V6 4motion poor cold start

[katmart]

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.:confused::confused::confused:

[dubcruiser]

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]

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]

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]

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]

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]

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]

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]

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]

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???

[Crasher]

It would be interesting to put a multimeter on a line 15 (ignition on) circuit and see what the voltage is on cranking, that strikes me as the ignition switch or ECU relay. The relay is in the small box in the left of the engine compartment on the strut housing and has 428 printed on top.

[katmart]

I will try that but it will probably be next weekend before I get a chance.
When I had a slave battery connected the ecu was showing good voltage. While looking at it this afternoon I managed to adapt the throttle body - did not help. I was checking values and the temperature in block 47 was showing -50*c !! I then cranked the engine and this changed to 5*c, I think that is the oil temp, do you know if it is? - no fault codes stored so may be irrelevent?

[katmart]

I got a coolant sensor and fitted it (not an easy job). I was not at all confident it would cure the problem but when I started it up (approx 10*c), the revs went up to just over 1100rpm which is something it hadn't done for a long time as if it were on choke.
The next morning it was about 1*c and I was hopeful but as before it just cranked over and would not fire unless a bit of throttle was given!

[Crasher]

Remove, clean and reset the throttle body.

[katmart]

I will clean the throttle body and measure terminal 15 voltage over the weekend. It does appear that the throttle just needs a little help, once the engine is running there is no problem. It is weird the revs did hold up over 1000 rpm just after changing the coolant sensor, I only remembered after it used to do this reguarly.
I dont think it is a voltage drop problem because provided the battery voltage is good (I charged the battery overnight and it was showing 13+v and still did not fire up cleanly) vagcom shows a similar volage at the dme (or is this terminal 30 that is shown). I will measure it sat or sunday.

[katmart]

Checked the voltage at term 15 relay(very cold) . Battery 12.05 relay 12.00.
Cranking battery 10.00, relay 9.90v.
There is a voltage drop when cranking but not excessive? Also there is a very slight drop at the relay.
I did not get time to clean the throttle body at the weekend but will try next weekend.
Since Monday the temperature is a lot higher (+8 as opposed to -3 last week), it is starting much better.

[RogerD]

Hi

Did you ever resolve the starting problems as I seem to suffer the same issues with my 4 Mo.

RogerD

[katmart]

Not yet, today I have removed & cleaned the throttle body, refitted it and recalibrated. It has been much better over this last week but not completely ok. I dont like to touch the throttle because you tend to rev it slightly as it starts and the oil pressure will not be built up, but it starts much quicker if you do.
What symptoms do you have, how long has it been happening? Have you tried slightly pressing the accelerater while cranking?
(I dont know if we will ever get to the bottom of this - it appears to be a quirk of these cars, it has always been like this but we have not had such cold weather for a while. I wonder how they cope in scandinavia etc)?

[katmart]

After cleaning the throttle body & resetting, 6 degrees c this morning - did not want to start again!
Since replacing the coolant sensor and it started up and revved up to 1100rpm after starting it has not done that again. Can anyone think of a reason why it did it that once?
Does every car (V5 & V6 do they have a common type of motronic system) suffer with this or is it fixable?

[katmart]

The temperature is low still and the car still does not want to start first thing.
I work for a Vauxhall franchise and we often have software upgrades we can carry out (called SPS by GM). Does anyone know if Volkwagen does the same thing? It is a Bosch Motronic system variants of which are used by many manufacurers including Volkswagen and Vauxhall? Or are there chips or upgrades from speciallists available?

[Crasher]

Yes, there are software updates from the dealer.

[katmart]

Do you know of any update for this issue? I think the car has had this problem from day 1. I remember some days it would be hard to start in the morning but I put it down to starting the car briefly the day before just to move it and it being flooded the next day. You also tend to forget about it through the summer because it only occurs when outside temp is low. As I have said it appears to be a very common complaint for V6 cars and they are not that common.

[Crasher]

My business partners V64M has always started first time since we sold it to the original owner back in 2000 when we imported it brand new. He bought it back in 2003 and it has always been faultless in all weathers until last year when it started acting up. We fitted a new battery and it was fine for a few weeks then went off again. I found the alternator output was low so we fitted an exchange genuine alternator and it has been perfect ever since. We had another in a few days later with the same symptoms and the alternator also provided a cure. We do a lot of Golf 4 V6 4M’s and these are the only two we have ever had cold starting problems with and in both cases a new alternator cured it.