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Hi

A friends RS4 which I am looking to purchase sometimes fails to start especially when left for 2/3 hours in the summer sunshine of Abu Dhabi where temperatures can reach 40C at this time if year. . The issue seems intermittent as it usually starts. The car was taken to Audi and they replaced the air mass sensor however this has not cured the issue. The battery is also new and from Audi.

I noticed that what the car starts normally, there is a slight sound of electric activity going on toward the rear of the car which can be heard from inside. When the issue occurs, there are no such sounds detected so not too sure what the issue could be. If the car is left for a few minutes it usually starts. Furthermore when the issue occurs, the engine is turning, but just fails to fire up the engine.

Any ideas please ?
Thanks
Sean

Could be an issue with a relay for the engine ecu

Being a complete novice here, I assume the engine ecu relay is soemthing major to put right?

Nah - shouldn't be. Engine relays are pretty standard things.

If the engine turns but doesn't fire the. I usually look at te fuel pump/ fuel pump relay or alarm.

I've no idea how sensible this is with an rs4 (so don't blame me if you break the car or blow up) but in the past I've hooked the fuel pump relay up direct to a battery effectively bypassing the alarm to investigate starting issues. Did work as car started and turned out the alarm ecu was broken.

What should happen when you unlock and first open the drivers door is hear the fuel pump prime.
Then again when you put key into the ignition and turn.

No not necessarily, I had a similar problem the relay was £20 for the part, he came out to my house diagnosed the problem and fixed it for a total of £70,relay part no was 8E0951253 this showed up on mechanics laptop

Thanks! Was you issue something similar, i.e intermittent starting issue?

Yes my car had very similar problems, would turn over but would not start, rang the mechanic he said he thought it would be a relay issue, and was spot on as this has completely cured the fault, this was an intermittent problem like yours

Thanks. Was thinking this could potentially be a bigger issue.

Spoke to Audi and they will perform a diagnostics test on the car to confirm. Will the diagnostics confirm the issue ?

Also do you think its only by coincidence that the issue only happens when the car is left in the heat and prior to starting the car is it normal to hear electronics starting up/humming from the rear of the car ?

Thanks
S

Diagnostics should confirm the problem, the problem on my car started when we had a few hot days, along way off the heat of Dubai unfortunately, not too sure about the buzzing sound maybe it's a fuel pump priming

Thanks

Thanks. Seller will be giving the car into audi tomorrow for a diagnostic check. Not sure how good they are out here so anything else I should alert them to check apart from fuel pump relay in order to isolate the issue.

I'm not sure if this was a fuel pump relay I will check with mechanic today and then update you

The relay was a fuel pump one

Right - I took the car into Audi for diagnostics.

Issues they mentioned reported were:

1-Relay
2-Throttle Body
3-Air Mass

Any idea how much this lot should cost to put right ?

Are these major ?

Beginning to question ownership of an oldish RS4....especially one that has lived in the middle eastern desert climate all its life!!

Im expecting higher than ave running costs but.....

I don't think these issues found will cost that much to fix, relay is cheap and air mass is not very expensive plus will improve performance, not to sure on price of throttle body but I'm sure it's not to much to worry about getting sorted

No expert, but replacing all 3 things at the same time (unless the cost is completely insignificant) sounds a bit over the top to me.