O2 sensor question...

[Chriskaw440]

Hello again, first of all, I took the advice on ordering suspension parts (control arm bushings) from ROCK AUTO PARTS and all I can say is THEY ROCK! great service, prices and fast shipping....I live in SC and every order I placed arrived in about 2 days time. Thanks for the tips! although replacing the actual busings in the control arms (rear end) is a bit of a bitch...I got it done, having to cut out the old ones and then grind the inner sleeves of the arms a bit larger for the new ones to slid into place using 2" diameter wire brushes and drill....and some drum sanding drill bits. Had to use a sawz-all to cut the metal sleeves of the old bushings out of the arms....they wont come out by sheer force or pounding! (at least not on a 1990 year pathy.) just cutting the metal sleeve of the bushing of course, not through the end of the arm.

 

Ok my O2 sensor question....my ECU has always shown the flashing code for bad knock sensor, but the engine still runs fun and I am told by the mechanics that verified the code that its running basically at a "base-line" mode, at least until the knock sensor is replaced....but they said since its still running great...dont worry about it!! it's about $1000.00 to do in any shop, unless I do it myself. So for now...it stays as is. My O2 sensor has NEVER been replaced far as I can tell, and since the computer has the engine running at a static mode (or base-line), will replacing the sensor even matter as its maybe not being recognized anyway?? I unplugged it at the harness in the engine compartment and ran it like that for a couple of days to no noticable difference in operation or performance, so I reconnected it.

 

so, with the ECU is baseline, is it going to recognize a new 02 sensor? I'm not sure how it all coincides and since a new one is about 100 bucks, I don't want to waste the $$ if its not going to matter anyway until the knock sensor is replaced and the code cleared.

 

234,000+ miles and still going great!

 

thanks, Chris Racine

[88pathoffroad]

What year and engine? A knock sensor error code won't cause the ECU to run in open-loop mode.

[Chriskaw440]

Hi,

 

It's a 1990 SE (VG30E)

 

Heck some Nissan Dealerships I called about the knock sensor told me my vehicle didn't have one....thank you goodbye! Duhh....in some parts of the country these models did have them, and some did not. They were just too lazy to know their stuff I guess. (even after I told them the ECU is flashing the code, they still said, our info tells us that it doesnt have one....sorry.)

 

Anyhoo.... I am not that knowledgable with how the ECU will operate or control the engine with that error code. Two places told me about it just running in "loop mode" and to just let it be, unless it starts running badly, then it would be time to get it corrected. The engine runs so good, especially now since I just did a tune up on it this weekend with new plugs, cap and rotor, etc..... smooth as silk, even with 234,000 miles on it.

 

I cant put anything less that premium gas (92 - 93 octane) in it or it knocks of course but I dont mind because I still believe the higher octane is better for the engine anyway. Otherwise, I get about 350 highway miles to a tank of gas, about 300 +/- miles around town driving per tank.

 

The 02 sensor looks like its been on the exhaust pipe since day one...and I have no records from whoever owned it before me 5 years ago. Its an easy thing to replace of course.

 

SO on that year and model, is the ECU in loop mode or still doing what it should be and regulating everything else?

 

thanks for any info and suggestions. -Chris

[88pathoffroad]

If your timing is adjusted properly and everything else is in working order, 87 octane should be fine in it. Using higher octane gas is neither "better for the engine" or easier on your wallet. If the knock sensor is shorted completely and giving the ECU the signal that it's constantly under heavy knock, it would retard timing for you and not ping anyway.

 

Try unplugging the knock sensor wiring?

 

The proper term for the "loop mode" thing is either "open-loop mode" or "closed-loop mode". In open loop mode, the ECU relies on a pre-set map of values for the engine to run on. Very baseline, not adapted for fuel economy or power. It will simply keep the engine running and not change the preset values according to any sensors. The engine runs in open-loop mode at idle, at full throttle, and at several other pre-determined points, depending on the input it recieves from all the sensors.

 

Closed loop mode is where the pre-set map is not used and the ECU instead relies on input from many sensors on the engine to tell it where the crank/cams are, where the ignition timing is/should be, how much throttle is being given, how much fuel is needed and how fast the engine AND drivetrain are moving.

 

As you can see, it is a necessity for all the appropriate sensors to be completely functional for the engine to run right all the time with 100% efficiency. Troubleshooting is the hard part...

[Chriskaw440]

Thanks for the info! I think I will start going through the system and replace the worn sensors (02) I'll have to see where the knock sensor wire connector is, and since the sensor is smack dab in the middle of the block under the intake manifold...It might be hard to reach the wire but I will check the wiring diagram and see where it goes....and if possible, unplug it and see what happens. Timing and all should be fine as a new belt and water pump were put on it by Nissan just about 2 years ago and I have hardly put any miles on it since then, as I work from home and don't travel a whole lot...we use the wife's vehicle when we do take trips

 

I also discovered a cracked vacuum hose at the very back of the plenum and replaced it (when I did the plugs, cap and rotor last weekend) and of course that made a noticible difference in idle...much smoother.

 

Sincerely, Chris