1993 940 wagon non-turbo - 272K miles

This is a clean and well-running vehicle bought from the original owner who servived it every 5K.
I've got all the warning lights and codes to clear by having the fuel injectors cleaned, replaced all the vacuum tubing under the hood.
It's passed smog with flying colors the last two times.

Yesterday everything tested O.K. but failed NOX and the Evap test. Evap I attribute to it failing the gas cap test and a loose evap canister hose as pointed out by the technician...I won't worry about that right now. I checked the filler neck rubber and it doesn't feel dry or cracked. I did buy a new gas cap as well.

The NOX I've been reading points to the EGR valve (per technician) or possibly the catalytic converter, or...?

I pulled the EGR tube that goes to the manifold back and ran a wire down it and flushed it with Sea Foam Deep Creep.
Manifold hole had some carbon, but not blocked. I also Deep Creeped the manifold at all the orifices I could find and through the throttle body. I'm running a bottle of Redline fuel treatment through it as well. This was recommended by two mechanics I spoke to.
I also replaced the flame trap which was fine.

What else should I look for? I'm wondering if I should pay to retest or take it in to smog repair shop first.

NOX readings: 15mph 674 ( 486 max) 25mph 790 (502 max).

 

NOx is produced from overly elevated combustion chamber temps. It's great that you cleaned the EGR passages...most folks lean or replace their EGR and never snap that the passages on some designs of engines are prone to clogging. The B230 F Ca version is pretty trouble free. Since you went to the trouble of cleaning the passages, I assume you checked that the EGR opened and closed freely without sticking or rough spots in its travel? Assuming that's the case, then it is probably time for a new catalytic converter. These are the two devices on the car that when they fail, raise NOx. Retarding the timing on an engine will lower combustion temps and reduce NOx significantly. For many years with my 84 760T I had to retard the timing to 8 degrees BTDC to get it to pass. Then I'd drive home and reset it. I had paint dots on the dizzy and block to make it a snap. Unfortunately, your car has LH2.4 and the distributor can not control timing. All is not lost however, as you can alter static timing by grounding pins on your ICU (NOT the ECU...the black one that controls ignition). I'd be glad to discuss it through pm. Truthfully though, the solution is, assuming the EGR valve works, is to get a new cat. Throwing a couple bottles of dry gas in a partially filled tank can't hurt either. It has methanol in it that burns cooler.

 

From reading on the Brickboard, some high NOX readings can come from leaks in the exhaust upstream from the catalytic convertor. Take a look and make sure that there are no leaks in exhaust manifold or where it joins the downpipe.

Also, you might want to take a look at this post:

http://www.brickboard.com/RWD/index.htm?id=1129821

Good luck

 

Thanks for the link, this is the second person who's said 'cat'.
Having 273K on it, I'd suspect that could be the case and I'll check it out.
There doesn't sound like any exhaust noises are present. Since it's a Southern California car there is no rust at all. Reason I bought the car is becasue the engine look like it came off the showroom floor!

As far as the intake manifold, it looks fresh as a daisy, the gasket looks brand new so I doubt any leakage there either.
I replaced all the vacuum hoses when I had the injectors sent out to be rebuilt as well.

I checked the EGR by applying a vacuum pump at the rubber tube going to the EGR at idle. The idle would stumble under pressure. When the pressure was released it would stabilize. I assume this means the EGR is working.
Not real clear on this I admit as the vacuum pump gauge, noot being entirely accurate, read between 5-10 lbs if I recall. I've read something about the EGR and too muc/not enough pressure, but didn't really understand it. So I'm unclear there.
To be truthful, I'd rather not tackle removing the EGR if possible.

As a note, the only noticeable ****le in the way the motor runs is when at a stop sign the car is in Drive foot on the brake, it doesn't idle cleanly, almost feels like it wants to die at times, especially in hot weather with the A/C on.
Before I did the injectors/vacuum hoses we had the 'Check Engine' light on constantly and it would die at stop signs. I found one bad thing was a melted wire on the speed sensor going to the tranny. That I replaced.
It had bad codes as well.
Now that's all cleared up, no bad codes at all, no lights on either.

What is 'dry gas'?

 

Dry gas is a generic name for any number of products, generally sold in pints, that are most effective in the north. It contains methanol and or ethanol and attaches itself to water droplets in the gasoline tank. In bitter cold weather, without it, gas lines can freeze up. I spent Christmas Day 1969 on a deserted interstate in North Dakota because of a frozen gas line. Alcohol burns significantly cooler and can reduce combustion chamber temps.
A lean condition can indeed raise combustion temps too but it's a rather uncommon condition in an LH2.4 Jetronic car compared to a dead "cat". LH2.4 will compensate for lean conditions and just throw more fuel into the mix assuming the O2 sensor is ranging properly. The safest way to check for intake leaks is to use a propane torch with the burner head removed. Take a 2-3 foot piece of vac hose and slide it over the end. With the engine running and the propane on, hold the hose about a half inch away from the intake mating surfaces, going all around it. A leak will be indicated by the idle increasing. You can use carb cleaner spray too...just like using propane as it's not as messy. There are some folks that will swear by stating fluid (ether) but the temp that it will ignite is amazingly low. Not talking flash point when a substance ignites with open flame but the temp at which it will ignite with a heated surface. So...check for intake leaks, listen for exhaust leaks with a hose...if you have an IR heat temp gun (Harbor Freight has 'em for cheap) check the inlet and outlet temps of the cat. A grossly failed cat will spew particles out the tailpipe onto your hand if a helper blips the throttle. The force of the exhaust will also be greatly reduced when blipped compared to a healthy car but that's pretty subjective. Volvos IMHO tend to run rich when old and modestly maintained. A rich mixture will hasten a cats demise. As to your poor idle, it would seem the Idle Air Control valve is not getting a good signal or is bad. Should definitely idle up when a/c is on. Rough idling? Lots of stuff and it seems you have covered most of the bases. The flame trap throws oily vapor into the throttle body to the point the blade will often not close properly. While most folks clean at the TB while on the car, I like to pull the TB and clean it spotlessly. Carb spray and an old toothbrush is all you need. Have a new TB gasket on hand as, if it has not been removed in awhile it will not survive! When doing this, it is a good time to reset the Throttle Position Sensor. After the TB is cleaned, hold itto your ear and move the throttle plate. You should hear a very faint click as the plate just begins to move. If you don't hear it, adjust accordingly. With the TPS dead or mis-adjusted, the ECU will not know you are idling and will not engage the IAC. Sorry for running on...some food for thought...

 

well, no leaks in the intake.
replaced the flame trap as mentioned, it was fine.

Doing some reading what I end up with for high NOX is:
NOx sensor _ assume this is the catcode Oxygen sensor, thinking of buying a new one before the smog test again.

Knock sensor - I can't even find this one

EGR valve - cleaned and function with the vacuum test I did.

My big worrie is the evap test. I replaced the gas cap that failed but I'm still not getting pressure release when I unscrew the cap. I've checked the rubber around the filler neck behind the inside panel but just a 'feel' test. Rubber feels good. One Volvo guy told me it's often the filler neck itself being out-of-round.
The other thing he mentioned was a slight possibility of a bad gasket at the gastenak sending unit. This one would be something I can't handle myself. Could be pricey!

Opinions on this are welcome.

 

Finally appplied for the California CAP program, getting $500 assistance to have the car repaired.
Mechanic is very capable but Friday toldme he's pulling his hair trying to get it to pass. 15mph good, 25mph no pass on the NOx.

Replaced CAT
Cleaned EGR valve and all passages
Checked all sensors including O2 sensor and everything checks out.
He's going to try replacing the O2 sensor with the OEM unit next.

I am waiting patiently...