Afternoon folks, banging my head against the wall with this one, 1.4 MPI 8V (AQW with Air con)

 

When cold, it starts up on the key, no issues. But when warm, it takes a few cycles of the engine to get going. 

 

Scanned a few times with VCDS, The other week i did have a Cam Position Sensor, signal too low, 16726 fault code. But following a bit of cleaning up of the connector, it as now gone away.

 

My only current fault code is:

 

00907 - Intervention Load Management (In Central Electrics)

 

 

Its weird as it just generally seems to drive better when warming up, rather than at temperature.

 

Its had a brand new Thermostat (OEM Temp sensor included), Radiator, water pump, Coolant etc. Recent Timing chain, oil pressure switch and oil/filter too. Also changed the battery ground lead (short one) with that from a 1.8T Ibiza (assuming they have a lower gauge for better current handling)

 

Only other problem is the Aux belt tensioner and pulley is grumbling/worn so i accept that the Alternator probably isnt charging properly as the belt isnt under constant and correct tension. 

 

But none the less i dont see how that could influence a bad start at temperature. In the back of my mind im wondering if the Cam Position sensor isnt working properly, but is still within tolerance and is still running. (logic being the Cam Pos sensor's performance varies with temperature)

 

Recently done 40+ mile commutes with no fault codes at all, returning an indicated 45-50 MPG. Although this morning in the traffic the car cut out a few times (believed electrical fault as the headlights flickered then went)

The camshaft sensors get worse once warmed up so could be that.

It hasn't been pretty much since the timing chain was changed was it?

Might be worth double checking the timing maybe.

Possibly slightly leaky/drippy injectors? A bit more-than-intended enrichment wouldn't be a problem at cold-start, but might make it just too rich for warm starting? Wouldn't throw any codes, I don't think?

Cheers for the responses guys,

 

Hutchy, Luckily the 1.4 MPI is Push rod, with a small chain, so in my experiance of doing them (twice now) its difficult to get it wrong,

 

The problem is i did the timing chain, drove it around for a month or so, put it into a garage and stored it SORN for a month and then go it back out of storage (at which point the radiator had sprung a leak) It has been since then its had this warm start issue. 

 

My only other thought was maybe head gasket as it did get warm (but did not reach the red) on the temp scale while the day before i changed the radiator.but the temp gauge has stayed perfectly fine ever since.

 

Wino, surely an injector fault would persist cold/hot?

I thought my second sentence covered the cold/hot difference?

 

been a long day haha.

Could still be temp sensor? My ibiza didn't throw a code for it when it first started going

But the OEM Thermostat comes in housing with a brand new temp sensor. 

 

been a long day haha.

Tell me about it, I can't even get the strength up to go get some wine yet. And it's only about two yards away.

But the OEM Thermostat comes in housing with a brand new temp sensor.

Not unknown for them to be faulty when brand new though

Hard starting when hot is more likely to be too lean, especially with that awesome mpg that you quoted, I suspect it's leaning off a lot when it drops onto closed loop, this could indicate a dodgy pre-cat lambda probe.

How can a lambda probe function/disfunction affect start-up? Don't they have to reach hundreds of degrees C before they do anything at all?

How can a lambda probe function/disfunction affect start-up? Don't they have to reach hundreds of degrees C before they do anything at all?

 

Because the ECU has learned to run too lean when the engine is hot, this makes it much harder to start, the dynamic map is too lean, clear the map by resetting the ECU, it should start much better when hot initially until it leans right off again.

Sounds like a useful experiment to try then.

Indeed it was!

 

Popped out to the car, i disconnected the leads, shorted them together to completely clear everything, also noticed with my torch that i have a blown flexi, its down stream from the Pre cat lambda but surely will still distort readings.

 

Starts alot better. for now that is. 

 

Also it does seem damn rattly. plenty of oil, but also found there seems to be quite a bit of crank case pressure. But... its not on a TEMAC headgasket so assuming its the OEM one, whats the chances of it blowing Combustion to oil? Please forgive the crude way of demonstrating it, but seems a little high pressure to me.

 

 

also reving

 

one thing slightly confusing, if lets say a lambda is reading a lean condition, i.e. too much oxygen in exhaust, surely it would try to compensate by dumping fuel in to counter the lean state?

 

leading to very poor fuel consumption.

I would still try another temp sensor but that's just going on my experience

That crankcase pressure is abnormal. Mine actually sucks not blows. I posted this video a few weeks ago for Alexandru who was having the same problem.

 

one thing slightly confusing, if lets say a lambda is reading a lean condition, i.e. too much oxygen in exhaust, surely it would try to compensate by dumping fuel in to counter the lean state?

 

leading to very poor fuel consumption.

 

I'm suggesting that the probe is reading incorrectly, a lambda probe can drift out of spec. over time and it won't trigger a fault unless it goes open circuit, this is also what happens to ECT sensors, because they're both analog devices the ECU has no reason to disbelieve their readings unless they go outside certain parameters, a faulty ECT sensor can tell the ECU that the engine is warm before it actually is, a faulty lambda can tell the ECU that the mixture needs further leaning even if it doesn't, over time your dynamic fuel map can gradually lean off until the car becomes hard to start when hot. Cold starts are only affected by the ECT sensor since the lambda is ignored until the engine is warm enough to go onto closed loop feedback. Hot starts are different.

 

Edit: The heavy breathing is normal, blown head gaskets affect the coolant and oil ways, not the engines internal voids.

Edited 8 April, 201511 yr by sepulchrave

There should be a slight vacuum in the crankcase. The crankcase is vented via the inlet manifold, to ensure the fumes from oil and piston blow-by are extracted and burned in the engine to meet emission regulations. If there is positive pressure it's not good news - either the crankcase ventilation system is blocked or there is excessive blow-by past the piston rings.

Yea exactly why i was concerned that it felt like the cap was beibg blown upwards

Yea exactly why i was concerned that it felt like the cap was beibg blown upwards

 

You will get positive crankcase pressure which is why there is a breather, it's connected to the intake to burn any oil mist, you'll never get a vacuum in the crankcase because two pistons are falling and only one has the inlet valve open to the manifold, there is always net positive pressure in a running engine.

 

Check the breather isn't blocked by blowing through it with the oil filler cap off.

Edited 8 April, 201511 yr by sepulchrave

Yea exactly why i was concerned that it felt like the cap was beibg blown upwards

 

How many miles has it done?

I've had that so called issue checked at a VAG specialist. He told me that when the Passat B5 came in his showroom and he started selling them, about all the owners came back with their brand new cars, with about the same "problem" as here. It seems to be quite normal for that engines, he said and that I shouldn't be concerned. As long as it doesn't spit oil with the cap removed, everything should be fine. Should I check another garage? 

Edited 9 April, 201511 yr by Alexandru

Definite negative pressure when I unscrew the oil cap on my BBY Polo (@119k miles), mild pull down at the start of my commute, more pronounced 5 miles later.

 

What is the breather arrangement on the MPI, basic, possibly?