Why a Volvo might not pass SMOG . . . .

Since it seems that we hear this same question quite often (why did I fail SMOG?), I've created a little article that might help that maybe we can refer to so we aren't diagnosing from readings and repeating the same things over and over.

Maintenance and proper running (Stage 0) is really the key, my '88 745T failed SMOG at around 90,000MI, since it's been in my ownership its always passed with flying colors even with the original cat at over 225,000MI and even with the new High Flow Catalytic Converter. My '87 740T at 267,000MI also passed SMOG with flying colors. Properly completed Stage 0 not only will enable you to pass SMOG, it can restore fuel economy, reliability and the overall performance of your Volvo.

Things that typically affect adversely affect SMOG (many of them extremely simple) . . . .

O2 Sensor (if it hasn't been replaced within the last 60,000-90,000MI it should be tested if not replaced depending on test results)

PCV System (Plastic V-Trap/Flame Trap/Oil Trap, black Breather Box below the Intake Manifold, PCV Valve on the Intake Manifold and all related hoses). Having a plugged or partially plugged PCV System can cause excess blowby which can cause a vehicle to do poorly in a SMOG test. The system should be checked and cleaned every 60,000MI especially if conventional oil (non synthetic is used) and ALL components in the system should be cleaned. A spotless and properly functioning PVC system can also reduce oil leakage from seals if the system was previously plugged up or partially plugged up and/or additionally reduce or stop excess white smoke from the exhaust.

If you have a stock airbox, make sure the preheated thermostat flap is not stuck open in the Airbox routing preheated air into the AMM screwing up it's reading/causing it to fry. If you have a post '90, also check for "deteriorating" Foam Insulation (sound deadening material) inside the airbox.

Fuel Pressure Regulator (usually if it hasn't been replaced within the last 90,000MI it should be replaced as preventative maintenance)

On pre late '88 Models, the wiring harness should be thoroughly looked at and inspected for any type of cracks in the wiring, exposed/damaged wires especially at the Fuel Injector grounds at the Fuel Rail. Exposed Fuel Injector Ground wires can cause a rich condition.

Incorrect Timing can also cause certain SMOG readings to be high

All Vacuum lines should be replaced after a certain age/so many miles (usually around 150,000 miles where they should all be replaced)

Dirty Throttlebody, Remove the Throttlebody Elbow, unscrew the Idle Adjustment Screw and pull it out for the carb cleaner to drain out if you have one. Open the Plate by moving the lever, spray it out with Carb Cleaner (don't overdo it), use a toothbrush if necessary, clean the plate, wipe it dry. On vehicles with a Idle Adjustment screw, the rubber O-Ring should be replaced after cleaning, this is just a standard rubber Dipstick O-Ring. After cleaning the Throttlebody it is not uncommon to maybe have a hard start after for the first one or two startups.

After so many miles (maybe around 150,000) it is a good idea to replace the Intake Manifold Gasket, Throttlebody Gasket and Fuel Injector Seals

New Ignition Components such as good plugs, Cap/Rotor, Wires can often help. Often gapping plugs a little wider than recommended if your coil is strong enough and you are not running much more than stock boost can often yeild slightly better results. Myself and others here on the forum have experimented with many Spark Plugs and have had great success with Autolite plugs in redblocks, either AP64's or a colder heat range (AP63's). After gapping them to .046 (stock boost), I noticed the engine seemed to idle even smoother, have a little more punch and fuel economy increased.

Cleaning ALL ECU/FI related grounds can sometimes help. Remove and clean ALL ECU/FI system related grounds, Fuel Injector Grounds at Intake Manifold/Fuel Rail, ECU grounds behind the ECU and Ignition Control Unit grounds on the driver side opposite the ECU grounds. Believe it or not this can sometimes make a difference even if they "appear" to be fine. They can be easily cleaned with a toothbrush and rubbing alcohol. Be sure to clean the grounding plates and mounting screws/bolts of the ground plates additional to the connectors themselves.

Try running some good Fuel Injector Cleaner (I prefer Marvel Mystery Oil).

Fresh oil and a clean crankcase probably isn't a bad idea. It can help reduce contamination from blowby and deposits from conventional oil. I have found Valvoline/Pyroil Engine Flush to be very cheap, quick and effective with all 3 Volvos I have owned. The good thing about this engine flush is that you do not drive it or rev it with this chemical in the crankcase and you only let it idle for a few minutes, then drain so it's generally pretty safe. Additionally, I also pour a half a quart of cheap stuff through and let it drain to make sure the chemical is completely removed. I purchased my 960 which had documented regular and before schedule oil changes by a Volvo dealer. I changed the oil with synthetic immediately after I bought it thinking that was good enough. The oil was still a light honey color on the dipstick and looked brand new after 200 miles. I decided to try this engine flush, I let it idle for 7 minutes (directions say 5), then drained and to my surprise the oil was black and thick.

Last, before getting a SMOG check be sure to allow your Volvo to fully warm up and even take it for a hard drive around the block, older Volvos are notorious for failing when cold and often only do best when fully warmed up.

All of this should be checked/and or done before even thinking about replacing the Catalytic Converter since a rich condition can ruin even a new unit after so long.


If anyone has any other SMOG tips or information feel free to contribute . . . .

Great write up. I found it very informative. I dont need to worry about SMOG testing as much as others but I still found this very helpfull, it just gives you a good fealing to know your car is running as well as it can be.
Great article!

-Jacob

Find a cool smog tech, then put a rag on the end of the probe. Voila!

sweet, you covered both reasons why i failed my smog..hahaha

warming it up is a fantastic free tip, it helps.

Don't use carb cleaner on the throttle body, It can ruin O-rings etc. They make throttle body cleaner that lubricates as well as cleans. fyi.

cool, thanks for all the comments guys! glad it's helpful!

Thanks for the info on the carb cleaner, it can ruin the Idle Adjustment o-ring below so I edited it to also recommend replacing the o-ring after.

cst805 said:

Find a cool smog tech, then put a rag on the end of the probe. Voila!

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hahaha, well yeah, anyone can do that. However it's best to do it the right way for the sake of restoring original performance, smoothness and fuel economy. All of which can be a major benefit to you and your vehicle not to mention can save you money while doing the enviornment a much needed favor.

its easyer to pass on a cool rainy day according to some sources.

I stopped registering my car back home and started registering it here at school just because I didn't want to drive back and do smog testing this summer. It was having reliability problems and I didn't have any $$$.

+1 for the importance of warmup. If you have to wait, go drive around, and come back.
Starting and immediately running the test(so even a good running car will fail), then selling you a repair is an evil pattern I see at way too many Smog shops that are not 'pass or no pay'. thy have a vested intrest in your failing. thtey already know if they run the car 10 mins, then test it will pass, so they might not even do the repair they sell you...

If NOx is a little high, it often helps to retard the timing a little(3 degreees off spec is allowed).
If idle is not smooth, it can help to raise the idle to max allowable(950? for 4 cyls?) setting to smooth thing out, but don't turn it up enough for the EGR to come on.

I have a friend with too many cars,...He keeps a NEW catalytic convertor, and installs it to go get smogged, then swaps it back to the shelf. Cats are realy effective when brand new, and will pass a car that should fail.

If you are missing emission parts, grab some random litlte check valve thingy off another car(yours or JY), and install it where the missing part should be, most of the time nobody notices.

I usualy passed
Now I own 3 exempt vehicles!

When my moms car kjet with no lambda failed, i pulled off a vacuum line and it leaned out enough to pass

nice write up, as a pennsylvania emmisions repair technician I notice a lot of emissions failures due to lack of maintenance. Most repairs I make usually include thermostat replacement, o2 sensor replacement, oil changes, and mass airflow sensor cleaning. sometimes a good seafoam treatment will repair marginal failures.

thanks, yeah definately . . . !

745 TurboGreasel said:

+1 for the importance of warmup. If you have to wait, go drive around, and come back.

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If your car came with a three+ wire oxygen sensor, make sure it still has one. The extra wires are for the heating element... good for keeping the ox sensor warm enough even if you've been idling for a while.

745 TurboGreasel said:

If NOx is a little high, it often helps to retard the timing a little(3 degreees off spec is allowed).

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For most red blocks, it's 10 +- 2 degrees, I believe. This is stated on the underhood smog plate. Of course, the red blocks don't have timing marks in one degree increments...

745 TurboGreasel said:

If idle is not smooth, it can help to raise the idle to max allowable(950? for 4 cyls?) setting to smooth thing out, but don't turn it up enough for the EGR to come on.

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That also depends a lot on the car (said info is also on underhood smog plate). However, the idle is of no consequence to most people in California (since most non-rural areas do dyno testing only).

745 TurboGreasel said:

I have a friend with too many cars,...He keeps a NEW catalytic convertor, and installs it to go get smogged, then swaps it back to the shelf. Cats are realy effective when brand new, and will pass a car that should fail.

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