Starting problems

T

t42

A2OC Donor
Hi all,

I'm in need of some help...
I've been having an ongoing issue with my TDi 90 with poor starting from cold. It seems to get worse with lower ambient temperature. On a good day it will turn over a few times before starting. On a bad day it will take 3 or 4 turns of the key (each a few seconds of cranking) before it bursts into life. Once started it runs fine and it can be fairly easily restarted for a several hours afterwards (although I think this depends a lot on the ambient temperature - it's always difficult to start in the morning but usually fine when I come to leave work 10 hours later in all but the recent coldest conditions).
On prolonged starting attempts it will throw on the engine management light and flashing glow plug light (and P0726 error). Very occasionally after a really difficult start the ESP light will come on but a restart clears that. It's never failed to start eventually.

Here's what has been done so far (that I can remember) with no long term improvement:
  • Crankshaft sensor replaced
  • Camshaft sensor replaced
  • Sensor wiring back to the ECU checked
  • All glow plugs replaced (with correct type for the TDi 90)
  • Brake light switch checked
  • Glow plug relay box checked
  • Earth lead checked and cleaned up
  • ECU temporarily swapped with a known working one
  • Parked nose down on a hill overnight

After replacing each of the sensors (during mild spells) it worked OK for a week or two, then got worse again. Other stuff was done to the car on both occasions (battery disconnected for prolonged period, wiring poked, new starter motor), so it's difficult to say what improved it briefly on those occasions.

The problem started around the same time I had a replacement (MYP) gearbox fitted (and new clutch & DMF at the same time), although I'm struggling to imagine what could link the two.

As you can see I've spent quite a lot of time (and money) recently but don't know where else to go from here. Any advice would be most appreciated!
 
I would check / replace the temperature sender (4 pin) that "tells" the engine how hot / cold the coolant is and if that fails to give the right info it will impact starting.

Steve B
 
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Birchall said:
I would check / replace the temperature sender (4 pin) that "tells" the engine how hot / cold the coolant is and if that fails to give the right info it will impact starting.

Steve B
Click to expand...

Many thanks for your input Steve. The temperature gauge reads OK, but I guess there are two halves to the sensor (hence the 4 pins)? Is it a simple DIY job to get at or a little more involved? (I tried searching but all the pictures seem to have been lost). Is there a test procedure to verify correct operation?
 
t42 said:
Many thanks for your input Steve. The temperature gauge reads OK, but I guess there are two halves to the sensor (hence the 4 pins)? Is it a simple DIY job to get at or a little more involved? (I tried searching but all the pictures seem to have been lost). Is there a test procedure to verify correct operation?
Click to expand...


Yes, two circuits, one for the temperature gauge and one feeds the ECU with temperature info.

It is a DIY job, get a genuine sender from Audi a new sealing rubber ring and a spare plastic clip.
You also need a the right antifreeze (from Audi ideally)

I will see if I can find the link to the "how to".

Steve B
 
t42 said:
Many thanks for your input Steve. The temperature gauge reads OK, but I guess there are two halves to the sensor (hence the 4 pins)? Is it a simple DIY job to get at or a little more involved? (I tried searching but all the pictures seem to have been lost). Is there a test procedure to verify correct operation?
Click to expand...


As for the test procedure (sorry just spotted that question) it can be checked with VCDS, you can see the temperature readings on that.

But if it was intermittent you might not spot it.

Steve B
 
Thanks Steve. It's been to A2Cars so they may have checked it already and I just don't remember. It's going back again in a couple of weeks anyway so I may leave it to the experts with VCDS...
 
t42 said:
Thanks Steve. It's been to A2Cars so they may have checked it already and I just don't remember. It's going back again in a couple of weeks anyway so I may leave it to the experts with VCDS...
Click to expand...

Checking the temperature sender readings is not part of a normal VCDS diagnostic check, unless there are starting issues.

Steve B
 
75hp TDI here. I also have cold climate bad starting.

The starter motor seems a touch lazy in any temperature, even at summer. It'll crank the engine over with mediocre enthusiasm and it fires up. At about minus 15 degrees Celsius the enthusiasm is gone outta window. It'll crank in slow motion, despite 5W winter classification engine oil.

I have detached and cleaned passenger side lamp earth strap. I did find some corrosion, but no help. I did add another earth strap parallel to the existing one, and replaced the battery with a brand new 95Ah AGM battery. Still very slow motion cranking.

I used to have a 1.9 TDI Passat with a large battery (either 95Ah or 105Ah). That cranked very well indeed. Superb cold starter. At once I had to start that Passat at minus 34 degrees Celsius without any external heaters. I switched the key on and off seven times to extract as much warmth from the glow plugs as possible before cranking - and it fired right up after a few rotations.

I wonder if our 1.4 TDI's have under engineered starter motor size for freezing temperatures?

I am going to run a proper earth cable from the battery all the way up to starter motor later this year, in an effort to ensure high amperage delivery.

Comments are welcome.
 
Artsi_L said:
75hp TDI here. I also have cold climate bad starting.

The starter motor seems a touch lazy in any temperature, even at summer. It'll crank the engine over with mediocre enthusiasm and it fires up. At about minus 15 degrees Celsius the enthusiasm is gone outta window. It'll crank in slow motion, despite 5W winter classification engine oil.

I have detached and cleaned passenger side lamp earth strap. I did find some corrosion, but no help. I did add another earth strap parallel to the existing one, and replaced the battery with a brand new 95Ah AGM battery. Still very slow motion cranking.

I used to have a 1.9 TDI Passat with a large battery (either 95Ah or 105Ah). That cranked very well indeed. Superb cold starter. At once I had to start that Passat at minus 34 degrees Celsius without any external heaters. I switched the key on and off seven times to extract as much warmth from the glow plugs as possible before cranking - and it fired right up after a few rotations.

I wonder if our 1.4 TDI's have under engineered starter motor size for freezing temperatures?

I am going to run a proper earth cable from the battery all the way up to starter motor later this year, in an effort to ensure high amperage delivery.

Comments are welcome.
Click to expand...


I think that you probably have a starter motor problem.

An A2 Starter motor with good earth connections will sopin up an A2 in even the coldest conditions. There are many owners in your area that do not seem to have the same problem.

Also worth making sure that you have the right engine oil, that is very important at low temperatires.

The same starter is used on the 1.9 tdi engines and they have an extra cylinder to spin up.

Steve B
 
I think I have the same problem as the OP, also after fitting an MYP gearbox and new DMF. I'd like to check the glow plug relay is working, does anyone know: if it was faulty, would I get a fault code /DTC? There is no fault code which has to do with the glow plugs, and disconnecting then trying to start gives exactly the same difficult start except 3 faults for 3 open-circuit glow plugs. So, where is the glow plug relay or module on a TDI 90? Thanks in advance, Matt


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If you get the errors when you disconnect them and no errors when they are connected it is a pretty safe bet to assume that the relay is fine or disconnecting them would make no difference to the error codes. Just an assumption but it seems to be logical.

So I would look elsewhere. Your car should start easily enough without the glow plugs working anyway. It is only cold temperatures where they are needed.
Mid anyone with a Tdi was to switch on the ignition and immediately try and start their car in these temperatures I am sure it would start up fine and the glow plugs will not have been on long enough to make a difference.

I would check for fuel leaks if you haven’t already done so. Disturbing the engine during the swap might have loosened a fuel pipe?

Steve B
 
Thanks Steve, there's nothing leaking from the tandem pump but I'm going to take a look now at the rest of the system - or what is visible. I know the fuel filter housing can be delicate on the ATL version and has led to problems for others so I've been holding off changing it until this starting issue is sorted. I don't think it could be the filter though as that would give the opposite problem as Mike suggests further up. I've found the 471 glow plug relay which lives in the underfloor bin, it is an electronic sealed unit I will leave well alone. Cheers, Matt


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I've now eyeballed every bit of the fuel system and found no signs of diesel leaking out. This included taking off the comedy tinwork covering up the fuel filter with its ridiculous corroded fixings. Of course there may be a tiny hole which is letting in air but miraculously not letting any diesel out. Thats the sort of thing which is a nice idea but sounds impossible to find or prove one way or the other. I've PM'd the OP to see if there was a fix in the end. Matt


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Im sure my tdi never showed a fault code but i did have 1 faulty glow plug , more noticable in cold weather as took 4 or 5 revolutions to fire up rather than on the button and just the flick of the key .. even in hot weather the glow plugs do come on although not for long and pre heat the cylinders and they also afterglow and alternate on and off while the engine warms up for the first min or so..


The only way i know of testing glow plugs is to remove them and use jump leads and a battery.. couple seconds and they will start to glow red hot and shows its working
Warning !! do not just attempt to undo glow plugs !!
firstly squirt wd40 around the base of the glow plugs and alough to soak in , possibly do this everyday for a few days , then youl need a deep 10mm socket and only remove from a warmed up engine never cold as they are known to snap in half while attempting to undo
 
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