I'm a newbie to the forum and hope to continue if i ever figure this yota out... Bought a 1993 4 runner (250kms on it) and need to do an e-test and PASS to put it on the road... it failed 2 times so far.

1st time the test was with old cat and muffler which failed NOppm. So, thinking the cat was the problem, we replaced the cat (which was much smaller than the original btw) and muffler (old muffler was not original, small and loud). 2nd time it failed again and the readings were way off to the other side of the scale... these are the results:

1st test: (@ 40km/h)

HC ppm: limit 52 / reading 16
CO%: limit 0.29 / reading 0.03
NO ppm: limit 0735 / reading 1429

2nd test: (@ 40km/h)

HC ppm: limit 52 / reading 172
CO%: limit 0.29 / reading 5.18
NO ppm: limit 0735 / reading 619

Another few notes... Between the 2 tests only thing changed was new sparc plugs & tightened up the pipe leading to the manifold.

Once the new cat was installed we took it to get tested (2nd test reading are listed above). Thinking the cat was the wrong one i called the parts store and they said i need to 'initialize the cat' by driving 200+k to break it in. After putting some 50k on it the 'check engine' light came on and off again twice since driving it 300k in total. Took it back a 3rd time (today) and it failed again with results same to 2nd test...

Please help.

 

Update: Ok we found a hose disconnected leading to the EGR valve so did another test and the NOppms went down great but the other two are still high:

HCppm: 241
CO%: 6.54
NOppm: 103

Had them do a quick diag and they concluded it is not going into 'closed loop' mode and staying in 'open loop'. Anyone have experience with this?

Thanks

Pat

 

check ur thermastate

 

Thanks Garth, i'll try removing it and testing it based on the service manual inspection instructions. After doing some research, i found this problem would cause the ecu to not get data from the O2 sensor, which might explain the high hc and co% delivering the unburnt fuel.

Will post a reply with results.

 

Another thing you might consider replacing are the 02 sensors. If there original its a good chance that there no longer functioning properly.

 

There's only one O2 sensor in front of the cat and it looks as though it's been replaced since original and seems to be working, would it not show a chk engine light if it were not working? I'm not sure but that's what my old man seems to think...

We took it off to inspect it and a part of the exhaust came with it due to corrosion so we had to weld another patch piece with a braket to re-install it. I guess we'll need to change the front exhaust piece if we put a new one though. We'll see what happens first with the thermostat but the O2 sensor might be the next thing to look at. Besides the visual inspection can it be troubleshooted or do you have to replace it to find out?

 

The FSM hast a quick test procedure for the O2 sensor. Basically it is heat engine up, run @ 2500 RPM and measure O2 sensor voltage changes, looking for about about 1 swing from ~0 volts to 1 volt per second. You'll need an analog meter or a very good digital meter to catch the fast changes. And the ECU will set a code if the sensor heater is dead (on a heated sensor) or sometimes if the sensor reads too rich or too lean when the ECU thinks it should not. But in between those extremes, the sensor can respond slowly or inaccurately and the ECU will not pick that up.

I hooked up an air/fuel meter on my dash and can see when the ECU is in closed loop mode by the cycling of the needle on the meter:
- http://www.4crawler.com/4x4/CheapTri...FuelRatioGauge

 

Checked the Thermostat - ok
Checked the O2 Sensor - bad, only 2ohm resistance (fsm says it should be between 5-7ohm)
Replaced O2 Sensor and went for 6th test & PASSED!!! Yeah! =D so happy!

These were the readings:

HCppm: 24
CO%: 0.00 !!!
NOppm: 0 !!!

I can't believe the difference, now for the replacement of all the control arms we should past safety =P

Thanks for everyones help, really appreciate it.
,
Pat