Hello,

I have an 88 Volvo 240DL that i've owned for a few years. It's passed smog twice most recently just three months ago. I bought it from my room mate (we co-owned it but he moved so I bought out his half) and had to get a smog test to transfer ownership. The muffler was cracked and needed to be replaced.

I took it to sort of a chop shop cheapo muffler place cuz it was cheap and they replaced the muffler.

I took it to have it smog checked at a different place and the NO emissions came out at like 1200!! The limit is like 560 or something! The thing is, the car JUST passed smog three months ago.

It seems odd that it failed right after I visited this sort of sketchy muffler shop. Do you think there's any chance the muffler guys chopped out my catalytic converter or something? Seems unlikely I know, but just three months ago the car was emitting 500 PPM NO and now it's emitting 1200PPM, weird....

At any rate, maybe the old muffler was cracked when it tested the last two times and that's why it passed, not sure really.

Can I please get advice on 1. my weird theory about the muffler shop thing, is that possible? Should I explore this or visit the muffler shop again? and 2. What can I do to diagnose and fix my NO emissions issue.

I'm mechanically inclined and have fixed lots of things on this volvo already. Thank you!!

 

Anything is possible but a muffler change should not cause this unless, well, nah... You can take a look and see what exactly the shop did--there should be a new shiny muffler there.
A "cracked muffler" would not help in passing the test as the computer would detect "dilution".
When is the last time you had something like a "tune up? A new O2 sensor does miracles for smog tests...

 

Never really tuned it up. It passed just 3 months ago and it has not been driven that much since then. What items should be tuned to effect the emissions? Is an OS sensor affordable and simple to install?

 

the O2 sensor is fairly easy to change. has 2 connectors, one is 2-wire (for the heater) and the other is single wire. on our 240, these are both on the firewall near the wiper motor. the O2 sensor itself is screwed into the exhaust pipe just forward of the catalytic converter. it can be corroded on their pretty hard, I used quite a lot of Kroil pennetrant on the last one I changed, and I used O2 sensor safe antisieze on the replacement sensor (being very careful not to get ANYthing on the actual O2 sensor tip).

 

Should I bother with taking the car to get a diagnostic test or should I just replace the oxygen sensor first thing?

Thanks.

 

I'd do a visual inspection of this muffler job before I did anything, and check the o2 sensor wiring. unluckily, your car is one year too old to have the onboard diagnostic module that would TELL you their was an O2 sensor problem.

 

Thank you. I'll take a look. Hopefully the location of both the cat and the o2 sensor are noted in my repair manual, it's a haynes or whatever, pretty good.

 

the exhaust manifold on the right side of the engine connects to a 'down pipe', this in turn connects to the catalytic converter, the O2 sensor sticks out the top side of the bottom end of that downpipe or the front of the catalytic converter, depending on the year/engine configuration. the back of the cat goes to a short pipe to a pre-muffler (sometimes called resonator), this in turn goes to another pipe to the main muffler, then out the tailpipe...

 

One more question, does the muffler have any effect on emissions? Maybe the muffler shop put on a bad muffler? I don't really know. What if the muffler guys put on an old one with lots of carbon deposits, think they could be effecting it?

I have this gut feeling that something didn't go wrong on my car in the last three months and that this emissions issue was caused by something the muffler shop did. It's a strange coincidence to get your car smogged, then three months later the muffler replaced, then RIGHT after that the emissions double...

 

Not a likely scenario. A muffler, even a new one is quite cheap--I doubt a shop would do that kind of a scam. Now, a cat. converter I can see, since it's a costly item...

 

If the catalytic convertor was missing, would I notice that a difference section of the exhaust system was cut and welded with something missing or replaced? The rest looks pretty much undisturbed.

 

if the catalytic converter was missing, there'd be no catalytic converter right after the downpipe and before the first resonator/muffler, just a stub of pipe.

 

Well I took the volvo back to the smog shop for my free re-test today and it passed. Emissions were half what they were last time.

All I did was fix the two automatic-fail items, new air intake hose and taped up one of the vacuum hoses coming from the intake/throttle body. Also I drove it around a bit more before testing it.

While the two items I fixed are technically part of the emissions system I was told by members from this forum they do not effect the emissions coming from the tail pipe, therefore I must assume the only difference here was adequately warming up the catalytic converter before taking it in.

Yay!

 

if by air intake hose, you mean the hose between the throttle body and the MAF (mass airflow sensor), thats absolutely critical to clean burning and efficient engine operation. any air leaks result in sub-optimal fuel-air mixtures.

and, if that vacuum line was in fact the one to the ICU, that also woudl result in sub-optimal ignition timing, which has a major impact on pollution.

 

I'm referring to the Heated Air Intake Hose- https://volvoforums.com/forum/volvo-...ke-hose-74305/

Pierce, you mentioned that one of the vacuum hoses that I referred to here- https://volvoforums.com/forum/volvo-...51/#post370313 - is either a hose that greatly effects the emissions reading out of the tail pipe and also drastically effects how well the engine runs, or it's something else that doesn't have anything to do with emissions from the pipe.... my car was running great with this hose busted, so I assume it wasn't the ICU hose you're referring to... but maybe it was!

 

well, trace it, and see where it goes. the carbon canister is that black plastic thing about the size of a pint paint can thats just behind the left edge of the radiator and down there, kind of half under the battery. the ICU is a flat rectangular box on the inside right fender, just behind the headlamp, and the vacuum hose goes to a 'bellows' like thing on the bottom front edge of it.

 

I'm having trouble tracking that vacuum hose, it seems to go down to a cluster of wires behind the left side of the front fender... I'm glad I didn't have to replace the whole hose because it looks like kind of a bitch to track exactly where it goes.

 

thats the left fender as in (US) driver side ? so, somewhere behind the battery? (I*think* the 240 battery is on the left, your right as you face the front of the car, but my 240 has migrated to the great pacific northwet with my college daughter).

 

Ya, i'm talking "left" to the driver, or, driver's side. At any rate, I fixed the hose that was torn, whatever it goes to...

 

the only vacuum consumer I can think of down there is the carbon canister. so likely the reason the car passed the actual emissions test was the air hose.... that or it was fully warmed up.

we had to replace the catalytic converter on our 87 a couple years ago to pass biannual smog inspection... 2 years prior it had barely passed by getting it as hot as possible and testing it immediately before it could cool down.