Car cranks but won't start when warm, glow plug light flashing - Help please!

R

RWhites

A2OC Donor
Hi all
I have done quite a lot of searching on this but haven't found an answer....

A2 tdi 90 2004. Approx 103,000 miles.

Occassionally a problem kicks in where the car decides not to start - the engine warning light comes on and the glow plug light flashes, the car turns over fine, but won't fire. It seems that it doesn't matter how long you crank for, it just won't start. When you leave the car in disgust, then come back to it some time later it will start first time.... Warning lights remain on / flashing the whole time the car is running. Eventually, usually after driving on very rough roads, the lights go out - but come back randomly a couple of weeks later.

This has happened quite a few times now, so I have the symptoms pretty well sussed. Basically, if the car is warm and the warning lights are on, if you stop the engine for more than about a minute it will not start again until the engine temp (based on the dash readout) is down to about 65 deg.

We had the problem this weekend when we were on a long journey and stopped (in a lay-by) to feed the (screaming) baby. 20 mins later we wanted to carry on, but the car decided it liked this particular lay-by.... and wouldn't start...! I took off the bonnet to speed the cooling process, and about 15 mins later we were on our way.... phew!

I conclude this is not ideal... the missus was not happy! Any tips / ideas? For the record, the glow plugs were replaced about 1,000 miles ago, and the problem has not changed a jot.
 
The glow plugs are irrelevant except in the depths of winter, so you can rule them out.

Sounds a bit like fuel starvation. A number of people have had trouble with clogged fuel filters - these should be changed on every second service, but is often missed. Make sure you use an original Audi fuel filter, not a copy. One person had a problem with the fuel pickup in the fuel tank.

There is also a sensor on the crankshaft, but I gather if this goes wrong the car will refuse to start regardless of whether it is warm or cold.

Which warning light(s) are flashing? A flashing glow plug warning light usually means that either the brake light switch is failing, or the brake light bulbs have blown. But that would not prevent the car from moving except in a 3L model (since it has an auto-box).
 
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Hi Mike
I immediately thought of fuel starvation of some sort, but couldn't get my head around how that could be affected by engine temperature....?? I'm very confused, and don't want to randomly buy parts on the off chance.

When it was serviced about 1,000 miles ago, the mechnic (independent) mentioned that the fuel filter housing had some kind of crack in it, but wasn't leaking so he was happy to re-fit it. I can't remember if a new filter was fitted, but I assume it was.
 
There are two possibilities which come to mind...

a) Possibly it's a 3rd party filter rather than an Audi filter. These sometimes don't fit properly and cause problems.

b) If the mechanic didn't replace the cracked fuel filter housing, probably air is being sucked into the fuel system.
 
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No, the problem existed before the service, and has remained pretty constant, so I'm not thinking it has anything to do with the service itself. The replacement glow plugs were their '1st go' at fixing the problem. I was skeptical at the time...
 
If it existed before the service, then option b) is still a possibility.


Is this independant a VAG specialist? The flashing glow plug light almost always means brake light switch problems on most diesel VAG cars, so it seems weird that the glow plugs themselves were changed.
 
Hi,

Have you have a scan performed? This will identify the fault codes (DTC's - Diagnostic Trouble Codes) that are present within the various ECU's. This would be the first step, hopefully avoiding the guess-work.

If you have had a scan, please post the results, if not, get one done.
VCDS is the best tool, unless you have the scan performed at a dealer.
Some cheap handheld scanners fail to pick up all DTC's.

If you fill out your profile with a more useful "location" then those who have access to VCDS in your area may be able to offer you some assistance.

Failing this, if you venture along to a social event, someone usually has VCDS and I'm sure will help you out.

There is a social taking place this weekend in Suffolk.
http://www.a2oc.net/forum/showthread.php?19654-July-is-a2oc-camping-time

Cheers

Jeff
 
MikeMarsUK said:
If it existed before the service, then option b) is still a possibility.


Is this independant a VAG specialist? The flashing glow plug light almost always means brake light switch problems on most diesel VAG cars, so it seems weird that the glow plugs themselves were changed.
Click to expand...

No, not a VAG specialist, but I find him to be generally very good.

Does the combination of flashing glow plug light and constant engine light suggest anything different to brake light problems?
 
Mustang-owner said:
Hi,

Have you have a scan performed? This will identify the fault codes (DTC's - Diagnostic Trouble Codes) that are present within the various ECU's. This would be the first step, hopefully avoiding the guess-work.

If you have had a scan, please post the results, if not, get one done.
VCDS is the best tool, unless you have the scan performed at a dealer.
Some cheap handheld scanners fail to pick up all DTC's.

If you fill out your profile with a more useful "location" then those who have access to VCDS in your area may be able to offer you some assistance.

Failing this, if you venture along to a social event, someone usually has VCDS and I'm sure will help you out.

There is a social taking place this weekend in Suffolk.
http://www.a2oc.net/forum/showthread.php?19654-July-is-a2oc-camping-time

Cheers

Jeff
Click to expand...

Hi Jeff
No scan yet for this specific problem - though I'm pretty sure one was done when they replaced the glow plugs. I guess you're right - I should go to get one done; I was hoping that I had a set of 'classic' symptoms that pointed to a specific problem, thus avoiding the hassle of taking it in just for a scan.

Location - near Leeds - in West Yorkshire. West Yorkshire isn't a big county, so it qualifies as 'useful' in my book... And Suffolk is a heck of a trip from here!

Is VCDS generic, or specific to VAG?
 
... Does the combination of flashing glow plug light and constant engine light suggest anything different to brake light problems?
Click to expand...


My guess is that you have two independent problems. Firstly the brake light switch causing the flashing glowplug light (this is very common - these stupid switches just keep failing - you can replace it yourself, £10-12 for the part, and 45 minutes. The instructions are on the forum). And secondly, whatever is causing the engine to struggle to start. Given that the fuel filter housing is cracked, and this looks like a fuel starvation issue, I'd say that is the most likely culprit.
 
Some slightly differet guesses -

In most cases a cracked fuel filter housing results in fuel draining from the supply lines so the longer the car is left standing (overnight would be worst case), the harder it is to prime the system and fire up. Its also usual for fuel to leak from the filter - any diesel puddles on the ground when parked?

Sometimes a failing crankshaft sensor will give up when it gets hot but recover when it cools down. Unlike the fuel filter problem starting from cold would not be a issue.

Another possibility is a dodgy temp sensor (coolant or fuel) as this could screw up the fuelling when the engine gets hot.

The diagnostic scan is the way to go before replacing parts

Cheers Spike
 
MikeMarsUK said:
My guess is that you have two independent problems. Firstly the brake light switch causing the flashing glowplug light (this is very common - these stupid switches just keep failing - you can replace it yourself, £10-12 for the part, and 45 minutes. The instructions are on the forum). And secondly, whatever is causing the engine to struggle to start. Given that the fuel filter housing is cracked, and this looks like a fuel starvation issue, I'd say that is the most likely culprit.
Click to expand...

I see your logic, but the starting problem is definitely linked to the warning lights in some way - the lights come on when I get a 'first re-occurance' of the poor starting after the warning lights have been off for a week or two. I never get the starting problem without the warning lights, and I never get the warning lights without a non-starting 'episode'.
 
spike said:
Some slightly differet guesses -

In most cases a cracked fuel filter housing results in fuel draining from the supply lines so the longer the car is left standing (overnight would be worst case), the harder it is to prime the system and fire up. Its also usual for fuel to leak from the filter - any diesel puddles on the ground when parked?

Sometimes a failing crankshaft sensor will give up when it gets hot but recover when it cools down. Unlike the fuel filter problem starting from cold would not be a issue.

Another possibility is a dodgy temp sensor (coolant or fuel) as this could screw up the fuelling when the engine gets hot.

The diagnostic scan is the way to go before replacing parts

Cheers Spike
Click to expand...

Hi Spike

No fuel puddles. Plus, continued cranking would eventually work if a leak was the problem - fuel would get there eventually - I presume.

I'm tempted to think one of the sensors you mention could be responsible - can anyone else narrow it down further? - Would a failing crankshaft sensor or temp sensor problem show up on a diagnostic scan? I've never used / seen the scanning kit, so I have no idea about the detail they go into.....??

Having said that, it does seem to be running fine - we did about 650 miles this weekend with no running problems - just a couple of starting issues!

Are any of the aforementioned sensors a DIY-able job?
 
RWhites said:
Location - near Leeds - in West Yorkshire. West Yorkshire isn't a big county, so it qualifies as 'useful' in my book...

Is VCDS generic, or specific to VAG?
Click to expand...

Haha.....I guess "useful" might not have been the right wording.

Perhaps if you add your postal town in your profile....Just trying to be helpful as there may be members close to you with VCDS, but without this info it's just guesswork. You will see I'm in Northamptonshire and have a genuine VCDS.

The below thread may help you locate someone close to you:

http://www.a2oc.net/forum/showthread...AG-COM-Members

VCDS (VAG-COM Diagnostic System) is specific to VAG.

Cheers

Jeff
 
Not all sensor faults log fault codes but the warning lamp is a good indicator that a fault will be logged. The coolant and fuel temp sensors are fairly easy to replace. I'v not done a crank sensor but suspect it needs to be done from underneath the car.

VagCom (VCDS) is a very powerful diagnostic tool and simulates the equipment used in Audi workshops. It can also datalog sensor outputs and recode the various modules (central convenience unit etc) on the car. There are cheap copies on e.bay but they are a bit hit and miss as some members have found them to do most of the basic stuff while others have been a dismal failure

Cheers Spike
 
Hi all.
Just a quick one to update you all with the eventual solution.... (I hope!)

A scan revealed a fault with the crank position sensor - which the mechanic attributed to its proximity to the deteriorating flywheel - which had also failed (different thread). Anyway, it has now been replaced and the car is running really well.

I have to say, I won't trust it until it has been running without problems for a week or two, but it all looks good for the time being. I'll post back if the problem re-occurs.

Many thanks.

Cheers.
 
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