1992 240sx coupe, unstable idle, hesitation, loss of power, and bad gas mileage

[skydragoness]

Help me out on this one. This has me super confused, and while my bf used to be a tech at Nissan he can't figure it out either. We just bought an ECU interface cable and Nissan Datascan software, I tried it out this morning.

Anyway, here's a rundown of what's going on.

Car has been running fine, plenty o' pep, however when I took it in to the DMV for what i thought would be a routine tailpipe test and get my sticker and leave. It FAILED. It failed low idle, but passed high idle.

HC: Low idle: 248 (limit 220)High idle: 108 (limit 220)CO: low idle: 1.9 (limit 1.20)high idle: 0.33 (limit 1.20)

Took it to the bf's shop where they have a tailpipe emissions tester. It was running super rich. (don't have the exact numbers from that machine, since it didn't do print outs). I pointed out that the 02 sensor wiring's shroud melted in 3 places due to it touching my header. He wasn't getting a reading on his ohmmeter from the 02 sensor so I got a new one (Bosch of coures) w/ new wiring and we put it in and tested it again later that week. STILL running rich.

The timing was around 15 degrees at idle, so he adjusted it up to 20..however he mentioned it was maxed out on the distributor (like he could barely adjust it anymore than that). Now the car hesistates/bucks and backfires thru the exhaust between 1500 and 2500rpm. And certainly felt like it had no power at all, i mean, a corolla could probably kick my *** right about now. The idle changed too, it actually went higher. Now it idles around 950 or so, and sometimes if I sit at a light long enough, it will start flucuating and drops down to 400 then back up again, usually several times.

So we suspected the knock sensor after reading some accounts similar to mine I got one, we put it in. NO CHANGE. The only change was the timing changed and he was able to adjust the distributor w/ more room now.

Soo.. i have no idea what to do. We get the software+usb cable, and I hooked it up today and started my car. I'm not good any gleaning what the numbers mean, but I noticed the timing at idle (after the car was already warmed up) was at 12!! O_O The longer I sat there letting it idle, it started to do it's backfiring thing and I noticed the timing started spiking up and down on the data log graph.Also the A/F ration was 'rich' at idle too. I also switched out the MAF for another I found. No change, although the timing is more steady it seems.

If anyone has the nissan datascan software I can send the log i recorded of it idling.

I'm pissed, someone help!

[MaximA32]

Check your TPS(Throttle POsition Sensor). I'd also check the throttle sensor ground splice. It's located near the cylinder 1 injector lead, in the harness, nxt to the valve cover. Should be black in color and the ground wires lead to pins 21 and 29 at the ECM connector. That splice also connects ground wires for the engine temp sensor and the EGR temp sensor.

[skydragoness]

Thanks. We'll try it this weekend. I hope it's something just stupid easy/obvious.

[thomasjamal]

any luck?

[Scudmuffin]

Wow thanks for the explanation!!! it actually makes a lot of sence!!! i had EGR problems code 32 for months!!! then my TPS code 43 came on!!! and since you said that they are related and have same grounding splice i think i just found out what that problem is!!!! Thanks a bunch!!!

[skydragoness]

I guess I should update this for anyone who searches for a problem similar to mine.

To sum it up short, it was a bad 02 sensor.. that went bad last year, but the ECU went into a learn mode and covered up any symptoms of a bad 02 sensor very well (no power loss, and it retarded it about 5 degrees so no real noticeable difference). It wasn't until I went to the DMV for what I thought would be a routine tailpipe pass, that i realized there was a problem.

So I replaced the 02 sensor since everything else was fine because the wiring did melt in two places and caused the sensor to ground out (initial problem to cause it to run rich, thus burning up the 02 sensor).

The problem didn't correct itself w/ the new Bosch 02 sensor and even after fixing the timing. My bf no longer was working at Nissan as this point and no access to the Nissan Consult diagnostic computer. The ECU kept retarding the timing even after he changed it back to stock. The car kept running worse..

so I bought the Nissan Datascan (consult copy) from our sponsor (blazt-something), figured it out, hooked the car up one day, and used the set timing mode in the software. It took 4-5 tries to make the ECU accept the new values. It finally did and it was running much much better, more power, etc..however at this point the new 02 sensor burned out in two weeks (bosch sucks btw) and it was still hesitating. So I bought another one, this time a Denso 02 Sensor (direct-fit and only $22ish at rockauto.com) and the hesitation went away. We checked it a few more times after that, and I decided it was time to try the inspection lane again.

It passed with absolutely flying colors! My car did a .36 and .47 for Hydrocarbons (compare with what it did in my first post!) .... eat that Honda!

So yeah, once the ECU goes into a learn mode you have actually force the new timing values into it w/ the 'set timing mode' via the diagnostic software.. there's no other way.
Modified by skydragoness at 6:58 PM 5/8/2008

[topless_240]

where did you get the software?

[skydragoness]

Sheesh holy old thread revival...Read the fifth paragraph and you'll find out. It's only on the right side of the screen too.

[topless_240]

oh gotcha..lol
Modified by WATERSxCORE at 4:23 PM 5/8/2008

[ohvictor]

i know its an old thread but after all the testing how did you come up with having to rest the values? just wondering, cause it seems having the same problem it seems, my o2 wire metled didnt notice till my gas mileage took a dump, and i started running rich, replaced my o2 but im still running rich.

[abc123omg]

maybe a vac leak?

[skydragoness]

i know its an old thread but after all the testing how did you come up with having to rest the values? just wondering, cause it seems having the same problem it seems, my o2 wire metled didnt notice till my gas mileage took a dump, and i started running rich, replaced my o2 but im still running rich.

You have to reset the values thru the ECU/diagnostic computer because:

a., Your O2 failed, ECU went into a 'learn' mode where it changes the timing to compensate (i.e. dumps more fuel) but you don't really notice because it happens gradually.b. You have to reset it thru the ECU/diagnostic computer because if you just set your timing manually it will just go back to where it was. You have to "force" the ECU to accept the "new" values (i.e. the oe timing specs) by using a Nissan Consult (i.e. take it to Nissan) or buy the cheap software that's available and put it on a laptop and do it yourself. Its a PITA, and I was only able to do it this way because my bf was a Nissan tech and figured out how to use the software. But the seller is helpful and there's a lot of FAQ's out there on how to use it, mainly Z32 people use this software. c. If you read my intial post, you'll see that unless you fix the running rich/timing problem or whatever is causing it to run rich, you will continue to destroy 02 sensors (when they are running super rich it just melts the Bosch 02 sensors). NGK or Denso is the way to go, they are made with better materials.

[ohvictor]

THANK YOU! =Pyeah i wanted to buy the software for my laptop but i just wanted to make sure i was heading in the right direction with it before i use anymore money