92 240SX failing smog for check engine light

[louisb323]

I keep failing smog check (2x) for check engine light. CEL is throwing code 32 but only the smog station can get the CEL to come on. I reset it and drive around, trying to duplicate smog check dyno rpm/speed, but it won't throw CEL for me!!?

I took it to a shop right after and had them diagnose. They said the BPT valve needs replacing and maybe the EGR valve. I've replaced the BPT valve.

Testing to see if I need an EGR valve I push up on the EGR diaphram while idle...it chokes but doesn't die all the way. (Maybe because it's hard for me to get my fingers in there to push up all the way??) I checked the vacuum between BPT valve and EGR valve by touch and there doesn't seem like a lot of vacuum. Should there be a lot or will just a little do?

I've checked the hose from the BPT to the EGR and it's clear and no holes. The other hoses look good but some are hard to get to so I'm not sure.

The bummer is that I can't tell if I fixed the problem because I can't get that dang CEL to throw...only the smog station will trigger it.

Any suggestions to help me be sure it'll pass smog? Should I replace the EGR valve or other???

thx.

[MaximA32]

Is it cheaper to pay for smog check or get new EGR valve?

[louisb323]

Uh, smog check, but if it fails I gotta replace the EGR and then pay for another smog check and hope that fixes it. Do you think it could be something else besides the EGR?

[louisb323]

Failed smog again...

Got a vacuum tester and tested the EGR valve. It lifts with the proper amount of vacuum. Then tested the line from the BPT valve to the EGR valve for vacuum by reving the engine and there's none!?! I already replaced the BPT valve so where does the vacuum in the line come from? Would it be the SCV control solenoid valve or the canister control solenoid valve? ...or something else?

[louisb323]

n/m...I found the diagnostic procedure 29 in the service manual. I'll run through that to diagnose.

[kenji_senpai]

Hey could you let me know how that turned out? I am having similar difficulty with my 92.

[louisb323]

Actually, I'm still working on it. I've been through the diagnostic procedure from start to finish twice; it hasn't led me to the culprit.

I've replaced the EGR valve (seemed functional, but did it anyway to make sure) and replaced the BPT valve (was pretty shot).

After doing those two parts as well as replacing some vacuum tubing and doing some component cleaning the EGR valve is still not lifting but I think I'm getting closer.

Now, with the engine warm and running at ~2400RPM I am getting a momentary vacuum from the BPT valve to the EGR valve whereas I wasn't before, but not a constant vacuum to keep the EGR valve up. For some reason I'm loosing vacuum and the suspect at the moment it the SCV solenoid...

So, right now I'm waiting on a new SCV solenoid. It's not a part that's associated with the diagnostic procedure, but it is part of the vacuum system and it IS faulty. (Tested it twice).

The part was on back order and was recently just released from the warehouse. I should get it next week which will put my wait for that part at about 1 month.

I'm hoping replacing the SCV solenoid will fix the problem, but if not I can at least go from there.

Anyway, if you haven't followed the diagnostic procedure I would start from there. If you need the fsm, pm me and I'll send it to you.

[zer0c123]

One of these could be the culprit 1.EGR Valve2.BPT Valve3.BPT tube (the weird thin curvy tube)4.EGR pipe (long pipe that runs right in the back of the engine. You have already replaced 1 and 2 (that must have been expensive), so maybe check 3 and 4. They don't need to be replaced just cleaned out if they're all carbed up. Have fun with the egr pipe. Lots of Pb and beer.

[louisb323]

Already took off and cleaned out the EGR pipe. Didn't help. Or maybe it did, but not enough.

Thanks for the suggestion.

[Q45tech]

Is your ignition advance oem correct, as 2 things will affect Nox egr and ignition...................but then again you didn't give us Nox only failed for code? Is there an EGR temp sensor on output of EGR [at plenum egr input port]?..........how ecu knows egr is working because the temp goes up when egr open from exhaust heat.

[louisb323]

My car tech terminology is not so good (i'm a noob), so when you say "ignition advance oem advance" do you mean ignition timing? If so, yes, it's set correctly. It was off at first (28) but I corrected it (to 20).

I also pulled my EGR temp sensor and tested it per the diagnostic procedure. It tested OK.

I've had the car smog checked 3x now. Here is the break down of why it failed each time...

1) Check Engine Light, Timing Off2) Check Engine Light3) Check Engine Light, HC 119 (118 max. allowed)

There is a dramatic inconsistancy between smog checks at the 15mph test. Here are the numbers...

HC (max 118, avg 31), NO (max 799, avg 237)1) 88, 1772) 118, 6013) 119, 527

Isn't it kinda weird that the HCs and NOs would jump so much between smog checks? The only thing I did different between test 1 and 2 was correct the timing from 28 deg to 20 deg. Do you know if a failed SCV solenoid would have an effect on the vacuum pressure for the EGR?

Is your ignition advance oem correct, as 2 things will affect Nox egr and ignition...................but then again you didn't give us Nox only failed for code? Is there an EGR temp sensor on output of EGR [at plenum egr input port]?..........how ecu knows egr is working because the temp goes up when egr open from exhaust heat.

[louisb323]

Ok, finally got the SCV solenoid and replaced it. While I was warming up the engine to do the egr lift test I was checking to make sure I didn't leave anything disconnected.

Well I put my hand on the EFI sub-harness connector and saw that it was a bit loose. I was examining it to see if there was a missing screw/tie/snap and found it easy slid off the mounting bracket. Twisting it around to see if there was a some way of securing it on the bracket suddenly made my engine idle rough. Hmmm, I wondered. I moved it around a bit more and my engine died!?! wtf...

So I restarted the engine with the connector on the mount and then pulled at the wires on each side while holding it firmly to the bracket to see which side of the connector was faulty. Well nothing happened. So I traced the wires on either side and found the cabling on the side that meets up with the throttle position sensor connector a bit bound up. I then move the throttle position sensor connector and found the engine stuttering almost to the point of stalling.

At this point I'm thinking short in my EFI wiring harness being that it looks like someone's had it apart and had taped it back together. So I start untaping the wiring harness from the throttle position sensor connector back towards the valve cover. Underneath the black electrical tape I found one of the wires wound in what looks like white(ish) electrical tape, so I begin untaping that seeing that the adjacent wires weren't exposed.

Underneath the white tape I found a tar-like goo covering the wire with exposed wire (looking like shielding or a ground) embedded in the goo. I pulled off most of the sticky tar-like substance to find the exposed wire coming out from under a sheath surrounding the wire. I've linked to a photo so you can see what I'm talking about.

#1 is the exposed wire.#2 is another wire similarly wrapped with the mysterious white electrical tape so you can see what it looked like before I unwrapped it.



(If the embedded photo doesn't stick, you can see it here... http://www.flickr.com/photos/louisb323/1415658058/ )

Now, here are my questions...

Is the white(ish) (electrical?) tape with tar-like goo normal?

Was this (now) exposed wire supposed to be wrapped like that or should it be grounded somewhere?

Should I keep trying to track an electrical short or should I look at my throttle position sensor?

Any other suggestions?

Thanks for any help you can lend a noob tech and sorry about the long winded post.

[louisb323]

Passed. Woot!

[kenji_senpai]

So what was it that caused it to pass? Faulty tps or an electrical short or what?

[mick]

So what was it that caused it to pass? Faulty tps or an electrical short or what?

Looks like we'll never know

[[email protected]]

this is your latest post i have a question but could not get access to you via email in reference to :zerothread?id=257238 you said you did the procedure in your car can you assist with pics or remembered knowledge as i would like to change my valve seals also but i dont want to take out the head also due to no space or place to work thanks