M30B35 Failed Smog! :(

[ForcedFirebird]

I totally understand that, and I've heard that before . BUT, since the NO is the only thing thats HIGH and the O2 sensor (PreCat) shows lean condition, and it seems that CAT does not reduce NO (per Snog guy)as much as the HC/CO, does it still make sense to swap the cat?

If it's the CAT, I am not swapping it. It's going to be a waste of $ / time since the cat will be useless to me after the smog test is done ;)

I already said this as well.

Tell me what you mean when you say the 02 sensor shows lean condition.

Sensor is not showing lean, the high NOx shows his combustion temps are too high, which is usually lean or faulty EGR - since there is no EGR, it points to lean conditions in the chamber.

EDIT: Even a brand new o2 sensor is not sensitive enough to know if it's a few points lean, it only tells the ECU when it's VERY lean/rich. Hence the name "narrow band".

[Jean]

White/ish like spark plugs when engine runs lean...

[Jean]

loosen the valves?

Maybe this too? Would too tight cause lean running?

[Jean]

I already said this as well.



Sensor is not showing lean, the high NOx shows his combustion temps are too high, which is usually lean or faulty EGR - since there is no EGR, it points to lean conditions in the chamber.

EDIT: Even a brand new o2 sensor is not sensitive enough to know if it's a few points lean, it only tells the ECU when it's VERY lean/rich. Hence the name "narrow band".

Understood. So since AFM/Intake Air Temp/Engine Temp sensors have been covered and there is no EGR would you agree it's likely a fuel delivery issue? Interestingly, car pulls to redline etc...so I understand it's possible for it to run LEAN yet not starve....but lean to fail the test. IF THATS WHAT IT IS :)

[ForcedFirebird]

Maybe this too? Would too tight cause lean running?

Valve too tight will cause some fuel to spill out the exhaust valves, over heating your cat and show "rich".

Understood. So since AFM/Intake Air Temp/Engine Temp sensors have been covered and there is no EGR would you agree it's lightly a fuel delivery issue?

Could be a fueling issue, that's usually the last thing on the list. Do you have access to a fuel pressure gauge? If it were a bad FPR, the tendency is again to see rich. The FPR is a simple devise with a diaphragm, if it goes bad, it will feed fuel through the vacuum reference line. Simple test: put vacuum on it and see if it bleeds down, or if the vac line smells of fuel in severe cases.

[Jean]

Ok so I'll check the valve adjustments and fuel pressure.

What else? Maybe I misunderstood you, are you saying it's likely a cat or no?

[ForcedFirebird]

I don't think it's a cat, I agree with your smog guy.

[LJ851]

Correct me if i am wrong gentlemen, but doesn't e30 motronic have a limit to how far it will add or subtract fuel? I know my mid 80's motronic 911 does (If you unplug the 02 sensor it goes default to full rich which is like 10% fuel added)

I have a wideband in that car and it was still very lean at idle and part throttle with the 02 sensor off. 15:1 idle, almost 17:1 part throttle.

If this is the case with jeans car it almost certainly is the worn AFM, barring a mech. issue like valve adj., etc.

I adjusted my AFM (internally and externally) to the best compromise via wideband and ended up with 14:1 idle and peaks of 15:1 part throttle and it transformed the car. Throttle response, lower oil temps, etc.

[Jean]

I would love to hear what you did with your AFM, since I've broken mine by trying to move the wiper arm (didn't think about moving the plate under it instead if possible), I can try and play with it and throw another arm on it.

How did you calibrate it? I imagine you can external resistors/l-pad to make adjustment that would effect the map(s) ?

So far on my list of things to check/replace-

a) fuel pump
b) fuel filter
c) fpr
d) re-adjust valves
e)

They did give me a $20 off next smog test, so I'll give it one more shot this weekend. I have a pump, have a line on a good FPR and I'll buy a new filter for it.

[LJ851]

Jean, all i did internally was loosen the pinch bolt and rotate the whole wiper arm assembly so for a given flapper door opening, the wiper contacts were a little further along the carbon track. It is pretty sensitive at low openings so a wideband is required.

Move arm, go for test drive, repeat. I got it so much better that i didn't even get into changing the spring tension to alter the "curve".

The whole reason i did it was because i borrowed a low mileage AFM and it read completely differently on my gauge (and drove way better)

[Jean]

I see, I totally would if I was keeping the m30 in the car. I can't wait to go away from the variable resistors/mechanical afm :)

How much of this affects smog I wonder, since it's tested specifically at 15mph and 25mph on the roller.




I guess here is why I don't understand why some say it's a bad cat - the o2 sensor indicates a running lean condition (its before the cat) and a new cat may hide this from the smog machine but it will not FIX the issue itself. So, wouldn't it make sense to figure out what is actually causing it to run lean first (cat won't do that I dont see how it can on a car with a single o2 sensor).

[smooth]

I see, I totally would if I was keeping the m30 in the car. I can't wait to go away from the variable resistors/mechanical afm :)

How much of this affects smog I wonder, since it's tested specifically at 15mph and 25mph on the roller.




I guess here is why I don't understand why some say it's a bad cat - the o2 sensor indicates a running lean condition (its before the cat) and a new cat may hide this from the smog machine but it will not FIX the issue itself. So, wouldn't it make sense to figure out what is actually causing it to run lean first (cat won't do that I dont see how it can on a car with a single o2 sensor).

My general impression of why people say it's a bad cat is because 9/10 times when someone fails a smog test the tech tells them it's a bad cat, new cats hide issues (as you mentioned), and a new cat usually cleans the numbers enough to pass.

It's a quick "fix" but expensive and somewhat sloppy if you want to fix the underlying issues.
If our cars had an EGR valve then threads like this would probably be filled with replace the EGR valve...then the cat.

I'm not saying people are wrong or right when they discuss e30 smog and cats. It's just that doing it the way you are doing it usually takes a very long time and a lot of money--as you're finding out.

On the flip side, I had similar issues three years ago and eventually did replace the cat. I wish I hadn't because the aftermarket cat actually caused me to fail as a gross polluter. I finally took it to a tech and paid for hundreds of dollars of time to have the entire system walked through. The end result was the cat was defective! The shop replaced mine with an OBDII cat and I passed. A year later, six months ago, I passed with 1 point under HC. So I suspect I'm going to have to do what you're doing now because there is no way the cat is bad after a year...I don't even drive 1000 miles a year.

[Jean]

I see. Yep, I guess I was/am thinking in terms of the underlying issue as you said. I'll just stop after replacing the fuel related issues, I've heard on mye28.com that the CA specific cats may be under warranty for 4 years....but I don't know how true that is.

Honestly, it's just almost not worth my time or $ to go further if the simple things won't fix the issue. I'll keep you guys updated, maybe it will help others in the future :)

[smooth]

I hope you don't give up. You've spent this much time and money and...

I'd like to see what your results were after each attempt at fixing in a full write-up so the rest of us can try and get to the bottom of whatever we're dealing with :)

It doesn't help that California keeps lowering the threshold until eventually we just won't be able to pass.

[Jean]

Yep, I'll do a couple more things and pay for another smog test...after that I am done. I don't want to buy another CAT as I am removing this whole swap out to make room for another :) Sorry.