E34 help. CEL on, won't pass smog.

[mbonanni]

I just recently bought a 1991 525ia Islandgrun-metallic 21x,xxx miles. It runs fantatsic. No idle problems, not cold or hot start problems, it simply runs great. Problem at hand is the check engine light is on and it fails smog. Code 1221 and 1222 are being thrown, which are for #1 o2 sensor and a lean air/fuel mixture. I assume that can mean many different things. I attached a picture of the smog test we received with the car, any guesses what I should replace to get it to pass?

I would replace the o2 sensor that code 1221 is for, but I figured with the horrible smog results there may be a deeper problem.

[GDA]

Numbers appear to indicate a pretty bad rich condition that the DME is attempting to lean out and then causing high combustion temps and very high levels of NOx.

Smoke test it first before just throwing parts at it.

BTW - it is not running that great as your CO2 numbers are in the low 14s and you still have oxygen left over after combustion. Both of which mean power is left on the table.

[mbonanni]

Going to replace the o2 sensor and do a tuneup in hopes of clearing the codes. I want to smog test the car myself. The couple whom owned it before me was older and probably did not drive the car enough to heat the cats up, giving it poor smog results. I will do that in hopes it that will give me better/more accurate results to see where I am at as far as smog. Then I will go from there. I wouldn't doubt some vacuum lines need to be replaced, but like I said the car runs amazing. No indication of a vacuum leak.

[GDA]

You need to understand that the numbers indicate you have incomplete combustion so it can't be running that great. Since your impression is that it is running good it is probably something minor like a vacuum leak or maybe a weak coil leading to minor misfire.

The fact that NOx is so high does indicate that this issue has been out there for a while.

BTW - a well running car does not need CATs to pass smog. Complete combustion puts out essentially single to low double digits on all tests (prior to even getting to the CAT) so saying your CAT was not heated up is saying you need the CAT to fix an upstream fault of incomplete combustion to get it to pass.

Just trying to help explain based on your combustion gas readings.

[mbonanni]

I'm not saying there isn't a vacuum leak, but other vacuum leaks I have experienced affected the way the car ran. When I say the car runs great I mean it starts effortlessly, has smooth power through all gears and rpms, and idles fine.

When I went to smog my e30 I failed with similar, but not as bad results, I simply threw in some better fuel and did 20 more minutes of highway driving and I passed with much better results. I didn't have codes I could read like the e34, but I knew my cat and o2 sensor were good. Cats that aren't at normal operating temperature can hinder results.

I am going to do a visual check on the vacuum lines and see what I can find. I put in an order for a new o2 sensor, oil, drain plug, oul filter, air filter, fuel filter, and spark plugs last night. Going to check the cap and rotor to see what condition they are in as well. I am hoping the codes will be erased after a small tune up so I can at least smog it and see if the results are any better. If not, the next plan of action will be vacuum lines.

I still have my e30 to drive in the mean time.

E30 > E34 ;)

[mbonanni]

And just because every thread sucks without pictures, here is some cell phone pics I just took. Featuring one of my e30s as well.

[mbonanni]

It also might be worth a mention. I checked the hoses, and visually they all seemed solid. Of course hairlines cracks could be a problem, as well as hoses I cannot see. I was able to clear the codes and the CEL. I drove the car anywhere from 4-6 miles and the CEL did not come back on. I didnt drive it far because the tags are out dated, I will drive it more once I get a temporary moving permit.

[Aleksey]

It also might be worth a mention. I checked the hoses, and visually they all seemed solid. Of course hairlines cracks could be a problem, as well as hoses I cannot see. I was able to clear the codes and the CEL. I drove the car anywhere from 4-6 miles and the CEL did not come back on. I didnt drive it far because the tags are out dated, I will drive it more once I get a temporary moving permit.

Visual check is garbage. You need a smoke test or do a propane test. Pressure is the key post MAF. Pull your plugs and post pictures.