I have this puzzle still unsolved of higher than normal HC emission at 25 mph on a treadmill emissions test. Early 90’s Corolla. It has always passed, but just barely. LIke the HC limit is 150, and the car tests 149. Folks here have suggested it might be the valve clearance, the O2 sensor, or the cat. I plan to check those one by one. This isn’t an emergency, I have a year before the next test. I’d like to avoid the Calif DMV “Circle of Hades”; i.e Dept of Auto Repair.
But I noticed something interesting the other day. I noticed when going through the test results – year by year over a period of 20 years – that once in a while the HC would test like 35 instead of the usual 145-149. It would pass easily. Then I noticed the times it passed easily, I had the test done earlier than normal. Normally I have it done in mid-April, but on the times it passed, I had it done in mid-March. So I’m wondering if the gas blend changes in that time frame, from winter to summer blend, and the car will easily pass on winter gas. If so, I can just save up some winter gas and pour it into the tank before taking the car to the test. I think in the winter they may add more oxygen compounds to the gas, like ethanol.
So would running E85 for the next emissions test help reduce my car’s HC emisisons?
Your early 90’s Toyota will not run well on E85, as it is not programmed to recognize and utilize this fuel.Putting it in the car will cause it to run less efficient than it does now, causing the emissions numbers to go crazy. I guarantee you will not pass.
Usually with Toyota’s and just barely high HC’s, the culprit is usually a lazy O2 sensor. Way high HC’s can be the fuel pressure regulator or bad KVAM. BTW, all these can be tested for proper operation before spending money to replace them. Don’t count on the primitive ODB system to tell you if it is bad. When I got my '88 Supra with the same ODB system, and it never gave me a code to a non-functioning O2 sensor. It just stayed in ‘open loop’ mode, and sent my HC numbers just high enough to fail. Plus, I discovered after replacing it, losing 2 mpg on average.
Another thought. I think your car does run better on winter blend, which has less oxygenaters in it, more than just ethanol. Here in GA, you can get an emissions test done anytime of the year, and the results are considered valid for 12 months. Check and see if CA is similar. I’d just get the test done in Feb or early March before the summer blend is used, if that is the case.
On an early 90’s Corolla, I think you have a pair of wires next to the distributor that have an unused plug on the end that is capped off with a green cap. It may be somewhere else but check around the distributor.
Anyway, warm up the engine, then open the cap and insert your voltmeter probes into the two sockets of the plug, an analog voltmeter is the best on these. With the engine idling, the voltmeter needle should sweep back and forth every few seconds from about 0.2V to 0.7V. If its not doing that, then you need to replace the oxygen sensor. The O2 sensor is not monitored by the OBD1 system.
I think that you threw people off a bit when you asked about E85. E85 is 85% ethanol and 15% gasoline. I believe that you meant to ask about E10/E15 (10-15% ethanol), which is (since the banning of MTBE) traditional wintertime gasoline.
The Energy Independence and Security Act of 2007 requires that fuel producers must increase their use of renewable fuels every year through 2020. With few options available, that means ethanol. As of 2013, it is tough to find any gasoline that is not at least E10. In California, I don’t think you could find non-ethanol fuel if you tried.
If, therefore, it was the oxygenation that drove down your HC readings (possible), then current and future smog tests should go well for you.
I suspect, however, that it is more likely that it was the volatility of the wintertime fuel, measured as Reid Vapor Pressure (RVP), that helped drive down your HC emissions. Winter fuel has more butane dissolved in it than summer fuel does. Butane vaporized easily and burns well. If that was the case then yes, saving some wintertime gas in a can, or getting the smog check between November and March, may help you pass.
@Manolito … yes, you are absolutely correct, I misunderstood what the phrase “E85” means. I thought it was 85% gasoline, and 15% ethanol. But like you say, it is the reverse, 85% ethanol. I was refering to a 15% ethanol blend, E15 I guess. In any event it seems there is little to lose by doing the test when winter blend is available.
@Keith … re: O2 testing. There’s a small “check connector” in the engine relay area which I use to set a jumper when I set the ignition timing. Setting the jumper puts the ECM in open loop mode. I think the O2 sensor leads come in there too. I’ll check the schematics to verify. I’ll be sure to do that test you suggest. The O2 sensor has never been replaced in 200K and that is a pretty severe location for it to last 200K and 20 years without degrading. I thought the ECM monitored the O2 sensor and reported it as a CEL if it isn’t working, even in OBDI, but apparently not. That’s good info.
How long do O2 sensors last I wonder? Do they last the life of the car usually?
I think I understand now how to check the O2 sensor and the valve clearances. But I don’t know of a way to check the cat. Anybody have ideas how a driveway mechanic can check the cat? I’ve heard someone say that one test is to remove the O2 sensor before the cat (on this car there is only one, before the cat) and install a pressure guage. A high pressure indicates the cat is failing. Anyone use this to check a cat? Any other ways?
The car is not meant to use E15. Only cars built after 2001 can use it as a steady diet according to the EPA. But for a short time period, it should be OK. You will replace it with E10 withing a week or so anyway. BTW, if higher ethanol content actually works, make sure the gas you use really has nearly 15% ethanol. The sticker on the gas pumps in MD says E10 has “up to 10%”, implying it could be less - maybe substantially less.
Somone with another 90’s Corolla who had an HC problem during DMV required emissions testing told me that what they did, is they retarded the ignition timing by 3 degrees, just for the test. Instead of 10 Deg BTDC, they set it at 7 Deg BTDC. Apparently up to 3 degrees deviation from the manufacturer’s timing spec for the engine still passes. I’m not sure why retarding the timing would improve HC emissions though. You’d think advancing the timing would give the fuel more time to burn, so advancing would be the way to decrease HC. There must be other factors involved.
" I’m not sure why retarding the timing would improve HC emissions though"
I did the same thing with my '81 Accord with a Weber carburetor, cam, Japanese market head, and other modifications.
(I’ve read that) retarding the timing raises the exhaust temperature enough to allow burning to continue in the exhaust manifold.