# Hard to start when cold, then runs fine



## wmorrison65 (Sep 7, 2014)

For about the past week, when the engine is cold, and I turn the key to start, the engine turns over strong, but doesn't start. Like it's not getting fuel, no ignition at all. I stop after 2-3 seconds, then try again. The second time it starts fine. This morning I let it crank 3-4 seconds, and after the 3-4 seconds it stumbled about a half second then started right up. Idles fine.

I haven't noticed this when the engine is warm. It doesn't seem to have any problems at highway speed or under acceleration.

Any diagnostics I can run to find where to start looking, instead of just throwing parts at it? I don't have a vag-com yet, but I have an OBD scanner/logger.

Fuel filters are cheap, but if it were that, wouldn't it have more problems under load than when starting?

Could the fuel pump be failing? Again, seems fine on the highway.

I know my long term fuel trim is about 21. I'd assumed this was vacuum leaks (and it still may be,) but wouldn't low fuel pressure also raise fuel trim?

Any ideas?


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## lite1979 (Sep 9, 2005)

Do you have any lean codes? Typically you'll get a Check Engline Light when you're running lean. Is your temp gauge working correctly?


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## Boulderhead (Oct 21, 2012)

wmorrison65 said:


> For about the past week, when the engine is cold, and I turn the key to start, the engine turns over strong, but doesn't start. Like it's not getting fuel, no ignition at all. I stop after 2-3 seconds, then try again. The second time it starts fine. This morning I let it crank 3-4 seconds, and after the 3-4 seconds it stumbled about a half second then started right up. Idles fine.
> 
> I haven't noticed this when the engine is warm. It doesn't seem to have any problems at highway speed or under acceleration.
> 
> ...


Hey mate, when is the last time you filled your tank? Have you run any fuel system cleaner through the car recently? No ignition could also be too much fuel especially if your fuel trims are on the positive side (the injectors are staying open longer). Pull your battery for 10-15 minutes one night when you get home and see if you have the same issue the following morning, as this will reset all fuel trim data.


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## wmorrison65 (Sep 7, 2014)

Car is new-to-me since September.



lite1979 said:


> Do you have any lean codes? Typically you'll get a Check Engline Light when you're running lean. Is your temp gauge working correctly?


Yes, I've seen a P1128. Also a P0422, main catalyst below threshold. Haven't cleared them recently. I've cleaned the MAF once. Temp gauge seems fine.



Boulderhead said:


> Hey mate, when is the last time you filled your tank? Have you run any fuel system cleaner through the car recently? No ignition could also be too much fuel especially if your fuel trims are on the positive side (the injectors are staying open longer). Pull your battery for 10-15 minutes one night when you get home and see if you have the same issue the following morning, as this will reset all fuel trim data.


Couple weeks ago, tank is just under half-full. (It's not my daily driver.) I haven't run any cleaners.


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## Chickenman35 (Jul 28, 2006)

Another possibility is that the one way check valve in the fuel pump is leaking down over night, or you may have a leaky injector.

When you start it in the morning, do you just jump in and turn the key to start right away? If so, try the following. Turn the key to the " On position " only. Do not crank the engine. Wait 10 seconds and then crank the engine. If the engine now fires right away, you can be pretty sure that the fuel rail is losing pressure over night.

As mentioned, could be a leaking injector or a leaking check ball in the Fuel pump. You can sometimes isolate a leaking injector by pulling the plugs when the engine is cold and having a close look at them. Sometimes you can see evidence of rich running or wet fuel on the plug with the leaky injector.

As mentioned, it would be a good idea to start running a good Injector cleaner in the Fuel Tank. Sometimes that is all that is needed to fix things. It may take several tank fulls. Lubri-Moly Jectron is good, as is CRC and Seafoam in tank fuel treatment.


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## wmorrison65 (Sep 7, 2014)

Chickenman35 said:


> Turn the key to the " On position " only. Do not crank the engine. Wait 10 seconds and then crank the engine.


Tried that yesterday, made no difference.



Chickenman35 said:


> You can sometimes isolate a leaking injector by pulling the plugs when the engine is cold and having a close look at them.


Good idea, I already have new plugs and wires I haven't put on yet.



Chickenman35 said:


> As mentioned, it would be a good idea to start running a good Injector cleaner in the Fuel Tank. Sometimes that is all that is needed to fix things. It may take several tank fulls. Lubri-Moly Jectron is good, as is CRC and Seafoam in tank fuel treatment.


I'll look into that. I read mixed reviews on the efficacy of injector cleaners, but they're relatively inexpensive to try.


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## bass 1 (Jun 11, 2013)

I have the exact same issue... must be losing pressure in the fuel rail. 

As suggested above, I have just gotten in the habit of turning the ignition to the "on" position, waiting 3 seconds (meanwhile putting my seat belt on), then cranking to start. Works every time.

I had tried new MAF, plugs, coil packs, and fuel filter.... still behaves the same. 



Is the check valve in the fuel pump, regulator, or lines? Or are there multiple check valves?


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## Chickenman35 (Jul 28, 2006)

wmorrison65 said:


> ( Snip) I'll look into that. I read mixed reviews on the efficacy of injector cleaners, but they're relatively inexpensive to try.


CRC's new product, " 1 -Tank Power Renew ", is supposed to be very good, but I haven't been able to find it yet in Canada.

http://crcindustries.com/auto/power-renew-rebate-coupon.php

I've personally tried Lubri-Moly's Jectron and it works very well. I had a badly plugged injector on my Audi and it cleaned it right up. Took a few applications ( tank fulls ) though. 

Ultrasonic cleaning is still the best way though.


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## Aaron16V1.8l (Aug 12, 2007)

I am having a similar problem, and looked in the Bentley - apparently the check valve is part of the fuel pump and cannot be replaced separately. I am just going to live with waiting a few seconds before cranking after turning the key.


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## wmorrison65 (Sep 7, 2014)

The problem seems to be intermittent. It's been starting fine all weekend and this morning, inserting the key and turning straight to crank without waiting a few seconds in the on position.

The only difference I can think of: Tank was near empty Friday, and I refilled it.


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## bass 1 (Jun 11, 2013)

wmorrison65 said:


> The problem seems to be intermittent. It's been starting fine all weekend and this morning, inserting the key and turning straight to crank without waiting a few seconds in the on position.
> 
> The only difference I can think of: Tank was near empty Friday, and I refilled it.


Same here. Mine wont have any trouble unless im below 1/3 tank. I wonder if it has to do with the check valve being submerged or something?


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## lite1979 (Sep 9, 2005)

I would definitely recommend running a fuel system cleaner through a full tank of gas. I usually run a bottle of Chevron Techron in a full tank (fill tank with Techron, then pump tank full of gas) to keep my sending units clean, but I'm sure it helps clean the entire system, so your injectors and fuel pumps should benefit as well. 

Speaking of fuel pumps, have you considered checking the resistance of your auxiliary fuel pump on the driver's side of the tank? The butterfly shape of the gas tank on quattro TTs means you have a second pump at the bottom of the driver's side of the tank to help get gas to the main pump on the passenger's side. If this pump is failing, you would only notice the symptoms with 1/3 a tank left. The gas gauge gives you the average reading between both sending units, so your "1/3" of a tank may be more like 2/3 of the left side still in that side of the butterfly while the right side is dry. That has the potential to cause some awkward starts, especially after the gasoline settles on its respective side.


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## Boulderhead (Oct 21, 2012)

wmorrison65 said:


> The problem seems to be intermittent. It's been starting fine all weekend and this morning, inserting the key and turning straight to crank without waiting a few seconds in the on position.
> 
> The only difference I can think of: Tank was near empty Friday, and I refilled it.


Make sure to run this tank down to near empty and see if your problem returns.. if it doesn't I would think you got a bad batch of fuel last round and this latest fill is a better batch.


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## wmorrison65 (Sep 7, 2014)

Update: Car has been starting fine until yesterday morning. when fuel gauge was showing just over 1/4 tank. Slow starting since then.



lite1979 said:


> The butterfly shape of the gas tank on quattro TTs means you have a second pump at the bottom of the driver's side of the tank to help get gas to the main pump on the passenger's side. If this pump is failing, you would only notice the symptoms with 1/3 a tank left. The gas gauge gives you the average reading between both sending units, so your "1/3" of a tank may be more like 2/3 of the left side still in that side of the butterfly while the right side is dry. That has the potential to cause some awkward starts, especially after the gasoline settles on its respective side.


Sounds about right. I looked in my Bentley manual. It doesn't show any electrical connections to the secondary pump. Is that right? It appears to be driven by a pressure hose coming from the main pump.


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## lite1979 (Sep 9, 2005)

It's electronic. The wiring goes from the main pump to the auxiliary pump inside the tank, iirc.


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## wmorrison65 (Sep 7, 2014)

lite1979 said:


> It's electronic. The wiring goes from the main pump to the auxiliary pump inside the tank, iirc.


Thanks. I found another writeup that says that.

Interesting... The Bentley says,

"The primary fuel pump creates a pressure stream that is forced into the secondary fuel pump via a jet. This pressure causes the fuel in the left side of the tank to be drawn into the right side of the tank."

(Page 20-15 yea verily etc. etc.  )


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## lite1979 (Sep 9, 2005)

I may be wrong. The wires going to the aux pump may very well go to the sending unit. If the aux pump is purely mechanical, it may just be a case of one of those hoses being undone or cracked...


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