Emissions failure on CO (Carbon Monoxide)

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Jul 11, 2008
London, UK & Lusaka, Zambia
Hi Guys,

my 93 (no OBD etc, 1FZFE) just failed with about 2 x the limit of NO. Other readings within limits.

My (front) O2 sensors are brand new Toyota, but I will still check to see if the voltage is "oscilating" as it should.

Criticise my logic here:
Assuming the car is going into closed loop (why would it not - faulty cooland sensor?), whatever goes on wirh regard to mixture should be sorted by the closed loop operation, unless air is leeking into the exhaust, giving the sensors a false lean reading ?

Unless the value are beyond the scope of compensation ?

I'm going to look at air filter.

Plus, wires, rotor and cap all only a few thousand miles / year or two old (yup it doesn't do many miles).

Other info - car has a restricion in the air intake ion the form of a LPG mixer venturi - it's dual fuel LPG - passed OK before though.
VAF might need some adjustment ?
Car has slighlty less power than my other 1FZFE.
No Check engine light or codes.

EGR is blanked off - this was not the case when last tested - but this shouldn't affect anything at idle, and regardless woudl affect NOX, not CO ?

PAIR system removed - as above - was not the case when last tested, but that just injects air on overrun - unless my blank plates are leaking ?? Can reinstate, removed as it doesn;t have any useful function on LPG.

Lastly, I wonder if running mostly on LPG and effectively not using the fuel injectors except at first startup has allowed them to get cruddy / gummed up ? An injector / fuel clearner (BG44k or somesuch) is on order.

Any help and advice appreciated. All my searches have fundamentally pointed to o2 sensors or clogged air air filters - my O2 are new.

Cheers - JB
I take it this is a UK MOT failure?

Mine failed emissions about 18 months ago because a corroded front cat was leaking and not getting up to temperature.

This meant that the O2 sensor (no rear O2 on UK spec trucks) correctly controlled the fuel delivery in open or closed loop, it ran just fine. However, the 'sniffer' being shoved up my tailpipe (ooo, matron) was giving a faulty reading. Repaired the exhaust and passed on the retest. I altered nothing else to get it through emissions testing.

I disabled my EGR many months ago and recently passed MOT and emissions no problemo!


EDIT - Just thought your '93 will be a 3FE ? Correct? I'd still closley check your exhausts.
What does disabling the EGR do and how does it affect driveability?
Yup, Uk emission, petrol, 1FZFE (jap import), no cats (has pipes) - been that way for years. Exhuast is basically in good shape (sence I welded / patched the holes ;) )

Car running on petrol.

I'm thinking the PAIR may have been masking the problem...(your's doesn't even have such a system)

EGR - just didn't like the idea of all that crap going into the engine - the NOX readings on this test were basically nil (although running rich would probably have helped). Throttle response seemed a tad better, but may have been placebo.
What does disabling the EGR do and how does it affect driveability?

Disabling the EGR prevents the partial feed of exhaust gases back into the intake manifold. Not a great design by Mr. T since almost all the feed goes into cylinder no. 6.

Disabling the EGR may lead to higher NOX readings. If you don't have an emissions test that looks at that parameter then no problem.

Driveability? Didn't notice any difference at all


JLBUK - then I'm not sure what to suggest other than a full sevice, all consumables and get that injector cleaner in there. After that, ? not sure, maybe get it into a garage and get it checked over and tuned up.
Well I've discovered the problem.. they did a cat test (0.3% C0 limit), instead of a non-cat test (3.5% CO limit).

So mine running at 0.5% was actually really good!

Now to convince them that it was imported as a non-cat - the fact that the pipes are solid rust should help !

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