strong possibility
sure any car can have any problem, but LS400's are generally more well maintained than other cars, were much more reliable in the first place, and tend to fail in the same areas, i.e. pattern failure - the only other widespread drivability issue on these cars is the famous trunk hinge wiring issue on 90-94 models!
One of the reason we love LS400's is their incredible reliability, even when they get old, they just don't seem to have those "all kinds of weird things are failing on this car", the head scratcher issues, and when they do, it is usually the trunk hinge wiring issue or these capacitors, the vast majority of the time, although the ECU issue was long misdiagnosed, until lately
I have been as ASE-certified master tech for over 30 years, and I am well aware that all kinds of cars can have all kinds of drivability issues, but LS400's just don't have all kinds of weird problems - like other vehicles, they tend to have the same old problems that all of the other LS400's had of similar generation! - that's why I used the word "likely"
sure any car can have any problem, but LS400's are generally more well maintained than other cars, were much more reliable in the first place, and tend to fail in the same areas, i.e. pattern failure - the only other widespread drivability issue on these cars is the famous trunk hinge wiring issue on 90-94 models!
One of the reason we love LS400's is their incredible reliability, even when they get old, they just don't seem to have those "all kinds of weird things are failing on this car", the head scratcher issues, and when they do, it is usually the trunk hinge wiring issue or these capacitors, the vast majority of the time, although the ECU issue was long misdiagnosed, until lately
I have been as ASE-certified master tech for over 30 years, and I am well aware that all kinds of cars can have all kinds of drivability issues, but LS400's just don't have all kinds of weird problems - like other vehicles, they tend to have the same old problems that all of the other LS400's had of similar generation! - that's why I used the word "likely"
12-14-12, 03:17 AM
#15
ASE?
rotflmfao! that dont mean a thing!
u say these cars fail in the same areas? look at all the threads here...the only ones mentioning any caps are you and yamae and u have others tearing apart their ecu's..they arent the root cause of every problem and until the car is diagnosed properly....thats not a reffrence point of diagnosing. do u understand that?
rotflmfao! that dont mean a thing!
u say these cars fail in the same areas? look at all the threads here...the only ones mentioning any caps are you and yamae and u have others tearing apart their ecu's..they arent the root cause of every problem and until the car is diagnosed properly....thats not a reffrence point of diagnosing. do u understand that?
Last edited by PureDrifter; 12-14-12 at 04:36 AM. Reason: now now...
