Use compressed air to back-flow fuel lines- tank screen?
 

After a seemingly endless battle to get our 82 300TD to quit being the worlds most gutless vehicle, I'm wondering about the tank screen.

I've been really good about keeping the filters fresh, adjusting the valves, cleaning the banjo bolts, adjusting the throttle linkage, air filter, etc etc etc.

This week, I installed freshly professionally rebuilt injectors...

She still smokes bad at idle, and if I rev her much over 3k, she lays down a smoke screen - and she's still gutless across the board.

I ran biobor for a good 4 tanks worth, and noted little in the in-line filter in the way of debris.

SO: is it, or is it not, a good idea to use compressed air at the in-line filter, and blow back into the fuel tank? Seems I could at least test, even if only temporary, whether the screen 'may' be the problem by doing so, but if for some unknown to me reason this is a bad idea - speak up!

Thanks - Joe

Someone suggested it on my 87. I did it, it ran better for an afternoon until the crap settled back on the strainer, but my tank is also FULL of rust. Didn't harm anything if that's your question. The strainers aren't hard to get out and aren't expensive. Pop it out when you have a near empty tank of gas and put a new one in.

I don't see why a clogged filter would make the car smoke at idle, if anything low pressure would prevent smoke. Is your alda working?

As long as you remove the tank cap first and don't get too carried away with the air pressure, you cannot hurt much.

Forgot about the cap thing, yeah make sure you have that off, you'll hear the bubbles from the front of the car.

If you do such a thing I'd use low compressed air and take it easy - start with 5 PSI or so if you can regulate it that low. If not just just a foot pump or a bicycle pump.

HOWEVER if I were you I'd go and get a 46mm socket (I'm pretty sure it is a 46 - I'll check) and take the tank screen / strainer out. I've done this quite recently. Siphon the fuel out of the tank first though - and disconnect the supply fuel line and the return lines at the tank before removing the strainer.

On the other hand have you done a leak down test on your engine? Got much blow by?

Too much pressure/volume can damage the screen if you're not careful!

The best way to ascertain whether your performance issue is fuel tank/system related is to simply rig up a bottle/jug under the hood and feed and return fuel from that as you take the car on a real world drive around town. If the performance improves it's the tank screen/lines from the tank, if performance doesn't improve the issue is further down the fuel stream or something more mechanically oriented, timing, compression, IP failure, etc.

The TD is somewhat easier to access the screen as it can be seen and reached directly from below. If you need to you can drain or run down the tank (drain it as far as possible by disconnecting the feed line at the tank and direct what flows out into a bucket), pull the screen and then use gasoline to flush things out buy pouring and catching a bucket full through the tank a number of times. Just let the run out settle some between pours and don't re-pour the stuff/particles/slime etc that ends up in the bottom of the bucket!

On the TD you also have the advantage of pulling up the liner under the third row seats/compartment and pulling the fuel sender, with that dome you have a perfect view of what's inside the tank at the fuel pick-up screen area!

Not sure what a "leak down test" is... I did check, then restore, the compression...

Our local Benz mechanic told us the ALDA diaphragm is bad - has a hole in it. Someone else told me it's 'supposed' to have a hole in it...(?).

This is the car which, when I take the throttle linkage in hand, and run up gently, doesn't really throttle up until the ip linkage is 1/8" or so from the full-open stop. because of this, I have to drive around with the pedal to the floor most of the time - unless I'm slowing down. And any typical hill on the highway is always a drop a gear and hope she'll maintain 45 mph thing. After 3 years of trying, I have to say I'm ready to fix it, or sell it :(

and the wife agrees...

You can also empty your tank by directly your fuel return hose in the engine compartment into a jug. You can completely empty the tank this way.

Another simply way to check if the tank screen is plugged is to switch the inlet and return lines. If it runs better, it's a good indication the screen is plugged.

But smoke about 3k rpm would tend to indicate that you are getting enough fuel and the problem is elsewhere. Have you checked the turbo? Is the smoke coming from bad turbo seals? Have you done a compression test? Have you checked to make sure your turbo is boosting?

Definitely a problem somewhere. Craig recently had a post on a gutless engine. Check it out. Problem was internal to the IP as I recall.

I've been suspicious of the IP, since I've tried pretty much everything else. Bench tested IPs are not inexpensive, I'm sure, so I'm trying to not overlook other, more simple tests/fixes.

Brandon (OR) looked at it last year - wondered at first how we could drive it at all - tried some things, then scratched his head, and mentioned he put a re-calibrated IP on his, and he couldn't be happier...

Oh, and I should include: 82 300TD 345,000 miles

Haven't really checked anything to do with the turbo myself. I will say, though, she's "all ahead slow" way before the turbo should have anything to do with it...

So, where does one get a re-calibrated use IP, and is this probably going to be the way to go (once we've ruled out everything else)?

Someone also mentioned removing the ALDA altogether - just to see if it's the culprit - does doing so make any sense?

Hey Joe, I've used compressed air to do exactly what you're thinking. If the screen is plugged up it will clear it for a little while. Be gentle with the air though, and make sure you take the fuel cap off, or you may inflate your tank. You can also switch the supply and return lines in the engine bay to bypass the screen. I wouldn't do this for the long term, but it's okay for a troubleshooting purpose. Also the tank screen on wagons does not require a 46mm socket. You'll need a 22mm allen bit socket, or a 22m bolt head with nuts cranked down on it, and a regular 22m socket to get the screen out. If you still have my number give me a call, maybe we can figrue out whats going on.

Hey Andrew! You know, as I get to thinking deeper about this - if you recall when you helped me (in your driveway) with Ava's first compression test, we both pondered at the fact she won't throttle up until the IP is near full throtle... so I'm thinking it MUST be in the IP.

I had almost forgotten an interesting event with this car -a few years ago.
Janet (my wife) embarked on a trip, but couldn't even get Ava up the hump at the end of the driveway onto the highway - it just wouldn't throttle up at all. Case (Independence mechanic) told us to start with diesel purge.

So, at that time, with the fuel lines both running into a container of purge under the hood, she would do no more than change pitch with throttle applied. After some minutes, she started to gain engine speed again.

Armed with this memory, I'm inclined away from thinking tank screen, and back to IP issues. Case (now retired and moved away local MB 'specialist') had first told us (a few years ago) she needed a new IP, but a year later switched his story to saying she needs only a new ALDA diagphram...

Head-scratching for sure...

Answer
 

If the ALDA is damaged..
It sounds like it is broken at maximum fuel = verify boost pressure is not to high, and replace the ALDA.

ALDA issue threads
http://www.peachparts.com/shopforum/diesel-discussion/239597-alda-issue-threads.html

Remove the fuel fill cap before blowing through the fuel line..

I have used compressed air to clear the tank. The pressure? I just used my mouth, and it was enough to drain the tank.

Answer
 

Call Lee = in my signature. :D