Toyot Previa Emissions,1996,2.4 Petrol

November 2, 2007

Can any one HELP?hi,i have a 2.4,1996 Toyota Previa,Auto,after owning the vehicle for a few months i have serviced it and recently had it checked out at a auto diagnostic centre to see if everything was running ok,i have a problem with the CO level.

Fast Idle, at engine speed 2543,i'm getting a reading of 0.91%(max0.30)

at Second Fast Idle,engine speed 2822,i'm getting 0.97%.

no diagnostic faults showing,new catlytic converter,front lambda sensor,plugs,oil,oil filter,air filter.the previa has a lpg system fitted but not connected(was working).

after hours of fault finding by the guy that checked the tune up his thoughts were that the ecu might have condition its self to reading the lpg emission and now the ecu was over riching the fuel injectors causing the high CO reading to be high?

i was going to relace the airflow meter and ecu to see if this would cure the problem as i,m now at a stumbling block.i would gratefully appreciate anybody with any suggestions to my problem,cheers,thanks.

November 11, 2007

ECU's have no adaptive intelligence. They respond to signals generated by various sensors and correlate these against preprogrammed variables.

In an instance like this you need to systematically go through the system to establish what is wrong. e.g.

Check for blocked filters

Vaccum leaks

Dirty/misfunctioning injectors

Low compression

Bad/faulty sensors

Trouble codes on the ECU

Faulty catalytic converter

NOTE CO = Carbon monoxide. The job of the catalytic converter is to convert CO to CO2 (carbon dioxide) I would start with the catalyst and the O2 sensors as clearly the job is not getting done. In order for the Catalyst to perform optimally it needs to have the correct conditions which are monitored by the O2 sensors and managed by the ECU. If you have an O2 sensor problem you should be getting a code 22 or 25 from the ECU if none then again I suggest the Catalyst maybe kaput.

I realise you have already changed the Catalyst but this does NOt mean that it is working. Also have it verified by another workshop. Your mechanics equipment may be out of calibration. Also juts because the ECU is not showing does not mean there is not a code in there. Have the ECU read out checked again to ensure there are no stored fault codes

I have no idea how good your mechanic is but my advice is always find an old school mechanic who still knows how to trouble shoot WITHOUT the need of a computer.

December 2, 2007

Ronaldo

I run a duel fuel 2.4 Previa... After she's been running on LPG for a while, she HATES petrol... I've been told that the LPG produces an oily residue that coats the O2 sensors, preventing the lamba system from operating correctly... After a few miles, this will burn off and the car runs normally on petrol again...

Other than that, I know of no other detrimental effects from running on LPG (Mine has 198K on the clock, so I don't think that valve recession is an issue on the Toyotas either...)

Doesn't a 1996 Previa have a maximum CO% of 3.5% on the MOT test..? I realise you might not be getting as good a fuel economy as is possible, or being as kind to the planet either, but buying a new ECU and air-flow mwter will soon put you off the Previa... I anticpate a 4-figure bill for those 2 items..!!

Miti

December 3, 2007

Very few cars WITHOUT a Catalyst have a pass value of 3.5%!!!! The Previa has a Catalyst and therefore must conform to a minimum CO of between 0.3 - 0.5%.

DO NOT just go out and buy parts without AS I SUGGESTED IN MY EARLIER POST getting the car checked at another site and have someone, (TOYOTA might be a good idea) analyse the car properly to identify the failed item.

Run it on a few tanks of Petrol first and then take it for the test and see if there is a difference.

December 4, 2007

ECU's have no adaptive intelligence. They respond to signals generated by various sensors and correlate these against preprogrammed variables.
In an instance like this you need to systematically go through the system to establish what is wrong. e.g.
Check for blocked filters
Vaccum leaks
Dirty/misfunctioning injectors
Low compression
Bad/faulty sensors
Trouble codes on the ECU
Faulty catalytic converter
NOTE CO = Carbon monoxide. The job of the catalytic converter is to convert CO to CO2 (carbon dioxide) I would start with the catalyst and the O2 sensors as clearly the job is not getting done. In order for the Catalyst to perform optimally it needs to have the correct conditions which are monitored by the O2 sensors and managed by the ECU. If you have an O2 sensor problem you should be getting a code 22 or 25 from the ECU if none then again I suggest the Catalyst maybe kaput.
I realise you have already changed the Catalyst but this does NOt mean that it is working. Also have it verified by another workshop. Your mechanics equipment may be out of calibration. Also juts because the ECU is not showing does not mean there is not a code in there. Have the ECU read out checked again to ensure there are no stored fault codes
I have no idea how good your mechanic is but my advice is always find an old school mechanic who still knows how to trouble shoot WITHOUT the need of a computer.