failed emissions test

[mva5142]

My wifes 93 3.2 failed the emissions test here in houston. It failed the hydrocarbon portion of the test, the NOx and O was fine. It blew a radiator hose in october and overheated. I replaced the headgaskets and had the heads decked as they were slightly warped. After putting it back together I noticed that the gas mileage was much poorer than prior to the overheating. I am planning on replacing the plugs and air filter, and checking the timing. Any other ideas? Would overheating cause problems with the O2 sensor or anything else that might affect the HC test? Thanks in advance guys.

Also, the inspection place offered to do a diagnostic test for 45$, but if the CEL light is not on, would it tell me anything?

[rodeo02]

Hi hydrocarbons indicates it's running rich. Could be a bad O2 sensor, MAF sensor, the cat is shot, severely clogged air filter, old worn out sparkplugs (misfire). If she runs well, I would not suspect a valve timing issue or a misfire. Start by cleaning the MAF and replacing the O2 sensor. Replacing the cat would be next. Oh and make sure she's good and HOT before smog testing. Cats only work when they are HOT.
G/luck
Joel

[mva5142]

Thanks Rodeo02,

I'll check the sensors. Is there a way for a DIy to check the cat? The haynes book tells you how to check the sensors, but for the cat it just says take it somewhere. Is there a quick and dirty test to tell if it is working? Thnaks, I'll let you know how it turns out.

[rodeo02]

The only tests I've heard of for cats is, by measuring shell temperature with an infra red heat gun or by smog testing. A good cat should get hotter than the surrounding exhaust. This indicates the catalyst is doing it's thing by converting hydrocarbons into CO2 and water vapor If your 1993 is original, you can almost bet the cat and oxygen sensor are worn out.

Joel

[mva5142]

I replaced the O2 sensor about 50k miles ago with a borg warner, would overheating damage it at all? I wouldn't think it would because it is exposed to high temps anyway, but I've always heard that they are pretty fragile elements in there so who knows. I think the replacement on them was 90k miles, is that correct or way to long? The cat is original. I'll let you know how it turns out.

[mva5142]

After some research, Having a coolant leak in the combustion chamber can produce silicone which will kill the O2 sensor. Having a blownhead gasket and warper head this happened. I replaced the O2 sensor and put in a new air filter. I have to replace the spark plugs and clean the MAF sensor, but not sure where the MAF is?

Can someone tell me where the MAF is and how to clean it? It's a 93 3.2L. There are a couple sensors that go into the throttle body, is it one of these?

Thanks.

[rodeo02]

Yep, coolant will kill O2 sensors and can sour a cat. Your MAF is hose clamped inline on the hose between the airfilter box and the throttle body. It's a big cylinder shaped flow meter. Use extreme caution cleaning it as you can destroy the wire/sensor easily. Spray electrical cleaner and a gentle cotton swab usually does the trick.

Joel

[mva5142]

Well I finished it up last night, changed the oil and replaced the plugs it runs great, so I think it should pass.

I was unable to find the MAF. I removed the air filter box and hose that goes to the throttle body, but there is no meter there, and no wires or anything go to anywhere on the hose. Is it possible that the 93's didn't have one? Thanks.

I'm taking it for the test tomorrow I think, will let you all know how it goes.

[Muddskipper]

mva5142,

Have them do a pre-test before you do the test that downloads the info in the Texas States system.

I'm also in Houston and hav'nt had my inspection done in 2 years.

I'v been real lucky, not to get a ticket.

Good luck and let us know if what you did helped.

Skipp

[php1]

I also have a 93 and it does not have a MAF. It's also not shown on the electrical diagram in either of the two books I have for Isuzu's.

[lavichia]

what to do? I bought a 1990 Toyota 4runner from a private owner. I agreed to pay for the smog, but the smog did not pass 2 times. If the car dose not pass smog than is it illegal for the owners to sell that car.

[mva5142]

took it in this afternoon, and it passed with with flying colors. It runs great, now if i could talk my wife into keeping it instead of buying a minivan!

Thanks fo all you input. I appreciate it and hope to return the favor someday.

[JStubbe]

Can you list exactly what you did to make it pass?

[mva5142]

With the exception of the O2 sensor, it was all pretty cheap stuff. I replaced the O2 sensor with a bosch one from autozone, like 70$, put a new air filter in 13$, replaced all the spark plugs with autolite brand from autozone, 2$/each, changed oil and filter, and removed and cleaned the pcv valve, just sprayed it down with carb cleaner. The results from the first test was that everything was ok except hydrocarbons, the limit for those is 143 on the low speed test and 147 on the high speed test. When it failed, the hydrocarbons were over 600, around 640 I think for both tests. After I replaced the above items the hydrocarbons were 42 on the low speed and 81 on the high speed test. After I replaced the O2 sensor I disconnected hte battery and let it set for about 30 minutes while I changed the oil and replaced the plugs. When I connected it back up and took it for a drive the difference was incredible. More power and so far gas mileage has improved noticeably. Previously, before it overheated we were getting close to 20 mpg in it, after the O2 stopped working it dropped to like 14-15. After the repairs, it is back to pre-over-heating levels. It idles great and runs like a dream. I seriously think I could get another 100k miles out of it.

[JStubbe]

Thanks for the info. My 96 was getting close to HC limits, so I did pretty much the same things except I also replaced the cat. I passed before going after the O2 sensors, which I've now replaced.