Smokey 2 litre

[Merlin8r]

Hi guys,
We recently bought our first VW, a 2000 Golf 2.0. Happy with it for the most part (seems built like a tank), but she's blowing an awful lot of black smoke. Black is better than blue at least.

I took it up to our local VW mechanic (Autohaus at Hornsby, I highly recommend them) for a quick diagnosis. It was Christmas eve and they were having a clean up day. He didn't really have to help me but he did. Anyways, I suspected O2 sensors, but they came back with no fault codes. The mechanic suspected a MAF sensor and replaced that, as well as resetting the computer. It made an improvement to be sure, but the fuel economy is still awful and under high revs she blows jets of smoke worse than the filthiest diesel I have ever seen.

I have replaced the air filter and spark plugs. The latter were badly carbon fouled. Today I took the car to the dealer (as it's still under warranty, phew), and had another diagnostic done.

Still no O2 faults, but it is reading multiple misfires, and saying it's running lean. Which explains why it's dumping so much extra fuel to try and enrich the mixture. SO.... am I right to assume the O2 sensors are indeed faulty, but just not telling the computer that they are?

I'll be taking the car back to our mechanic on Monday morning and giving him the story, just wondering if anyone has some ideas and what else it could be.

Cheers in advance!

[h100vw]

Coolant temp sensor is always a favourite for bad running. You would be able to see the output of the sensor with the VW diagnostic tool or VAG-COM. Proving it to be good or not.

No fault code doesn't automatically mean it's ok. There's plenty of parts in the loop that don't throw faults.

You can also check the MAF/airflow meter in real time, so you might be able to get your old one back.

Take the vac pipe off the fuel pressure regulator too and make sure that's not got fuel in it.

Gavin

[Merlin8r]

Thanks Gavin,

I still have the old MAF sensor, but it is better with the new one.

I didn't see any fault in the temp sender unit, and it was replaced about 2 years ago.

I don't know where the fuel pressure regulator is!

[Golf Loon]

You should replace the magic 3 at the same time.
MAF, 02 sensor and Temp Sensor.
That almost always fixes the problem and is what they would do at the dealership.

[h100vw]

Temp sensor doesn't put up a code unless it is broken. They give out duff info and kid the ECU into thinking the engine is cold, which dumps in extra fuel.

Even a new one could fail.

The FPR is on the fuel rail, not familiar with your motor so you may need to remove and engine cover. Held in with a U clip.

http://www.buzzle.com/articles/symptoms-of-a-bad-fuel-pressure-regulator.html

Gavin

[Merlin8r]

Ok, is the temp sensor not coupled to the temp gauge? I run at a steady 90 degrees.

[h100vw]

Ok, is the temp sensor not coupled to the temp gauge? I run at a steady 90 degrees.

It is the same item but there are 2 sensors in it, one for the gauge and one for the ECU. Either can fail......

Even re-racking it might fix it up. They are NTC, negative temp co-effecient. They start at a high resistance and drop as the temp rises. If the contacts in the plug are dirty, this may cause the problem. Don't hold your breath though.
Gavin

[Jmac]

Temp sensor failing generally upsets the gauge too, its a good sign when the gauge is all over the place, steady 90 slap bang in the middle generally means itll be ok, vagcom , vchecker or any decent diagnostic scanner will read live data, that way you can keep an eye in the sender activity. Check the vac pipe to the fuel pressure reg, if its split then the pressure reg will be operating without vacuum thus you will have higher fuel pressure thus more fuel. Also you mention your mechanic said the system was lean, secondary air, split vac pipe, air hose, common at the air intake elbow from the airbox, this will lean the system and the o2 sensor will sense it and richen the system. Sounds like your mechanic uses a scanner, get him to read the live data and watch the 02 sensor activity, should be switching very quickly, get him to trick the system by introducing more air and watch the 02 sensor richen up and then spray some carby cleaner into the intake and watch the sensor react to the that, should be almost instant, if not suspect a lazy 02 sensor. I say this after he has checked for splits and leaks of course, as the ecu may already be getting "tricked".
Cheers
Jmac

[Merlin8r]

Just got the Black Beast back from the mechanic. Since the dealer is paying for the parts I insisted on having the O2 sensors replaced. To my surprise it only has one!

Anyways, initial results are great! Nice improvement in zippiness, and no more awful smell when pulling up our steep driveway. I'll have to drive it for a week to see if the fuel economy has improved (it can only get better). There is still an occasional puff of smoke, but he did say it would do that as it burned of the residual carbon in the system. The sensor pulled out was absolutely caked in it.

Draining the oil now, then taking her for a spin up to Brooklyn.

[Merlin8r]

OK, so had a full weekend and a bit to road test the machine.

She's fixed! Runs clean, more power, double the fuel economy, no bad smells. NOW I'm getting what I expected from VW ownership.

The morale of this story is, don't rely on the computers to tell you what's wrong with your car!

[barrenjoey owl]

OK, so had a full weekend and a bit to road test the machine.

She's fixed! Runs clean, more power, double the fuel economy, no bad smells. NOW I'm getting what I expected from VW ownership.

The morale of this story is, don't rely on the computers to tell you what's wrong with your car!

So what was the final diagnoses and fix?

[Merlin8r]

Bad O2 sensor. Was still functional, but so full of carbon it was giving dud instructions to the ECM.

The MAF sensor and coolant sender had been replaced 2 years ago. Good bet that the O2 should have been replaced too.