Alfa Romeo Forums banner

1 - 5 of 5 Posts

·
Registered
Joined
·
1,125 Posts
Discussion Starter #1
My L-Jet flunked NOX and HC. NOX was 1864, needs to be 1438. HC was 208, needs to be 187. Smokes on hard acceleration, noisey valves despite new valve adjustment and a rather ominous deep ratel tied to acceleration at the top of the torque curve. Suggestions? About 95,000 miles.
 

·
Administrator
Joined
·
16,661 Posts
Generally, prior to an emission test, one should change the oil and then take the car out for a long ride (45 - 60 minutes is good). Make sure it is fully warmed up for the emissions testing.

How old are the O2 sensor & the catalytic converter? Neither lasts forever, 50,000 miles is a typical life for the O2 sensor. If the sensor fails, the ECU (computer) will default to an 'open loop' mode which is slightly richer than ideal. And a richer mixture will shorten the life of the catalytic converter...

Also, is the CTS (Coolant Temp Sensor) working OK? This item tells the ECU the engine has warmed up and then it comes out of open loop mode and begins to use the O2 sensor's output to adjust the mixture. (this is not the gauge sender, BTW)

If you need to replace the cat, note that the front pipe/cat assembly retails for $300 - $500! But you can buy a replacement cat for about $100 and have the old one cut out and the new one welded in for about $25 - $50.

Is the emisions test done at idle or higher RPM? At idle the O2 sensor may not be warm enough to come into play and the ECU goes back into the 'open loop' mode. For idle only emmisions there is an 'idle bypass screw'. Do you know if that has been messed with? Or if the AFM (Air Flow Meter) flap spring has been 'adjusted? Adjusting the spring was sometimes done in attempt to increase fuel flow for more power.

More info here: Spider L-jet tune up & diagnosis
 

·
Premium Member
Joined
·
21,386 Posts
Sounds like the car may not be running all that great in the first place. High NOx generally is caused by excessive leanness; high HC is caused by misfire or otherwise unburned fuel; might be poor compression? I might install new plugs too.

Andrew
 

·
Registered
Joined
·
1,233 Posts
You have high HC and NOX (I would guess your CO is high too). Without knowing you car more, I would take a quick guess to say you probably have some air leak that cause some ignition misses (due to mixture too lean). This will give you high emission on all three (CO, HC, NOX) with a hot engine. So, first thing first, check that you have a tight intake system with minimal air leak. Then a strong ignition system ...

I just got a '86 quad to pass MA emission yesterday. The inside of the cat was all broken up and one big piece was plugging up the tailpipe when I started on it. The O2 sensor was dead and I think this was why the cat was damaged due to overheat . The O2 sensor looked original (car has 120K mi) and it was fused to the downpipe. I had to take the downpipe out to cut out the sensor (heat didn't work). I also removed whatever remained inside the cat (it mostly all broken up already) and I put on a Bosch 13953 O2 sensor (listed for Ford Taurus, somewhat cheaper) . I knew without a (working) cat, it was going to be a challenge and a balancing act to get all three emission components low enough! ... But it did pass the dyno emission test :)!
 
1 - 5 of 5 Posts
Top