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92 LS400 with 380k mile failed CA smog test with HC too high at 25 mph. HC already closed to Max when I purchased in 2005 with 238K miles. Major tuneup: replaced timing belt, idler, PCV, coolant, water pump ...
Please advise how to reduce HC. 92 LS400 smog check result. 92 LS400 smog check history
As I see the results, CO is also much higher than before although it's still within the spec. O2 is also much higher. These simply mean that the fuel is not burnt well enough. Slight miss firings or a minor vacuum leak may be happening. I'd check the ignition system and the vacuum leak.
Yamae, thanks for your suggestion. I will check both. Power steering lose fluid slowly. I plan to replace air control valve. Hope this is part of vacuum leak I need to fix.
My mechanic replaced power steering air control valve (vacuum leaks), 2 front oxygen sensor, and coolant temperature sensor. HC still too high
Compared earlier smog check, it seems got worse on 15mph.
Should I reset ECU after replacing these sensors?
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The NO while not out of range is also up there. NO and HC can be attributed to the EGR valve function too. Check those vacuum lines and that the EGR valve is not fouled with deposits.
Probably you need to use a good smoke machine to pinpoint the leaking point.
This is just an exapmple but one of high HC problems I have found the leaking source was the throttle valve's shaft. The O ring there was cracked. It was at a local Mitsubishi dealer. The manager there is a good friend of mine and he and his members have spent a whole day to find the cause of the high HC problem. Finally he asked me for a help thinking that the ECU was a culprit. But it was not the ECU. I found the leaking point using my home made smoke machine. Mechanics there already have checked the vacuum leak only using a can of parts cleaner but that was not enough. They didn't know about the smoke machine. I found it useful when I was working in the USA. In Japan, it is not well known.
Thanks for RA40 and Yamae's suggestion.
Idle speed jump from ~650 rpm to ~900 rpm after replacing O2 sensors and ECT sensor. Does this mean vacuum leak?
I add Toyota Red coolant without adding any water since I bought the car (2005), will this affect HC?
I connected home made smoke machine to air hose after removing AFM. Smoke comes out of EGR Vacuum Modulator.
Any other location I should connect to smoke machine to check?
EGR leaks: Leaks at the EGR valve may be detected during a vacuum leak test. If you observe smoke exiting from the valve’s seat, gasket or diaphragm, disconnect the EGR’s vacuum hose/line and push smoke directly into the EGR valve. This will help to determine if the valve seat or diaphragm is leaking. If you suspect that the EGR ports are clogged (common problem), you can remove the EGR valve (exposing the ports) and introduce smoke through the exhaust pipe (no or little smoke indicates plugged ports).
In order to test the EGR pintle shaft, the engine must be off, and don’t cap off any part of the engine. Introduce smoke through a direct manifold vacuum source (the power booster hose for example). Turn on the smoke machine tester and observe the EGR. If a noticeable amount of smoke exits the valve, cap off the intake and plug the exhaust pipe tip. Introduce smoke. A small amount of smoke indicates an acceptable EGR valve.
I passed smog check after replace MAF. I bought a new third party MAF, it does not work. Other 3rd party has similar structures. I do not want to try again. I bought used ones from ebay. It is pure luck. 2 out 3 does not work and show engine light.
There is web site test 90-94 MAF has detail information on how to check whether MAF is working.
Mine I noticed that the HC has been increasing over the years when getting it tested. At 15MPH it read 26 and at 25MPH was 31. That is 2 ticks below max acceptable readings. The rest of the smog readings were good.
05-31-20, 07:46 PM
92 LS400 HC too high
That chimes with this discussion: