Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 10-31-2005, 01:49 PM
Registered User
 
Join Date: Oct 2005
Posts: 45
'91 350 SD Turbo problem

This car was bought on ebay by a friend who didn't know not to buy a 350 . It ran from PA to MT but top speed is 70 mph. The turbo was exposed and the fan can be seen to turn, waste gate appears to be closed, but lack of power persists. Can the turbo spin but not sufficiently? Seems like the advise (other than selling it) for turbo problems is to get a rebuilt from turbocity.com or tubonetics.com. Advice?

The car starts great, doesn't smoke until you step on it, and seems to run perfectly. It has 230k, well maintained.

Before we start investing $ into it, should I advise to sell and start over? Thanks for any input, I'm prepared for the worst, just hope the owner is too!

Reply With Quote
  #2  
Old 10-31-2005, 10:40 PM
Registered User
 
Join Date: Oct 2001
Location: around Charlotte NC
Posts: 578
check for fuel - alda

Try a 0-60 run for a benchmark. New was 11-12 second range. My old 300 SDL was in the 19-20 second range and NO acceleration at highway speeds. The overboost protection switch was out ( drivers side fender near the fuse box). You can bypass to check out to see if the boost signal is working or not. This will make a huge difference if not working.

Chuck
Reply With Quote
  #3  
Old 10-31-2005, 10:49 PM
t walgamuth's Avatar
dieselarchitect
 
Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 34,900
and if you

are running wo an air filter hooked up better get it hooked up.

diesels are particularly vulnerable to dirt in the air.

tom w
__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
Reply With Quote
  #4  
Old 11-05-2005, 11:02 AM
Registered User
 
Join Date: Oct 2005
Posts: 45
The air filter is hooked up and everthing stock and in place. I could not locate the turbo relay on the driver side fender. 0-60 is over 20 seconds. Lower speeds are ok, but at 45 mph when I stomp on it the rpm's go to 4000 and the car doesn't accelerate.

Thanks for the advice!
Paul
Reply With Quote
  #5  
Old 11-05-2005, 01:03 PM
Registered User
 
Join Date: Jun 2005
Location: NJ
Posts: 1,182
redline on the 3.5 is around 4200 rpm.
the rods are the weak link w/ the 3.5.
if the rods are good then it's not a 3.5 issue.
burning scary amounts of oil is one symptom of bent rods.
are your fuel filters clean?
__________________
82 300D....went to MB heaven
90 350 SDL....excercising con rods
Reply With Quote
  #6  
Old 11-05-2005, 04:13 PM
Registered User
 
Join Date: Oct 2005
Posts: 45
Good to know it's not going over red line! The car had a full tune up but I'll double check the fuel filters, and no excessive oil use or smoking.
????
Reply With Quote
  #7  
Old 11-05-2005, 04:15 PM
Registered User
 
Join Date: Oct 2005
Posts: 4,263
Quote:
Originally Posted by andmoon
burning scary amounts of oil is one symptom of bent rods.
are your fuel filters clean?
What? They still run? Not that I don't believe you, but that's just odd.
Reply With Quote
  #8  
Old 11-05-2005, 04:19 PM
Registered User
 
Join Date: Oct 2005
Posts: 45
I'll take you for a test ride if you'll promise to buy it afterward.
Reply With Quote
  #9  
Old 11-06-2005, 11:41 AM
rdanz's Avatar
Registered User
 
Join Date: Sep 2002
Posts: 1,158
Quote:
Originally Posted by bozemanbiofuels
The air filter is hooked up and everthing stock and in place. I could not locate the turbo relay on the driver side fender. 0-60 is over 20 seconds. Lower speeds are ok, but at 45 mph when I stomp on it the rpm's go to 4000 and the car doesn't accelerate.

Thanks for the advice!
Paul
When you say the engine goes to 4000 and the car doesn't accelerate sounds like you mite have a transmission problem.
Reply With Quote
  #10  
Old 11-06-2005, 12:05 PM
Registered User
 
Join Date: Oct 2005
Posts: 45
We thought that also, and maybe the linkage needs to be adjusted to coordinate shifting. But since it shift down (to 2nd I think) and you can shift it up by letting off on the accelerator, it seemed like it was a power issue but there isn't much logic in that statement....

Do you think the transmission is being told to downshift when it should not?
Reply With Quote
  #11  
Old 11-06-2005, 08:38 PM
Registered User
 
Join Date: Oct 2001
Location: around Charlotte NC
Posts: 578
double check fuel

Again,

I recommend checking the overboost / alda fuel enrichnment circuit. My old 300 SDL would run to over 4000 rpm with no acceleration. It would downshift... still no zoom. Once the fuel problem was fixed, at 2500-2800 rpm there was a very noticable boost. If you are not feeling this you are not getting enough fuel to match your boost. Boost with no fuel is no more hp. Good luck, hope you find the problem.

Chuck
Reply With Quote
  #12  
Old 11-07-2005, 12:07 AM
Registered User
 
Join Date: Oct 2005
Posts: 45
Chuck,
Can you tell me more about the fuel unit near the fuse box? I know you are relating from a 300D, but I couldn't identify the box. Size, number of wires on it, does it have wires leading to the turbo or something I could trace it back from?

Seems like whenever I find a manual for benz diesels the 350 is skipped.
Thanks for persisting, it does sound identical in symptoms,
Paul
Reply With Quote
  #13  
Old 11-07-2005, 09:29 PM
Registered User
 
Join Date: Oct 2001
Location: around Charlotte NC
Posts: 578
overboost protection switch

Paul,

It is on the drivers side inner fender well, up near the fuse box but on the engine side of the second firewall. It should have a boost line coming from the intake or turbo side ( forget which) to the switch, then to the Alda. The alda is buried under the intake behind the IP. The overboost switch also has a set of wires going to it. Many folks here have SDL's and may be able to take a picture of it for you.

You can directly connect the boost signal to the alda ( bypass the switch). It is not recommended for a long term solution, but for testing if this is the problem you will know right away. When mine was bypassed I went from the 19-20 second 0-60 to a 12-13 second 0-60 time. The boost really came on in the 2500-2800 rpm range.

This is a reasonably common failure ( oil or crud in the lines, leaks, or a bad switch). There are of course multiple other areas to check. The Alda itself could be bad, the overboost valve on the turbo could be leaking.... but you can try the switch for $0 and 10 minutes of effort.

Good luck! I went from cursing the slow SDL to zooming and loving it.

Chuck
Reply With Quote
  #14  
Old 11-08-2005, 10:35 AM
thtguy's Avatar
What?
 
Join Date: Sep 2005
Location: Tampa Bay
Posts: 73
I am betting the boost sensor line from the intake to the overboost switch to the ALDA is clogged with EGR TAR. my 87 300D had the same power problem. EGR tar is a very sticky mixture of oil and soot. some oil, even on a new engine, comes through the crankcase breather which then mixes with soot from the EGR system. take off those lines and clean them... or in my case i just replaced them all (it was easier)
here are the connections of the hoses you should check

Last edited by thtguy; 11-08-2005 at 10:47 AM.
Reply With Quote
  #15  
Old 11-08-2005, 12:13 PM
thtguy's Avatar
What?
 
Join Date: Sep 2005
Location: Tampa Bay
Posts: 73
that pic is from a 93 so the overboost sensor is in a different place. but the connection on the manifold and ALDA should be in the same place and you should be able to trace it to the overboost.

Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 05:29 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page