85 300D turbo next to no boost - PeachParts Mercedes-Benz Forum

funola · #1 05-26-2014, 01:49 PM

I have been getting poor fuel economy in my 85. Best was 23 mpg and worst was 20. Timing is spot on at 15 deg ATDC, valves adjusted. Starts and runs well. Just a puff of gray smoke if I floor it and no black smoke. Have not pulled the injectors to pop test them yet but from how quick it cold starts, the injectors are probably ok.

I just tee-ed in a boost gauge at the ALDA. Strips of elastic cut from bicycle inner tube works great as very small diameter hose clamps for low pressure application.

Ran the boost gauge out the hood and went for a test drive

To my surprise I was getting max 1 psi when I floored it! Car was not a total dog so it never raised an alarm. So I pulled the line from the manifold to the boost safety solenoid and connected the boost gauge directly to the line, revved the engine at idle and got the needle to move so the manifold line is not completely clogged. Took out the boost safety solenoid and it didn't click when connected to the battery. Blew into it by mouth and was able to blow through it slightly. It was leaking boost constantly, no wonder I wasn't getting any boost to speak of.

I sprayed all 3 ports of the solenoid with solvent then rapped it a few times with a pair of pliers, shook it out and some carbon came out. Repeat a few times then connected it to the battery and it clicked! Some more solvent and blew it out with compressed air and it seems to be working on the bench and sealing and opening with power.

Took it for a drive and felt instantly more power and was able to get max boost of 8 psi in 1st gear going up a slight hill.

I am going to give it an Italian tuneup and see if the boost increases. I think spec is 11 psi max so there is room for improvement.

If it doesn't improve by itself, what should I do next?

Not having boost for however long (I have put on less than 1000 miles since acquiring the car) and don't know how long it's been like that. Can anything bad happen to the turbo having no boost for extended periods?

cho · #2 05-26-2014, 02:16 PM

.

50 mph steep uphill to be sure about proper load
and if you can not see above 8psi stil you can pop the wastegate cap
and do full CW turn which should give you 1.5psi more.

I dont think you do anything serious to the engine or turbo except
over fueling...bad mileage as a result......

cheers

mach4 · #3 05-26-2014, 02:58 PM

The solenoid (boost pressure aneroid) should never activate, at least not under normal conditions. It's there as an over-boost last-resort safety device, dumping boost pressure to the ALDA if for any reason the turbo were to put out 15psi of boost. If it was blocked, the ALDA wouldn't get a pressure signal to increase fueling based on the increased boost. Sounds like it was almost blocked, hence the ALDA didn't increase the fueling past ambient even though the turbo was putting out.

I think you're pretty well on your way at this point. At sea level you should likely see 9 psi boost, maybe a little more. You need full throttle and close to 3000 rpm to see max boost, at least in my experience.

In normal cases, where you tee into the ALDA line doesn't make a difference, but I'd tap into the line upstream of the solenoid to compare readings. You might well see 9 psi pressure there.

The solenoid has no hysteresis, so if you ever did get into an overboost situation you'd seen the gauge fluctuating wildly as the solenoid cycled between full boost pressure and full dump to ambient at the 15psi set point.

It's also possible that your overpressure switch on the intake manifold is bad. If it sends a signal to the solenoid to dump pressure, you'll never get an increase in fueling based on boost pressure.

funola · #4 05-26-2014, 04:35 PM

Mach4, I wasn't thinking straight. The solenoid was mostly blocked, should be full open normally until it see voltage, then it should vent to atmosphere. Do I have that right?

I am going to rig up a light bulb across the solenoid coil, route it out next to the boost gauge and make sure it never comes on.

No steep hills around here. Here's video on the flats, got it up to 8 psi floored.
CLICK TO PLAY!

After driving it a few more miles, got it up to 9 psi so it is improving.
CLICK TO PLAY

I am going to take out the banjo bolt on the manifold and clean it as well as take out the boost dump valve and spray brake cleaner through it and see if it improves further.

Gotta rig up some sort of tripod for the camera phone. Not safe what I am doing operating it with one hand. Just saw a tip about using a paper coffee cup cutting slots in it to make an emergency tripod. Have to give that a try.

mach4 · #5 05-26-2014, 06:20 PM

Quote:

Originally Posted by funola

Mach4, I wasn't thinking straight. The solenoid was mostly blocked, should be full open normally until it see voltage, then it should vent to atmosphere. Do I have that right? ...After driving it a few more miles, got it up to 9 psi so it is improving.

That's right, normally open (straight through to the ALDA), then it will vent to atmosphere to prevent over fueling if boost hits 15psi.

I think you might be there. 9 might be all you get without messing with the turbo.

rscurtis · #6 05-26-2014, 08:35 PM

My signature car, which runs great, will do about 10 PSI max.

funola · #7 05-26-2014, 09:03 PM

Quote:

Originally Posted by mach4

That's right, normally open (straight through to the ALDA), then it will vent to atmosphere to prevent over fueling if boost hits 15psi.

I think you might be there. 9 might be all you get without messing with the turbo.

Took out the solenoid, sprayed with brake clean, blew out with compressed air, put in some kroil, installed it and wired up a light bulb across the solenoid coil and brought bulb out the hood next to the boost gauge. Also moved boost gauge line to the inlet manifold side of the solenoid.

Went for a test drive. Boost on the flats, floored from a standstill was just under 10 psi. When it shifted, went momentarily up to 10.5 psi. Light bulb across the solenoid did not come on- a good thing.
CLICK TO PLAY VIDEO!

I recall on my 83 300D turbo, I got the boost up to 9 psi and no further and had to adjust the waste gate spring to get it up to 11 psi, which gave further performance improvement. The 83 had a T3, which was a PITA to adjust. I think my 85 is also a T3, not looking forward to adjusting it.

funola · #8 05-26-2014, 09:25 PM

One more thing. There was no black smoke when throttle was floored. Does the Alda need adjustment? The cap is still on- it's never been touched.

Diesel911 · #9 05-26-2014, 11:09 PM

Test Specs from Manual:

Diesel911 · #10 05-26-2014, 11:13 PM

Quote:

Originally Posted by funola

One more thing. There was no black smoke when throttle was floored. Does the Alda need adjustment? The cap is still on- it's never been touched.

Before doing anything I would have someone follow behind you and see if the Car actually smokes or not if you stomp on the Pedal. A little bit of Smoke is often not easy to see while driving.

If you are happy with they way the Car runs there is no need to alter it.

mach4 · #11 05-26-2014, 11:26 PM

Quote:

Originally Posted by funola

One more thing. There was no black smoke when throttle was floored. Does the Alda need adjustment? The cap is still on- it's never been touched.

No, that's what you want...extra fuel to take advantage of the boost, but no excess that would produce smoke.

I generally drive really easy, so I tend to get lots of soot building up in the exhaust system. Occasionally when I get a Prius tailgating I'll jump on it and blow all the soot buildup out of the tailpipe in a thick cloud of black smoke (particulates).

funola · #12 05-28-2014, 07:22 PM

Quote:

Originally Posted by mach4

No, that's what you want...extra fuel to take advantage of the boost, but no excess that would produce smoke.

I generally drive really easy, so I tend to get lots of soot building up in the exhaust system. Occasionally when I get a Prius tailgating I'll jump on it and blow all the soot buildup out of the tailpipe in a thick cloud of black smoke (particulates).

With age (mine is aound 159k miles), doesn't the spring inside the ALDA weaken, requiring adjustment to deliver the correct amount of fuel? Isn't it supposed to be adjusted so you get a slight amount of smoke when floored?

Anyway I pressure tested the aneroid with a bicycle pump and it held 10 psi.

Got the plastic ALDA adj cap off with a hook (what a PITA), it left a sleeve which was a pain to get out. What's the trick? I had to use a narrow tip ginsu knife to cut bits of it away.

Made 2 flats on a 10 mm thin wall socket to fit a 11 mm wrench which made easy work of adjusting the ALDA. Turned it 1/4 turn CCW but have not road tested it yet.

Changed air filter to be sure no restriction. Housing looks very clean, no oil buildup.

toomany MBZ · #13 05-29-2014, 08:52 AM

^ Yes, very clean.

When I removed the ALDA cap on the SD, I was able to finally peel the thin metal surround away.

1983/300CD · #14 05-29-2014, 10:03 AM

I removed mine carefully with a Dremel cutting tool, then made a cap to fit over it.
The cap is a press fit, but the lip has to really squeeze over, so it isn't going anywhere.

funola · #15 05-29-2014, 10:11 AM

Quote:

Originally Posted by toomany MBZ

^ Yes, very clean.

When I removed the ALDA cap on the SD, I was able to finally peel the thin metal surround away.

How was the metal surround attached. Why did you peel it away?

Took the car for a short drive and the 1/4 turn CCW on the ALDA adjust did not produce any more smoke when throttle was floored. Boost didn't go up by much either. I'll give it another 1/4 turn and try again.

Here's the latest video. CLICK TO PLAY!

Overall, getting the switch over valve (I had been calling it the boost safety valve) to work made it feel like a different car. Much less throttle input is needed now to get the car to move.

The last fill up was only 4 gallons w. 64 miles on the odo, not the most accurate but that's 16 mpg! I was doing a lot of idling (estimate 1 to 2 hours) while doing tests on my RIV Xenon timing light so that surely made it worse. How much fuel is burned idling for 2 hours? Hopefully having boost now will get the fuel economy up to normal.