300SDL=low boost - PeachParts Mercedes-Benz Forum

WANT '71 280SEL · #1 06-10-2005, 03:11 PM

Since I got the records from the PO earlier this week, the last service he had done, stated low boost that should probably be addressed before selling. The service before that mentioned the same thing though they tried to fix it. They cleared out the vacuum lines going to the switch-over valve and the paper said that made it better, but still not right. The paper doesn't say what they think might be wrong, so, with the vacuum lines being clear, why low boost? I'm going to try and go to the hardware store and find a guage to make into one since the auto parts stores want $60+ for one. The shaft spins very easily and does not grind, wobble, or have stiff spots. Oh yeah, they also said the cross-over switch was cleaned out as well.

Since I've had the car I've turned the ALDA about a half turn which didn't make too big of a difference but that shouldn't affect the boost though should it? Since I've owned this car I haven't been that impressed with the power it produced. On the highway, when downshifted, it really just makes noise and doesn't really accelerate very quickly when really these engines should pull.0-60 times done in my head have been around 15 seconds. I know there are more reliable ways, but "1 mississippi, 2 mississippi" is good enough for me. I don't think I'd be that far off. I remember GSXR saying a decent SDL should be around 12.

Thanks
David

dieseldiehard · #2 06-10-2005, 04:24 PM

I and a few other people I know have had the waste gate stuck partially open on the 603 engines. Carbon builds up on the edges where the flapper normally resides when non operating. This prevents a good seal and the result is slow spool up and loss of boost. If you put a boost gauge on the intake manifold you will see pressure not jumping up and never reaching close to 8 to 10 psi range.
The symptom of such a problem is a car that is sluggish off line but acceleration finally builds up to fairly good power when rpms get up, and there will be a possible increase in blackish smoke (besides the little poof of smoke these engines have at start up). Its a cheap but dirty fix to remove the turbo and clean it out with scrapers and wire brushes and some Liquid wrench helps too.

Hatterasguy · #3 06-10-2005, 06:42 PM

At 70 mine turns about 3k rpm which is right where the turbo starts to kick in. No downshift needed for passing she pulls real nice.

You need to do two things. No offense but the counting thing is nothing but a ballpark figure. You need a watch and to do two 0-60 runs and average the times. You also need to determine what boost you are currantly putting out.

How much boost should these things be putting out anyway? I should check mine.

dieseldiehard · #4 06-10-2005, 07:13 PM

I remember seeing waaay over 15 psi briefly as I pinched off the wastegate sensing hose once on a 167 diesel. The turbo is similar in these engines, the method of controlling the wastegate is different however. The Boost spec for the 603 is just a hair under 1 Bar max, or 11 - 12 maybe even 13 briefly. I wouldn't settle for less than that range under initial takeoff. How fast it comes up is important, maybe more indicative of turbo condition than the final resting pressure. If you're going to achieve 0-60 under 13 seconds the spool-up time is critical. I've come to know that these engines live by and for their turbo.
My sick turbo was just able to hit 7 psi, and the car was very sluggish. The worst sluggish 603 I drove was one that was for sale. It had to have a plugged trap or sick turbo or both, a 240D could have beat it!

t walgamuth · #5 06-10-2005, 11:10 PM

i had an 84 300sd that acted like that. ran good, got great mileage, but down shift at 60 and it would accelerate almost not at all. the dealer said it was ok....and couldnt find the prob. a good indy found it in 2 minutes. it was a cracked plastic hose that ran behind the back of the head to the injection pump. dont know the name of the function but it added fuel when boost came on. with the crack no fuel was bening added and hence no extra power.

yours sounds the same. i dont know if the 603 engine works the same way but it sure sounds familiar.

WANT '71 280SEL · #6 06-10-2005, 11:30 PM

My mom took the car for the weekend to the Indianapolis area so it won't be bnack till Sunday evening. I found a guage at a relative's house that measures up to 15 psi so I'll use it then post back Monday evening. I hope it's not the wastegate problem as I just had the turbo off the car and man what a pain to re-install! Of course now it would be easier since I somewhat know what I'm doing and where everything goes.

Thanks
David

WANT '71 280SEL · #7 06-16-2005, 02:01 PM

I measured my boost at the manifold and got up to 13.1 psi. Should I check on the other line coming out of the cut-off switch to rule that out? It seems like I'm getting the proper boost after all. I just wonder why the car feels like such a dog? I wish I could drive another one to compare this one to. The ALDA has been adjusted to make for pretty smooth acceleration. The timing chain has been replaced in the past and the pump timing was done at the same time. I'm still going to check the timing stretch just to be sure.

Thanks
David

dieseldiehard · #8 06-16-2005, 02:08 PM

OK, and boost is getting to the ALDA in the same range? 13 psi is fine. I believe the wastegate is not the problem. I reread you post and noted you had the turbo off, you would have seen lots of carbon build up on the flapper if it was bad.
Timing might be the issue. I throw in the towel after that.

WANT '71 280SEL · #9 06-16-2005, 02:14 PM

I agree about the carbon build up. I physically closed and opened the flap and it definitely sealed. To get the wastegate back on to the flap however I had to use a big screwdriver and pry the rod out a little to make it go on the flap, is this normal? The rod looks like it could be adjusted in or out by spinning the shaft. It had a place on it for a wrench. I guess I might have to wait for Dave to get on? Also, will I need to replace my valve cover gasket or can they be re-used? I know they're thick rubber.

Thanks
David

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