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2003 Audi A8L Fuel Pump fix.. Help!

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2003 Audi A8L Fuel Pump fix.. Help!

Old 06-12-2011, 11:13 PM
2nd Gear
Thread Starter
Join Date: Jun 2011
Posts: 1,186
Default 2003 Audi A8L Fuel Pump fix.. Help!

Hey Guys,

I've been a lurker for a while and have found lots of information and help from searching through this forum but now I need to dive in a ask for some input on a problem I'm having with my wife's 2003 A8L.

First off, let me say that I'm an experienced mechanic and have been working on older Porsche and Audi cars for almost 20 years. I have an 87 Porsche 944, an 84 Porsche 928S, a 76 Porsche 914 2.0 (All original), an 87 Audi 5000S Quattro, and finally the newest member of the stable, the aforementioned 2003 Audi A8L.

This is the first real repair I've had to make on the A8 and it's got me puzzled. Some background on the problem. For the past few months the car will start right away, and sometimes you will have to turn the engine over for a couple or three seconds before the engine will fire. It's always ran smooth either way. A couple of weeks ago the problem has gotten worse and week before last my wife calls me from work and tells me the A8 will not start. It turns over but won't start.

I go up to check it out, tools and all. I get to checking and start with the basics. Fuel? Spark?.. I crack the fuel line open at the engine and not a drop comes out. I have the wife turn the car over with the fuel line slightly open and no fuel. I'm thinking, and hoping it's just a relay issue. After searching for the relay that evening, I can't find it. So we leave the car and I come home to browse through the ElsaWin CD Manual and find the blasted thing.

I take the wife to work the next morning and uncover the relay. I can feel it engage when the engine is turning over. Unlike the Bosche Injection Systems I'm accustomed too, the Motronic System on the A8 does not tell the fuel pump to run until the engine is turning over. (I'm used to the fuel pump coming on for a second to prime the system before turning the engine over.)

Anyway, I pop the relay out and pop the cover off. Clean as a whistle. I still take some 800grit and hit the contact points just to make sure since I've got it apart. No joy.

Next step, testing for power at the fuel pump plug on top of the tank. Getting power there too. So it's definitely the fuel pump.

In the meantime I'd called my Dad to get him to come and haul the car to the Machine Shop so I can work on it.

After more research on this forum and finding that excellent video on YouTube by Bob, I avoid having to buy the $700+ fuel pump assembly and get just the original VDO fuel pump from an Ebay vendor in England.

I did NOT get the new gasket set that everyone recommends because the o-rings and main pickup gasket on my car looked fine. However, I think I'm going to end up having to pull out the pump again and replace the gaskets because of the following.

Once I wrestled the assembly back in place (I got pretty good at it after the 5th run), the car would not start. No fuel even at the banjo fitting at the tank. I'm thinking, maybe I didn't get it seated right. I pull everything back out and double check everything. Put it back in. Even without using the neat little bore-scope Bob used in the video to verify the secondary fuel pick up had seated correctly. I can look down the opening where the sending unit goes in and see that the pump assembly is correctly aligned with the pick-up adapter in the tank. The long bolt started easily by finger and according to the ElsaWin Repair CD, this is one of the verifying factors that tell you that you've got it seated correctly. Not to mention it was sitting in the opening flush and level like it's supposed to.

Still.. No joy. I then go and get 5 gallons of gas to put into the tank that already has at least 3.5 gallons in it. The fuel in the tank was just over the top of the pick-up bowl on the adapter in the tank. After about 5 seconds of cranking the car fires up and runs fine.

I let the car run for a few minutes to work any air out of the filter and fuel system up front. A half hour later, I crank the car and it fires after the normal second or two of cranking. I then get on the the road for the 35 mile drive home. Experienced no issues at cruising speed (55-60mph) for the first 25 miles of the trip. Got to a traffic light and the car hesitated slightly on acceleration and then the ABS and ESP indicator lights came on. Second traffic light and a little more hesitation on acceleration. The last 10 miles home at 55-60mph it did fine. Check engine light did NOT come on though.

Yesterday, I disconnect the battery to let the computer reset thinking maybe this would clear any codes and reset things. Reconnected after a half hour and it seemed to be a little better. Took the car for a short drive in town and didn't notice any hesitation on acceleration.

Today. ALL to HELL.. The car took 4 or 5 seconds of turning over to fire. Ran ok. Stopped at the gas station to put an additional 5 or 6 gallons in the tank thinking the secondary fuel pickup tube o-ring was leaking and I planned on driving the car back down to the shop. Pulling out from the gas station, it hesitated big time, I tromped it, she picked up and shortly after than, the Check Engine light came on along with the ABS and ESP indicator light. The car ran fine after that at highway speed for 10 miles. Hesitated on acceleration at the traffic light like it did on the trip home a couple of days before.

Sorry to be a little long-winded on the post but I wanted to put as much information out there as I could on this. I'm going to order the gasket set (part number 4d0 298 133c) tomorrow and hope that this fixes the problem. I'm almost positive it's sucking air and the fuel pressure is fluctuating causing the problems. I'm at a loss over the ABS and ESP indicator light though. Perhaps the ECU is freaking out over the fuel pressure..

ANY input on the situation would be most appreciated.

Old 06-14-2011, 10:12 PM
2nd Gear
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Join Date: Jun 2011
Posts: 1,186
Default Update

Well, I think I've narrowed it down to a possible leak in the pickup gaskets. More than likely it's the smaller secondary pickup o-ring gasket that is normally replaced with the pump assembly. Today I cleared the ECU again by disconnecting the battery and following the newly discovered (to me) procedure of putting the key in and turning the ignition to "on" (position 2) and waiting at least 6 seconds (I waited 15) and then try to start the car. I didn't turn the key back to off after the 15 second wait and tried to start it. After 5 seconds of turning the engine over, it would not start. I then turned the ignition off and then tried starting it again. Fired right up.

I then drove the car 5 miles (with no hiccups or warning lights) and filled the tank up to make sure BOTH areas where air can get sucked into the fuel pump were covered with gasoline. It took 8 gallons to fill the tank (it had at least 12 in it). I then drove the car the remaining 30 miles home with no issues at all.

I'm going to drive the car (keeping a couple or three gallons of gas in the trunk) until starts to hiccup again. IF it doesn't, I guess it the clearing the ECU might have fixed an issue of left over garbage information from the previous faulty fuel pump.

We'll see.

Old 07-03-2011, 07:41 PM
2nd Gear
Thread Starter
Join Date: Jun 2011
Posts: 1,186
Default Update and some advice for fellow A8 owners.

I finally tracked down the issue with the car. Actually there were two. Audi recommends that you replace the little o-ring on the secondary pickup port and the rubber/metal gasket on the bottom of the pump assembly for a reason. Apparently the o-ring on the secondary pickup port was leaking just enough to cause an issue at below half-full tank fuel quantities. I was able to find a suitable replacement in a left over engine (or transmission) rebuild kit at my Dad's Auto Machine shop. The bottom main pickup gasket looked perfectly fine to me and it seems to be ok so I opted to keep it. Replacing the o-ring seemed to fix the issue for a short time.

A couple of days later and at over 3/4 of a tank full of gas, the car started to buck on accelerations especially after downhill stops. So I pull the pump assembly again to check things. The previous 5 (no kidding) times I had pulled the assembly (practicing getting the thing seated properly) I could have sworn I checked the rubber hose from the pump to the top of the assembly for signs of cracks. Well, I found one. Right at the crimp connector at the top. I bent the hose to inspect it and the crack opened up into a nice big RIP...

I think the small crack in the hose was the culprit that did in the original fuel pump. The new pump was able to deliver more pressure at startup and I guess it made the crack even larger with each passing minute. So, I cut the hose right at the crimp leaving me just enough length as not to have to replace the entire hose. The rest of the hose looked to be in fine shape. I took the metal part of the hose that attaches to the top of the pump assembly off as not to pose a fire hazard when I took the trusty Dremel tool and cut off the crimp. The left a nice metal fitting which was ideal to slip the hose back onto and gently clamp back together (remember to always use 100% stainless steel clamps inside the fuel tank, that ethanol crap will corrode anything else) thus finally fixing the entire problem. I'm convinced the very process of crimping the hose at the factory crushes the hose too much leading to a failure of the hose in that area.

SO.... If ANY of you out there are having to crank you 2002-2003 A8s for more than one full second before it fires, this could be a sign of in tank pressure hose leak which can lead to a pump failure. A quick way to check for excessive leak down on the fuel system would be to crack open the fuel connection at the engine or at banjo fitting on top of the fuel pump assembly to see if the fuel pressure has dropped to nothing after letting the car set for an hour or so. If there is no leak in the system, you still should have enough residual pressure as to have a nice spray of fuel come out. Mine would have no spray and just a few drops of fuel would come out.

Audi has replaced the serviceable pump assemblies with a non-serviceable assembly that will set you back $700 minimum. Apparently they have replaced the hose with a hard part inside those assemblies and have made it impossible to replace the pump by itself. In effect making it a $200 pump surrounded with $500+ of plastic. But the pumps are obtainable from an Ebay vendor in England for $200. The gasket set (Audi Part # 4D0-298-133-C) is readily available at GenuinAudiParts.com for $115 (kind of expensive but...) So you can rebuild your fuel pump assembly for around $300 and change if it's one of the original multi-part ones..

The hard part is learning how to remove and reinstall the assembly. It is a fine art of maneuvering if you've never done it before.


Last edited by dave944; 07-08-2011 at 11:40 PM.
Old 04-09-2012, 05:23 PM
1st Gear
Join Date: Apr 2012
Posts: 1
Default a8 re seating housing

hi mate going through this now new pump and gasket set but still sucking air and can not see why and this is about 6 times in and out also when you have found the cup from the small pick up on the side when they meet together should they go all the way in as i have about 3mm that not go down any more could that be my problem thanks from phil
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