Missfiring like its gone out of fashion.

[ColinBarber]

Only Bank 1 Sensor 1 and Bank 2 Sensor 1 could have an affect on the engine, the downstream sensors just monitor how well the cats are working and produce an error if necessary.

If both cats are getting hot then it sounds like the engine is running lean. If it was just one cat then it could be blocked but I cannot see two cats getting blocked at the same time. Also the fact the both cats are excessively hot kind of rules out that an O2 sensor is at fault because each upstream sensor controls just one bank of the engine, you would expect only one cat to get hot. You are therefore looking for something common across both banks, such as fueling, ignition and air control. If this issue is with both petrol and lpg then you can also rule out fueling therefore an air leak, faulty MAF sensor, ignition or poor electrics are likely causes.

[Spacewagon52]

This is the nightmare we all fear with a problem that is very difficult to diagnose. Spending money on a cure is one thing but replacing expensive parts and then possibly finding that was not the problem is very frustrating. I had a problem with my catalyst on my Space Wagon - it would have been cheaper to buy the original part (we live and learn) - never did get it sorted so sold it very cheap. Really hope they can solve the problem Mike. My gut feeling would be to replace the cheapest parts in order and see if it solves the problem. Good luck.

[The-Acre]

10 hours ago, Bluesman said:

The thing is we are on our 3rd opinion and at some stage you have got to trust what is being told you. It doesn't help to have already been told various things by two other so called professional Lexus Technicians and them leaving the car on double yellow lines without doing anything to the car for over 3 weeks. What I am being told now makes sense they are people I know I just wasn't aware that the Auto Electrician who has the car now had the ability to read the computers which the others said they could but couldn't. He works next door to the local garage that has serviced our family cars for nearly 30 years and I trust what he tells me. Anyway which ever way it goes I will let you know. Mike.

I think it's time to start taking bets, you could make a fortune, especially if the problem is a real outsider!!

[runsgrateasanut]

Good luck with how it turns out.

[Bluesman]

News from the battle front. Have just had my garage ring me to say that the right hand side cat is blocked (checked by putting a pressure sensor on the exhaust) I think that's what he said, I have decided to have both cats replaced at a cost of £400 for the pair. He said that the miss fire has gone completely so fingers crossed the problem has been solved. Will post a further bulletin when the job has been completed. Mike.

 

[Malc]

...  I have been following this thread with interest ..  and how some professionals haven't a clue which is very disconcerting !

So do tell, what does cause a cat to block ?  Is it something simple and preventable ?

Malc

[Bluesman]

2 hours ago, Malc said:

...  I have been following this thread with interest ..  and how some professionals haven't a clue which is very disconcerting !

So do tell, what does cause a cat to block ?  Is it something simple and preventable ?

Malc

My understanding is that the cat ran so hot 400 degrees that it simply melted the inner core. But cats can fail for all sorts of reasons especially if your local exhaust center gives it an almighty wallop with a lump hammer and the insides just collapse. As for my own saga I am hoping the ending is in sight. Mike.

[Malc]

............  oh dear, the incentive is there for the repairer to instigate a simple collapse then, or to be simply careless in handling the issue, job creation springs to mind ......  as if !!

Hope it sorts out soon, must be soooo frustrating, especially after so many years of more or less trouble free and inexpensive motoring .........  which we all usually enjoy.

I suppose these issues arise so rarely with our Ls400s that repairers, no matter where from, just have zero experience of dealing with them.

Malc

 

 

ps  my indy who now has experience of the Ls400 through me alone ( 8.5 years ), has told me quite bluntly that he has absolutely zero experience of dealing with the proposed 4th generation Honda Legend I propose getting late summer ( for the g/f ) .......  no surprises there really with only about 515 ever sold in the UK !

Not many Honda main dealers even have that experience either I'd surmise ...  it must be rarer than the Ls400

[Bluesman]

52 minutes ago, Malc said:

............  oh dear, the incentive is there for the repairer to instigate a simple collapse then, or to be simply careless in handling the issue, job creation springs to mind ......  as if !!

Hope it sorts out soon, must be soooo frustrating, especially after so many years of more or less trouble free and inexpensive motoring .........  which we all usually enjoy.

I suppose these issues arise so rarely with our Ls400s that repairers, no matter where from, just have zero experience of dealing with them.

Malc

 

 

ps  my indy who now has experience of the Ls400 through me alone ( 8.5 years ), has told me quite bluntly that he has absolutely zero experience of dealing with the proposed 4th generation Honda Legend I propose getting late summer ( for the g/f ) .......  no surprises there really with only about 515 ever sold in the UK !

Not many Honda main dealers even have that experience either I'd surmise ...  it must be rarer than the Ls400

I have had her for 7 years now and this is the first time she has let me down. Had the RAC taken me to a garage who could have dealt with problem in a professional manner all I would have had to pay for was one Oxygen Sensor and it would have been back on the road in a couple of hours. So as far as the car is concerned that is all she has cost me in time and money. Rubbish professionals have cost me the rest of the time and money. I should have looked for those horses better than I did, I can only assume they had them hidden in a building somewhere. Hopefully I will get her back at the weekend or just after.

[cleverdick]

Thermal shock can cause this too (obviously), such as from driving through a ford.  One to beware of.

[runsgrateasanut]

19 hours ago, Bluesman said:

News from the battle front. Have just had my garage ring me to say that the right hand side cat is blocked (checked by putting a pressure sensor on the exhaust) I think that's what he said, I have decided to have both cats replaced at a cost of £400 for the pair. He said that the miss fire has gone completely so fingers crossed the problem has been solved. Will post a further bulletin when the job has been completed. Mike.

 

If the misfire has gone completely what did he do to fix it? If he replaced a coil pack then surely the cause of the different pressure was owing to one side not firing. Now firing, why change the Cats? Has he told you that he actually removed the Cats to get the Car to run properly?   To remove these are usually a pain. 

A dodgy coil would have cost £25 aftermarket.

[Bluesman]

1 hour ago, runsgrateasanut said:

If the misfire has gone completely what did he do to fix it? If he replaced a coil pack then surely the cause of the different pressure was owing to one side not firing. Now firing, why change the Cats? Has he told you that he actually removed the Cats to get the Car to run properly?   To remove these are usually a pain. 

A dodgy coil would have cost £25 aftermarket.

The coils have all been checked and are OK. See above for how the cats were tested. I called it misfire because to me that's what it sounded and felt like but its more rough running caused by the naff Oxygen Sensor.  "Has he told you that he actually removed the Cats to get the Car to run properly?" Yes.

If he told me the engine needed replacing I would believe him, the garage it is with now has serviced the families cars for the last 30 years and in all that time he has never ever been wrong and I have never ever had to take his work back because the work hadn't been done properly. The cats are on order and as soon as he has time to fit them we will see if he is correct. Mike.

[runsgrateasanut]

It will be good to get your car back.  Original Cats have a scrap value of £90 (so I was told ??) so hopefully you will be able to offset some of your expense.

 

[Bluesman]

2 hours ago, runsgrateasanut said:

It will be good to get your car back.  Original Cats have a scrap value of £90 (so I was told ??) so hopefully you will be able to offset some of your expense.

 

Looking like Tuesday as we need the Screw Doctor for the manifold end of the cat has a broken stud in it. I realise the old cats still have a value but we are going to split that between me and the garage. So roll on Tuesday, I can wait. Mike.

[steve2006]

Did you get the chance to have a look at the faulty cats Mike? Just wondering what they look like internally as I know with good ones you can see light through them.

[Bluesman]

55 minutes ago, steve2006 said:

Did you get the chance to have a look at the faulty cats Mike? Just wondering what they look like internally as I know with good ones you can see light through them.

Hi Steve, I am going to photograph them tomorrow morning. One is blocked solid and you cant see anything through. I am not sure of the other one but it was my choice to replace both of them, just made sense in my head. I post the pics tomorrow. Mike.

[Bluesman]

Here we go. One blocked and the other still useable but I decided to have it changed as well.

[Spacewagon52]

I would replace both - not worth the hassle if the second one goes.

[Bluesman]

1 hour ago, Spacewagon52 said:

I would replace both - not worth the hassle if the second one goes.

Both have been replaced, made sense to me.

Below shows the nuts from the cat, left one OK  the right ones had a melt down. Demonstrates just how hot the cat got.

[mikeyv]

On 01/04/2016 at 6:02 PM, steve2006 said:

The VVTI engine has combined coil/igniters over plug and these are all operated from the ECM from individual ports.

There are common connections to each coil with a blue wire/red stripe and then 2 outputs from the engine ECU which each feed 4 coils these being the plain yellow wire or the yellow wire with a green stripe, if you have lost one of these outputs it may explain why you have a complete bank of cylinders down.

It would be a case of checking the connections to the coils on the defective bank.

Also given the known problems with the engine ECU capacitors it may be worth investigating this also.

It does sound more ignition related as the black plugs indicate fuel is being injected but not being burnt.

Not sure if misfire monitoring is performed on the LS400 engine so the EML may not illuminate.

After the O2 sensors were replaced the car then drove OK for a short while then reverted back to misfiring, this could be another indication of a faulty ECU as those capacitors are affected by heat, could you leave the car to cool right down then restart and see if the engine behaves until warmed up?

The only other thing I can suggest is a blocked catalytic convertor on that bank, everything else like the AFM is shared across both banks so can be eliminated as a possible cause, may be an idea to get the garage to hook up a back pressure tester via the O2 sensor hole.

Third post of the thread, well done Steve!!

Glad your back in the driving seat Mike.

[Bluesman]

39 minutes ago, mikeyv said:

Third post of the thread, well done Steve!!

Glad your back in the driving seat Mike.

Not yet Mikey, thread doctor is coming tomorrow to sort the threads on the manifold end of the Cats and then I will truly be back in heaven. Cant wait. Mike.

[Bluesman]

Shes back and running like a new baby.

I got lost on the way back, I am not sure what happened, must have taken a wrong turn somewhere.

Took me 45 miles to get home, garage is only 4 miles away.

I am just so happy. Mike.

[Malc]

...........  absolutely brilliant, many congratulations

Malc

[mikeyv]

Happy days!

In the days before cats, I had an old Vauxhall Victor FB estate, and it suddenly refused to go above 30 mph, though still ran smoothly.

I was clueless as to what was wrong, having checked all the usual ignition and fuel supply suspects.

Brother in law just happened to mention his scooter did the same thing, and it was collapsed baffles in the exhaust.

I promptly disconnected mine at the manifold, and it took off like a very noisy rocket.

One new exhaust later, problem gone.

Not come across it in the forty years since though, so I guess you can count yourself a bit unlucky.

[RgrWynne]

Really pleased for you,

Enjoy,

Roger