S-10 02 sensor testing....???

["Turbo-T"]

Here goes...I have a 93 S-10, 2.8 liter V6 engine, 5 speed trans, 2WD.

The 02 sensor wire managed to mate up with the passenger side exhaust manifold and as a result the SES light come on. The wire burned in half before the plug. The code in the ECM was code 13.

So I reconnected the plug to the wire with a new piece of wire. Then i replaced the 02 sensor. At first I didn't disconnect the batt like I should have, so the code was in the ECM and the SES would occasionally come on and go out.

So one day I unhooked the batt neg side and let the truck sit for 24 hrs with no juice.

Hooked it back up and checked the ECM...no codes stored. (got a code 12...let it run thru the cycle)

Well now the SES light comes on again. It usually seems to come on if the truck is ran down a long stretch of highway. It will come on and stay on 1-2 minutes and go out again.

Recheck the codes...code 13 is in the ECM again.

On top of that, the mpg seems to have gone down from 20-26 to 15-17.

I want to unplug the 02 sensor and take a reading....can I do that? If so, what should it read? Where should I set my multi meter at?

What else should I check for?

Thanks.

 

[DailyDrifter]

Set DVOM to millivolts and tap into the wire with a T pin or some type of backprobe. I would leave it connected and look for oscilating voltage. Is the truck misfiring? Those 2.8's are beast's , I'm suprised it doesnt have a knock yet.

 

["Turbo-T"]

Thanks....also not sure which setting on my meter is millivolts...remind where the decimal is? :redface:

 

[DailyDrifter]

Thanks....also not sure which setting on my meter is millivolts...remind where the decimal is? :redface:

I forget myself :redface: My meter has an autoscaling feature. I think you move the decimal 6 spots to the left. .000001v or maybe 3 spots

 

["Turbo-T"]

I will check. No the truck is not misfiring, but it is running a little rich and not getting as good of MPG as it should. It still drives fine, just only averaging 15-17 mpg when it should get 20-26. Why would it be knocking??

 

[DailyDrifter]

2.8's are very well known for rod bearings going bad. I had an 88 Camaro that had a rod knock. How many miles are on it?

 

["Turbo-T"]

You might be thinking of the earlier 2.8's....

The 2.8's before 1986 were known for throwing rods and breaking cranks and assorted engine problems.

1986 they finally beefed up the bottom end of the 2.8 for the upcoming fuel injection set up.

My 2.8 had 182,000 original miles on it, and it's seen 6000 rpms before. I've kept the oil changed every 3k miles but have been sort of unmerciful to it. But never once has it given up on me.

 

[DailyDrifter]

I asked my parents if I could put a 350 in after the engine blows up, they didnt have a problem with it, but I beat the hell outta that thing and couldnt get it to blow But I did feel the power decline considerably (not thats much there to begin with )

Anyways did you solder the new wire in? Sounds like the ecm isnt seeing the correct o2 voltage. IF the ecu is seeing that it will probably default to a rich setting so it doesnt lean out. I would double check the connection of the repaired wire, I'm not doubting your abilities but I dont think the ecm is seeing the correct o2 signal. You could also have someone sit in the driver seat and you can wiggle the wire around and see if the SES comes on or not.

 

["Turbo-T"]

I did solder the new wire in. I just did have someone tell me that's a bad bad thing....and I thought soldering wires together was the best....better than solderless crimp terminals......

 

[TURBOTWIN2]

Is this a one wire O2 sensor? Which part of the wire was melted by the exhaust, sensor side or harness side?
On a one wire oxygen sensor, you can unplug it from the harness, run the engine up to operating tempature (2-5 minutes)and read the output directly with a voltmeter on low scale. You should be seeing less than 1 volt. It will vary on either side of .45 volts, i.e. switching between .1 to .9 volts. You will probably .3 then .8 then .2 then .6, etc. Above .45v is rich condition and below .45v is lean condition. It should be CONSTANTLY switching. Let us know what you find out. HTH.

 

[DailyDrifter]

The solder may be messing it up. If it has more resistance in it the ecu may be seeing a lean condition and makeing the mixture richer.

 

["Turbo-T"]

Is this a one wire O2 sensor? Which part of the wire was melted by the exhaust, sensor side or harness side?
On a one wire oxygen sensor, you can unplug it from the harness, run the engine up to operating tempature (2-5 minutes)and read the output directly with a voltmeter on low scale. You should be seeing less than 1 volt. It will vary on either side of .45 volts, i.e. switching between .1 to .9 volts. You will probably .3 then .8 then .2 then .6, etc. Above .45v is rich condition and below .45v is lean condition. It should be CONSTANTLY switching. Let us know what you find out. HTH.

Yes it is a 1 wire sensor. The part of the wire before the female plug for the male plug to the sensor was burned on the exhaust. So...harness side.

I will definitely try what you just said. Just waiting on the weather to warm up.

 

["Turbo-T"]

Well I managed to do some testing, and it's wierd....

Hooked up my multimeter and set it to the 0.00 position.

Started the engine. It had been sitting maybe 20 minutes after being ran at full temp.

The temp on the gauge was like maybe 140....

Got a reading of .84 on the meter. Also the engine idle would go down and come up.

Finally the engine temp gauge read 200. Got a reading of .23-.25. Revved it a few times and it shot up to .38 and that was it.

 

[TURBOTWIN2]

If I'm reading right, that's a dead sensor. You did disconnect the sensor from the connector back to the car's wiring, correct?
Also, what got burned, part of the wire of the senssor or part of the wire to the car's wiring. If it's just the pigtail part of the sensor, replace the sensor and be done with it. HTH.

 

["Turbo-T"]

I took the readings with the sensor still hooked up.

The cars wiring up to the pigtail is what got burned. I replaced all that and just went ahead and replaced the sensor too.

 

["Turbo-T"]

Well, here's an update...

I went ahead and replaced the 02 sensor with a Bosch p/n 12014. Then undid the batt terminal on the neg side for an hour. Code erased.

I also replaced the wire that I originally soldered on. This time I twisted the bare wire ends together and used solderless caps on the ends. So no more solder on the wires.

This morning letting the engine idle it ran fine when in the open loop mode. As soon as closed loop kicked in, the engine rpm would decrease, then increase, then decrease, then increase.....sort of like a slow surge.

Got in the truck and drove it 100 feet to the stop sign when the dang SES light came on again.

So now I don't know what happened. I don't know if the ECM is going bad. I don't know if I am getting a bad batch of 02 sensors. I do know I am tired of not getting the usual 19 mpg on a 2.8 liter V6. Last tank I calculated I only got 12.5 mpg to the gallon. This is not good.

Too bad I don't have the cash or I'd V8 the thing, at least then I'd have a good reason to only get 12 mpg.