Every time I look under the hood of my '98... - PeachParts Mercedes-Benz Forum

KarTek · #1 11-04-2007, 10:29 PM

I notice something else screwy... Today I was looking it over and I started it up cold, with the hood up. The sun was in the perfect position to illuminate the fuel lines and I saw quite a bit of entrained air in the fuel line going from the bottom of the pre-filter down to the injection pump. The bubbles were really moving through. What effect does this have on engine performance? I know it can't be good for it. Anyway, I guess I'll need to find that guy who sells Viton O-ring kits...

Another thing I noticed was that there was a significant buzz coming from the upper mount of the engine damper shock in the front of the engine. I could put my finger on it and it was really vibrating. Is there a replacement bushing for the shock? Also, after about 3 minutes of running, the buzz suddenly quit as if it was shut off by a switch. I don't know if it's just a resonance thing or what...

jkoebel · #2 11-04-2007, 11:54 PM

Does it keep bubbling like that, or does it just bubble for a minute and then settle out?

My car always jerks and shudders and wants to stall out for about the first 15 seconds of being on, when air is going through the fuel line. I just give it some throttle and it clears out and is good from that point on.

Although, if there wasn't a leak/something someplace it'd probably not be getting air in at all...

Hatterasguy · #3 11-05-2007, 01:17 AM

If you see air bubbles in the clear lines you have an air leak. Its most likely the clear lines, they are a problem area.

TMAllison · #4 11-05-2007, 03:37 AM

Evan - Based upon where you saw air, you've got a bad seal at one of four o-rings; a) at either end of the fuel line leading from the fuel pre-heater entering the top of the pre-filter, b) the o-ring beneath the pre-filter, or c) the top of the line exiting the bottom of the pre-filter to the SOV.

The buzz from the belt damper is a fairly common failure as the bushing begins to wear. Making certain it is tight is about all you can do other than replacing it whenit gets too annoying. Top bolt is 13mm and bottom one 11mm. Not certain what the "switch" sound you mentioned is, probably initial drag from a belt driven accessory cycling off, belt vibration or maybe the t-stat openning.

KarTek · #5 11-05-2007, 06:50 AM

The bubbles stream constantly, almost like a foam.

As far as the damper is concerned, I got to thinking last night and had the same idea, Terry. I'm thinking it must be the drag from the alternator while the glow plugs are active. There's not a "switch" sound per se, it just quits instantly at some point while warming up and never returns.

Thanks for the replies...

TMAllison · #6 11-05-2007, 04:26 PM

From the sounds of it you're going to need to resolve that leak fairly soon. Phase one will be hard starts as the IP attempts to eliminate the air, phase two will be no start.

DieselAddict · #7 11-05-2007, 04:52 PM

Quote:

Originally Posted by KarTek

As far as the damper is concerned, I got to thinking last night and had the same idea, Terry. I'm thinking it must be the drag from the alternator while the glow plugs are active. There's not a "switch" sound per se, it just quits instantly at some point while warming up and never returns.

I noticed the same thing on my car and your explanation makes sense. My belt tensioner and shock absorber are fairly new though, so I think this noise is normal while the glow plugs are on.

KarTek · #8 11-05-2007, 05:11 PM

I just ordered my Viton O-rings so I'll replace them when I replace the feed line to the pre-filter. (which I cracked trying to pry it out of the housing... DOH!)

Skid Row Joe · #9 11-05-2007, 05:46 PM

Quote:

Originally Posted by KarTek

Another thing I noticed was that there was a significant buzz coming from the upper mount of the engine damper shock in the front of the engine. I could put my finger on it and it was really vibrating. Is there a replacement bushing for the shock? Also, after about 3 minutes of running, the buzz suddenly quit as if it was shut off by a switch. I don't know if it's just a resonance thing or what...

I'd guess the "buzz" was the water thermostat.. Then when it opened, the "buzz" stopped.

KarTek · #10 11-12-2007, 08:36 PM

I fixed the buzz today. I took off the damper and worked some super glue into the small crack that had developed between the steel ring and the rubber bushing. After the glue dried about 30 min, I hooked it all back up and it's dead quiet. We'll see how long it lasts...

I also replaced one of the fuel lines and about 10 of the O-rings. It got rid of most of the air but I found another bad fuel line so I'll be ordering another now...

TMAllison · #11 11-12-2007, 08:47 PM

If your damper breaks the belt will probably jump.

I would not expect super glue to hold for more than a few moments in that application personally.

nhdoc · #12 11-12-2007, 08:49 PM

Quote:

Originally Posted by TMAllison

If your damper breaks the belt will probably jump.

I would not expect super glue to hold for more than a few moments in that application personally.

Yeah, I second this...the only cure for a bad bushing is a new dampner. Glue will not hold it at all. They are not too costly, even from the dealer. Replace it and all of the fuel system seals to find that air leak and you should be good to go.

KarTek · #13 11-12-2007, 08:59 PM

Arrrgh, the forum locked up when I was trying to post a reply...

Anyway, I didn't use the glue to hold it together, I simply worked it into the space between the rubber bushing and the steel ring around it in order to take up the slop and quiet it down.

It was never in danger of breaking. If it was really coming apart, I'd have used twine to hold it...

Parrot of Doom · #14 11-12-2007, 09:18 PM

The damper is very cheap and easy to replace. You can actually remove the bottom bolt in-situ, the head of the bolt will squeeze by the flywheel - just. To replace it just put a big strong lever in the plastic block at the top of the spring, undo the bolt holding that block in place, then carefully lower the spring down (with your lever).

When you remove the damper, keep it. The new one will 'go' after a year or so, and its often just the bushing that 'goes'. You can push the good bushing out of your old damper and use that as a spare for the new one.

If I were you I'd replace the spring as well. Mine snapped at the hook a while after I replaced the shocker. Metal fatigue, and you can't drive without it.