The "Diseasel" - '86 300SDL - Page 13 - PeachParts Mercedes-Benz Forum

Diseasel300 · #1 01-24-2019, 09:45 AM

These relay contacts are not copper. They're some sort of Nickel, Silver, or Indium alloy to withstand the high current and arcing that happens with DC circuits. Like breaker points, they're a solid slug of metal, not a plated contact like most ice cube relays. They can stand a decent scrub when they get rough like mine and helps them to last longer. Eventually they'll get to the point that the relay has to be replaced, I'm just getting more time out of it before its time is up.

Regarding the boost problem....10-12PSI is stock for the 617's, 12-14 for the 603's. If you're running the ALDA, it would be worth your time to pull it and replace the 2 O-rings in it (test if the ALDA holds vacuum with a mity-vac. It should hold strong vacuum indefinitely). If it's never been done before, they're toast (probably like hard plastic) and it has a dramatic impact on how soon and how smoothly the boost comes on. Before replacing the ones in my car, boost wouldn't really build until >2100 RPM, then came on all at once. Really fun to drive in the rain! NOT! After replacing the O-rings, boost starts building meaningful amounts ~1700-1800 RPM and comes on smoothly. When driving normally, you don't even feel it come on. You'll notice from a floored standing start, but it's not the rough kick in the rear that it was before.

vwnate1 · #2 01-24-2019, 11:57 AM

Thank you Sir ;

I've been meaning to vacuum test the ALAD as it was leaky before so i got another and immediately noticed less smoke and more power .

One of the Mity-Vac's I have won't hold vacuum unless the trigger is squeezed about 1/2 way in......

I dunno what's the deal but I guess it'll have to be taken apart to see if I can fix it , it's not old and had little use before beginning to fail like that .

Diseasel300 · #3 01-24-2019, 12:28 PM

Any leaks upstream of the ALDA will cause the same behavior as the seals in the ALDA itself leaking. The ALDA works by having a set of copper bellows (the aneroid capsules) that compress under boost pressure and lift the fuel limiting peg on the top of the IP as boost builds. ANY leaks (and I mean ANY) will cause the fuel trim curve to be wrong and run lean. The volume through the ALDA sense line will have to flow enough to overcome the leak and make enough apparent boost pressure at the ALDA to enrich fuelling. People on this forum always swear up and down that the IP's wear "lean" and that simply isn't the case. Screwing with the ALDA settings is a band-aid, not a solution. When the ALDA wears out and leaks, your IP will start underfuelling. Check that switchover valve on the firewall if you have one too, they can leak or get stuck!

vwnate1 · #4 01-24-2019, 04:28 PM

Thank you ~ I'd not taken the old leaky ALDA valve apart but now I will .

I'm aware of the importance of leaks and also clogged plastic ALADA sensor pipes as well as the overboost protection valve you mentioned, getting stuck or clogged ~ most I've tested were partially or fully clogged, easy to clean out using the Sam's Club industrial degreaser Rich so kindly suggested .

The spray nozzle has both 'spray' and 'stream' positions making it a simple thing to squirt some degreaser directly into the valve or whatever small opening you're wanting to clean .

Let sit a bit then blow clean, rinse well, an amazing amount of crud will come out and return the valve to as new service again .

Similar to the old BOSCH air by pass valves used in 1960's~ 1980's F.I. systems to provide fast idle when cold .

I do need to take all this apart and test / clean as necessary, the banjo bolt in the intake manifold too .

Diseasel300 · #5 01-24-2019, 07:54 PM

Sounds like you're on the right track. You can still build full boost PSI but run lean if the ALDA isn't working like it should. If the air is there, you need the fuel to match it, that's where the power comes from. When working properly, it's smooth and refined when the turbo starts making power, just like you'd expect a Mercedes to be.

vwnate1 · #6 01-25-2019, 09:36 AM

Just so ~ it comes on pretty smoothly now and no smoke but the fuel economy as dropped to a consistent 22 + MPG, down from 26/27 and one tank in Nevada a while back @ 29 MPG .

After I last posted here I went home and checked, the ALDA is holding pressure so next to check the overboost valve, pipe and banjo bolt in the intake manifold .

Diseasel300 · #7 01-25-2019, 02:04 PM

Definitely worth sorting out, the fuel economy tells the tale. My SDL went up 4mpg by tweaking the IP, fixing the turbo, and advancing the timing. I used to run ~20/26, I've been routinely hitting 24/30 post-tweak. Not only did fuel consumption go down, but power went up noticeably.

vwnate1 · #8 01-25-2019, 10:05 PM

Understood .

The ALDA was broken and the used one I sourced had been fiddled with so I did some experimenting and discovered ore diesel smoke comes from lean than rich mixture .

Diseasel300 · #9 01-25-2019, 10:09 PM

Quote:

Originally Posted by vwnate1

I did some experimenting and discovered ore diesel smoke comes from lean than rich mixture .

Having spent over 2 weeks fiddling with settings internal to the IP and tweaking my ALDA, I think you'll find that statement is quite wrong. Black smoke comes from a surplus of fuel and from no other source. If you have white or grey smoke, you have timing or injection problems.

vwnate1 · #10 01-25-2019, 10:21 PM

Thanx ;

I've spent far longer then two weeks fiddling with it, the smoke got worse as the engine lost power when I leaned it out.....

Maybe I should re check the timing .

Diseasel300 · #11 01-25-2019, 10:24 PM

Possible you're making it richer and not leaner? Turning the ALDA screw CCW enrichens fuel. More fuel than you need will actually make acceleration more sluggish as well as raising EGTs. A lean burn won't cause smoke, but will reduce power greatly. Leaning the fuel curve is essentially the same as you trodding lighter on the throttle. It is nothing like adjusting a carburetor or K-Jet distributor.

vwnate1 · #12 01-27-2019, 12:26 PM

Boy howdy are you right about the learning curve ! .

OTOH, when I turned the ALDA screw clockwise, the power dropped off and the smoke increased ~ I don't understand why / how but that's what happened .

I'm about 360* in from fully CCW now and it seems to run O.K., some times after a long red light I see a cloud of fuel smoke as I pull away from a stop, others not .

Filters look clean .

Maybe a crappy injector ? .

In time I'll pull them and pop test .

Diseasel300 · #13 01-27-2019, 01:03 PM

Quote:

Originally Posted by vwnate1

OTOH, when I turned the ALDA screw clockwise, the power dropped off and the smoke increased ~ I don't understand why / how but that's what happened .

I'm about 360* in from fully CCW now and it seems to run O.K., some times after a long red light I see a cloud of fuel smoke as I pull away from a stop, others not .

What color is the smoke? Because of how the diesel operates, if it was going to smoke at idle, it would do it all the time, not after a delay of sitting at a light. Rich (injection quantity) smoke is black. Injection/Timing smoke is grey or white. Oil smoke is blue/grey. Based on the red light statement, I'd be more inclined to suspect oil smoke than fuel smoke. The ALDA has no effect on injection quantity until the turbo starts to build boost, it has no effect on injection quantity at idle and very little effect at low throttle positions.

qpooqpoo · #14 01-28-2019, 10:17 PM

Great car! The 300SDL really is the perfect mercedes diesel to restore. It has all the classic charm in design and the engineering ruggedness, yet its modern enough to daily drive and just old enough were you can do everything yourself. Its a timeless car. I've restored two of them, so let me know if you have any questions.

I respect what you've done with the interior. Though I would have gone the "purist route" and installed good condition used stuff, you have added a ruggedness and a utilitarian feel which is very nice not to mention stress free.

Oh, and you should delete your EGR asap. Very simple, and very good to do. They still might have kits for that floating around...

vwnate1 · #15 01-29-2019, 12:47 AM

Quote:

Originally Posted by Diseasel300

What color is the smoke? Because of how the diesel operates, if it was going to smoke at idle, it would do it all the time, not after a delay of sitting at a light. Rich (injection quantity) smoke is black. Injection/Timing smoke is grey or white. Oil smoke is blue/grey. Based on the red light statement, I'd be more inclined to suspect oil smoke than fuel smoke. The ALDA has no effect on injection quantity until the turbo starts to build boost, it has no effect on injection quantity at idle and very little effect at low throttle positions.

Thank you .

The exhaust some -looks- black to me, it only puffs a cloud when I accelerate off idle or am moving slowly in traffic andget the chance to speed up .

I had the engine re sleeved and so on less than 20,000miles ago and one cylinder has slightly lower compression than the rest, I hope it isn't oil smoke

.

Because it doesn't emit smoke every time I accelerate off idle I'm won dering what it is .

It's my daily driver and I'm now retired , no longer have access to a full shop with leak down testers and the air supply to operate them .

Fuel economy has tanked of late, down to 22 MPG's, I can't stand that .