smog test problems

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Dasque
Posts: 6
Joined: Mon Dec 11, 2017 2:43 pm
Car: 1993 240sx

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Hey guys, I've been lurking here for a while and I've got a doozy on my hands here. Hoping you guys can help me out.

Daily Driver 1993 KA24DE all stock/OEM

DEQ (idle test only here in OR) failed me for high HCs and CO. I can smell gas at the tailpipe at idle.

I'm thinking this is from running rich based on that result. New (less than 500 miles) plugs have soot on them, no ECU codes.

Here's what I've done on the car thus far to try to narrow this down:
Oil/filter and air filter are new.
Checked MAF sensor, cleaned it. Sensor gives fairly linear ramp in volts while revving.
Throttle body is clean.
O2 sensor is good according to the ECU (the blink test thing).

Any ideas?


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centralcoaster33
Posts: 2769
Joined: Tue Apr 05, 2005 10:41 am
Car: 240SX #5-1997
Location: Central Coast, CA

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Hi and welcome to NICO Club!

Sorry about the smog issues. It's good you had a smog test because these poor numbers mean it's not running that well. There's some stuff to do. One is to get OBD-1 codes from your ecu using the lights. You did something like that, what code numbers did you read off? There should be at least one code, 55 if all is well. Don't forget to put the ECU back into Mode 1 when your finish pulling numbers.

Here's what I suggest. Install a new fuel filter and run some injector cleaner through the system. You need your fuel delivery cleaned up a bit I think. Use premium 91 octane for this and until you pass your smog test. Spray a can of carb cleaner around your intake top, bottom, front, back and side and up the line to the brake booster while the engine is running and make sure you don't have any vacuum leaks (do this before setting your timing). Also, check the resistance of each injector with a voltmeter and see what Ohms you get. Check voltage on your TPS. Get a timing light, a screw driver and a socket. Use the FSM procedure and set your idle (with IACV screw) and timing (rotate your distributor).

If you have no codes, then your sensors should be fine. If codes, then replace. O2, TPS and MAF are the main ones for this stuff. Please keep us posted and ask any detailed questions as they come up. Good luck! :bigthumb:

Go here, load PDF, hover over the upper right hand corner and an arrow icon appears, use that to download the PDF to your device...
http://www.nicoclub.com/service-manual? ... 1993_240sx

PS - you have a CAT on there right? It's not hollowed out? Gonna need a working one of those... the exhaust smells funny when these go bad, like rotten eggs.

Dasque
Posts: 6
Joined: Mon Dec 11, 2017 2:43 pm
Car: 1993 240sx

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Thanks for the reply.

ECU code is 55, so no apparent sensor issues.

Fuel filter's only about 2500 miles old (had an injector go on me a couple months back and did the filter at the same time) and I've got a bottle of cleaner running through it this tank. The car's had nothing but 92 octane for the past decade - I did some tests and got enough better mileage to pay for the pricier gas and then some.

Tried to check TPS earlier today, couldn't get a backprobe connection. I'll check the injectors in a bit.

Grabbed the FSM a few months ago thanks to these forums, it's been a lifesaver.

PS - yep, cat's on where it should be, exhaust smells like gas, not like eggs.

amc49
Posts: 1183
Joined: Mon Jun 19, 2017 7:24 pm
Car: '11 Nissan Versa
'17 Nissan Altima

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Not familiar with that particular car but apparent running rich, might check fuel pressure or any pressure regulator in there. Check fuel pressure fall-off after engine gets cut off, the pressure dropping rapidly could mean a leaking injector. The cat even if in place is likely poisoned and no good, they only smell when dying and once dead the sulfur smell goes away as the catalyst then does not work any longer. The plugs must be the correct heat range and the full gap open. Any pollution equipment involving air injection needs to be working too. Advancing the timing a bit to give more burn time may help. Any vacuum advance unit if used and not working will kill you there. Not a vacuum leak, that makes mixture lean not rich. Run a compression test, any low cylinders do not burn completely and the HC goes up like a rocket. Engine needs to run at fully heated, wrong stat opening too quick will increase HC, which lowers with more heat. HC also goes up with any ignition misfire at all.

Mileage? You'll be amazed at how much a new cat can clean an engine up if the old one ws simply worn out.

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centralcoaster33
Posts: 2769
Joined: Tue Apr 05, 2005 10:41 am
Car: 240SX #5-1997
Location: Central Coast, CA

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Well, fuel delivery and timing are mainly what I was getting at. So filter and injectors came to mind. That you've worked on them recently is a clue to double check the work maybe and an Ohms test is easy. You used new O-rings with your new injector? Hopefully it's not leaking. Then timing and idle (which you can't set properly with vacuum leaks, so I mention that check first). I'm not sure about advancing timing, I'd just set it to factory (20 I believe). When I smog here (CA), idle speed and timing are things they check and they'll tell you if it's they're of spec and send you home. Is that a fix or a work-around anyway? I thought of a compression test, but that takes a tool I don't have and would tell me news I don't want to hear, haha. Maybe you can borrow a tool and do that with fingers crossed.

Dasque
Posts: 6
Joined: Mon Dec 11, 2017 2:43 pm
Car: 1993 240sx

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Update:

No apparent leak on the new injector (yes, used new o-rings and lubed them well before installing).

TPS is fine

One of the older injectors ohms at 105, others are in spec. All of the plugs are fouled in the same way, would that one injector going be bad enough to cause all of this?

All they check up here is what comes out of the tailpipe and that nothing seems to have been mucked with.

I don't have a timing light or a compression tester. I'm trying to track down a light.

No apparent vacuum problems either. Is there an easy way to get to the FPR vacuum line to check it for fuel?

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centralcoaster33
Posts: 2769
Joined: Tue Apr 05, 2005 10:41 am
Car: 240SX #5-1997
Location: Central Coast, CA

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Well, make sure you're reading 105 and not 10.5 ohms. around 11-14 is correct iirc. If it is indeed 105, that's a bad injector.

I don't know if that could foul all the tips and think it wouldn't.

I think checking the timing is important. Not sure about there, but around here you can borrow from Autozone for free with a deposit.

The FPR vacuum line goes from the fpr at the end of the fuel rail near the firewall, down around the egr valve and to the back corner of the intake manifold, sort of between the IACV adjustment screw and fuel filter.

Dasque
Posts: 6
Joined: Mon Dec 11, 2017 2:43 pm
Car: 1993 240sx

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No, it's definitely reading 100ish. I could maybe see it messing with all of them if it's not able to open fully, which makes the O2 see lean and try to pump more gas to compensate. That would make everything else run somewhat rich but the O2 would think everything is fine because it's getting the average of okay? There'd be more gas in the exhaust from that I'd imagine.

I looked at autozone's catalog and they didn't have one listed for loaners but I'll give them a call to make sure.

EDIT: Yeah, autozone up here doesn't have timing lights in the loaner program.

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centralcoaster33
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Joined: Tue Apr 05, 2005 10:41 am
Car: 240SX #5-1997
Location: Central Coast, CA

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Okay, I think you need a new injector and to get a timing light. Injector being #1 priority. Consider the cost of a matched set compared to individual replacement if your budget allows.

When is registration due? Even if you're not ready for smog, be sure to pay that on time. You can be late for smog and you don't get your sticker, but at least you don't get late fees for the registration. When you do pass smog, you can take the paper in or wait and you'll get your sticker at that point.

amc49
Posts: 1183
Joined: Mon Jun 19, 2017 7:24 pm
Car: '11 Nissan Versa
'17 Nissan Altima

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I assure you advancing timing helps to drop HC, although NOx will greatly increase. That alone not enough here though to cure the issue likely. O-rings for injector can only cause an external fuel or a vacuum leak, if somebody has an OBD2 scanner you can watch the first O2 output as well as the fuel trim to tell if it is a vacuum leak causing the others to overcompensate with fuel. An exhaust leak before the O2 can do the same thing. The one injector off a mile ohm wise has something wrong with it. I myself NEVER change entire sets of them, I saw plenty of people who did that for no result all day long but many injector changes are like that anyway and wasted money. Just buy a single good branded one for the correct application. The PCV must be open and working and the IAC needs to be clean too at the valve metering spot. I'd for sure be checking that FPR line for leaks too.

Can again be a dead cat involved in there somewhere, mileage has still not been stated yet. Run the car rich enough and the cat dies in 15 minutes. If a TWC cat and air is supposed to inject between the two cat sections and it's not that will be part of the issue too. A clogged cat will make the engine seem richer even though it's at normal computer settings, the stackup of exhaust pollutes the intake mix to then slow the burn way down and then HC is everywhere.

Dasque
Posts: 6
Joined: Mon Dec 11, 2017 2:43 pm
Car: 1993 240sx

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Timing bang on 20 BTDC without adjustment, when I ohmed the bad injector before pulling it out to make sure I was remembering right which one it was that was acting up it gave me 12.5 (at operating temp). The rest matched it.

Oregon doesn't do late fees for reg, we just have cops who want to protect the roads from dangerous unregistered vehicles.

AMC: 1993 model year was before OBDII was a thing. It's been a daily driver for all 25 years of its life and has 233k on it. It's not been rich enough to have any negative effects on drivability

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centralcoaster33
Posts: 2769
Joined: Tue Apr 05, 2005 10:41 am
Car: 240SX #5-1997
Location: Central Coast, CA

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I'm guessing a dying cat would have had poor numbers the previous smog check as it goes downhill. So, if you were passing fine before and now aren't it would have died quickly and been noticeable. Just a guess though as I haven't had one die on me yet.

I'd keep an eye on that injector. It could be 'sticky' and on it's way out, ohming fine one day and being stuck open the next. I had one fail and it was odd and intermittent for a while before I was sure what it was. I did replace just the one, not a set, but considered it.

Seems like a new 02 sensor could help. Check for exhaust leaks around and before cats and sensors. Maybe those new spark plugs are the wrong ones. It's recent work and recent work is always a suspect. Maybe the smog station screwed up the testing somehow.

Dasque
Posts: 6
Joined: Mon Dec 11, 2017 2:43 pm
Car: 1993 240sx

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Success!

I went ahead and replaced the dodgy injector, too it a few miles down the freeway to get the bubbles out off the fuel system and warm the engine up and no gas smell. Took it through deq and passed with room to spare.

I'm glad I caught that injector at a time it was reading as being off.

Thanks for the help man. :)

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centralcoaster33
Posts: 2769
Joined: Tue Apr 05, 2005 10:41 am
Car: 240SX #5-1997
Location: Central Coast, CA

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Woo hoo! :cool:


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