Hi,

Im having a poor mileage on my RVR 4G63 93 model and read that it might be the O2 sensor so I tried reading the voltage of the O2 sensor thru the pin in ECU. The reading I have is 0.91 V (warm/cold engine) which means Im running rich. I tried revving upto 4000 rpm (not running - P mode) and suddenly depress the pedal but the reading does not change.

Is my O2 sensor defective or it just my car getting rich mixture always (thus poor mileage)? If it reads rich (approx 1V), supposedly the ECU will make it leaner right? How come I still have poor mileage?

Please give me some advice.

BTW, I observe that when I drive my car for a long time without resetting the ECU (unplugging the negative terminal of the battery), the car stalls for sometime. However, if this happens, I just reset the ECU and I can run normally again.

I already changed the ff:
1. Fuel filter
2. Air filter cleaned
3. Engine oil changed
4. Spark plugs cleaned
5. ATF fluid changed
6. Re-timing the belt
7. Changed the ECU capacitors

Im using unleaded petroleum with 93 octane.

From your description I would say your O2 sensor is dead. It should change for different throttle settings and if it does not your ECU will run into a open loop mode meaning rich AF settings. Not sure if this would affect your engine dying senerio but it may be related (ie injectors getting clogged due to over rich supply).

I would start by getting a diagnostic test done to see what fault codes pop up. You may have some surprises which can dictate where you start.

Jim

Thanks for the inputs.

Unfortunately the Mitsubishi shop in our area cant read Japanese cars codes. I tried making my own OBD-1 cable but was not able to make it function. Any ideas on what cable and software that will function on this kind of vehicle?

The codes are not Japanese but digital flashes which indicate faults. Almost any garage should be able to download the codes and then you can look up what the resulting faults are.

If you cannot get the codes or interpert them I would suggest you replace the O2 sensor as from your test it is bad and then remove and clean each one of your engine electrical connectors in the engine bay. Common problem with Mitsi's is intermittant connector problems and you must clean, lightly sand with some emery cloth and then make sure they a positive connection to the female end. I slightly bent the pins in so that they made this connection.

Apart from this suggestion I would only be guessing at what to check & replace next. Start at the basics like spark plugs, leads and induction componets and then work your way from there.

Hope that this is of some help.

Jim

Thanks a lot Jim. Ill try removing the O2 sensor this week to look for a replacement. Hopefully I can get one locally. Otherwise, I need to order outside the country.

Ill keep you posted.

Jim,

I got my O2 sensor replaced with the one at the garage. When I measured the voltage again when in Neutral mode, it now varies from 0.1 (sudden release of accelerator) to 0.3 v (4000 rpm). Is this normal? Though I havent tried measuring the voltage when running. I will try it when I get a chance.

Regards,

Harry

Doesn't sound correct to me. Can only be checked while running and should vary between 0 and 2.5volts I believe. There is a whole test procedure for O2's that I've seen with other cars. Try to google it and find out the info first.

Jim

Can anybody give me the part number of O2 sensor 2-wired for 4g63 rvr 93 mdl?

Try looking at the attached links for stock and aftermarket part numbers. Their deals are pretty good but you may need to get someone to forward on from the States.

http://www.autopartswarehouse.com/

Jim