Engine cuts out at cold start and then looses compression

[Mustafa.T]

Hi all.
I'm facing a weird issue with my car. I have an A4 b7 1.8t cabriolet BFB engine.
On cold starts, car would start first time and then all of a sudden would cut out.
When I attempt to start it again, the engine cranks but the cranking sound does not seem normal. Its more of a "weee" sound as if there is not compression. I have checked and the engine does turn but but with out compression.
After about 10 mins of rest, I'll try again and it would crank fine and then start, however, engine would start to misfire for about 5 mins. It would then stabilise.
Once the engine has been running, I would have issues starting it later in the day.
Once its been left off for a while, it would do the same thing again.

What could this be?

[Mustafa.T]

** once the engine has been running, I would not have any issues.

[IbisB7stage2]

how many miles on the car? I've heard carbon build up can cause misfires when the car is cold because the valves dont seal, and they seal better as the carbon build up warms up.

[Mustafa.T]

Hi ibisB7stage2,

The car has done 103000 miles now.
I have recently rebuilt the head and grinded the valves and tested them, so there shouldn't be any carbon build up at all. But what I don't get is, it just shouldn't start at all if the valves stay open (enough to loose compression through all cylinders). The fact that it starts after a while of waiting, and then abit of misfiring, it's absolutely normal.

Also, the timing has been changed and checked. Everything is spot on.
Changed valve changed.
Sometimes, when I stop at the lights, I can smell burnt oil in the cabin, and the moment I take off, the smell goes away.
Could this be related to the EGR?

[IbisB7stage2]

sounds like PCV issues perhaps, since you're smelling oil when stationary

[Mustafa.T]

Changed pcv valve 2 weeks ago. :-(

[Mustafa.T]

Is there a way we could eliminate the egr?

- - - Updated - - -

What i mean is, is there a way that we could check if the EGR is fine

[IbisB7stage2]

But something is wrong if you smell oil, it should be a closed system. There's many components to the whole pcv system. A cracked valve cover or cracked hose could be the culprit, among other things.

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[Mustafa.T]

Agreed. I will revisit that tomorrow and update accordingly

[Mustafa.T]

Just an update,

Checked the PCV system as a whole. All ok. No cracked pipes or issues.

What could cause this?

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[Mustafa.T]

Had a similar situation again, but this time, after waiting a while, I can feel that compression seems to come back very gradually you can hear it fire up internally. Here is a link (you may need to put the volume up)
https://drive.google.com/file/d/1sWI...w?usp=drivesdk

Could someone please guide me.

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[Brillo]

I agree with you that the cranking does not sound normal but your video does not demonstrate the "low compression wee sound" mentioned in your original post. In all my experience with engines I've not come across one that had low compression and then suddenly had high compression. First thing, check the battery connections and assess the health of your battery. The next thing that comes to mind is to do a compression check (on a fully charged battery), dry then wet. Better yet, do a proper leak-down check which can differentiate any issues between the valves and rings. Get back to us with the results.

[Brillo]

Two things that can result in burned oil smell in the cabin at stop light. One is a small oil leak on the exhaust system, and the other is bad valve stem seals. Both dissipate quickly with any speed. Have someone drive behind you to see if any smoke comes out of the tail pipe when you pull away from a stop. If yes, it's not an oil leak onto the exhaust system. What is your oil consumption like? Also, how reliable was the shop that did your head rebuild?

Not sure I understand your sentence copied below. "The timing has been changed"?? and "Changed valve changed" ??

"Also, the timing has been changed and checked. Everything is spot on.
Changed valve changed. "

[Mustafa.T]

I agree with you that the cranking does not sound normal but your video does not demonstrate the "low compression wee sound" mentioned in your original post. In all my experience with engines I've not come across one that had low compression and then suddenly had high compression. First thing, check the battery connections and assess the health of your battery. The next thing that comes to mind is to do a compression check (on a fully charged battery), dry then wet. Better yet, do a proper leak-down check which can differentiate any issues between the valves and rings. Get back to us with the results.

Hi Brillo,

Unfortunately, I only started recording it after waiting for about 10 mins after my first attempt at which it wS "the weeee" sound.
I will try an catch it again the next time I do it.its just getting on my nerves.


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[Mustafa.T]

Two things that can result in burned oil smell in the cabin at stop light. One is a small oil leak on the exhaust system, and the other is bad valve stem seals. Both dissipate quickly with any speed. Have someone drive behind you to see if any smoke comes out of the tail pipe when you pull away from a stop. If yes, it's not an oil leak onto the exhaust system. What is your oil consumption like? Also, how reliable was the shop that did your head rebuild?

Not sure I understand your sentence copied below. "The timing has been changed"?? and "Changed valve changed" ??

"Also, the timing has been changed and checked. Everything is spot on.
Changed valve changed. "

I had an extensive look around saw no leak at all. I read somewhere that the oil burning smell can be caused by a bad PCV system. So I changed my pcv valve. Still the smell is persistent.
The car does smoke abit when it starts and engine shakes and misfires.

That was a typo. What I meant to say was that timing belt has been changed, and then double checked.
The rebuild of the head consisted of the valves being grinded/reseated by lapping compound.
Both of the above were done by myself as iv been doing this for my previous cars as well so nothing new for me.
The timing chain tensioner was changed and reset to the TDC marks with 16 links end to end.
Everything seems normal. During the rebuild, I checked all the valves and the lifters and none were bent or stuck.


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[Brillo]

I'm assuming you used a new head gasket and new TTY headbolts on reassembly of the head. Can you do a cold enging compression check to rule that out?

[Mustafa.T]

I'm assuming you used a new head gasket and new TTY headbolts on reassembly of the head. Can you do a cold enging compression check to rule that out?

Hi mate.,

Yep, new head gasket and and head bolts.

Will update you with cold engine compression results

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[Mustafa.T]

Hi mate. Apologies for the delay.

I just carried out the compression check on a cold engine. All were around 120 psi.

Once the check was completed and all coils put back, I attempted to start the car. The crank sound was as it should be.
Car fired up, and 1 second later shut off.
Tried to fire her up again, and now sound is what I mentioned at first, "weeeee", with no compression

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[Mustafa.T]

Did a compression check again, and cylinder one showing 40psi

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[Theiceman]

Looks too me like car does not have enough battery energy to start..
If you are checking compression with a weak battery you will get low results.. wonder if alternator is putting out enough or dead cell in battery maybe?

Just trying to think out of the box. Have you tried jumping it when this happens.?

Maybe does anyone else not think it is turning over slowly?.



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[Mustafa.T]

This was my initial thought aswell..however, when I did it the first time, I changed the battery and then it was all ok. But it did the same again a few days later when it wasn't touched.
It's very hard to pin point what could be causing it.
As soon as its left for about 10 mins to rest (after multiple attempts to start and then loosing compression), it starts to gradually crank normally and starts although it misfires for the first 5mins, then steadies itself.
I took it to a audi "specialist " a couple of months ago and apparently it was the coolant temp sensor according to them (which they ended up changing). And apparently it never had any issues starting in the morning for the 5 days it was with them. That's strange to believe when it happens everyday with me.



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[Mustafa.T]

Any ideas?

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