Emissions question HCs

[providence]

1991 325i Stock m20 Failed emissions due to high Hydrocarbons at idle and 2500 rpm.. 220 was the limit mine were around 281 and 289. Changed sparkplugs, did cataclean treatment, changed the oil and the shop said it still wouldnt pass. O2 sensor passes the tests in the Bentley.. continuing with more tests but wanted to get some insight. The shop will pre-test for me but they're pretty slow so I want to cover as much as I can before I bring it back.. not really in a position right now to throw a $$ new cat in there based on speculation. There's a leak at the connection after the cat.. in what way would that affect the emissions reading? Would that explain the fail? Thanks for any input.. not trying to cheap out just working with limited funds and time on my DD.

[jlevie]

O2 sensor tests only tell you that the sensor is doing something, not whether it is actually working correctly. If I were working on this car I would immediately:

1) Replace the ignition wires, distributor cap, and rotor with new OE parts
2) Replace the O2 sensor with a new OE part
3) Adjust the valves
4) Smoke test the intake/engine and fix any leaks
5) Verify that the engine stabilizes at normal temperature ~80c
6) Verify the ECT signal is correct at the DME
7) Verify the rail fuel pressure
8) Eliminate any exhaust leaks
9) Have the injectors cleaned. rebuilt, and flow tested

Depending on how the engine is behaving at that point there are other possibilities that might have to be investigated and fixed. There is a good chance that the catalytic converters will have to be replaced since a rich condition results in over heating and damage to them. But deal with everything else first.

[providence]

Thanks for your reply Jim-it's all solid advice, but by step 2 I'm already around the $300-400 range in parts hahaha.. actually cap and rotor are new OEM parts and very recent valve adjustment as well.. My current situation I just gotta try and get it to squeak by.

[jlevie]

If the cap and rotor are new OE parts you can skip those. Do the rest.

The parts listed in steps 1 & 2 are there because those parts have a scheduled replacement interval. The ignition parts are scheduled for replacement every 10yr/100k and the O2 sensor at 100k. Either, or both, can result in higher HC in the exhaust if beyond their replacement interval.

Any vehicle needs regular maintenance over it's lifetime. E3's are relatively inexpensive as compared to later BMW models, but even they need ~$1000/year spent on them after the first 4-5 years or 50k. If that has not been done, the bill eventually comes due.

[providence]

Oh absolutely.. I actually installed this used m20 about a month ago after a failed tensioner pulley, so after basic gaskets fluids belts from that job the old wallet is still a little sore. At least a portion of whats under the hood now is fresh parts. Thanks again.

[providence]

Thanks for the input guys, Passed emissions with a new O2 sensor and coolant temp sensor. Your input is much appreciated.