Lankan

Received my Denso O2 sensor, spark plugs, and oil filter. All installed. Funny thing is, the O2 sensor that was in there had a slightly larger diameter electrode/sensor than the one I received (I did order the correct part number for mine: 234-4052), but the lengths are the same.

Should I go in for the smog right away? I have a weekend trip where I'll be driving about 600-800 miles... would it be any better to do the test sometime next week?

What timing should it be set at? I have read many threads with regard to timing set to maximize the possibility of passing the smog (for guys like me who have "NO" issues. People say to retard the timing. The state allows +/-3 from what's specified (which is 10*BTDC). Should I keep it at 10* or retard it to 13*BTDC?

Lankan

Bad news, I thought I would follow the FSM and duplicate the test that made me certain that it was the oxygen sensor that was bad (just to make sure that the new O2 sensor was working properly). To my disbelief... the check engine light came on!! This is the procedure I followed:

DTC 25 Air Fuel Ratio Lean Malfunction
DTC 26 Air Fuel Ratio Rich Malfunction
Malfunction: Open or Short in Heated Oxygen Sensor

(1) Disconnect the fuse EFI (15 A) for 10 sec. or more, with IG switched OFF
(2) Initiate test mode (Connect terminal TE2 and E1 of DLC1) with IG switched OFF
(3) Start the engine and warn n it up with all accessories switched OFF
(4) Idle the engine for 3 min.
(5) Quickly race the engine to 4,000 rpm 3 times.
(6) Drive at 50 – 96 km/h (30 – 60 mph) (Engine speed 2,000 rpm) for 90 sec.
HINT: If a malfunction is detected the Malfunction Indicator Lamp will light up during step (6)

When I connect terminals TE1 & E1 to read the code, it's giving me the 25 code again! What do you guys think it could be?? Along with changing the O2 sensor I also installed new Denso plugs and an oil change, but I'm quite sure these two items would not effect the test. I'm thinking it can't be the downstream O2 sensor, as "Dirt Driver" pointed out, that would be code 27.

Dirt Driver

Check all the O2 sensor wiring and connections.

Lankan

Did this already under the vehicle... near the cat. The upstream harness seems to be in stock form (no damages at all). The downstream harness has been cut and a new harness attached. All the wires are connected properly though. Even if there was an issue with this sensor, it would be giving me code 27 right? How do I check if the signal from the upstream O2 sensor is actually getting to the ECM?

SoCal

Are you aware that the LAW in California is for the SELLER to provide a smog Cert when a used vehicle is sold. You should be contacting them...... You Can get them to pay for any and all repairs for your vehicle to pass smog.

Certainly it will be a hassle now.

Read this link in the middle of page http://www.dmv.ca.gov/vr/smogfaq.htm

Lankan

I know that the seller is responsible for the smog, however I bought it at a good price knowing that it may have an issue. Other than that the truck is in very good condition, so the ball is in my court to get it fixed. Any other ideas? I'm going to start checking all the other things I haven't checked that could throw a code 25:

• Engine ground bolt loose
• Open in E1 circuit
• Open in injector circuit
• Fuel line pressure (injector blockage,etc.) (Did the FSM test for this, and the check engine light did not come on)
• Open or short in heated oxygen sensor circuit
• Heated oxygen sensor (the upstream one was replaced)
• Ignition system
• Engine coolant temp. sensor
• Volume air flow meter (Air intake)
• ECM

Any other ideas, or should I take it in for a smog to see if I get lucky and pass, cause I'm completely frustrated at this time.

SoCal

If you think it will fail try finding a gas station that sells E85 you know 85% ethanol and put in a few gallons mixed with a tank of Premium and get a test.

Dirt Driver

I haven't had to do it myself, but I would think by probing terminals on the ECU plug.

sdhunter

At this point, I would almost recommend taking it to a Gold Shield repair station and throw a couple hundred bucks to them to diagnose the issue. They can at least make a change and put it on the sniffer to validate repairs....

Lankan

"Gold Shield" repair station... is that a smog test station that also does diagnosing and repairs?

ChefYota4x4

iTrader: (5)

WOW, this is NOT A GOOD FEELING, Lankan.... I know very well! lol... I have been chasing a 'bad mileage' and 'mysterious miss' gremlin for 2 YEARS! lol... But with a fully rebuilt motor, fairly new 02, 1.75yr old CAT, ...I FAILED NOX MISERABLY! .... See, with my 87, I have NON heated 02, no second 02, and an AFM, not a MAF... NO EGR temp sensor or cooler(which should have tripped a code if it was bad, the guy should have told you)..... And btw, I failed with 1600nox, 99 HC on 15mph testing and I'm allowed 1100 Nox on the 25mph test and 114 HC or something on the 15mph testing... hehehe. Replaced the CAT and dropped the HC to almost nothing, CO to almost nothing, 02 to almost nothing, nox to 34 on the 15MPH test and yet.... Nox on 25mph test was STILL 441ppm.... WTH? lol.



I was baffled, too, Lanken... I have TONS of power for a 22RE, no pinging, no popping/misfire/backfire, ....90mph no problem.... yet it still failed! But my symptoms are a lil different... I have TERRIBLE city mileage and decent hwy. I mean, I can live with 20-21 hwy in an 87. Your 94 should be more like 22-23mpg!

I have a great read on this stuff, which I found AFTER I passed... But people like Dirty and more are FANTASTIC with this kinda stuff... You'll get it, don't worry. I will find the link on my thread and slap it on here, just for S&G's, ok?

Lankan

Thanks for the encouragement ChefYota4x4. I really want to get to the bottom of this problem, but it just takes so much time, learning, and patience! Sometimes it just gets to ya as you feel that you've done everything possible, and still there's a problem. I've read most of your thread and many other threads and taken notes on what to check for. Gonna buy a multimeter today and start going through the FSM and checking stuff.

ChefYota4x4

iTrader: (5)

Well,..... my next comment might surprise you... but I WOULD NOT do it the way I did, again(For one, because I didn't SOLVE anything, really..... just had a new CAT suck up everything, lol.. And two, because I could have probably figured out FOR CERTAIN what was wrong through a guy that, well, DOES THAT ALL DAY LONG! lol).... now in your case, that's different, because your rig can 'tell you' so much more through testing. And, the smog repair guys told me, "Actually, we like your type because there's less to 'have a glitch' and we can then pin it down by 5way testing/scope, etc."....

I STILL am tempted to let someone figure out whatever is up FOR ME, because I've just spent ENOUGH time to earn the self respect I need to not feel disgusted with myself! hahaha. We'll see.... I think I have mine narrowed down to either an EFI issue(possibly even mechanical, therein, with a sticking open injector/injector Y-connection messed up or something..... Or maybe even a Fuel or IGN related gremlin).... I've even seen, in 2 CASES out of 1000, lol... > a couple guys with iffy distributors that were confusing their ignitors, causing inaccurate injector/spark timing, then unburnt fuel to get back there and then confuse the 02 and thus, ....causing the ECU to 'LEAN IT OUT'. Their air gaps, resistance, everything checked out, just like mine... But see, there's the thing... I'ma go spend 180$ on a Napa or other dizzy to find out either way? HECK no! lol. Ignitor? Not at all likely. Ground? Been through them so many times, can't see that.... Nope, my lil critter in there is clever, like a mouse hiding in thistle brush! lol.

I AM WATCHING! Hope you get it soon, Lankan!

PS> Sorry that you had to read through that whole thread! hahaha. But hey, it has SOME good stuff in it, thanks to lots of good dudes on here and some research of my own. AND YES, HOLY CRAPOLI does this one require patience! lol.

854x4

Yes gold shield stations are for diagnosing and repair you pay a diagnose fee and they start checking and call when they find the problem or problems. Start looking for vacuum leaks and make sure your timing is at 10* BTDC with you distributor not maxed out this would indicate a slipped timing belt or distributor off a tooth. Does the engine miss or have a rough idle? As for the Nox problem check the egr with a vacuum drop test to make sure its not restricted sometimes they can test good but still be restricted. Also make sure the trucks not getting hot this will cause nox to go up.

MaxwellE54

I've got a shell in my town that sells 100 octane racing fuel... I've used that a couples times for passing that ol smog test. I had the same issue with not getting a smog cert when I got my runner. Then again I didn't give him one either..

Lankan

854x4, the engine does not miss... it runs very smooth. The EGR was checked with a vacuum drop test at idle and the engine started to stall, so I'm assuming that it's working okay. Got a multimeter today, and here's what I've checked so far, and have been to spec:

1) EGR gas temperature sensor
2) Volume air flow meter (air intake)
3) Engine coolant temperature sensor
4) Heated oxygen sensors (both upstream and downstream, and the one I just replaced).
5) The 3 engine ground bolts and wires are all there/not damaged.

There seem to be no blockages or an open/short in the injector circuit, as I have followed the DIAGNOSTIC TROUBLE CODE DETECTION DRIVING PATTERN two times, and both times the check engine light has not come on.

What I have not checked, and cannot find in the FSM how to check:

6) Open in E1 circuit
7) Open/short in heated oxgen sensor circuit (not the sensors themselves, but the wiring that carries the signals to the ECM).
8) Ignition system (not sure what to check here). If it's to make sure that the spark is occuring, it's fine.
9) ECM. Suppose the only way to check this is to replace it or use someone else's right?

I did another driving pattern test today to double check the new O2 sensor. The check engine light came on again. But what I did realize is that the instructions in the test procedure say:


NOTICE: If this procedure is not strictly followed, you cannot detect the malfunctio

What hit me is that both tests I have conducted AFTER installing the new O2 sensor, the check engine light came on after 90 seconds (usually at about 105-110 seconds). See item #6 and the HINT afterwards. Both times I thought I was trouble free and kept going as I needed to drive down the road that I was doing the test on to get home. The very first time I did this test (with the O2 sensor that was in the truck when I bought it) the check engine light came on at about 80 seconds into the test (as described in step 6 of the procedure). Maybe I should do the test again tomorrow and pull over after the 90-second test! Am I onto something, or its' just wishfull thinking??

ChefYota4x4

iTrader: (5)

Maybe the "Ignition" portion of this testing would be in the 'IGN' portion of the FSM? Maybe testing for 'ignitor resistance', dizzy air gap', 'dizzy secondary coil resistance'..... ???? I believe if you have a problem with the dizzy, it can then relate to a problem in the injectors firing at the wrong time, .... because the ignitor is going by 'dizzy timing', not piston location or anything else. USUALLY, ignitors, themselves, just, well, GO BAD! lol. So I would doubt that's even a suspect. BUT, ....it's an easy test for resistance, etc., ya know? Even early on in the FSM, there's a section that goes through those basic/crucial components... At least in my FSM there are, lol.... Maybe I can take a look tomorrow when I have time and you can look in your year one for it?(I believe it's AFTER the engine assembly section, etc.)... And I KNOW it will be in the IGN section, no doubt.

NO CLUE if you're thinking in a wishful way or not, regarding the 02 stuff's at the end. I would just go by the testing procedure and conclude thereafter whether you have an issue or not. Keep it simple, right? BUT, I'm fairly certain that IF you have an issue with the heater wiring IN the harness, BEFORE the connector... it could very likely throw a code.

Lankan

ChefYota4x4, today I will go ahead and check the resistance of the ignition components. In your sencond paragraph, you mentioned:

"BUT, I'm fairly certain that IF you have an issue with the heater wiring IN the harness, BEFORE the connector... it could very likely throw a code."

What's this heater wiring your referring to?

ChefYota4x4

iTrader: (5)

Hey Lankan.... firstly, HANG IN THERE! lol..... I KNOW the cold sweat/eyes crossed/twitch/frustration causing realm you're in, very well! hahaha....

Well, I was referring to the 'HEATED' wiring of the 02/Through the ECU. I believe your ECU(Unlike mine) has 'PINS' within it, leading from the 02 sensor wiring, dedicated to the 'heated wire' portion of the 02 Circuit. Just like your ECU has an 'EGR Temp Sensor' Circuit which mine doesn't have, right?(Going by memory from another 'couple' guys whose threads I've read/as I'm sure you have likely read as well, lol).

Well, the IGNITION(IGN) portion of the vehicle is also tied to the ECU. Think about it, .... what causes the Injectors to fire when they do? The Ignitor, right?(RIGHT guys? lol).... It's told by the dizzy when to send signal to 'fire the injectors'(as the dizzy is telling the ignitor, thereafter, when to 'send fire' through the coil to burn said fuel). Also in the same wiring, the 'injector solenoid resistor' is taking the voltage sent to the injectors and limiting it to 5V(I believe it's 5V in my case, not sure on yours???).

So, it's not just the "Big 4"(Fuel/Spark/Compression/Timing), it's the 'semantics' therein, which control the 'where and when and how'... Which can get complicated(obviously, you can see I'm still a lil confused, hahaha)...

Something interesting to me; You have issues thereafter the CAT.... but your second 02 is not throwing a code at all? I'm curious as to why. I believe the smog standards are set up to 'require the same emissions output as in 95', NOT more stringent(I believe they did dyno testing by 93, so your rig would have been tested on a dyno brand new/Mine was NOT dyno tested, as far as I know through Roger/4crawler and tutorials that I've read).

The reason I mention the 'heated wire' portion of the 02/ECU relationship is, well, because I see it in the 'TEST THIS' stuff you posted, ya know? Problem is, .... if you're driving around plenty before the test, etc., it should be PLENTY hot! The heated wire portion is meant to 'SPEED UP' the ability of the 02 to enter the picture/decrease the time that the vehicle is in 'open loop', which will reduce emissions as the vehicle isn't having to dump so much fuel for so long when cold(like mine does, as it does not have a 'heated 02' ) However, since the 02 is downstream much further, unlike mine(which is right on the exhaust manifold), maybe it's just that 'LILLLLLLL BIT' beyond specs of 'staying hot enough' without the heated portion of the 02 circuit. (I can't know.... , because it seems odd that the heated wire would bring the 02 to 600*F........ But I guess it would HAVE to in order for the 02 to even help the computer come out of open loop>>>>>> ???????)

I'm really not sure where to point you on that, Lankan... I have limited knowledge of how it's wired, etc.... But I KNOW it IS wired to the ECU(the heated 02 circuit).... I just, also, have no clue how likely it would be that this would be causing you an issue.............. soooooooooo..................

..........Moving on from there, for now, I see no issue with moving on to testing the IGN portion of the system for now. The first bank 02 is reading stuff BEFORE your CAT, and it's obviously, under load, when you're holding it for several seconds at higher RPM,...well, UNHAPPY! lol. Question is, ..is the 02 THE PROBLEM? .........Or is it SOMETHING ELSE, such as the IGNITION or components therein causing a "OOOOH, yucky, no likey" reaction from the 02? You have to FIND that 'CAUSE FOR CODE 25', plain and simple, before you can determine what's going wrong. I PRAY it's not mechanical... But seeing as you don't have a chunky miss, etc., ... "It's running smooth", you said, .... well, I doubt it. Sounds like a 'clean lil rig' that's got a 'thorn in her side', lol. Nearly 20 years old, that wiring, etc., Lankan, ya know? Some, like "Grego", have NO ISSUES..... Others, like myself and you? Mehhhhh! lol.

ChefYota4x4

iTrader: (5)

PS> .... "Coolant Temp Sensor".... Are you SURE that's reading VERY nice/accurate resistance throughout the temperature sweep? How well have you tested that? (Remember, you have a CODE, and unfortunately, due to the DANG DESIGNER, lol.... 'You don't know which portion, IGN, INJECTOR, CTS, 02, ETC., is causing the issue'.... right? ). I only mention the CTS, because it's purpose is to relay the temperature of the coolant to the ECU, for WHAT? >>> to tell the ECU "It's cold" or "It's hot", thereafter adjusting the amount of fuel it allows.... I KNOW that some have had issues where that CTS has caused very rich issues(that doesn't sound like yours)... BUT, when the rig, at the 02, sees "RICH", what does it do after 90 seconds or so? 'LEANS IT OUT', right? Doesn't take long, AT ALL, for the internal combustion temps to get hotter... And yours are NO WHERE NEAR what mine were(1600ppm at 25mph-2500rpm NOX)..... <<<<< hahaha... Even then, I've seen worse from my buddy Teuf, who's in an 88... He was at 2600ppm on the same portion, I believe...AND rich in HC's on the same portion as well. Replaced his 02 and CAT and VOILA, solved.... OR IS IT SOLVED?????? muahahahahahah! HAHAHA. Teuf came DANG near being a gross polluter... Mine wasn't close. Still, I didn't pass, did I? lol. You're CLOSE to passing... AND, you have a code.. That HAS to go to pass, ya know? So I would focus solely on ridding it of that... And I BET you will pass with flying colors. A new CAT, even for you, WOULD NOT help you 'PASS'... Because you'd still have a code, right??????