Voltage reading at OBD port

[Mercury]

Hello, all!

I'm curious what voltage an OBD scanner should read. I know with a DMM I should see about 13.5 to 14, but at the moment I'm far away from my tools. Last night I was averaging 12.9 while on the interstate, down to 12.6 while at idle. My battery is about toast and I'm replacing it soon, starting to wonder if it and a sick alternator are causing my rough idle and stalling.

 

[Jerry Bransford]

12.6 is what you'll see from a fully charged wet cell battery without the engine running, 12.9v while driving sounds about right which just shows the little boost it's getting from the alternator. AGM batteries will show 12.8 volts when fully charged without the engine running.

 

[Mercury]

12.6 is what you'll see from a fully charged wet cell battery without the engine running, 12.9v while driving sounds about right which just shows the little boost it's getting from the alternator. AGM batteries will show 12.8 volts when fully charged without the engine running.

Okay, good, I didn't want to replace the alternator this month so that helps, thank you. Though now I'm left wondering where this rough idle/stalling issue is coming from.

 

[Jerry Bransford]

Though now I'm left wondering where this rough idle/stalling issue is coming from.

Does that happen both when the engine is cold and after it has warmed up, or just after it has started to warm up?

 

[Mercury]

Does that happen both when the engine is cold and after it has warmed up, or just after it has started to warm up?

I noticed it Friday, and it was after I had been driving for two hours on the interstate. I was at a long stop light and after about twenty seconds it the RPMs started to drop, bounce up, drop, struggle, and it tried to stall. I hit the gas and it fired up and I got through the light.

I tested it last night after it was plenty warm after getting some gas. Idled fine for about a minute, then same thing with the RPMs and stalling.

I ran my scanner and it showed bank one sensor two, which is strange because I replaced both O2 sensors a month or two ago. Used either NTK or NGK, can't remember which, and they were the correct part numbers I pulled off the recommended equipment list.

I can test the issue while cold if I need to.

 

[Mercury]

Started cold, idling rough. Kind of hiccuping. No massive RPM drops, no stalling so far. Put it in first gear without hitting the gas and drove it for about a hundred feet just to see if the extra pressure would stall it and so far everything is fine.

 

[Jerry Bransford]

Try cleaning your Idle Air Control module with some aerosol throttle body cleaner. Start the engine and keep it at idle rpms while you spray the TB cleaner into the throttle body. The cleaner will get sucked into the IAC and fill it up so the engine will die which is normal, just restart the engine and do it again and again until 1/3 of the can has gone through the IAC. Don't raise the engine rpms to prevent the engine from dying, the TB cleaner will only get sucked through the IAC and its air passages inside the throttle body at idle rpms. The IAC is what provides ALL of the engine's air at idle rpms. Remove the air intake tube from the top of the throttle body, you only need a philips head screwdriver to do that.

Don't remove the IAC to clean it. Doing it as recommended above will also clean the IAC's air passageways that are part of/inside the throttle body.

 

[Mercury]

Try cleaning your Idle Air Control module with some aerosol throttle body cleaner. Start the engine and keep it at idle rpms while you spray the TB cleaner into the throttle body. The cleaner will get sucked into the IAC and fill it up so the engine will die which is normal, just restart the engine and do it again and again until 1/3 of the can has gone through the IAC. Don't raise the engine rpms to prevent the engine from dying, the TB cleaner will only get sucked through the IAC and its air passages inside the throttle body at idle rpms. The IAC is what provides ALL of the engine's air at idle rpms. Remove the air intake tube from the top of the throttle body, you only need a philips head screwdriver to do that.

Don't remove the IAC to clean it. Doing it as recommended above will also clean the IAC's air passageways that are part of/inside the throttle body.
View attachment 408907

Funny enough I did this a few weeks ago. I saw a post of yours in an old thread and decided to do it as some preventative maintenance. It did run smoother after doing it.

Did the whole process including letting it die a few times and then revving the engine and emptying the second half of the can.