Cure Found for 1985 245 High NOX Emissions – Unusual Cause?

I have read many posts on the Brickboard concerning high NOX emission test failures. Although there are numerous possible causes (lean mixture, advanced timing, carbon buildup, over heating, etc.) the failure mode described here may be frequently overlooked.

I recently bought a nice, straight 1985 245 with a manual transmission and 186K miles for $450. The wagon had been under the care of a medical student during the last year or so. He had installed a new engine wiring harness and four new tires, but wasn’t successful in registering the vehicle. Two smog tests had been failed and “Earl” as we now call him, was labeled a “gross polluter”. “Earl“ was frightfully high on all the critical measurements (hydrocarbons, carbon monoxide and oxides of nitrogen) and morbidly low on self-esteem.

Having serviced my own fleet of 240s over the last 16 years, I jumped in and covered all the basics (new air filter, plug, cap, rotor, throttle body, etc.) and some of the less obvious (oil cap gasket and oil dipstick o-ring). Three major corrections were:

1. Obvious and noisy exhaust leak at the manifold/header pipe junction. One nut was found to be missing. New gasket and nuts were installed.

2. Timing was found to be 4 degrees BTDC and was corrected to 12 degrees BTDC.

3. Catalytic converter was checked with an infrared thermometer and found to be non-functional. A used converter was installed. This was a direct fit aftermarket converter purchased for $120 in 2001. It had seen 12K miles of service and had then sat unused in a car that had been parked for the last two years.

“Earl” felt he was ready, so off he went to my favorite Asian run test-only smog station (they do a free re-test). This is Southern California and a two speed dynometer test is required. “Earl” was shocked when he FLUNKED on low speed NOX:

15 mph - max/measured
HC 133/26
CO 0.82/0.03
NOX 1125/1707 - Failed

25 mph - max/measured
HC 108/23
CO 0.62/0.02
NOX 955/742

Hmmm, maybe the converter hadn’t aged well? I was willing to install a new converter on the car, but was suspicious that only the NOX stage had failed. “Earl” had a very slight exhaust noise noticeable around the engine compartment. I might not have noticed it, but for the fact he sounded just a bit different than all my other 240s. I couldn’t find an obvious leak. I used a length of hose to listen along the exhaust from the manifold to the converter. I heard a very muffled putt-putting near the rear of the first heat shield at the L-bend in the header pipe. This was just discernable above the background engine/exhaust noises, but not by much.

A LOT of internet research lead me to some interesting information and identification of ”Earl’s” true problem. Because there are pressure pulses in the exhaust, a leak will pull in outside air, as well as, vent exhaust gas. Excess oxygen in the converter will enhance the conversion of hydrocarbons, but will IMPEDE the conversion of NOX.

Removal of the first heat shield on the header pipe revealed a crack on both sides of the left portion of the pipe at the L-bend. Was this the underlying cause for the high NOX reading?





A replacement header pipe was obtained from FCP Groton ($89, Borsal – made in Canada). With no other changes, “Earl” then was able to produce the following impressive results:

15 mph - max/measured
HC 133/40
CO 0.82/0.02
NOX 1125/122

25 mph - max/measured
HC 108/25
CO 0.62/0.01
NOX 955/89

My other 240s have typically shown cracking at the “Y” junction in the header pipe. Considering the magnitude of the effect of excess oxygen, a brand new converter may well have not be able to even mask the problem in order to past the smog test. With High NOX emissions, you would do well to check all gaskets between the cylinder head and the converter along with the integrity of the exhaust manifold and header pipe.

Regards,

Tatra Mike
San Diego, California

1985 244 "Alfsen" (wife's car - the good one)
1984 245 "Buster" (in Seattle with the kid}
1985 245 "Cosmo" (currently at anchor in the driveway)
1985 245 "Daisy" (back seat down, full of tools, the work truck)
1985 245 "Earl (Hurray, another stick shift!)

Hi Mike

I live in San Diego too and I'm having problems with my 85 Volvo 240.
Passing smog can you refer me to a competent Volvo smog mechanic in the area?

Thank You

hi javier,
please read "lucid's" post above (bruce young). bruce has since passed, a major contributor to bb.

it worked for me, and he's the one who discovered it.

regards,
byron golden
86 245
92 245
94 940

Hi uneekneek,

Hope you are at least in fine fettle.

Tatra Mike has not posted on the brickboard through his account since Sun Dec 20 15:15 CST 2015. This thread dates as 2006.

Are you also unable to pass CA-state emissions inspection, what some call the "smog inspection"? High exhaust Nitrogen Oxides, or Oxides of Nitrogen, or NOx? Or another issue?

The solution in this thread suggests a source of high nitrogen oxides is an exhaust leak somewhere in the header pipe. Usually the header pipe at the Y-weld, routing two exhaust pipe section into one, is a suspect. If you may or may not hear an exhaust leak. ON a cold engine and exhaust, one method is a spray bottle full of a strong mixture of dish detergent and water. Spraying around the exhaust from the cylinder head gaskets (all four) to the header pipe outlet to catalytic converter input. One clue leading to failure of any union is connection, or lack of it, if the header pipe to the bracket that secures to the RWD Volvo (as you set in the RWD Volvo) transmission bell housing header pipe exhaust support bracket is missing.

Spray the detergent - water mix around the exhaust at union and else where. Ask an assistant, with transmission in park and parking break on, to start the engine. Continue to spray and where you find bubble forming, you have found an exhaust leak.

Though exhaust leaks downstream of the catalytic convertor can effect emissions.

Further, your 1985 uses the Chrysler-MPG ignition ECU module that secures to the windshield washer fluid basket frame. Though I'd not actually tested the description as is in prior posts on this topic to effect NOx (or HC exhaust content), the aging Chrysler-MPG ignition ECU module may deliver a dwell duration that is too long (the spark endures). A solution was to disconnect the vacuum line from the Chrysler-MPG ignition ECU module and plug the vacuum line and vacuum line connector on the Chrysler-MPG ignition ECU module. In CA-state, you would conceal the vacuum line so the inspector cannot see the change. Maybe disconnect the vacuum line from the air intake manifold.

Further, inside the air filter box is the preheater flap valve that blends the ambient air with air preheated at the exhaust manifold heat shield or shroud. There is a silver accordion-style hose between the heat shroud and the air filter box lower air inlet obscured by the water pump fan cowl or shroud. As you are in CA-state, some may block clog the air filter box preheater air inlet, remove the preheater flap valve assembly from the air filter box, and restore the air filter box so it appears the preheat function appear to be connected.

The preheater flap valve is controlled by a thermostat. After market is Borg-Warner Wahler PN 70411. Replace every two years or so I read. Or get the Volvo OEM version, I guess. As Volvo is now owned by China Geely, OEM parts are no longer the quality they were.

If you find your air filter box preheater flap valve stuck to all hot all the time, the AMM / MAF can fail. You won't pass emissions.

You may want to test other sensors like the oxygen and engine control coolant temperature sensor ECT (not the temp gauge meter).

Read here, to start. See also engine sensors in the FAQ.

https://www.brickboard.com/FAQ/700-900/EnginePerformanceSymptoms.htm

You will need a digital electric multimeter to test sensor and devices at the sensor or device and through the wire harness.

I'll guess the engine control wire harness has been replaced. 1985 is in the year range of the 'rotting wire harness'.

Others can suggest good repair services for you in the San Diego, California area. You can also check here at these links (copy and paste into a new browser tab or window), and verify with the BBB and with social media comments.

- https://www.brickboard.com/SHOPS/
- https://www.volvomechanics.com/
- https://www.cartalk.com/mechanics-files
- AAA or other motoring club, yet they usually recommend premium price repair services.

You may be able to use Google and Bing to find shops not listed through these resources I post for you.

Questions?

Hope that helps.

Duffed.
--
Donate NOW! Give your brickboard.com a big DONATION!!! Find the on brickboard pages!

Dear Mike,

after 3 failed smogs and extensive coverage on diagnosing, checking, and fixing pre emission problems, my 86' 740 Barely passed Nox. My Swedish Mechanic told me to change the header pipe. Your posting gives me so much hope for my next smog in
Sept/2016 when I'll remove, check, and/or change the pipe. Thank You for posting all the text and photos.

Thanks, Wayne Garabedian, Fresno

Very nice writeup.
It is ovious that the intermittent "vacuum" caused by the pulsating exhaust draws in outside air and corrupts the reading of the o2 sensor too...

Greg Mustang
www.volvoclassic.bravehost.com

Mike, thanks for sharing your story. I have seen this info from this link (posted here):

My next test was to monitor the oxygen senor for proper switching with my lab scope. But as I was connecting the scope to the O2 senor, I realized that I had an exhaust leak at the donut located a few inches below the O2 sensor. I verified that I had good O2 sensor switching, but my mind went back to the theory. The reduction catalyst does not like oxygen. Could the exhaust leak be causing enough of an induction of oxygen to thwart the best intentions of the new catalyst? And, yes, in case you didn't know, an exhaust leak to the outside will also draw oxygen inside due to the pulsations in the exhaust system. So I recommended replacement of the exhaust donut as a possible cure.

This simple fix, which turned out to be only the tightening of loose nuts on the flange, had spectacular results.

Real-World Repairs for Real-World� NOx Failures - Motor Age

--
Norm Cook; Vancouver BC; 1989 745T 220,000KM

Norm,

Yes, that link describes the senario exactly. What's interesting is the vehicle (a Ford) was failing horribly on NOX even though a new converter had been installed. I wonder how many 240 owners who don't do their own work run into this problem, throw their hands up (after spending many dollars) and send the poor car off to the wreckers. Sad.

Regards,

Tatra Mike
San Diego, California

1985 244 "Alfsen" (wife's car - the good one)
1984 245 "Buster" (in Seattle with the kid}
1985 245 "Cosmo" (currently at anchor in the driveway)
1985 245 "Daisy" (back seat down, full of tools, the work truck)
1985 245 "Earl (Hurray, another stick shift!)

Great post! This not only applies to the 240, but any engine with a cat converter. My wife's A6 with 2 separate exhausts had both flex pipes break and that produced a bad reading for the rear O2 sensors. Dealer wanted to replace both converters for $1300 each! A local muffler shop cut out the flex pipes and welded in new ones, problem solved for $200.
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My name is Klaus and I am a V♂lv♂holic

This should be put in the FAQs -- it's a great example of what makes Brickboard so useful!

Thank you for sharing!

Those are impressive results.
And potentially useful information for all of us!
--
Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.

Great job troubleshooting. I too had done a search awhile back to find info on high NOX causes. My '87 had failed twice because of it. I only came across one listing that talked about exhaust leaks ahead of the cat as being a cause. I'll have to check mine. I removed the heat shields due to rattling some time back. I should probably check the pipe for cracks. As far as being an unusual cause, probably not that unusual. Just that the other causes probably have a greater effect.

"I too had done a search awhile back to find info on high NOX causes. My '87 had failed twice because of it."

I've been posting on this since discovering it a couple of years ago. It's been found that the V/C Ignition can contribute to High NOx, and that plugging the vacuum line to the ICU can reduce NOx levels, with little or no effect on normal operation. Note that this is not a guaranteed fix, but worth a try if your other numbers (and cat) are good.

=======(canned Post)==============>

This is my canned post on this subject. It might work for you as it has for several others, especially with a new cat.
The first link explains the cause/effect theory. I didn't write the tech info -- I only found it on a 'net search.

For a technical description, see my original post here, and a success story here.

Other positive responses are posted in this thread and this one,
and one more here.
Yet another one .
And another on 2/04/06.

<==================================

--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Thanks Bruce, I have a copy of your original posts saved. I ultimately passed emissions both times without plugging the ICU. First time was replacing the cat (it was gutted; straight pipe, nothing inside). That dropped NOX to extremely low levels. Two years later I failed but passed on the restest (performed right after the failure) by about 3 points. Figure if I don't find any other problems I will do the ICU next year.

Thanks Mike
Great Info!
Ken
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White 86-245 DL, M 46, IPD bars & Wagon Overloads,Commando Bumpers,SS Belly Pan & Air Pickup,Straight-Shot EMT Chassis & Tower Braces,Scorpius Alloys,2 Belt No AC Conversion,Black POR-15 No Glare Front End