V6 4motion poor cold start

**katmart** · 31-12-2008,06:05 PM

My 2002 V6 is intermittantly a pig to start when cold. It cranks really well but doesnt want to fire. It may spin over for 3 - 4 seconds then chug into life as if it is flooded. I never touch the throttle until it has started, there are no fault codes in the management and it runs perfectly afterwards and restarts ok. It is in a garage so not damp, has had a service recently with new plugs and one new coil. It has been like this for a while but seems to be much worse with the cold weather.Any ideas?
Also I think the wrong oil was used at the service (Quantum Syntra 10/40 vw 505.00) is this ok? It is changed yearly , approx 6,000 miles and uses very little between services but I am paranoid about damaging the engine
Any ideas appreciated.

**dubcruiser** · 01-01-2009,12:13 PM

Sounds ignition issue especially as you say its worse when cold. I would get the plugs and coil packs checked seeing as they have been changed recently. If you think the wrong oil has been used then if it were me I would get it changed but I don't see how that would be effecting the start of the car...

Could possibly MAF related but then you normally get poor running with that to...

**v6dub** · 01-01-2009,06:39 PM

temp sensor, if its a pig to start when cold, that is where i would start, if you plug vag com or some other scaner see what the temp sensor is reading when the engine is running, also have a look to see if it is a green sensor or the orginal black one, very easy to find, it is to the left of the thermostat houseing, take to top engine cover off you see better.

**katmart** · 01-01-2009,09:33 PM

The temp sensor must be in range or it would throw up a fault code. I will have a look at the reading tomorrow. What is the significance of the colour of the sensor?

**v6dub** · 01-01-2009,10:37 PM

might not always log a fault, that is what i would go for very cheap part, easy to change. they changed them to green because the black ones where so unreliable, so vw changed the design and construction and the colour so you could tell if it had a new temp alredy put in. the only reason i say about the temp sensor is that my friend polo was doing the same, with no fault recored so i sugested the temp sensor and it works just fine now.
10w-40 is ok that is what is recomended for fixed serviceing and 0w-30 for long life servicing, however i use comma 5w-40 syner-G full fully synthetic. which i change every 3000miles or 6months.

**katmart** · 02-01-2009,07:14 PM

I checked the temp today using vagcom, coolant temp was 40c (this is approx what it was at the time. I looked for the temp sensor and there is a green one on the front of the cylinder head (is this the one you mean)? I tried to disconnect it to see if this put in a fault code but could not release the connector. I also cannot see how the sensor is secured (no hex or flange on it). I will read the temp tomorrow morning before it is started.
I also wondered about the air mass sensor? I know these are fragile, it is original with 59000 miles. (I am getting roughly 13 - 14 g/s - grams / second?? - at 3000 rpm) does anyone know if this is correct?
The throttle body looks clean and once started idle speed is stable.
When you open the car door you hear the fuel pump prime so I dont think it is fuel pressure, but might be able to borrow a gauge and connect up.

**v6dub** · 03-01-2009,12:09 AM

that is the right one, the temp sensor is connected using a small clip that holds it in to place, with a rubber o-ring to stop it leaking! not sure if the air mass is correct, and if the TB is clean, i would look at the lamba probes.

**Crasher** · 03-01-2009,01:00 AM

The lambda probes have no effect on cold start, they only come into play when they are warm enough to measure the oxygen levels in the exhaust and that is at least 25 seconds after start up, after the secondary air injection pump (the load whining noise) has stopped running.

I have had a number of V6 4M’s play up on cold start due to low to battery voltage. I had a couple last year (one was my business partners) and they would both crank over fine and not start for quite a few seconds then fire up. We fitted a new battery to both and they were fine for a few days and they went off again. We found in both cases the alternator was weak and the battery voltage quite low on cranking although the starter didn’t show any sign of a low battery, I suppose they must have very powerful starters. In both cases, a new genuine (pattern items suck) alternator cured the problem permanently.

**katmart** · 03-01-2009,06:01 PM

The car had a new battery approx 18 months ago. It spins over really well on the starter so I would be surprised if this was the problem. I connected vagcom this morning and the temp readings were. Ambient temp1, oil temp 2 and coolant temp 5. There is a slight difference but 5*c is surely deemed as a cold start by the ecu?
Crasher, I must admit the battery voltage reading in the ecu was slightly below 12v (the other half usually leaves the heated seat and rear window on - I wish they would always default off like some manufacturers). When cranking this dropped below 10v, the car did not start well but when it did cut in voltage went to approx 13.5v straight away. Possibly a poor earth or feed to the ecu? I will check voltage at the battery tomorrow - maybe try jump leads and a known good battery to get the voltage up. I think the spec figures are 11 volts minimum? - motronic?
Is it worth cleaning the thottle body? I hve tried readapting it with vagom but the instructions are vague. I think this happens automatically if you turn on the ignition but dont crank it - after about 30 seconds you hear the throttle go through a self test.
I may try a coolant sensor because they are reletively cheap and other postings seem to say the result is good even when the original cannot be faulted (are they easy to fit - I cant see how it is held in but I think it is a horseshoe clip you pull up that holds it)?

**katmart** · 04-01-2009,03:21 PM

Looked at it again this morning. Temps - ambient 1, oil 1, coolant 5.
Voltage at the battery was 12.1v, this dropped to just under 12v with the ignition on (same as the ecu is showing so no voltage drop). Again it did not want to start so I connected it with slave leads to my Astra. With the Astra engine running the voltage shown at the Golf ecu was 13.8v. I tried to start it again and although it was spinning really fast it did not want to fire. If you lightly press the throttle it does help but obviously you shouldn't do that.
I will get a coolant sensor this week and try it.

Any more thoughts???