Well after all the work I've done on my '91 240 wagon auto, I still can't pass CA smog. I've tested three times after doing various repairs. Below are the readings and associated repairs before each test:

1. Replaced: in-tank fuel pump, fuel filter, flame trap and lower hose; Oil change

RESULTS 15MPH / 25MPH
HC 106 on max of 81 (fail) / 45 on max of 63
CO% .42 on max of .52 / .17 on max of .43
NOx 988 on max of 554 (fail) / 571 on max of 511 (fail)

2. Replaced: knock sensor, ECT, air filter, EGR temp sensor, TPS, throttle body gasket; Adjusted throttle linkage; Tested EGR system; Cleaned IACV, throttle body, AMM; Checked and cleared ECU codes (knock sensor); Checked thoroughly for vacuum leaks

RESULTS 15MPH / 25MPH
HC 165 (yikes!) on max of 81 (fail) / 59 on max of 63
CO% .72 on max of .52 (fail) / .19 on max of .43
NOx 1391 on max of 554 (fail) / 564 on max of 511 (fail)

3. Replaced: O2 sensor, cap, rotor, plugs, wires; Checked compression (185-191 across all cylinders) and visually inspected plugs (all similar with normal wear pattern/color)

RESULTS 15MPH / 25MPH
HC 105 on max of 81 (fail) / 62 on max of 63
CO% .34 on max of .52 / .19 on max of .43
NOx 721 on max of 554 (fail) / 509 on max of 511

So it got worse before it got better but I still haven't been able to impact the original HC problem at all--In fact its worse @ 25mph. I just checked the timing and I'm sitting @ 10 degrees @ 750rpm idle which is also what the smog report shows--The test before shows 12 degrees. Is there anything there that can indicate a problem? Is the ECU adjusting for the new O2 sensor? I did drive it about 85 miles after installing it so the ECU could adjust.

Any thoughts would be MUCH appreciated. I know the cat is next, but I want to make sure I'm not missing something else first. Also, since I've been able to impact the results, I feel I can get it better before going for a new cat--I also don't want high HC burning out a new cat. Maybe speed sensor? Fuel injectors? FPR? Is there a reference sensor for the timing somewhere?

Thanks in advance and I really appreciate any help!!

 

I can't offer any technical help, but I will say I feel for you. Those CA smog tests always gave me more test anxiety than any exam I ever took in college! I do miss the weather, but I am glad to have moved away from the emissions test. Good luck nailing down the issue!

 

Yeah, they are a real pain and give me more trouble than any test I've ever taken! I've also got an '88 BMW 535is that's a gross polluter, but I can't let it go! First things first though, need to get the brick to pass. It runs so well (compared to my '90 wagon that DID pass right before I crashed it) so I'm really confused. Its gotta be (I've said this many times) the cat but I want to leave no stone unturned before swapping that out.

Thanks for the support!

 

You need a new cat. That is the short answer.
My 82 was similar, after a new high flow cat, the car burned super clean.

As for trying to get the numbers down, not sure how much room you have to play with.
It is not a programmable ecu where you can change the tune.

 

Agree its mostly likely the cat. I'm being a bit obsessive with it trying to get it running absolutely perfectly. Also, since I've gotten readings from 165-105 in HC and 1391-721 in NOx, I'm just wondering if there's anything more I can do first. The change in timing is a bit curious going from 12 degrees to 10 degrees in just a day and 85 miles later. I think the ECU is still compensating to the new O2 sensor. I also just re-checked codes and got 2-3-2 (Fuel system compensating for rich or lean air/fuel mixture at idle) which could be from the compression test and 2-1-2 (O2 sensor missing or faulty) which could just be from when I replaced it, although I don't remember turning the ignition on with it disconnected. I'll check again after a couple hundred miles or so.

Thanks!

 

Yep. Timing the motor will effect it for sure. but I am not sure how much adjustment you can do. I'm no expert.

High NOs is from high engine cylinder temps. Caused by lean or rich conditions.
An EGR valve helps lower the cylinder temps.

I bought a new O2 sensor for the 82 when it wouldn't pass smog, and notices the Bosch numbers where different. Not sure if they updated the numbers, but The 82 didn't run right with the new O2 sensor. I know it needed a new fuel filter, but never got around to that before the car was totaled.

On the cats... You should be able to get a standard cat from magnaflow and have it welded or bolted on. I believe the stock size is like 2.25"...
they are like $150-$250 depending on sizing.

 

Well I guess I need to be wary of the non-Bosch O2 sensor that I installed. I had it laying around new in-the-box and figured I'd use it. Its the right one for the car, but I guess specs can be different. Why can't things be simple! I do have a Volvo OEM cat (made by Bosal but sold as Volvo OEM and in a Volvo OEM box) that I can install so good to go there if I don't find anything else wrong first.

 

check your egr system, if you have one (most california cars post 1989 do). unplug the vacuum line that goes from the EGR control valve to the EGR actuator, and hook it up to a 'mity-vac' style vacuum pump. start the car, then pump down the vacuum line, the engine should stumble and almost stall, and recover and soon as you release the vacuum.

on the LH2.4 'onboard diagnostic', theres a process called "DTM#3" which exercises the various actuators on the car, doing this test on the ignition side of the OBD cycles the EGR control valve, so if you take a clean vacuum hose hooked up to the control valve and blow into it, you should feel your air flow cut off/on/off/on as the test cycles the actuator.

see Engine and OBD Diagnostic Codes for the OBD stuff, including this EGR test

 

Thanks pierce. Yes, I checked all the EGR stuff. I immediately thought that was my problem given the high NOx and tested all the components and everything is working properly.

It would be great to know what the optimal smog readings should be without the cat so I can baseline whether I still have any problems or not. I wish I had such expensive equipment!

 

put the car in 3rd (OD disabled) and drive the snot out of it for 30 minutes, maintaining high RPMs on the freeway. that will often burn enough crud out of the cat to get the numbers back down.

 

HA! That's worth a try. Should be fun too!

 

Absent any more thoughts, I'm going to try the 3rd gear high rev burn-off suggestion and also drive it a couple hundred more miles to see if the idle adjusts back to 12 degrees--That might tell me the ECU has adjusted to the new O2 sensor. I may re-test at that point just to see if anything has changed then do the cat replacement.

I just ordered an iPD sport exhaust system with the resonator delete and 240 turbo muffler. I know when I get under there to swap the cat, I'll end up needing to do the whole cat-back and this sounds like a good option that's hopefully not too loud--It shouldn't be based on the feedback I've read. We'll see...

 

I put a few hundred more miles on it and went in for another test (They gave me a free one!) The timing is back to 12 degrees BTC so I figure the ECU has adjusted. I also drove it at high rpm for a awhile on the freeway to try and burn any of the crud out.

RESULTS 15MPH / 25MPH
HC 86 on max of 81 (fail) / 43 on max of 63
CO% .19 on max of .52 / .11 on max of .43
NOx 679 on max of 554 (fail) / 593 on max of 511 (fail)

The HC dropped to the lowest levels yet and the CO% dropped a lot and is around the averages. NOx didn't change much but the 679 is the lowest reading so far and less than half of my highest reading. I started another thread on 'cleaning the cat' which I've seen people do online. It might be worth a try?

 

I suspect you need a new cat. and maybe your EGR is plugged.

 

I had a somewhat similar experience with my '87 240 sedan about 6 years ago maybe more. I replaced the catalytic converter and it still failed. I then replace the Mass Air Sensor. It failed. I was at whits end, so I took it to a Volvo dealer. They said that they just needed to do a calibration on the Mass Air Sensor. It passed.

Since then I found an independent Volvo mechanic. He says the trick is to to make sure the car is nice and warmed up before testing. Perhaps, he is doing the "Italian Tune up" that Pierce describes before testing. It does seem to work. I haven't had problems since then.

Good luck. I know from experience how frustrating this is. Keep us posted.

 

california lh2.4 240's have EGR, and when the EGR pipe or valve gets plugged up, you get high NOx.

the quick and dirty test is to warm up the car, leave it idling, disconnect the EGR vacuum line at the control valve, and connect it to a mityvac. suck a few PSI vacuum on the EGR actuator, and the engine should stumble and stall as exhaust gases are let into the intake manifold at idle. release the vacuum and it should immediately return to running normal.

the EGR pipe goes around the back of the engine block, one end is on the exhaust manifold, the other end is on the EGR valve thats attached to the side of the engine block below the intake manifold. the EGR valve is connected via a pushrod to the EGR actuator. the actuator has a vacuum line to the control valve, which is near the power steering reservoir, and that control valve in turn has another vacuum line to the vacuum tree on the throttle body and intake manifold.

the ICU electrically pulses that control valve to suck on the actuator and let exhaust gas into the intake to reduce the amount of air (and fuel) in the engine at medium RPM and low throttle settings, this cools the engine and reduces the amount of nitrous oxides.

the pipe or valve get plugged up. they also get incredibly rusty. sometimes you can poke them clear with a steel cable

on these LH2.4 cars, there is an onboard diagnostic box under the hood, with a jumper wire, 6 numbered holes, a push button and a LED. normally you use this to read error codes from the ECU (slot 2) and the ICU (slot 6). You can also run some computerized tests with this, Diagnostic Test Mode #3, in slot 6 (ICU), this will cycle the EGR control valve, so you know the electronic side is working.

 

Thanks again for this info. I thought EGR first myself and I've done all the tests to confirm everything is working including unnecessarily replacing the EGR temp sensor and actuator itself. My problem is something else and hopefully I can figure it out and it will help others. The AMM is a good thought. I did clean mine and have another one from my previous 240 so I can swap that and see if anything changes too. I don't have any error codes.

I haven't had a chance to replace the cat yet but will post results after changing that.