Hi

My 2000 Audi A6 2.8 30v APR engine will crank fine, but is just not starting. The main issue is the 'fuel pump' does NOT prime / turn on when you turn on the ignition key. The car has been running absolutely fine previously, but this happened after I replaced all the vacuum lines (they were seriously brittle / broken) don't think that's related though?

Anyway things I've done thus far :

1. Replaced Fuel Pump Relay (although original tested fine)
2. Replaced Fuel Pump fuse # 28 (although tested fine)
3. Tested 12v power at the relay panel - fine
4. Measured voltage at fuel pump connector (across pins 1 & 4) - 12v ok
5. Bypassed Fuel Pump Relay to provide 12v directly to Fuel Pump (Fuel Pump activates just fine!)
6. VagCom engine output tests carried out - can hear fuel pump, fuel injectors spray, solenoids etc.. - all seem ok.
7. Replaced Crankshaft Sensor (although original tested fine with Vagcom) - Get ~ 160/200 Engine RPM when cranking engine
8. Removed Throttle Body, cleaned, re-installed and did adaptation with Vag-com.
9. Added 10L of fuel as car was low on fuel (always put in high Ron fuel - Momentum 99)
10. Tested all other fuses in side panel - all ok.
11. Tried cold-booting the car. Remove both battery cables from the battery, shorted the battery cables together (away from the battery) for about 20 secs

12. NO vag-com engine error codes displayed at all.


For some bizarre reason the fuel pump relay is just NOT activating the fuel pump when turning on the ignition key.

I've read when some of these cars are started the ECU/ECM looks for a signal from the crankshaft sensor. If it missing it will not activate the fuel pump relay - preventing it from pumping fuel in case of an accident where a fuel line gets ruptured - but I've already replaced the Crankshaft sensor, and tested it with Vag-Com to no avail.

Next, I thought it might be the ECU relay, but could not locate it in the ECU Box Plenum Chamber under the windscreen, in fact nothing there other than the ECU itself - then phoned Audi who confirmed my particular engine does not have one!

Things it could be? -

1. Ignition switch - although all electrics work fine, windows etc
2. Starter relay - although can't locate it
2. Air lock in fuel delivery - accidently opened a fuel line when removing the throttle body, spilt a little fuel, but put the hose back on..
3. Should I try spraying some 'easy start' ....?
3. Fuel pressure regulator
4. MAF

But I don't think any of the above would prevent the fuel pump relay from turning on when the ignition key is turned on? There is NO sound at all emanating from the fuel pump when the ignition is turned on..

Any advice much appreciated!

 

Could be the ignition switch as the start position uses different contacts than run. You could try the starting fluid, then if the engine starts you know there is a fuel delivery problem. If it still does not start you should check for spark.

 

I have a similar issue. 1998 A6, 2.8 30V, vin has a B in it. Car had problems starting, mechanic got transmission speed sensor error code. Bought part from dealer, that solved the no start problem. Mechanic is good and has a new VAG (code checking) computer, but a general mechanic not an Audi expert. He had the car for a week, encountered same problem but no codes thrown.
But there is still the intermittent start problem. Cold the car starts right up. The worst situation is driving less than a few minutes, stopping, then car will not start. Dashboard lights up and car cranks but does not start. After 10-20 minutes will start. I replaced the fuel filter, but that did not make any difference.
Over last few weeks problem has gotten worse and now car will just die at a stop sign or red light. Again sit there for 10 minutes will start.
Also now has issue while driving, seems like wants to stall when I let off the gas. Like when going 45 down a slight hill. I have an extra car so this got to a point I just parked the A6 last week until I have time to deal with it.
No check engine lights or additional codes.
The car has 220,000 miles on it. The original engine was replaced 3 years ago and has 90,000 miles on it. I can replace the fuel pump myself (approx $200) or take it to a repair the local Audi/BMW/Mercedes shop?

 

Did you change the camshaft position sensor? If it fails it will cause the same symptoms. It should also report a fault in the ECU if you have a VAG-COM. Perhaps when changing the vacuum lines you either broke the sensor or mistakenly unplugged it.

 

hi guys - no I haven't changed the cam sensor, as this would surely log an vag-com error, if it was faulty or playing up.. and NO error codes at present.

thought I'd just try something. Disconnected battery. Removed ECU, cleaned connectors with electrical cleaner and refitted - then reconnected battery, and did a TBA (throttle body adaptation)

Now, the fuel pump primes when turning on ignition!

Fuel pump Fuse #28 went on then off, with ignition key, and now stays on whilst cranking. Fuses 29 & 34 (engine management) give +12v with cranking also. (tested with test light)

Still - no joy, cranks but doesn't turn over..

So, I have just 'carefully' sprayed a few short bursts of some fuel injection & carb cleaner into the intake 'avoiding the MAF' ...and .. car started!.. albeit for 2secs then died!! doh!

sounds like no fuel in the lines.. although fuse #28 is now on whilst cranking which is good.. might try priming the fuel pump / lines a few times.. ?

Battery is a bit worse for wear now - so sticking it on charge for a while.

@Euge82 - sounds like your fuel pump may be on it's way out? fairly easy to change, if you need to -
AudiWorld Tech Articles

 

So. Thinking the engine was flooded - I tried pulling the pump fuse and cranked the engine with a wide open throttle for ~15 seconds, then replaced fuse and waited for a mo. I then tried and it fired up!

BUT, it is idling very badly / engine popping / misfiring... - without putting your foot on the gas, it cuts out. Still no engine errors codes reported in vagcom, which seems a little strange.

wondering if when i replaced the vac lines, I put the vac line from the fuel pressure regulator back on wrongly - at the mo it goes straight to the EGR Vacuum Solenoid Valve via a t-piece. Should the vac-line from the fuel pressure regulator go via the non-return check valve, then onto the vacuum solenoid? Can anyone quickly check theirs...?

Although, I don't think this has a bearing on why the engine is mis-firing - but nothing else other than the vac lines has changed, since it ran last ok..

Thinking now I could have faulty ignition HT leads and / or fuel injectors?

 

You may want to take a good look at the plugs, as they may have gotten fouled while you were trying to get the engine going.

 

thanks - I'll check the plugs, although they were replaced with NGK oem, only couple of months back..

So, as above just require some confirmation on the vacuum lines on my Audi A6 2.8 30v.

Should the vac-line from the fuel pressure regulator go via the non-return check valve (part # 433 862 117) blue/black valve, then onto the vacuum solenoid? ..wondering if when i replaced the vac lines, I put the vac line from the fuel pressure regulator back on wrongly - at the mo it goes straight to the EGR Vacuum Solenoid Valve (part # 026 906 283 H) via a t-piece - gold colour solenoid in pic.

After doing the vac lines it is idling very badly / engine popping / misfiring... - without putting your foot on the gas, it cuts out.
No engine errors codes reported in vagcom, which seems a little strange.. Could someone quickly please check their vac lines for me.. many thanks

Audi EGR Vacuum Solenoid Valve - 026 906 283 H (gold colour solenoid)
Audi Non-Return Vacuum Check valve - 433 862 117 (blue/black check valve)

 

FYI, there should be a vacuum diagram sticker under the hood.

 

thanks guys for the replys - finally sorted out the issue with the rough idling / mis-firing etc.

I had taken off the throttle-body for a good clean, and failed to screw it back on properly with the gasket - doh!

I sprayed some intake cleaner around the engine to see if they were any vacuum leaks, and there was a significant leak around the throttle body!

Many thanks for all the tips, but just a heads up -

If you ever encounter any rough idling, mis-firing etc please first check your vac pipes (replace with silicone, very cheap) and then clean and 'carefully' put back your throttle-body and do a TBA.

Engine is now running better than ever.