This happens on a car that I am looking at buying and want to know if it sounds like just the O2 sensor is failing, or if there are bigger problems...

He says when he is cruising at highway speeds 70+ mph the CEL comes on, and ONLY at these speeds does it come on, and it consitantly comes on at these speeds. He read the code as an O2 sensor code.

Does the O2 just need to be replaced or are there A/F or Ignition problems hidden behind this??

Thanks

Matt

 

Might be a problem with the catalytic convertor. Running too rich and too lean will typically throw their own codes...at least on an OBD-II. Is it OBD-II or I or 0?

 

Its a 91 Integra, i think the O2 sensor is before the cat on it, so I think that rules that out.

The reason i am asking this is to know if its a problem with the car that may cost me money later, I just hope that its not running to rick/lean for any reason, I hope its just the O2 sensor going bad, but it doenst sound like it since it only happens at one speed...

Anyone have any ideas?

 

You can pull the plugs and check to see if it's running too rich or lean.

 

I assume you mean spark plugs right? at first i thought you meant the wires on the O2...

I know that if it is black that would be if it was running too rich, what are the signs of lean-ness?

Also I am going to have it taken in for an inspection, would they be able to plug somthing up the tailpipe and tell me the A/F ratio?? If there is such a test let me know so i can have it done.

This is a mystery to me since it only happens at one speed...does it just sound like a fouled O2??

Thanks for the help

Matt

 

Yes, the spark plugs, sorry. You can tell if its too lean by a white powder on the plug. You might also pull the connector for the O2 sensor and check it out. If there's black marks on either of it's faces it's a pretty good indication you need to change something (arcing between the electrodes of the connector... it's less likely than just a bad sensor, but worth the two minute check).
When you take it in for inspection, you can take it to an exhaust shop and have them stick a four-gas sensor in the tailpipe. That'll tell you the fuel ratio, as well as a number of other things. It's a good test for fifty bucks.

 

I just talked to him about this, and he says its throwing a code 43, which is a generic fuel system code. He also said it did this same thing before the motor was swapped, so the only 2 fuel parts that are the same are the fuel pump and this O2 sensor. He said that everyone he talked to about the code 43 told him it was the O2. The CEL goes away if he turns the car off and back on again...

So sounds like it is the O2 sensor just going out if it happened before the motor swap also (done about 40,000 miles ago)

Thanks for your help

 

If you're paying a lot of money for the car, you could always just make him change the sensor out before he sells it to you. They aren't that expensive, and take about 10 minutes to change out. Then you'll know for sure and won't have any lingering worries.

 

Just a little note on spark plugs, this site is helpful in reading them: http://www.dansmc.com/spark_plugs/sp...s_catalog.html

 

Here is the troubleshooting guide from my '93 Integra Helms manual for a code 43. The wiring may not be identical to your car but it should give you an idea of what to do.