tired wastegate fix? - PeachParts Mercedes-Benz Forum

Fredmburgess · #1 01-16-2003, 05:25 PM

Opinions please. Boost gauge shows that my '84 300Dt makes 7 or 8 pounds of boost at the 4,000 rpm/full load condition the manual calls for. I wanted to adjust the spring preload on the wastegate and bring boost up to about 12 psi but can't get that stupid cover off!

If I restrict the wastegate hose with a needle valve I can get the boost I want.

Question is...is restricting the flow to the wastegate accomplishing the same thing as adjusting the wastegate spring. Gauge says yes, but I'm just curious.

What do you guys think?

thanks -

Fred

engatwork · #2 01-16-2003, 06:17 PM

Restricting the line is pretty much the same thing. I adjusted the one on the 300D up to 11.5 psi by cranking down on the spring about 8 full turns (I had been running only 8-9 psi boost). The way to get the round cover off is to use a big ol "c" clamp and tighten it down on the center of the cover until you can get the clip out then slowly release the spring. The installation is the reverse. Pretty straight forward. I think when I put the engine back together I am going to crank down on the spring another 4 turns

.

Nate Stanley · #3 01-16-2003, 06:54 PM

Engatwork-
Did you notice any measurable change in power with your first tweak?
Also, what happened to fuel consumption?

DieselHead · #4 01-16-2003, 07:06 PM

I have a great brass boost controller that I bought online for about $25 (I forgot exactly how much). It sits inline between the wastegate and turbo and acts as a secondary spring that you can adjust to specify exactly how much boost you want. I have a VDO boost gauge permanently installed in my car and the boost cranked up to 14psi. When I get home from vacation, I will post the website address for that boost controller. A few others here have used it as well.

Alex

speedy300Dturbo · #5 01-16-2003, 07:12 PM

Was it the one from www.dawesdevices.com?

I had one, and it worked well. Simple to install too, and easy to change the boost settings between test drives.

DieselHead · #6 01-16-2003, 07:19 PM

Yes, you got it. www.dawesdevices.com

It's been great and hasn't needed adjustment since I set it.

Alex

engatwork · #7 01-16-2003, 07:26 PM

I did notice a power increase and actually ran it up to 100+ mph. I purchased a pressure regulator as referred to by DieselHead but pulled/disassembled the engine before I got around to installing/testing it and before I could get any fuel mileage numbers.

Fredmburgess · #8 01-16-2003, 08:59 PM

Engatawork,

Thanks for the C-clamp idea. I actually thought of that the other night but was too darn lazy to go down in the basement and dig out the clamp...then I got frustrated and gave up!

I got a big boost in power (of course) when I cleaned the bolt and banjo fitting on the intake... then put the boost gauge on and found I was only getting 8 pounds, max. Restricted the hose as a test by dialing in a needle nose vicegrip on it to get 14 psi at max load. Drove like a completely different car. Much better performance off the line and up to highway speeds.

...The second big hit came when I turned the ALDA screw CCW 1/4 turn. 1/8 turn didn't change anything, but 1/4 turn and yahoo!

Thanks for the comments and the link, everyone. I'll try to track mpg for the record but it's tough because I switch back and forth between diesel and veg oil (heated tank in the trunk).

And by the way..with boost and ALDA adjustments 100mph comes right up with no fuss. Not bad for 18 years and 384,000 miles!

psfred · #9 01-16-2003, 09:48 PM

Don't go over 13 psi for boost pressure on a 617, you will seriously reduce the engine life. The were NOT designed to take that much boost, and not only will the pistons overheat, but the bearings won't take the load...... 11.5 psiis a much better max pressure.

Peter

psfred · #10 01-17-2003, 07:22 PM

I've seen sodium filled exhaust valves so worn they could not be resurfaced -- not sure if this was from excess heat of combustion or just too tight adjustment.

You will achieve 13.5 psi on a long grade, even if not a full throttle, so it might be adviseable to limit it a bit. You might also not ever have any trouble. That surge is from high compression and lots of fuel, hence lots of heat on the piston crowns and pressure on the bearings on the compression stroke.

Certainly, don't exceed the 14 psi overboost limit!

Peter

rwthomas1 · #11 01-17-2003, 08:35 PM

It is my understanding that the overboost protection decreases fuel delivery to non-turbo levels if an overboost condition exists? If this is the case then as long as the injection pump is sensing boost all the way up to this point it will be delivering maximum fuel. The MB system is fairly sophisticated for a mechanical system. If they designed it this way then there should be no problem. Granted I wouldn't run on the ragged edge, maybe a max boost of 13psi. MB's have fairly high compression ratios, I believe about 21:1. Add about 15psi and a good heavy sustained load and you will quickly approach peak cylinder pressures that will likely blow a headgasket and possibly damage rod bearings. There simply isn't enough room in the combustion chamber for all that fuel/air and the heat it creates. Intercooling would go a long way to improve durability if you insist on running higher boost levels with high compression. I doubt you will do any real damage unless you use your MB to tow or drive WOT up very steep mountain passes every day. If you do intend on running max boost get an EGT gauge. That will tell you what is really going on in your engine. Modulating the "gas" pedal to control boost is a bad idea. Often EGT's will skyrocket as the boost decreases. The reason is there is now less air to burn the fuel and cool the engine. RT

Fredmburgess · #12 01-18-2003, 10:57 PM

Thanks, all. PSFred, I just ran the car at 14 psi (peaks only, full load) to see if it made a difference while still staying below the point where the pressure switch would cut the fuel. Installed a brass needle valve in the wastegate hose and dialed it in so max boost (only in the peaks at shift points) is 12 psi.

I've got a boost gauge and exhaust gas temp gauge. No significant change in exhaust gas temp, but I don't work the car hard anyway. Biggest benefit I see is driving in town. Seems to build a little boost earlier than it did with just the wastegate spring making the decision.

Fredmburgess · #13 01-19-2003, 11:45 AM

I found that the EGR on this car had expired so I blocked the vac line and put a block off plate under the EGR itself. Since I run either 100% waste veg oil or 20% blended in the regular tank, I rationalize that I'm making less pollution anyway. One thing is certain - on straight veg oil there is no black smoke cloud under any condition and it's barely noticeable with the 20% blend!

Like you, though, I'm keeping an eye on things since increasing the boost. I'd like to get this car to 450,000 or 500,000 miles before having to rebuild or replace.

F

CJ · #14 01-19-2003, 11:52 AM

How do you adjust the boost on a 602.962 motor, ie 1991 300D 2.5? Any pics??

mreid · #15 01-20-2003, 12:05 AM

Increasing boost will have little effect on egt. In fact it may even lower the temps. Adding extra fuel and boost and then you can get some interesting temps. 14 psi will not hurt these engines as long as it is kept to short periods.