Hesitation (Misfire) When Cruising At 40 To 60 Mph

[ehabmarco]

I am sharing my experience with this chronic problem of misfire at a certain speed when cruising that I see repeatedly in this forum

First I admit that this forum helped me a lot to find the cause of my problem but unfortunately after spending lot of money in changing many parts

First thing I want to say is that many issues can lead to the same symptoms of hesitation or misfire between 40 to 60 mph

Hesitation at this speed does not mean that the engine is only hesitating at this speed and THIS IS THE TRICK

The misfire is clearly felt at this speed because the torque converter clutch is engaged that means the engine and transmission are considered as 1 unit so any slight misfire in the engine will be felt in the transmission and this is happening only when cruising

My advise is to go with the following sequence:

1- check spark plugs and wires (must be original)

2- Oxygen sensors (and this was my case one of the 2 main oxygen sensors was dead and caused the random misfire)

3- throttle positioning sensor

4- throttle body

These are the most common causes of misfire

Hope this helps

[curiousB]

Misfire is due to ignition, or lack thereof. That rules out 2, 3, and 4 of your theory. You don't even mention coils which are a known weak link of these cars.

1) Throttle body is more of a rough idle phenomenon, not very noticeable at higher speeds as the caked up residue is insignificant at wide open throttle positions.

2) O2 sensors will effect your fuel mix and could cause too rich or lean a mix that will create problems but doubtful it would be isolated to a narrow band of speed like you saw.

3) Throttle Position sensor can play havoc with the ECU if there is a dead spot on it such the ECU gets an erroneous reading at certain pedal positions. But this too would be noticeable at many speeds.

[jaswood]

Misfire is due to ignition, or lack thereof. That rules out 2, 3, and 4 of your theory. You don't even mention coils which are a known weak link of these cars.

1) Throttle body is more of a rough idle phenomenon, not very noticeable at higher speeds as the caked up residue is insignificant at wide open throttle positions.

2) O2 sensors will effect your fuel mix and could cause too rich or lean a mix that will create problems but doubtful it would be isolated to a narrow band of speed like you saw.

3) Throttle Position sensor can play havoc with the ECU if there is a dead spot on it such the ECU gets an erroneous reading at certain pedal positions. But this too would be noticeable at many speeds.

Why don't we agree to call the described symptom as engine "tugging" rather than "misfire" which could be misleading.

Tugging can be the result of ignition, EFI, fuel pump pressure, and even the secondary "Trac" engine de-throttling servo. If it happens mainly with acceleration, even slight acceleration, you may have a plugged catalytic converter.

Also, a loose motor mount, or rear diff'l mount, might result in a tugging feel due to the resulting "in and out" action of the lockup clutch, at those speeds. That was EXACTLY the complaint, tugging between 30-40 MPH, the most often driver of our '95 LS400 had. Replaced the rear differential's front mounting cushion to clear up the problem. The 2 rear diff'l mounts are still in the freezer awaiting a nicer day.

The frustrating thing about the diff'l mount failure symptom is that there was no CEL at all.

[ehabmarco]

Actually I called it misfire based on the link below which explains that misfire can be caused by one 3 things:

1- loss of spark

2- the air/fuel mixture is too far out of balance to ignite

3- loss of compression

http://www.autotap.com/techlibrary/diagnosing_misfires.asp

In my case a random misfire (hesitation) was happening every 4 to 5 seconds and was caused by a bad air/fuel mixture (lean misfire) due to the bad oxygen sensor

This sensor was causing a rough idle too, after changing it, no more hesitation when cruising and idle became much smoother

the link below helped me to test the sensor

http://www.lexls.com/tutorials/EFI/mainoxygensensor.html

[jaswood]

Actually I called it misfire based on the link below which explains that misfire can be caused by one 3 things:

1- loss of spark

2- the air/fuel mixture is too far out of balance to ignite

3- loss of compression

http://www.autotap.com/techlibrary/diagnosing_misfires.asp

In my case a random misfire (hesitation) was happening every 4 to 5 seconds and was caused by a bad air/fuel mixture (lean misfire) due to the bad oxygen sensor

This sensor was causing a rough idle too, after changing it, no more hesitation when cruising and idle became much smoother

the link below helped me to test the sensor

http://www.lexls.com/tutorials/EFI/mainoxygensensor.html

First, a word about that latter, last, link.

The O2 heater resistance quoted as being required is quite a bit out of range with the actual factory shop/repair manual specification. For myself I would accept that any heater resistance up to 18 ohms would suffice.

And be aware that exposing a perfectly good, even brand new, O2 sensor to our oxygen rich atmosphere while the sensor element remains heated will/might "spoil" the sensor, cause a CEL, for the first 100-200 miles. I had suspected such for quite some time and just recently tested the theory by heating a new sensor on an electric stove element. I took several days before reseting the CEL "took".

That's also why a crack in the exhaust, even downstream of the O2 sensor element, will result in a CEL, oxygen can get to the sensor before it has time to cool.

[jaswood]

Actually I called it misfire based on the link below which explains that misfire can be caused by one 3 things:

1- loss of spark

2- the air/fuel mixture is too far out of balance to ignite

3- loss of compression

http://www.autotap.com/techlibrary/diagnosing_misfires.asp

In my case a random misfire (hesitation) was happening every 4 to 5 seconds and was caused by a bad air/fuel mixture (lean misfire) due to the bad oxygen sensor

This sensor was causing a rough idle too, after changing it, no more hesitation when cruising and idle became much smoother

the link below helped me to test the sensor

http://www.lexls.com/tutorials/EFI/mainoxygensensor.html

Sorry, I find it a bit hard to accept that a defective MAIN O2 sensor in an engine with TWO sensors, would result in a lean misfire. Over the years I have been reponsable for the care and maintenance of a '90 LS (a Bill Gate's trade-in), a '91 LS, 3 '92's and a '95. The '90 and one of the '92's are now off the list. Amongst that group, all now pushing close too or over 200K, I have encountered numerous instances of O2 failures. ALL have result in a CEL but NONE exhibited any physical indication of fault. I assumed that once the ECU detected that one of the sensors was faulty it simply relied on the opposite for fuel trim corrections/adjustment.

Why, if you think it through, should it be otherwise.

I suspect you cleaned, as anyone would, the MAF/IAT sensors at the same time, more likely the actual "misfire" cause, as installing the O2 sensor.

[curiousB]

Sorry, I find it a bit hard to accept that a defective MAIN O2 sensor in an engine with TWO sensors, would result in a lean misfire.

I tend to agree. Recall the primary O2 sensors are to trim (fine tune) the fuel map. When the engine is first started cold it is running open loop and the O2 sensors aren't used at all. While not optimal from an emissions perspective the cars still ran fine. Prior to EFI there was no feedback loop on fuel trim (remember those things called carburetors?). Those cars ran fine as well.

I could see a faulty O2 sensor leading to a failed emissions test or lousy gas mileage but dramatic engine mis firing at a narrow band of speed seems something other than fuel trim is at fault.

[landar]

90 LS (a Bill Gate's trade-in)

Bill Gate's would stoop to driving an LS? With his money, I would think he would be more of a Bentley man. Must have been his 'beater' car. ;)

[ehabmarco]

Actually I called it misfire based on the link below which explains that misfire can be caused by one 3 things:

1- loss of spark

2- the air/fuel mixture is too far out of balance to ignite

3- loss of compression

http://www.autotap.com/techlibrary/diagnosing_misfires.asp

In my case a random misfire (hesitation) was happening every 4 to 5 seconds and was caused by a bad air/fuel mixture (lean misfire) due to the bad oxygen sensor

This sensor was causing a rough idle too, after changing it, no more hesitation when cruising and idle became much smoother

the link below helped me to test the sensor

http://www.lexls.com/tutorials/EFI/mainoxygensensor.html

Sorry, I find it a bit hard to accept that a defective MAIN O2 sensor in an engine with TWO sensors, would result in a lean misfire. Over the years I have been reponsable for the care and maintenance of a '90 LS (a Bill Gate's trade-in), a '91 LS, 3 '92's and a '95. The '90 and one of the '92's are now off the list. Amongst that group, all now pushing close too or over 200K, I have encountered numerous instances of O2 failures. ALL have result in a CEL but NONE exhibited any physical indication of fault. I assumed that once the ECU detected that one of the sensors was faulty it simply relied on the opposite for fuel trim corrections/adjustment.

Why, if you think it through, should it be otherwise.

I suspect you cleaned, as anyone would, the MAF/IAT sensors at the same time, more likely the actual "misfire" cause, as installing the O2 sensor.

Yes before changing the O2 sensor, The MAF/IAT sensors had been cleaned AND even changed without any improvement

One more thing I want to mention is that the O2 sensor was completely dead (no reading for any resistance)

I knew that this sensor was faulty (I had a CEL) but I could not imagine that this is the reason of misfire, that's why I left it to be the last option

[jaswood]

Actually I called it misfire based on the link below which explains that misfire can be caused by one 3 things:

1- loss of spark

2- the air/fuel mixture is too far out of balance to ignite

3- loss of compression

http://www.autotap.com/techlibrary/diagnosing_misfires.asp

In my case a random misfire (hesitation) was happening every 4 to 5 seconds and was caused by a bad air/fuel mixture (lean misfire) due to the bad oxygen sensor

This sensor was causing a rough idle too, after changing it, no more hesitation when cruising and idle became much smoother

the link below helped me to test the sensor

http://www.lexls.com/tutorials/EFI/mainoxygensensor.html

Sorry, I find it a bit hard to accept that a defective MAIN O2 sensor in an engine with TWO sensors, would result in a lean misfire. Over the years I have been reponsable for the care and maintenance of a '90 LS (a Bill Gate's trade-in), a '91 LS, 3 '92's and a '95. The '90 and one of the '92's are now off the list. Amongst that group, all now pushing close too or over 200K, I have encountered numerous instances of O2 failures. ALL have result in a CEL but NONE exhibited any physical indication of fault. I assumed that once the ECU detected that one of the sensors was faulty it simply relied on the opposite for fuel trim corrections/adjustment.

Why, if you think it through, should it be otherwise.

I suspect you cleaned, as anyone would, the MAF/IAT sensors at the same time, more likely the actual "misfire" cause, as installing the O2 sensor.

Yes before changing the O2 sensor, The MAF/IAT sensors had been cleaned AND even changed without any improvement

One more thing I want to mention is that the O2 sensor was completely dead (no reading for any resistance)

I knew that this sensor was faulty (I had a CEL) but I could not imagine that this is the reason of misfire, that's why I left it to be the last option

The 2 wires leading to the sensor element will always read open. The only way I know to test those is to heat the element in our oxygen rich atmosphere and test for the output voltage to be in the proper range. It appears that if you had "read" the actual code it would indicated an open O2 sensor HEATER, not the sensor itsself. the heater is only used during initial engine start up. Once the exhaust is supplying HEAT the sensor will provide good outputs.

[fsuguy]

Good work ehabmarco. To quote a phrase, "If you eliminate the impossible..., whatever remains, however improbable, must be the truth!"

[ehabmarco]

Good work ehabmarco. To quote a phrase, "If you eliminate the impossible..., whatever remains, however improbable, must be the truth!"

Thanks fsuguy

Now I need help and I am not sure if I should start a new topic or not

This is related to error code 47 in traction control (When idle switch is ON, sub-throttle position sensor signal is 1.45V or higher)

Any ideas if that means that I should replace the sensor or it can just be adjusted

Thanks

[ehabmarco]

Actually I called it misfire based on the link below which explains that misfire can be caused by one 3 things:

1- loss of spark

2- the air/fuel mixture is too far out of balance to ignite

3- loss of compression

http://www.autotap.com/techlibrary/diagnosing_misfires.asp

In my case a random misfire (hesitation) was happening every 4 to 5 seconds and was caused by a bad air/fuel mixture (lean misfire) due to the bad oxygen sensor

This sensor was causing a rough idle too, after changing it, no more hesitation when cruising and idle became much smoother

the link below helped me to test the sensor

http://www.lexls.com/tutorials/EFI/mainoxygensensor.html

Sorry, I find it a bit hard to accept that a defective MAIN O2 sensor in an engine with TWO sensors, would result in a lean misfire. Over the years I have been reponsable for the care and maintenance of a '90 LS (a Bill Gate's trade-in), a '91 LS, 3 '92's and a '95. The '90 and one of the '92's are now off the list. Amongst that group, all now pushing close too or over 200K, I have encountered numerous instances of O2 failures. ALL have result in a CEL but NONE exhibited any physical indication of fault. I assumed that once the ECU detected that one of the sensors was faulty it simply relied on the opposite for fuel trim corrections/adjustment.

Why, if you think it through, should it be otherwise.

I suspect you cleaned, as anyone would, the MAF/IAT sensors at the same time, more likely the actual "misfire" cause, as installing the O2 sensor.

Yes before changing the O2 sensor, The MAF/IAT sensors had been cleaned AND even changed without any improvement

One more thing I want to mention is that the O2 sensor was completely dead (no reading for any resistance)

I knew that this sensor was faulty (I had a CEL) but I could not imagine that this is the reason of misfire, that's why I left it to be the last option

The 2 wires leading to the sensor element will always read open. The only way I know to test those is to heat the element in our oxygen rich atmosphere and test for the output voltage to be in the proper range. It appears that if you had "read" the actual code it would indicated an open O2 sensor HEATER, not the sensor itsself. the heater is only used during initial engine start up. Once the exhaust is supplying HEAT the sensor will provide good outputs.

Yes you are right but it seems that by chance the sensor itself was also out of order

But could you elaborate more how to test it I did not understand how to test the voltage? which of the 4 wires to connect?

Thanks

[fsuguy]

ehabmarco,

Is your question about how to test the oxygen sensor? If so, I can post the diagnostic procedures from the '92 Repair Manual. Not sure whether the procedures are applicable across all 1st gen models, though. Let me know and I will post them.

[ehabmarco]

ehabmarco,

Is your question about how to test the oxygen sensor? If so, I can post the diagnostic procedures from the '92 Repair Manual. Not sure whether the procedures are applicable across all 1st gen models, though. Let me know and I will post them.

Thanks fsuguy

Yes my question was about testing the oxygen sensor, it is a 4 wires type (2 black, 1 blue, 1 white), it would be great if you can post it

About the other trac code error 47, it was a little adjustment that needed to be done to the traction control sensor position and the code now is cleared

Thanks a lot

[curiousB]

I have a Denso 234-4167 Oxygen Sensor that I ending up not needing. Its new in box and I'm happy to pass it on for less than I paid for it (I paid $65.00). Its the Bank 1/2 post CAT sensor. All 4 are the same sensor its just the cable lengths which are different. So if you are handy with a soldering iron and shrink tubing you could adjust the cable harness length to suit.

Send me a private message if you are interested.

Here's an excerpt on the various sensor cross referencing (of part numbers):

There are four O2 sensors in the LS430. They are as follows:

Bank 1 Sensor 1 - Driver's side (left front) on exhaust header. Lexus # 89465-50120 / Denso OEM # 234-4138 / Denso Universal # 234-4209 / Bosch OEM # 13441 / Bosch Universal # 15733

Bank 1 Sensor 2 - Driver's side (rear) near catalytic converter. Lexus # 89465-50140 / Denso OEM # 234-4167 / Denso Universal # 234-4209 / Bosch OEM # 15272 / Bosch Universal # 15733

Bank 2 Sensor 1 - Passenger side (right front) on exhaust header. Lexus # 89465-50130 / Denso OEM # 234-4630 / Denso Universal # 234-4209 / Bosch OEM # 13632 / Bosch Universal # 15733

Bank 2 Sensor 2 - Passenger side (rear) near catalytic converter. Lexus # 89465-50140 / Denso OEM # 234-4167 / Denso Universal # 234-4209 / Bosch OEM # 15272 / Bosch Universal # 15733

[yotoy82]

What year is your LS400... are you sure this isnt about that engine ECU problem where at 45 mph it feels like your engine hits something, like a super rough shift boom? Very common problem on the LS400 specially 1995/1996

[landar]

I have a Denso 234-4167 Oxygen Sensor that I ending up not needing. Its new in box and I'm happy to pass it on for less than I paid for it (I paid $65.00).

Actually you can probably get your purchase price back very easily w/o reselling. If you purchased it locally and do not have the receipt, just take it back and they may have the sale on record. Even if you purchased it online, you might be able to get a store credit at a local retailer like Autozone, Advance, Pep boys, O'Reilly's, etc. if they carry the part. I have done this before and it worked out beautifully. I always need things like oil, filters, shop rags that I can purchase with the credit.

[yotoy82]

I find the best price for oxygen sensors, and quality, the densos on amazon are pretty much literally a perfect fit just like OEM