$20 to anyone who can figure out what's wrong

[Nameless EJ6]

Well, when I just unplugged it, the a/f would get about 2 points richer, so it IS working, I just meant it didn't make a difference on the hood issue.

It's working, sure, but you don't know what it's putting out. Don't rule it out yet untill you're 100% sure. Same goes for ALL sensors. Make sure they are all within the proper range. That's the only thing you can do with a problem like this.

Since your wiring is done correctly to the best of your knowledge, befopre you suspect it's a wiring problem again you should check all of the sensor output's at the ECU.

You have a ECU pinout sheet, there you go. I've done this a million times, although usually with a breakout box.Do you have a multimeter?

[goofynick6]

Of course I have a multimeter....I'd be lost a million times over w/o it. And yes I have the pinout sheet, or I'd be lost as well..heh.

I've tested the coolant temp sensor the way the manual says with the ohm readings at different temps and it seems fine...it reads .22 at hot temps (fully warmed up and after a short drive)...the manual says .34 at 165 F, so I'm guessing .22 is ok? Dunno.

If you have any other voltages or ohms that are correct lemme know.

Nick

[goofynick6]

New theory:

Around the time this started happening (I think), my exhaust manifold started leaking between the head and it. Sooo, perhaps when I close the hood the maf is ingesting hot exhaust gases that are leaking?

I don't know if the lack of oxygen from exhaust gases would contribute either..thoughts?

Nick

[Wulfgang]

I don't know if the lack of oxygen from exhaust gases would contribute either..thoughts?

Nick

That sounds reasonable, I guess, but you'd have to suck in an awful lot of exhaust to go that lean. Could be possible tho, since your engine creates about 50% more inert gas volume from burning the fuel. How big is that exhaust leak???

Think of it as a massive dose of EGR

[goofynick6]

Yeah, when I thought of it as EGR, it didn't seem rearsonable. The leak isn't really terribly audible until you rev it a little, but you can see exhaust gas shoot into the engine bay a little bit.

So, I thought that the hot exhaust gas would fool the IAT, and the lower oxygen content would cause it to run more lean possibly...dunno, like I said it was a theory...I have a friend stopping over today to help diagnose.

He had similar problems on his sr20 before with his maf exposed to air in his wheel well and it would cause it to run lean and rough because the maf was too sensitive.

I'll let you all know.

nick

[AmoebAssassin]

A MAF sensor by itself has no way of discerning oxygen from CO2 or other post-combustion gasses, It simply measures the mass flow of gaseous material through it.

When your MAF is sucking up exhaust fumes, it treats it as if it is sucking up air, and will inject the proper amount of fuel. However, it is running under the assumption that the air it is sucking up is the typical mixture of oxygen, nitrogen, etc. whereas it is also comprised of your exhaust gasses (CO, CO2, NO, etc.). Therfore, there is less oxygen than what the MAF is assuming and if anything, you will be slightly running rich, not incredibly lean.

[goofynick6]

FIXED!

After hours of trying everything, my buddy recommended cutting the o2 sensor wire. I did, and now the car runs great....a tad on the rich side but better than the 19:1 a/f we were getting!!!

WOOHOO!

It was a generic bosch o2 sensor I'd bought new, and it was meant to be heated, but I wasn't running it heated, and maybe that was the problem, maybe not, but it was the o2 sensor ultimately. Somehow the underhood temperatures were messing with it or something.

I'm sooo super excited now, this problem has existed since October 04!

Thanks for all the help everyone; I'm gonna buy my buddy a case of his favorite beer.

Nick

[Nameless EJ6]

Awesome!

I've always hated Bosche o2's..

[BoostFab]

i like corona...so hurry up lol j/k

[Wulfgang]

That kind of sucks. Even if the O2 sensor was totally bad, you wouldn't expect to go that lean on closed loop! I had heard before that Nissan was a bit aggressive on closed loop control, but giving the ECU that much leeway on AFR adjustment is just ridiculous. IMHO the ECU should just register an error code for the O2 sensor if it has to make more than say 10% adjustment to the base map during closed loop.
Modified by Wulfgang at 2:15 PM 3/21/2005

[goofynick6]

Agreed! A bit rediculous that it would it let it go that lean..no codes or anything. And how weird, it was so greatly affected by the underhood temperatures; there was a definite cutouff point where it would run ok, or run 20:1 lean.

Anyway, now I'm unable to keep traction, even though I have yet to retune it, but at 11:1, 2.5" exhaust (my 3" cutout closed), exhast manifold leak, 16 psi, it is dangerously fast..haha. Feels faster than it ever did before. It's easily mid 12's at this point, if not better. Can't wait to get it all straightened out at the frame shop, paint job and then dyno/racing

Nick

[BoostFab]

so your O2 sensor is not connected at the moment?

[goofynick6]

That is correct. THe car (once warmed up) is idling at 14.2:1 roughly and it is actually pretty good with my tune, I may just not put one back on.

I hooked up a different o2 sensor today from my ka and it made it run 11:1 rich..wtf? I hate o2's.