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Hi! I have a US market 1995 200SX (SE-R) with about 148K mi. Over the course of the past year, milage has been slowly dropping (from 27 to 22 mpg). Now, when I brought it in for inspection, it failed emissions due to high HC (it literally pegged the machine). Eventually I was able to get it to pass (once) but it still seems to run rich. So far, I've ruled out the following causes due to replacement of parts: MAF, O2 sensor (the one in the exhaust manifold), coolant temp sensor, timing, plugs/cap/wires/rotor, ECU, and timing. So I am stuck with a (probably) intermittantly rich running engine that doesn't respond to any of my fixes. The only check engine light I have gotten is a flashing check engine light that I was told is the cat overheating trying to break down all the emissions. I was wondering if anyone had similar problems with a US market SR20DE. BTW, the engine and emissions equipment are completely stock. Thanks.
 

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run lower octane fuel and see if that helps. for some reason you seem like the kind of person who runs premium ( dont get me wrong, that stuff is good for cars), but premium burns SLOW, and if you have HC's coming out then you'll want a faster burning fuel, IE 87 octane.

you might also want to check some junk on the fuel system, specifically the injectors. if they are not operating correctly they could be squirting gas(as a liquid) instead of misting it(as a vapor). liquid gas does not burn and that could cause high HC.

seems like you've got everything else covered though, so see about those.
 

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bcubed said:
The only check engine light I have gotten is a flashing check engine light that I was told is the cat overheating trying to break down all the emissions.
According to the Factory Service Manual a blinking MIL is due to a misfire (P0300-P0304) which can cause catalytic converter damage.

You can retrieve the code even though the Check Engine light is not lit since the ECU stores all codes.

Possible causes for these codes is:
1. Improper spark plug
2. Insufficient compression
3. Incorrect fuel pressure
4. EGR valve
5. Injector circuit is open or shorted
6. Intake air leak
7. Ignition secondary circuit is open or shorted
8. Lack of fuel
9. Magnetized flywheel or drive plate (A/T)

The easy ones to fix are 1 (replace spark plugs), 6 (it will be a big leak to cause a misfire), and 7 (replace spark plug wires, rotor and distributor cap).
[1 and 7 are the most common causes]

With 2, 5, 8, and 9 the engine will run poorly.

Examine the spark plugs. If one or more cylinders is running lean (due to an air leak, bad injector, or lack of fuel) they will be white and blistered.

If one or more cylinders is running rich (due to defective injector or intermittent no spark) the plug will be black, sooty, and possibly wet with gas.

Lew
 
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