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Intermittent starting issues, need help

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Old 08-02-2014, 08:30 AM   #1
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Default Intermittent starting issues, need help

I have a 1999 d2 a8 4.2 quattro. I recently replaced the fuel pump/filter and fuel pump relay. The car will start and drive fine however when the car is parked for longer periods of time the car will not start. I think it has something to do with low fuel pressure. When I turn the ignition on to the on position several times and try to start the engine it will start occasionally. I'm not sure if it's a fuel pressure regulator bad plugs wires etc? However I am going in for my timing belt service in about a week. Can the timing belt towards the end of its life have something to do with its intermittent starting issues? what could be the culprit?
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Old 08-02-2014, 08:33 AM   #2
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I think the timing belt being worn out may be causing problems with the compression... Am I incorrectly understanding this?
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Old 08-03-2014, 05:01 AM   #3
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Timing belt isn't the problem. Could be leaky injectors.
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Old 08-03-2014, 05:57 AM   #4
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Originally Posted by d2audia8guy View Post
I think the timing belt being worn out may be causing problems with the compression... Am I incorrectly understanding this?
Sorry, but completely incorrect there...nothing to do with compression, unless the belt jumped time, which would cause misfiring all the time and timing codes.

Have run a VagCom on it? ...NOT just a simple code reader (only reads codes associated with

You are describing a likely loss of residual fuel pressure after shutting off the engine...all it takes is one tiny leak from an injector, not closing completely...you'd never see it or smell it. If it was not doing this before changing the fuel filter (almost NEVER a needed change...waste of time, money and exposing an otherwise clean system), you may have introduced just enough dirt on the clean side of the filter to cause this...doesn't take much.

I'd start by putting a bottle of Techron (PROVEN: NOT ANY OTHER BRAND...USELESS) in 1/4 to 1/2 tank of gas...Then do it again on the next 1/4 to 1/2 tank. Many posted reports of this doing the trick...if it can be cleaned, this is the ONLY stuff that actually works.

If that doesn't work, you'll need to go deeper...pull injectors, test pressure regulator, check fuel pressure and pressure bleed-down, etc...
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Old 08-03-2014, 06:48 AM   #5
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Sorry, but completely incorrect there...nothing to do with compression, unless the belt jumped time, which would cause misfiring all the time and timing codes.

Have run a VagCom on it? ...NOT just a simple code reader (only reads codes associated with

You are describing a likely loss of residual fuel pressure after shutting off the engine...all it takes is one tiny leak from an injector, not closing completely...you'd never see it or smell it. If it was not doing this before changing the fuel filter (almost NEVER a needed change...waste of time, money and exposing an otherwise clean system), you may have introduced just enough dirt on the clean side of the filter to cause this...doesn't take much.

I'd start by putting a bottle of Techron (PROVEN: NOT ANY OTHER BRAND...USELESS) in 1/4 to 1/2 tank of gas...Then do it again on the next 1/4 to 1/2 tank. Many posted reports of this doing the trick...if it can be cleaned, this is the ONLY stuff that actually works.

If that doesn't work, you'll need to go deeper...pull injectors, test pressure regulator, check fuel pressure and pressure bleed-down, etc...
Are you suggesting a higher concentration than suggested on the bottle? What size of bottle have you used?

Thanks.
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Old 08-03-2014, 07:45 AM   #6
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Are you suggesting a higher concentration than suggested on the bottle? What size of bottle have you used?

Thanks.
YES, I am.

I put 12 ounces (12 gallon treatment) in about 1/4 to 1/3 tank (5-8 gallons)...NEVER more gas than that...Why dilute it any more?

You could fill your tank with pure Techron and if it would burn, it wouldn't hurt a thing....especially to treat an existing problem (not just preventive maint), diluting it too much will only render it ineffective.

The label instructions are to make it look better than it is...but read carefully >>> 12 ounces "Treats *UP TO* 12 gallons"...Translation: Put it in LESS than 12 gallons for more effectiveness...12 gallons would be the MAXIMUM dilution without rendering it ineffective.

I've used it in high concentration on all my cars (all present and a few past) with nothing but good results.

P.S. Whatever size bottle, I always try to put 2 ounces per gallon rather than the MINUMUM of 1 per gal.

"UP TO" >>>


Click the image to open in full size.
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Last edited by silverd2; 08-03-2014 at 07:49 AM.
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Old 08-03-2014, 09:18 AM   #7
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Hello

Prior to changing the fuel filter I had been told by a German specialist that there was a problem with my fuel sending unit. About 4 months later the fuel pump died. I replaced the fuel filter prior to the pump in case it was clogged (it had never been replaced at 188k.) I wasn't having intermittent starting issues until I replaced the fuel pump. The car will drive perfectly and idles fine, although, the car immediately shut of out of nowhere a couple times while in traffic. She starts back up no problems. What's weird is that no start issue only happens when it sits over night and loses compression? Possible fuel regular bad?? Also I recently used two bottles of "liqui moly" to clean out fuel injectors....I will get pressure tested....one last thing...when I replaced the fuel filter I accidentally cut the line...had the line repaired using a "stint"...tested for leaks....any other ideas??
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Old 08-03-2014, 09:40 AM   #8
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YES, I am.

I put 12 ounces (12 gallon treatment) in about 1/4 to 1/3 tank (5-8 gallons)...NEVER more gas than that...Why dilute it any more?

You could fill your tank with pure Techron and if it would burn, it wouldn't hurt a thing....especially to treat an existing problem (not just preventive maint), diluting it too much will only render it ineffective.

The label instructions are to make it look better than it is...but read carefully >>> 12 ounces "Treats *UP TO* 12 gallons"...Translation: Put it in LESS than 12 gallons for more effectiveness...12 gallons would be the MAXIMUM dilution without rendering it ineffective.

I've used it in high concentration on all my cars (all present and a few past) with nothing but good results.

P.S. Whatever size bottle, I always try to put 2 ounces per gallon rather than the MINUMUM of 1 per gal.

"UP TO" >>>
Thanks for clarifying. I got excited when I read this thread and put a 20 ounce bottle in a full tank (23 gals). Next time around I'll definitely try at a higher concentration. In my case it's just preventative maintenance. Always good to hear that someone with the same car has had success with a particular brand of magic-in-a-bottle. You had me add ATP AT-205 to my Amazon wish list as well :-)
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Old 08-03-2014, 10:11 AM   #9
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Originally Posted by Kneale Brownson View Post
Timing belt isn't the problem. Could be leaky injectors.
Would you recommend a leak down test?
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Old 08-03-2014, 11:26 AM   #10
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I was able to get the car to start and let it idle. After idling for about 5 minutes the engine started shaking and sputtering. I revved the engine and when I hit the gas it chokes, when I let go of the gas it revs to higher rpms but returns to rough idle. I went to listen to the new fuel pump and it was making weird noises almost like it was malfunctioning..instead of having the quiet & constant buzzing noise... I'm going to pull my fuel sending unit back out and replace the entire unit...the pump is brand new so I can't imagine its actually malfunctioning....
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Old 08-03-2014, 12:59 PM   #11
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Originally Posted by d2audia8guy View Post
I was able to get the car to start and let it idle. After idling for about 5 minutes the engine started shaking and sputtering. I revved the engine and when I hit the gas it chokes, when I let go of the gas it revs to higher rpms but returns to rough idle. I went to listen to the new fuel pump and it was making weird noises almost like it was malfunctioning..instead of having the quiet & constant buzzing noise... I'm going to pull my fuel sending unit back out and replace the entire unit...the pump is brand new so I can't imagine its actually malfunctioning....
The symptoms do seem to describe fuel starvation.
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Old 08-03-2014, 01:03 PM   #12
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Quote:
Originally Posted by d2audia8guy View Post
I was able to get the car to start and let it idle. After idling for about 5 minutes the engine started shaking and sputtering. I revved the engine and when I hit the gas it chokes, when I let go of the gas it revs to higher rpms but returns to rough idle. I went to listen to the new fuel pump and it was making weird noises almost like it was malfunctioning..instead of having the quiet & constant buzzing noise... I'm going to pull my fuel sending unit back out and replace the entire unit...the pump is brand new so I can't imagine its actually malfunctioning....
Where did you source the pump?

Is it the correct Seimens/VDO pump? Statistically, ANY other brand is a mistake.

ONLY correct pump >>>

Audi A8 Fuel Pump - Original SIEMENS VDO | World Car Parts > Store
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Old 08-03-2014, 01:59 PM   #13
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After some thinking...I'm going to do a leak down test and fuel pressure test.
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Old 08-04-2014, 10:35 AM   #14
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OK guys...I solved the issue. It was a bad CRANK SHAFT POSITION SENSOR. The symptoms will resemble fuel not getting to the engine, bad o2 sensors,bad fuel pump or relay. What I did was replace the relay to see if it made a difference.... None.....OK fuel pump already replaced..checked fuel sending unit and relplaced o rings...?? New fuel filter too..and new air filter....cleaned injectors with liquimoly...spark plugs semi fouled because of normal wear most likely..I thought it was due to bad fuel pressure regulator....all Wrong....the main symptoms for the CRANK SHAFT POSITION SENSOR going bad is that you park the car over night...in the morning it'll crank with a no start....once you get the bitch to start she runs like normal....shut it off...starts back up no problems....its only over night that it won't start the next day...
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Old 08-04-2014, 10:38 AM   #15
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Where did you source the pump?

Is it the correct Seimens/VDO pump? Statistically, ANY other brand is a mistake.

ONLY correct pump >>>

Audi A8 Fuel Pump - Original SIEMENS VDO | World Car Parts > Store
I sourced it from vdo OEM parts. AutohausAZ.
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Old 08-05-2014, 06:37 AM   #16
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OK guys...I solved the issue. It was a bad CRANK SHAFT POSITION SENSOR. The symptoms will resemble fuel not getting to the engine, bad o2 sensors,bad fuel pump or relay. What I did was replace the relay to see if it made a difference.... None.....OK fuel pump already replaced..checked fuel sending unit and relplaced o rings...?? New fuel filter too..and new air filter....cleaned injectors with liquimoly...spark plugs semi fouled because of normal wear most likely..I thought it was due to bad fuel pressure regulator....all Wrong....the main symptoms for the CRANK SHAFT POSITION SENSOR going bad is that you park the car over night...in the morning it'll crank with a no start....once you get the bitch to start she runs like normal....shut it off...starts back up no problems....its only over night that it won't start the next day...
Congratulations on finding the root cause. Interestingly I had the exact same issue on another car many many years ago and it turned out to be the crankshaft position sensor. Due to the intermittent nature of the issue it took a long time to troubleshoot. The actual sensor ended up being ok; however the connector it used to the engine wiring loom was the problem.

I'm glad your problem is solved.
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Old 08-05-2014, 09:22 AM   #17
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OK turns out now there is no spark? Can't get it to start....wtf!!
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Old 08-05-2014, 11:36 AM   #18
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OK turns out now there is no spark? Can't get it to start....wtf!!

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OK guys... "bad o2 sensors," "the main symptoms for the CRANK SHAFT POSITION SENSOR going bad is that you park the car over night...in the morning it'll crank with a no start....once you get the bitch to start she runs like normal.."


Where are you getting this info? ...what are you reading or being told?

O2 sensors will NOT stop a car from starting or shut one off...they only trim the fuel mixture within a small map set by the MAF. The MAF can stop a car from starting or stall it out, but not the 02 sensors.

That is not necessarily a "main symptom" of the engine speed sensor ("crank position sensor") being bad...nothing to do with parking over night. The crank position sensor simple sends a signal to the ECM which in turn grounds the fuel pump relay to allow it to work...that's it, fuel or no fuel.

Have you run a VagCom on it (read codes) ?

If you are truly getting no spark (are you sure), look at your ECM...water in it? ...corroded connections?
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Old 08-05-2014, 11:20 PM   #19
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Where i am getting the info is from what the car was doing....i am honestly doing a lot of guesswork here...I'm having it towed to a German specialist tomorrow morning, I'll keep you posted. Haven't checked the ecm myself, water got into cabin due to clogged drains awhile back...unclogged and pulled carpets to dry...ecm was fine....running out of ideas here....don't ever buy relays from O'Reilly auto parts...they are *******s if want to return it...I'll post the bag codes shortly...I haven't run them in last week or...the codes are from a month ago
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Old 08-06-2014, 04:01 PM   #20
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Car is running now...I'm so pissed...thing didn't have gas in it apparently??? My fuel gauge is allegedly broken but I swear I had at least a half tank....twilight zone? I probably spent about $1000 over this while dilemma...grrrrrrr...pathetic
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Old 08-06-2014, 04:01 PM
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