Catalytic converter? Hope not!

[Skyeman]

Hi all,

Just joined - migrated from 'that other' forum (where very little happens)

As mentioned in the title I have a possible cat problem. I do a lot of miles in the Amazon (currently 118k). Bought it 4 or 5 years ago just converted to lpg (flashlube fitted) with about 50k on it, and it's full MDSH. In August, heading for the continent, the check engine light came on, along with 'vsc trc' and 'vsc off' lights (was told by Toyo garage these 2 come on automatically if the CEL is lit).

It drove perfectly normally so we pushed on, and on returning to UK (2000 miles later) it went in to Toyo main dealer for interim service and investigation. Garage changed both pre and post cat oxygen sensors on the left hand bank, in response to fault code p0420. They road tested it for 30 mins and all ok.

However, after about 60 miles, back to square one! I've since had it to my local mechanic (non Toyo but I trust him) and he did a smoke test and found a couple of small leaks on the inlet side - base of the oil filler neck, and a rubber breather pipe on top of the engine. Both fixed and fault erased, but after another 60 miles - you guessed it!

The exhaust is in good condition (no leaks), so wondering where to go next. Mech says it could be a failing plug or coil pack, but I would have thought it would then throw up a more specific fault code.

Obviously I'm resisting changing the cat until I'm certain that's the fault - would hate like hell to spend all that cash and see the fault reappear!

Does anyone on here have any pearls of wisdom - anyone been down this road with a V8?? (no pun intended!)

Incidentally running just on petrol instead of lpg makes no difference - I put a full tank of Shell V-power through it (ouch!) to no avail.


regards

Rick

 

[OG.]

I suppose you could try this....

http://www.youtube.com/watch?v=5icTmYItwiE

 

[Gav Peter]

Welcome along Rick - nice to have another V8 owner amongst us

'Fraid I can't help with your problems - hopefully JW will be along soon with some thoughts.

Cheers

 

[Gary Stockton]

Google offers up this:

http://www.obd-codes.com/p0420 which says "Catalyst System Efficiency Below Threshold (Bank 1)"

Which has a host of other info for you.

HTH

And welcome!!

 

[Skyeman]

Thanks for quick replies guys - certainly more activity on here!

OG - yes saw that youtube video - would scare me a bit putting stuff like that through the engine - might it cause other problems?
As for removing and washing - mmmmm, would have to cut the pipe and then weld back on afterwards but might be worth a try - anyone tried this?

Gary - yep - read about 0420 on google until my brain has dried up and blown away.

I'm offshore at the moment in Norway but will pick up the cruiser on Thursday and continue the head scratching - I'll keep you all posted.

Rick

 

[OG.]

Lacquer thinner is almost entirely either acetone or Xylene. We used to use Xylene as an octane booster years ago when I was rallying and never had any ill effects.

If all else fails the bucket of soapy water is worth a shot I guess.

 

[Gary Stockton]

If you've swapped out both O2 sensors and they're reading properly, and checked for leaks etc. and found none, then seems last resort is the cats - so maybe switch them round (can you?) and see what happens, or get a couple from a scrap yard (or try Karl) and see what happens?

 

[Jon Wildsmith]

See if you can find an MOT tester that will do an exhaust gas analyser test on it for you. If you have the tickets from previous tests you can compare them but the MOT man should be able to tell you if the readings are consistent with a failing CAT.

You don't have ticking (leaking) exhaust manifolds do you? Could be wrong but they might upset the lambda readings.

I never messed with the OEM CAT's much, that was another reason to dump the OEM exhaust before it could give trouble Gav

 

[Rob]

I have exactly the same issue on my Volvo (and I think I have finally solved it). What is happening is the ECU is using data acquired from the MAF and 1st lambda sensor and comparing it with the lambda sensor after the cat. This means that if there is a leak anywhere between the MAF and rear lambda sensor then the ECU will blame it on the cat. Same can happen on really fussy ECUs (like a Volvo ME7 ) if you have a fuelling issue (eg low fuel pressure), misfire or low compression. Check all the vac lines, all inlet and exhaust manifold gaskets for leaks and get them sorted. Then move onto the fuelling/misfire/compression checks so check if you have adequate fuel pressure etc. Now if after you have put this all right and you are certain that the lambda sensors can be trusted then it will probably be the cat.

If your car passes emissions without issues then why not just fit a lambda sensor spacer on the rear sensor? It will fool the ECU into thinking everything is working as it should. All the rear sensor does is check the function of the other sensor and condition of the cat, and is much cheaper than a new cat.

https://www.google.co.uk/search?q=l...&sugexp=chrome,mod=8&sourceid=chrome&ie=UTF-8

 

[Skyeman]

Aha - lots of ideas and all much appreciated.

So I think compression test next. Also will dig out emissions results for the last mot and compare with present figures.

I presume the smoke test (already done) will have ruled out any more leaks on the inlet side.

Check exhaust manifold.

Possible misfire - ? check all plugs for condition? (no misfire codes being generated by the ecu).

If a lambda sensor spacer is used, how will the mot tester view that if he sees it? Or will it not matter as long as the emissions are ok? It looks like a nice simple, cheap fix!

It's due for mot next month and the tester is also my mechanic.....

Good to have a plan!

Rick

 

[Rob]

No misfire codes does not mean there is no misfire. You could have a small misfire which could be contributing to the problem so listen very carefully when the engine is idling. Not sure if there is a check you can do on the coil packs. I had to replace all my coil packs on my Volvo as I still had a small misfire even after I replaced the plugs and suspect coil pack. Misfire has now gone.

As the MOT only checks for emissions at this stage it should not be an issue. I think the MIL is not part the the new MOT regulations so the spacer should be fine. I have only just fitted my lambda spacer and I have only driven 30 miles in it, will know later on in the week if the problem has in fact been "sorted". I say "sorted" as a lambda sensor is not really a fix, just a way of convincing an ECU your cat is in great shape.

The way I figured out that the cat needs to be replaced is when all the issues were put right after doing the checks above (everything was bad except fuel pressure), replacing both lambda sensors and then I got a competent main stealer to compare the readings from both sensors and plot them against time as my OBD2 reader cannot read the front wide band sensor output. It turned out the rear sensor was oscillating at exactly the same frequency as the front one meaning the mixture leaving the cat is affected by the mixture going into the cat. This does not mean my cat is completely gone, you would need to calibrate you voltage outputs of both sensors to the oxygen content in the gasses to establish the efficiency of the cat. It just means that its operating outside the manufacturer's limits.

 

[Skyeman]

Thanks Rob,

Home again for a couple of days, & I just looked up the service record and it's done 60k since the last set of spark plugs, so I think i'll replace them as it's straightforward and relatively inexpensive, then move up the list. I'll check with mech today re MOT/emissions and take it from there. Wish I had more time!

Rick

 

[Skyeman]

Quick update - got my mechanic to do an emissions test and it passed with flying colours.

So..... Had a look and can't even SEE the plugs - aargh! So much for that 'straightforward' job.

Well my mech says it will pass the mot no problem so that's the next thing I suppose. Just done about 50 miles this afternoon and it's never gone better - smooth and responsive - if only that bloody light would go out!

 

[Rob]

Just to give you an update, after fitting the lambda sensor spacer and driven about 500 miles the light has not come back on my Volvo. ECU thinks everything is fine so I am happy with the fix (until it fails an MOT on emissions that is).

 

[Skyeman]

looking at spacers online and they all seem to be cylindrical. my lambda sensor fitting is sort of oval with two fixing bolts - mechanic says this is an old type - anyone seen spacers to fit these?

 

[majic79]

This may be relevant - have you checked the inlet sensors? My missus hyundai came up with a light, related to lambda sensor, turned out the MAF was dirty, took it off, cleaned it with carb cleaner (others have had good results with brake cleaner - it needs to be a solvent that leaves no residue whatever you use) and it's been fine since.

Bear in mind, the ECU manipulates outputs (injectors/ignition) in response to what it sees going into the engine (at the inlet side, so either MAF sensors, or MAP + Temp sensors) and feedback from the process output (lambda sensors/temp sensors), so while the "fault" is indicated by the lambda sensor, it can be caused by the inputs being in fault.

It may not be a solution for you, it's done the job for us

 

[nathanrobo]

cleaned it with carb cleaner (others have had good results with brake cleaner - it needs to be a solvent that leaves no residue whatever you use) and it's been fine since.

I use IPA (Isopropyl Alcohol) for cleaning, that leaves not residue - just evaporates off. Also known as rubbing alcohol

 

[Rob]

Can you not separate the mounting plate from the sensor? Looks like a normal sensor just screwed into a plate.

 

[Rob]

Looks like you can:

http://www.auto-sensors.co.uk/toyota-4-runner-oxygen-lambda-sensor-direct-fit-89465-29465-786-p.asp

 

[Skyeman]

yes, Rob it certainly looks that way. I'll crawl underneath and have a closer look - just as soon as it stops raining! (and when it's daylight, which is a rare commodity in these parts at this time of year).

the good news is that the truck sailed thru the mot today. So I'll check to see if we have any isopropyl alcohol (we've got most other types!) and whip the hot wire off tomorrow - easy, 2 or 3 screws and a plug.