ALZ (1.6 petrol) hard starting when cold

[kevinb6]

Hi, firstly this is actually an A4 B6, but posting here are it seems very few A4s have this entry level engine, and I got good help here before with an unrelated issue.

Problem is I have very hard starting from cold. It will crank OK, fire up to about 600 RPM then die, backfiring and spluttering before it dies . Have to repeat this several times before it kicks in and idles at about 1,000 RPM and runs fine. If I let it warm for 2 or 3 min and then turn off, it will start fine. This has been an issue for several years.

There is no engine light and I scanned it with VCDS Lite (with a cable borrowed from a BMW owner, not a great connection, but was able to get a reading) and this showed no codes.

On advice elsewhere I replaced 2 x coolant temp sensors (back of head and bottom of rad), no effect. The crankshaft position sensor was replaced a while ago (unrelated failure) and I have replaced the plugs and fuel filter.

Now the interesting bit - if I unplug the MAF sensor, it will start perfectly from cold. Naturally this throws an error and does not run very well (flat spot 2-3k rpm). I tried cleaning it twice, no help.

Assuming this MAF produces a DC signal out, I back probed it and got 1.4v at idle rising to 3v at high RPM from Pin 1, so this suggests to me it's working, but I have been unable to find the specs on it to say what I should be getting (or maybe it's a pulse output?).

I suspect that unplugging the MAF is causing the ECU to run a default map that facilitates starting???? Or do you think the MAF is bad?

Since it seems to be temperature dependent, I think I might look at the inlet temp sensor, where is that, or could it be build into my 4 pin MAF?


The other thing I should mention, years ago a cheap scanner said the secondary air pump was bad, I put 12V to the motor and it did not run, but left it at that for some reason. VCDS did not flag this. Could this cause my starting issue?

I include a pic of the engine and a video (link at end of post) of it starting , thanks for reading!

alz.jpg



A4 B6 1.6 petrol starting issue - YouTube

EDIT I just seen this video while looking at mine, same issue he said it was the "temperature probe", is there more than 2 temp sensors? And sorry about the advert on mine, I'll try to remove it.

https://www.youtube.com/watch?v=KswyH3zGfeo

[Crasher]

The ALZ is a bit foggy to me now, been a while, but I do remember their Air Mass Meters being by Hitachi and a pain in the ****, we would insist on genuine VAG replacements but the exchange part is now obsolete and strangely it is still available new genuine under number 06A 906 461 B but is daft money at £361.20; at that age, if it didn’t sell well, VAG would drop it. I fitted one to a Passat a few months ago to cure running issues and it worked which was a relief as the car was a shed and throwing that money at it HAD to work. I always used to (not so much now) work by the rule that no codes and running problems meant new GENUINE AMM first and it nearly always worked. Int olde days of AMM failure we used to keep a wide stock of all genuine VAG AAM’s so I could plug and test at will without an expensive mistake.

[kevinb6]

Hi, thanks for that.

Is the Air Mass Meter another name for the MAF? Or another sensor.

As you alluded to, I'd be very reluctant to buy one without being very confident that's the problem, on a '02 car. Is there any way to find the specs for it so I can compare outputs first?

[Crasher]

Air Mass Meter is the correct name, not an Americanism.

[ianhayter]

Since it's an easy fit, perhaps buy a 2nd hand one off eBay for around £20. If it fixes the problem you can then opt for a new one if you deem it necessary.

[kevinb6]

Thanks, that sounds like an idea.

I was just thinking though, why would it work after warming up for 3 min? if it just that the engine is easier to start when warm, of could it be another component being temp sensitive?

[Crasher]

Possible temperature compensation change.

[kevinb6]

Possible temperature compensation change.

Hi Crasher,

Would you be able to explain that a bit more please?

[mickeybo]

The maf sensor on your a4 1.6 2oo1 model year the maf sensor 0n these has a 4 terminal connection 3 of these terminals has a ecu switched earth at ecu pin nos 1-2-4 its very importent that these has to be checked out at corresponding ecu pin nos. the maf sensor measures the temperature volume in the inlet system

[Crasher]

Hi Crasher,

Would you be able to explain that a bit more please?

Not this far down a glass