GolfGTIforum.co.uk
Model specific boards => Golf mk2 => Topic started by: jmsheahan on 22 September 2010, 20:22
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Hi all,
My 8v digi has been running a little rich recently and smells quite fumey from the exhaust. Just had a search and I'm working my way through a list of what it could be but is there anything I may have missed? I had the CO level checked today/put on an emissions machine and the Hydrocarbon reading is apparently quite high although not enough do fail an MOT. Unfortunately I do not have a print out.
The car goes ok although idle sounds a bit lumpy which I'm wondering is a possible air leak? The best way I can describe it is the exhaust note sort of 'bobs'. Not enough to make the rev counter needle move. In addition the car pops a little on over run. The car had a head rebuild about 5k ago (new headgasket, stem seals, lifters, guides etc) as background info.
So far:
- New genuine blue temp sender
- New Bosch spark plugs
- CO level is bang on the money
- Cam timing is correct and ignition reset
I've just ordered a new Beru dizzy cap, rotor arm and leads to rule those out, as well as some replacement vacuum hoses in an effort to find any escaping air. Would an injector cleaner be worth a shot or is this just snake oil? Not a huge fan or redex.
Is there anything else I have missed or any new ideas?
Cheers
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High HC readings could suggest that the HG is on its way out.
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Does the throttle switch still work it might be faulty? Or lambda probe is giving wrong temps?
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I thought high HCs were an indication of oil burning?
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I thought high HCs were an indication of oil burning?
I thought HC standands for Hydro Carbons?
Which can mean oil or the car is running a tad rich?
I think the fact he said the idle was a bit lumpy sugested an over fueling isssue or bad mixture?
Saying that if the co2 was good it could be that it needed a really good thrashing before the test?
Jim was the engine warm when he tested it? Or was it a short journey to the MOT station?
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For some clarification (I think I'm wrong :embarassed:)
A. WHAT CAUSES HIGH HYDROCARBON (HC)?
Below are common failures which are likely to produce high Hydrocarbon HC. Hydrocarbons are basically raw fuel, otherwise known as Gasoline. High Hydrocarbon (HC) emissions are almost always a sign of poor fuel ignition. However, it's not always that the engine's ignition system is responsible for high Hydrocarbon emissions. Read on.
1. Improper Ignition Timing - Engine ignition timing is measured in degrees before or after Top Dead Center (TDC). Example of an ignition timing failure would be in the case where an engine's ignition timing is required to be set at 10 degrees Before Top Dead Center (BTDC) and instead is set to 15 degrees BTDC. This fault will not only cause a smog check "functional failure", but will increase Hyrdocarbon (HC) emissions as well. California allows 3 degrees +/- off of the manufacturer's required setting. Note: Late model vehicle's may not have a distributor, and therefore no timing adjustment will be needed. On these engines timing is electronically controlled by the ECU (Engine Control Unit).
2. Defective Ignition Components Your vehicle's ignition system consists of the ignition coil/s, distributor*, distributor cap*, distributor rotor*, ignition wires, and spark plugs. If any of these components are defective the engine will produce high hydrocarbons. A common reason ignition components perform poorly is due to carbon build-up. High ignition voltage traveling through the air pockets within these components form carbon. Carbon acts as an insulator between paths of electricity, decreasing the energy required at the spark plug to ignite the air/fuel in the combustion chambers properly. *Distributor-less engines do not have these components.
3. Lean Fuel Mixture - Any condition which will cause unmetered air to enter the intake manifold, and ultimately the combustion chambers, will cause high hydrocarbons (HC). This condition is called a lean miss-fire. Such faults as vacuum leaks and gasket leaks will cause lean fuel/air mixtures. Broken, disconnected or misrouted vacuum hoses will do the same. It is also important to note that many engine components rely on engine vacuum for proper operation. If any of these components are defective, externally or internally, they may cause large vacuum leaks as well. A good example of such a component is your vehicle's power brake booster.
Miles:
Which Type Should I Choose?
* Failed High HC Emissions
* Failed High CO Emissions
* Failed High NOx Emissions
4. Defective Catalytic Converter - A defective catalytic converter (CAT) may be responsible for high HC, CO, and NOx emissions. The Catalytic Converter, commonly referred to as the CAT is a component designed to continue the combustion process within itself and emit a more thoroughly burned and less harmful emissions containing exhaust. The most accurate way to find out if your vehicle's CAT is working efficiently is by using an exhaust gas analyzer. Unfortunately this tool is fairly expensive. Testing the CAT should be conducted at a smog check repair station.
Some obvious symptoms of a bad CAT could be any of the following:
a. Major loss of power over 15-25 mph. This may be an indication that the catalytic converter is plugged up and restricting exhaust flow.
b. Strong sulfer or rotten egg smell emitting from the exhaust on an otherwise good running vehicle. This may be an indication that the Catalytic Converter isn't burning fuel completely, instead storing it, then releasing it as hydrogen sulfide.
c. Loud rattle being heard from inside the CAT. This may indicate a broken Catalytic Converter substrate. You may want to insure this sound is not due to loose exhaust components, i.e. broken muffler flanges, loose exhaust pipes, loose or cracked exhaust manifold.
5. Defective Air Injection Components - Faulty smog pump and related emissions system components will cause high HC. The air injection system is designed to introduce additional oxygen, after the metering system, to the engine exhaust as it exits the exhaust manifold, or directly before it enters the Catalytic Converter; thus burning whatever remaining fuel (HC) in the exhaust completely.
6. Low Cylinder Compression - This fault is one of the less common high HC causing problems we encounter. Reasons an engine may have low or no compression in one or more of its cylinders may include things such as burned intake or exhaust valve/s, defective valve guides and/or seals, defective piston rings, and burned head gasket/s. A wet/dry cylinder compression test will diagnose this fault. More then often if such a problem exists it will be very apparent. You should notice rough idle.
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Why all the chat about cats?
There's no cat or lambda on the back of the PB motor in a Golf2.
What's more likely is that the engine temp sender has failed, causing the motor to run rich, but it's OK boys, grab the HC thing and run for the hills with it.
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Why all the chat about cats?
There's no cat or lambda on the back of the PB motor in a Golf2.
What's more likely is that the engine temp sender has failed, causing the motor to run rich, but it's OK boys, grab the HC thing and run for the hills with it.
My IH had a lambda sending wrong info to ECU DH TBH I thought all digipants had some sort of Lambda controls?
Lambda= just a temperature probe to determine if mixture is correct?
As for Ben that was helpful fella and if his compression is down it would cause HC to rise in reading!
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No UK market G2 had a lambda as far as I'm aware.
Continental ones certainly did.
Digi on the PB certainly has no lambda or emissions controls - it wasn't for no reason we were referred to as the 'dirty man of Europe' at the time.
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No UK market G2 had a lambda as far as I'm aware.
Continental ones certainly did.
Digi on the PB certainly has no lambda or emissions controls - it wasn't for no reason we were referred to as the 'dirty man of Europe' at the time.
Right so my Rallye due to being a left hooker had one, it had a cat aswell!
But my point is any temperature sensing device sending signals to the ECU is a Lambda IMO non?
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Non.
http://en.wikipedia.org/wiki/Oxygen_sensor
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thin layer of platinum and comes in both heated and unheated forms. The planar-style sensor entered the market in 1998 (also pioneered by Robert Bosch GmbH) and significantly reduced the mass of the ceramic sensing element as well as incorporating the heater within the ceramic structure. This resulted in a sensor that both started operating sooner and responded faster.
The sensors only work effectively when heated to approximately 316 °C (600 °F), so most newer lambda probes have heating elements encased in the ceramic that bring the ceramic tip up to temperature quickly. Older probes, without heating elements, would eventually be heated by the exhaust, but there is a time lag between when the engine is started and when the components in the exhaust system come to a thermal equilibrium.
Still think many are heated sensing types after all the ECU interprets the speed and heat variables of the element the result might be a pre set function of amount of oxygen, but oxygen reacts in air temps?
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can also be caused by car being too lean, my hc were thru the roof due to it being mega lean. what were your HC and CO readings?
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Good god, this thread has gone a bit mad since I left :shocked:
In regards to the readings like I say unfortunately I do not have a printout which is a very annoying but I'm sure it was tested when up to temp.
Looks like I'm on the right lines with replacing the vacuum lines and ignition components then. If it's running lean and the ignition timing is correct am I right in thinking this points to suspicions of an air leak?
It never cuts out but sometimes it can be a bit temperamental to start, especially when hot but that could be a separate issue. Never overheats, water temps are fine but oil temps can be a tad high. Better not be the headgasket, like I say all of that has just been done.
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Still sounds like the engine temperature sender to me.
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Still sounds like the engine temperature sender to me.
Where abouts is that Diamond Hell? Do you mean the blue temp sender for the ECU etc?
Have just replaced the leads, cap and rotor arm. Seems a little smoother but the old ones weren't awful. Cheap things first and all that. I did noticed that one of the vacuum hoses on the airbox looks perished as well as one on the throttle body so these can't be helping. Hopefully the replacements will turn up tomorrow.
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Where abouts is that Diamond Hell? Do you mean the blue temp sender for the ECU etc?
Yes
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Where abouts is that Diamond Hell? Do you mean the blue temp sender for the ECU etc?
Yes
Already been replaced recently with a genuine VAG one unfortunately so can rule that one out. No change from the old one.
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Replaced all of the vacuum lines this morning. Annoyed at myself for overlooking this job - a few rather perished hoses. Car felt smoother to drive on the test run although I still have a slight exhaust 'bob' although it is better. Quite a bit of fuel vapour on start up but this cleared as well as smelling of fuel quite potently. Car running well on test drive though.
I've exhausted my ideas now, perhaps time to go through the digi tuning guide again as the new lines may have thrown something out, unless anyone else has anything fresh to add?
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can also be caused by car being too lean, my hc were thru the roof due to it being mega lean. what were your HC and CO readings?
Sorry to dig up an old thread but I have some proper HC readings now after today's MOT. Car has been off the road for a while so not had a chance to do much with it.
HC: Max 1200ppm Actual Value: 817ppm.
It's a pass but seeing as it was 70ppm last year something isn't right :undecided:
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what were the co readings
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CO was 0.74%
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bit lean, I'd set it to 1.5-1.8 ish. as i said earlier, if its too lean the HC goes up ;)
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Cheers RJ