Audi Repair: hard starter, mechanical faults, coolant temp

Question
QUESTION: Thanks for your reply re hard starting audi 1.8t. You advised me to replace the 4 pin temp plug, do you mean the coolant temp sensor, if so i have allready replaced this. I have also viewed this on vag com and the temp reading on block 011 is ok. It seems the longer the car is left the harder it is to start. between 5-8 secs. Once started car runs fine.

ANSWER: Hi Howard,

Are there any other faults logged in the memory??
Sounds like an over flooding fault, some times the injectors 'dribble'(caused by dirty/faulty injectors that dont seal off completely when the engine is switched off) i.e. leak fuel when the engine is stopped, the longer it is left the more fuel leaks past the injectors and hence the harder it is to start,

whats the current mileage of the vehicle, are the spark plugs in condition, flooding can also be caused by a weak spark that fails to set of combustion properly,

best way to find the exact cause is to remove the spark plugs when the problem occurs and read them for faults, a wet plug means that the fuel is not being ignited, either because of a faulty ignition or because of excess fuel.

also check the colour of the plugs (do not mix them when you remove them so you can isolate the faulty cylinder/s) look for differences in colour between the cylinders either too dark(too rich) or too light(too lean) from the rest. ideal colour is a beige some times with a tan tint (caused by the unleaded fuel-the red is the additives added to replace the lead)

it may also be worth to have the compressions checked, both when cold and hot, some mechanical faults cause compression to fall when hot and in turn cause hard start. (personally its highly unlikely but it costs nothing to be sure)

P.S

If you do need to have the injectors replaced then some shops offer reconditioning services or swaps, which might be a cheaper option then buying new injectors.

---------- FOLLOW-UP ----------

QUESTION: Hi Naushad,

Thanks for all of your helpfull advise. The car has done 90000 miles, all of the plugs are relatively new. I will check the plugs as you have advised.
I am quite sure the injectors are not leaking as fuel pressure did hold when tested, fuel pressure was 60psi with engine running and with engine switched off pressure dropped to 40psi over 30mins and 20psi after 1 hour. There are no fault codes logged. Could you confirm that the fuel pressure readings i have given are normal.

Many Thanks
Howard


Answer
Hi Howard,

the specifications for a 1.8T engine(I used an AWT engine code) are as follows:

3.5 bar with the pressure regulator vacuum hose connected
4.0 bar with the vacuum hose detached
and a holding pressure of at least 2.5 bar after 10 minutues.

you mentioned that you have VAGCOM, try this link that I found that is specifically for 1.8T on the TT version  but also has a lot of generic information for 1.8T engines.

http://www.wikitt.org/wikiTT/images/f/fc/TTweakers-Guide.pdf

As the disclaimer on the site says you use the information at your own risk, it sounds mean but that disclaimer applies to me as well, use the info at your own risk. Sorry :)



the fact that there are no fault codes logged leads me to suspect 2 things,

either the fault is fully mechanical, and therefore diagnosis cannot pick up the fault, or.

the fault is electrical BUT is still small enough that it is still within the parameters not to log a fault.

the best way is to use the measured block function on VAGCOM to read the data off the various sensors to find which one is not within the safe parameters.

As an after thought, have you checked the basics like: the air filter(blow it out with compressed air) the fuel filter(maybe blocked and when the car is resting the dirt collects but when the ignition is switched on the fuel pressure moves the dirt away) the battery terminals and connections, can cause electrical faults)

Also what fuel grade are you using?? higher fuel grades need a bigger/stronger spark to set off combustion and can take more ignition advance(thats why on performance cars using higher octane fuel-100RON onwards!! the ignition is also upgraded) while lower fuel grades set off more quickly but cannot take higher ignition advance, and are more prone to detonation.

Audi spec for the AWT engine is 95RON(research octane number) but can also use 91RON but with reduced performance(the lower grade fuel detonates more easily hence the knock sensors reduce the ignition advance and thereby causing the reduced performance).

Also you mentioned that the vehicle has only done 9000mls which is a relatively new vehicle, as an Ex-audi dealer tech sometimes we'd get 'updates' for the engine control data that we use to upgrade the vehicle programs.(this info was not necessarily given to the owners but the updates were carried out when the vehicle was in for regular service, maybe you missed such an update if your vehicle was only maintained for the first service/s but im not too sure if your vehicle  applied)

hope this info helps and tell me how the link worked out for you.