VR6 running rich, thoughts? - updated

[Mystic Rado 0]

Hi guys,

 

My VR6 is having an extended dummy-spitting session. Couple of months ago the coilpack died on the M1 in super vile wet conditions, ended up driving about 50 miles running on four. New coilpack sorted that, also changed the oil and filter to get rid of any fuel contamination in the sump.

 

New coilpack and it seemed to be running fine, then steam from under bonnet and radiator is dead. Replaced radiator for Christmas and drove to Lakes and back mostly motorway. Fuel consumption was relatively high compared to normal, around 30mpg and when I got back there was a strong smell of petrol in the oil again, not good as anything residual should have evaporated at normal running temperatures I think.

 

The car's actually running pretty well. Tickover and starting are both excellent, very smooth, no hassle. Feels quick as when you boot it, I'd say though that the power delivery on part throttle is a bit soft and the engine feel isn't very, erm, 'spangly' to use a motorcycle engine tuning term. On a quick 30mph run out yesterday on Peak A-Roads it managed a poxy 21mpg which along with the fuel smell from the sump makes me think it's running rich.

 

I'm just about to change the blue sender on the thermostat housing for starters, but I'm suspecting the O2/lambda probe as a more likely culprit given that as I understand it, it only has an effect at part throttle conditions. Is it likely that the unburnt fuel that I'm suspecting would have been chucked down the pipe when the coilpack was dying could have shagged the lambda? The engine's done 92,000 miles and there's no history of it ever having been changed, so it's probably the original sensor.

 

Anything else I should be aware of? I guess the other possible scenario is bore wear and associated bore wash or worn valve guides, but I'm obviously hoping not.

 

I'm going to change the blue sensor and the lambda, but is there anything else I should be looking at. Also just replaced a broken crankcase breather that some previous owner had superglued back together then covered in tape, but I'm thinking that's coincidental.

 

Anyway, any input welcome, thanks :?

[dr_mat 0]

I wouldn't touch anything till I'd consulted the ECU for it's idea of what's wrong myself...!

[AlgarveVR6 0]

Deffo agree with Dr Mat

Vagcom it first and go from there. You could end up chasing your ass for years.

Other than that, the Blue temp sensor is a likely culprit and only 10 bucks, but vagcom will confirm it. Lambda is a git to do.........

Dic

[Mystic Rado 0]

Cheers guys, makes sense. I've just popped a new blue sensor in anyway, but will get it hooked up and see what gives. I kind of forget that there's a diagnostic thingee, spent too long with a Mark 2 GTi where it's all trial and error.

[Mystic Rado 0]

Thought I'd update this seeing as it's kind of irritating when you search the forums and find loads of unresolved threads and problems lying about. Anyway, to cut a longish story short, I seem to have half fixed my issues - just back from a variable paced spin round the Peak and mpg is back at around 29mpg compared to the awful 20-ish I got before, and the engine's pulling like a proverbial train.

 

Didn't have access to VAG-COM but borrowed a standalone VAG fault reader which only gave the cam speed sensor fault that they all, apparently give, when stationary. Then like a muppet I cleared the codes, so presumably all codes including the ones the scanner couldn't read, doh.

 

I'd managed to lose a load of coolant while replacing the blue sender on the stat anyway and needed some more G12+ so couldn't get out for a test drive. Anyway, then managed to set up my Macbook to run VAG-COM using an old beta of Boot Camp and the work Windows XP licence, so ended up with access to it unexpectedly.

 

Anyway, changed the blue temp sensor, also the yellow ones as the terminals looked a bit sad. Also replaced the disc-type crankcase breather thing which someone had superglued and taped in the past with oily mist apparent and the plugs. While I was at it, I thought I might as well stick a new cam speed sender in as well. When I had the plastics off, I noticed a loose connector - turned out the auxiliary water pump had slid down through its rubber ring mount and pulled out of the connector and was just hanging there, nice. Also the locking wire bit of the connector was missing so the connector wouldn't stay put.

 

Zip-tied the connector in place, refilled the cooling system, ran it up to temp etc, all good. Turned the ignition off and the aux pump was making a noise like a cement mixer, not good. So... bought a new auxiliary pump, Bosch from GSF for an eye-watering 70 squid plus VAT and fitted that along with new mounts and a strategic zip tie. Lovely and quiet, well pleased. Runs for ten minutes after you switch the ignition off but you can barely hear it.

 

Finally stuck a new air filter in and gave the MAFF a careful spray with some electrical contact cleaner. Changed the plugs for NGK, the ones in there were Bosch Super (?), 1, 6 and A.N.Other had some minor white deposits from burning oil I think, the other three looked mint

 

So, just back from a test run, pulls like a train and mpg is back up to normal levels despite some erm, spirited acceleration :) So all good on that front. On the down side, there's still a faint smell of fuel in the oil despite two oil changes after an hour of driving with oil temps around 90, but given the fuel consumption, I'm wondering what's going on - valve seals, bore wear or something else.

 

Alternatively, does the ECU need resetting? Could there still be values from before which are upsetting the fuelling? If so, do I need the full version of VAG-COM to do that? No fault codes on the engine at all btw and as I said, it feels really strong. Thoughts appreciated. Otherwise I'll throw it at Awesome or maybe Stealth and see what they suggest.

 

Sorry I can't tell you what specifically sorted the fuel consumption, I'm thinking probably the blue sender, but I'm quite happy to have changed the other stuff and he's driving really nicely bar the petrol smell in the oil :?

[dr_mat 0]

It might be worth doing the ECU reset procedure, but you don't *really* need anything more advanced than a spanner so you can disconnect the battery for 30 seconds ... Do the search, there's a pattern of driving you need to do afterwards to "program" the ECU the characteristics of your engine.

If you're getting fuel in the oil long term though, chances are you have a mechanical problem, not an electronic one ..

[Mystic Rado 0]

It might be worth doing the ECU reset procedure, but you don't *really* need anything more advanced than a spanner so you can disconnect the battery for 30 seconds ... Do the search, there's a pattern of driving you need to do afterwards to "program" the ECU the characteristics of your engine.

If you're getting fuel in the oil long term though, chances are you have a mechanical problem, not an electronic one ..

 

Yep, that's what I'm thinking. I'll get the top end looked at professionally if it doesn't clear up. Have already done the battery disconnection / driving procedure thing btw.

 

Options for petrol getting into oil? Over-fueling I guess, worn bores / rings allowing blow-by, valve seals / stems, leaking injector(s). Anything else? The back to normal fuel consumption kind of suggests to me that it's not running that rich overall, unless it's just at a certain point in the rev range.

 

I'm assuming that at normal running temperatures, any combustion by-products that find their way into the sump are going to boil off and evaporate via the crankcase breather, so if it continues as is, contaminants are finding their way into the sump faster than they're boiling off, mind you, a little petrol goes a long way when it comes to smell.

 

Ah well, I guess if nothing else, I now know that the various senders, plugs etc I've replaced are all good and I have an auxiliary water pump that's working. tbc :?

[Kevin Bacon 5]

On the down side, there's still a faint smell of fuel in the oil

 

Neat petrol smell or a rich burning kind of smell mixed in with the oil?

 

The latter is common and expected. My girlfriend's 2006 Polo 1.8T is exactly the same. Black oil that stinks of fuel!

 

I would leave it, drive it for 1000 miles then check the plugs again.

 

Sounds like it was the cam sensor if your power and economy have been restored. They're not very reliable, which is why I keep a spare and a 5mm allen key in the glove box ;-)

[Mystic Rado 0]

On the down side, there's still a faint smell of fuel in the oil

 

Neat petrol smell or a rich burning kind of smell mixed in with the oil?

 

The latter is common and expected. My girlfriend's 2006 Polo 1.8T is exactly the same. Black oil that stinks of fuel!

 

I would leave it, drive it for 1000 miles then check the plugs again.

 

Sounds like it was the cam sensor if your power and economy have been restored. They're not very reliable, which is why I keep a spare and a 5mm allen key in the glove box ;-)

 

I dunno, my fuel-sniffing palate isn't what it used to be :) I'll have another tasting later... There's definitely some aroma mixed in with the oil that has a tint of neat petrol to it, but maybe I'm getting paranoid or there's a bit of residual left over from before that's not burned off, thought that seems unlikely. I'll see how it goes, put some more miles on it and go from there. I'm starting to think Corrados run on neat paranoia, 100-octane notional fault juice. Driving really nicely now though :)

 

I'm thinking I ought to have the chains/tensioner done in the next year or so, so if there is a top-end / bore issue, I can sort it all at the same time. I suppose the upside is that I'm slowly sorting through the quirky horrors left by the previous owner(s), stuff like the auxiliary pump and breather.

 

One other thing, I found a loose wire with a very small two-pin connector down below the thermostat housing while I was changing the senders there. Looks like it hasn't been connected to anything for a while and I can't see where it would go, front of the block maybe. I'll have a look again later, but it's nothing obvious, any thoughts anyone?