Greetings all, 'been lurking for a while... now I've got a question...

I'm about 90% through a restoration project on my '87 5000CS Turbo Quattro... it wasn't too strenuous as I'm the original owner. But lately I've noticed a periodic vibration - almost a buzz - seemingly from the area of the fuel pump (submerged in the tank) or in the vicinity of what appears to be a fuel pressure regulator located inside a starboard frame rail just forward of the R/R wheelwell. It manifests periodically in the sense that it occurs only once in a great while - and typically quits the moment I try to trace it.

The car has about 107K miles, and is all original but for factory spec (Audi) new suspension components, to include new steering rack and CV joints.

Any thoughts on the "buzz"..? Oh yeah, I know the difference in sound that the fuel pump normally emits, and this ain't it...

 

I know the noise exactly! Weird buzz that gets your attention but then just as quickly disappears so tracing it is almost impossible. It happens while driving, idling, hot, cold, etc. I think that it is the check valve that is making the noise. My 1991 100Q has 178K and has been doing it since 99K.

 

Check valve..? Is it in the pump, the regulator, or what..? Please forgive the many questions, and thanks for the response, Offramp.

Is it something that merits more concern, or is it another aspect of the well known "character" these fine machines develop with... uh, I almost said "age"... but a better term comes to mind - let's call it "seasoning"... In short, does it herald a problem, or should I not worry about it..?

In retrospect, it's not really that annoying... but it's not "right" either... I can be kinda **** in a restoration sense.

 

If you do a system and a residual pressure check and everything is within spec, I wouldn't worry about it. Like I said I have been driving with the noise for more than 4 years and 79K on top of the 99K when I bough the car used. Actually I think that the part is called a Pressure Damper and it sits on top of the fuel pump. It goes for about $125 but changing it in a sedan is a major PITA.

 

Mike,

There is a noise damper, then there is a check valve, available here: http://www.sjmauto.com/epcMake.epc?y...5&clientid=sjm

Check valve is a 25 buck item. The book makes it out to be no big deal to change. Thing is, if you have no starting problem, as though you lost all your residual fuel pressure, not the check valve.

What it MIGHT be, I don't know. Any other thing could cause a buzzing is at the front of the car.

You want a fuel diagram, holler.

Cheers,

George

 

One thing I don't remember is whether the fuel pump housing needs to come out or not in order to change the damper. I had the pleasure to examine the fuel pump with all it's mountings at a local bone yard. The fuel tank was already removed from the car and lying out in the open. Based on what I have seen I definitely don't want to do this in the confinement of a trunk with any amount of fuel in the tank. The access port for the pump is on the floor under one of the rear speakers, you know that cramped narrow space all the way by the back rest. Not only do you need especial wrench to unlock the fuel pump holder and housing but it sits inside firmly seated in the bottom of the deep tank in a special holder with three grommets firmly securing the whole thing. The job probably rates up there in complexity together with the heater core minus the explosiveness!

 

Many thanks for the guidance, gentlemen. BTW, I have the appropriate Bently Manual, but I think brainstorming issues with more experienced colleagues is usually most beneficial - I certainly appreciate your perspectives.

As the intermittent "buzz" appears to be merely annoying (no starting, running or acceleration problems... I haven't yet done a systems pressure check), and in truth now that i'm focused on it and actively trying to diagnose it - the damn thing won't manifest, no matter what I do... And in due consideration of the potential labor involved should it turn out to be the worst case scenario (Murphy's Law)... I think I'm gonna just live with it (of course if it surfaces again, I may have an episode of **** retentive relapse syndrome - and renew the gremlin hunt with obsessive fervor).

Whoever said that restoring antiques was theraputic... didn't have a passion for cars and motorcycles...

 

You guys are going to make me go lift the rear seat from both my 87 and my 90 to see if the access port is under the rear seat, as I have said, not in the trunk.

NOT hard to remove, spark free (brass drift, or the proper spanner), remove the vibration damper, pull the pump.

But, it does not seem as though your intermittent "buzz" is fuel pump. That would be continuous.

You need pics, I might be able to provide them, but only to '88. Far as I can see, my book is quite pertinent to my '90, hence to the '91 100, 200.

Cheers,

George

 

WRONG! Go ahead take that seat out on your 5000! According to the manual "remove luggage compartment cover" and not the back seat. On my 1991 100Q there is no tank under the rear seat you will find some empty space on one side and the battery on the other, no access ports! Most new cars have the tank mounted over the axle and between the wheels for extra protection in an accident. It's been a while since my last trip to the bone yard but I think that the tank location is different on the 90 models so I am going to leave it out of this argument.

The housing is made form plastic, be my guest if you want to whack it with a hammer!

The damper/silencer and check valve are located inside the tank. In order to change it you have to pull everything out, sender and pump. Regardless of what the Audi manual says you probably have to change the pump in the reverse order of how it was put in at the factory. Lift the car drop the fuel tank and remove the pump. When I saw the Audi 5000 tank lying around at the bone yard I just couldn't resist! I had to see how the pump was mounted and if it would be an easy job. Taking the pump out was a bitch but putting it back in is going to a major bitch especially in the confinement of the trunk. Why is it a BITCH? You have orient the whole assembly carefully, through a small hole and snap the tree rubber bushings into the three holders. Otherwise the pump will be bouncing around in the tank. No wonder why a dealer wants $1000+ to change the pump!

Honestly I would love to hear from anybody who has actually changed the fuel pump!


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OR,

You're right. Pre-84s are under the rear seat.

Just went out to check my 87, it ain't there, looked under my 90, it extends only to the rear axle.

My 79, 80 and 82, it was under the seat, and my 78-83 manual says the sening unit was accessed from under the rear seat, external fuel pump then.

Sorry,

George