Search tells me it's time for a new cat, but I can't help but ask - sorryu

[MartinF]

Hi guys

I'm guilty of not being able to spend money without asking a second opinion! Thoughts much appreciated...

My 2001 PFL failed MOT on Fast Idle emissions:
103k on the clock. Car runs really well from idle to redline. Feels right on power. No error codes. It does smoke a bit on startup and burns a bit of oil when thrashed (usual valve seals and oil rings/holes I suspect).

CO 0.45% FAIL (max 0.30%)
HC 39ppm PASS (max 200ppm)
Lambda 0.985 PASS (0.97 - 1.03)
(The natural idle test was a pass at CO 0.47% (max 0.50)


These readings are consistent before and after the following:
-new air filter.
-new plugs (the old ones had brown ash deposits but were not sooty or oily).
-new oil and filter.
-bottle of Cataclean.
-damn good thrashing.

-then I  got out Elmscan and Torque apps:

-MAF sensor looks nice and linear as revs rise.

-MAF sensor reads 0.37g/s with engine off (throttle closed) and 0.4 with engine off and throttle open. During a normal journey the MAF read from 1.450 to 39.620. At idle it reads from 1.85 to 2.26. At 2500rpm it reads steady at approx 6.5 g/s.

-Throttle sensor is linear from 12.16% to 78.82%

-Temp sensor ok.

-"Calculated load" is 12.5 to 16.5 at idle

-Vacuum reading steady at idle at 12.5

-Precat O2 sensors have a nice high/low graph waveform on Elmscan. Both have a similar response time and graph similar lean/rich highs and lows.

-Postcat 02 sensor has a flatter waveform and settles around 0.7v to 0.75v at 2500rpm when warm, but it does jump about a bit.

-Long and short term fuel trims jump around a bit, but adding them up doesn't get near 10%.

Question is, do the odds favour buying a new cat before my free retest runs out and it costs me another £45, or do I get stuck into further testing on other things that I guess could make it run rich/dirty like:

-Fuel pressure (or it's  vacuum hose?)
-Evap valve?
-Fuel filter (but can't this only cause a lean condition?)
-PCV system (just put a new valve in last year)
-Injectors?
-Something major like compression?

Any advice from the fountains of knowledge on here would be much appreciated!

Cheers
Martin

[jvanzyl]

A new cat with fitting is about £120 delivered from Cats2u.

If it doesn't resolve it, put in on the shelf until the original cat gets annoying due to rattles and is knackered and then fit it. my 2 cents.

[Carolyn]

You're obviously pretty clued up on diagnostics.

This issue with these symptoms has cropped up a few times. A new cat has always solved the matter.

Jvanzyl is giving good advice.

Cats2U offers a cheap and cheerful aftermarket cat that does the job just fine, and is a hell of a lot cheaper than OEM.

They do a fitting kit too, though most have found their crush-ring gaskets not too great. OEM is more reliable.

[MartinF]

Thanks guys - if I even look like I know anything then it's because I learned it on places like this from guys like you!

[jvanzyl]

The other advantage of the Cats2u version is that it is SIGNIFICANTLY lighter than OEM. You will notice the difference.

[MartinF]

Final o2 sensor check done - I created a vacuum leak by disconnecting the hose to the evap system (valve on the air inlet was powered open at warm idle). All three o2 sensors quickly reflected the lean condition.

Cats2u here I come. I'll post back with results.

Thanks guys

[MartinF]

I've also ordered 3 new amigos and new OE crush washers from TCB Parts in readiness for the fun and games getting the old one off...

[shnazzle]

Looks like new cat will do the trick. 
Did you make sure the cat was hot hot hot at time of MOT? 
Doesn't really hit peak CO conversion until it's quite hot. 

Running a tad rich. So a further tip for MOT as your rings are probably past best; undo the pcv hose, grab an old spark plug,shove it in the hose. Tuck it away nicely.
Hey presto. Your engine can still breathe but none of the oily air is going into your intake and burning away, reducing your CO and HC. 
When MOT pass, remove spark and put hose back into PCV valve.

[MartinF]

Thanks Shnazzle. I'd driven the socks off it for a whole quarter tank and it only stood idling for a minute while they booted up the tester and I reversed it in. About as hot as I could make it.

Interestingly, I learnt from Fiat DPF issues that the best way to get heat into a DPF was a low revs/high load approach. This was much better at getting heat into the system than caning it. I wonder if it's the same with a petrol cat?

I have been wondering about the slightly rich readings. The plugs don't show signs of a rich mixture but something must be going on. My pcv system is clean but it couldn't hurt to stop the oily fumes getting burnt-thanks for the tip.

[MartinF]

2 amigos down, one reduced to shards of metal but still clinging on tenaciously! Not even enough left for the nut removers and it already bent the blade of my cheapo nut splitter. No space for a grinder so currently hitting remains with a cold chisel. Plumbing torch out of gas. Great way to spend a Sunday evening.

Just noticed the new Cats2u cat is missing the heatshield mounting bracket - is that just mine or is that why some of you guys run without a shield? It would be nice not to have to swap it over if I don't have to!

Grrrrr...must stay patient....

[shnazzle]

2 amigos down, one reduced to shards of metal but still clinging on tenaciously! Not even enough left for the nut removers and it already bent the blade of my cheapo nut splitter. No space for a grinder so currently hitting remains with a cold chisel. Plumbing torch out of gas. Great way to spend a Sunday evening.

Just noticed the new Cats2u cat is missing the heatshield mounting bracket - is that just mine or is that why some of you guys run without a shield? It would be nice not to have to swap it over if I don't have to!

Grrrrr...must stay patient....

It should have a heatshield on it when it arrives. No need to re-use. 

But, you can always wrap it. Mine's just wrapped. 

Be careful with the hard hammering..dont want to damage your mani

[MartinF]

Good tip - I can be ham fisted with a hammer!

The cat is this one (the type approved one):
https://www.ebay.co.uk/itm/TOYOTA-MR2-1-8-VVTi-10-99-06-07-TYPE-APPROVED-CATALYTIC-CONVERTER-CAT/164011354456?hash=item262fd6a958:g:2MMAAOSwWy5eCccy


No separate or obvious heatshield but perhaps it is built in like a double skin on the cat section? what do you think?

[shnazzle]

Good tip - I can be ham fisted with a hammer!

The cat is this one (the type approved one):
https://www.ebay.co.uk/itm/TOYOTA-MR2-1-8-VVTi-10-99-06-07-TYPE-APPROVED-CATALYTIC-CONVERTER-CAT/164011354456?hash=item262fd6a958:g:2MMAAOSwWy5eCccy


No separate or obvious heatshield but perhaps it is built in like a double skin on the cat section? what do you think?

@jvanzyl or @Carolyn could tell you first hand what is included with these but I always thought they had a modest heat shield on them.

If not, a 10m roll of exhaust wrap is cheap enough from ebay.
It's a good idea to have a shield or wrapping for two reasons;
1) retain heat. They need to get to and stay above 600ish degrees to be effective 
2) people's nappies have caught fire/smoldered from uncovered cats  

As for 3 amigos; mole grips and a lot of plusgas soaking may be your only rescue now. Alternatively, hammer a slightly smaller imperial sized socket onto the remains of the nut. But yeah, plusgas and a few hours of soaking

[MartinF]

The bracket that secures the heat shield is absent on this one. No inbuilt heat shield as far as i can tell. Wrap will be the only choice I guess.

Given up on 3rd amigo and time for bed. New plan tomorrow possibly involving someone who can weld a big nut onto the stud.

[Carolyn]

The Cats2U cat does not include a heat-shield.  It does pass MOT, so long as the tester gets it good and hot - but that's true of a lot of cats.

I've run one for a few years.  It passes mot.

You may have to drill out the nut and stud from below.  I'd use small bit to get the hole going and centred and work up with bit size. Then nut-and-bolt it when you install the new cat.

Alternatively, you could drop the cat and manifold as one piece and tackle it off the car.

[jvanzyl]

You don't need additional heat shielding for the cats2u cat.
I can't quite remember the timeline, but I'm pretty sure that mine passed MOT quite happily... I'd just enjoy the fact that the thing weighs less.

[MartinF]

It's off! Brute force and much ignorance won the day. Will post later how the emissions look.

Carolyn-do I recall you had a source for those pesky maf sensor o rings? What a fun game reinstalling that is once they stretch with age! Cheers!

[Carolyn]

It's off! Brute force and much ignorance won the day. Will post later how the emissions look.

Carolyn-do I recall you had a source for those pesky maf sensor o rings? What a fun game reinstalling that is once they stretch with age! Cheers!

They stretch if you get carb cleaner on them.  That source would be me.  Send me your address by Pm and I'll post one out. Small donation to the club please?

[MartinF]

Thanks Carolyn - will do.

Busy couple of days but cat is on and MOT gained. Phew and thanks for all the help on here.

Not quite as I expected though.This was the sequence when we did a trial emissions test.

-Popped the probe in the exhaust at idle with a nice hot engine - emissions clean enough to eat your dinner from. Basically 0% CO, HC less than 30ppm and lambda at 0.994.

-Fast idle at 2500, and readings stayed rock steady for 2-3 minutes, then suddenly CO jumped up to over .40% (limit is 0.3).

-Back to idle, CO quickly dropped back to near zero.

-Fast idle, same thing - CO near zero for a few minutes then climbed over limit.

-Disconnected evap valve - no difference. (Didn't have time to try PCV).

-Disconnected MAF sensor, engine stalled. Quickly reconnected and restarted engine and the CO dropped right back to zero even at 2500. Ran it for couple of minutes again before CO went up again.

My madcap theory is this - one of the sensors (I vote MAF) is drifting off spec when given a workout. When I disconnected the MAF sensor it dropped back into open loop and ran correctly with low emissions until it went closed loop again after few minutes.

This theory is based on the assumption that the car uses a base map for the MAF sensor when in open loop mode. Does anyone know if this is true? I suppose only the O2 sensors need heat so why would the car ignore MAF in open loop...rapidly reaching my knowledge barrer....

Again - thanks to anyone who reads all this rambling!

[shnazzle]

Aahh... My favourite field  

Car most certainly does not ignore MAF.
Except for when you disconnect it, in which case it drops into an odd mix of AlphaN fueling (based on throttle position and rpm, with feedback loop from o2). 
Open/closed loop only refers to the ecu's use of o2 sensors for fueling feedback. Open = map+long term fuel trim, closed = map + short/o2 + long term.


Your CO would typically only increase if you're running too rich. 
One definite option is exhaust leak, fouling your o2 sensors. 
Leak causes o2 sensors to read lean, ecu dumps in more fuel, now you're running far too rich, CO shoots up.

Checked for leaks? 

[MartinF]

Ahhhh...good to know the whole loop business is based around the O2 sensors.

So if the O2 sensors in the manifold read lean then is the only possible leak in the manifold to block gasket?

Also I seem to remember some wise chap (possibly you Shnazzle?) pointing out that the MR2 uses the post-cat sensor as part of it's feedback loop as well, extending the potential location of leaks.

I am thinking I should do an extended fast idle test with Elmscan and look for the average voltage on the 2 pre-cat sensors - I guess if they don't both come out around .45v then I may see the issue.

[shnazzle]

Ahhhh...good to know the whole loop business is based around the O2 sensors.

So if the O2 sensors in the manifold read lean then is the only possible leak in the manifold to block gasket?

Also I seem to remember some wise chap (possibly you Shnazzle?) pointing out that the MR2 uses the post-cat sensor as part of it's feedback loop as well, extending the potential location of leaks.

I am thinking I should do an extended fast idle test with Elmscan and look for the average voltage on the 2 pre-cat sensors - I guess if they don't both come out around .45v then I may see the issue.

Leak can also be between cat and manifold, and at a stretch, cat flexis (post-cat sensor fouling). 
Remember that the voltages will swing. That's by design for the cat. Reset the ecu let it settle at idle. Warm the engine so as to allow for closed loop operation. Then rev it at 2500 for a bit,see how it responds. Give it a second to respond.

You're looking for lean readings (<0.45) and positive fuel trims at fast idle. I.e. "I'm reading too much oxygen, so I'm adding more fuel over and above what the map tells me". 

Pay attention to which bank it's looking skewed on. Could indicate whether it's a leak on one side of the manifold or the other, or if an injector is leaking. 

Fingers crossed it's an easy fix. Usually is.

[MartinF]

Thanks Shnazzle - something to get my teeth into. At least I have spent enough time under the car lately to know that my subframe definitely isn't rusty!

[shnazzle]

Thanks Shnazzle - something to get my teeth into. At least I have spent enough time under the car lately to know that my subframe definitely isn't rusty!

Hey! That's a win in my eyes. A good subframe is great news!

[MartinF]

Trouble is with the new cat it looks so much better with the nappy removed. It's tempting to leave it off and have everything get mucky.