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 > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 07-11-2019, 02:56 AM
Actros617's Avatar
Ich fahre dieseltypen
 
Join Date: Apr 2008
Location: Oklahoma
Posts: 1,105
1994 S350 slow acceleration diagnosis input appreciated

Well recently i've acquired a 1994 S350 for a hardy laugh (~$200) and for the price it came with some perplexing problem. Now I'm well aware of the 3.5L OM603 been the infamous rod benders but I'm beginning to doubt that its plagued problems is in this case.

Initial Problem
Very slow acceleration almost like driving a 240D on its last legs 0-60 is 40-45 seconds,

So what do we have:
*A W140 350K miles chassis with a probable (undocumented) engine replacement some time within 2-10 years ago.

*Previous owner bought it in 2015 and drove it till 2017 then it sat in a shed till 2019 after it begin to developed poor acceleration, unable to maintain speeds higher than 70 mph (floored) and previous owner loss interest

*Hack job straight piped the exhaust with 3 replaced pipes welded to stock (Resonator, catalytic converter? and muffler delete)

*Possible rust/bio growth in tank as there are few sediment in the new primary filter.

*A clean valve train and what appears to be a recently replaced new timing chain and chain guides, (when i replaced the valve cover gasket)


What i've done so far:

*When thru all the vacuum rubber lines in the engine bay and replaced them.

*When thru all the hard plastic vacuum lines and intake manifold port clean them out as needed (near the intake manifold ports for the ADLA were clogged!)

*Replaced the vacuum hose on the turbo transducer (will be converted soon to pressure setup soon)

*Replaced, fuel filters both primary and secondary, air filter, engine oil (delvac 15w40 for now)

Diagnosis performed so far

*Vacuum leak check as followed:
A. Turbo wastegate vacuum pod, no leaks, actuates with vacuum
B. Egr pod slow leak 5mmhg per second (disabled and plugged),
C. Vacuum transducer not holding pressure but will go up to 10 mmhg and leak out
D. Brake booster line to vacuum pump check valve no leak

*Turbo boost checked as followed:
A. Initially 0 psi and was very loud exhaust suspected wastegate was not closing
B. Sorted out various vacuum leaks and replacing the rubber lines in transducer got boost but very low 6-9 psi will reach 10 but at 3500-4000 rpm (Nominal boost 12-14 psi @ 2500 rpm), acceleration much improved can get up, maintain and exceed 60 mph but still slow acceleration 0-60 25-30 seconds
C. Check for boost leak from turbo to intake manifold none found
D. Attached a hand held vacuum pump to turbo wastegate vacuum actuator, was able to shut wastegate completely but still low boost 6-9 psi till 3500 rpm then goes up to 10 psi, acceleration still slow
E. Turbocharger inspection, very little shaft play forward and backward, almost no play in up and down, compressor wheel has some strange looking rust spots on one of the blades, other wise some fine scoring on the compressor turbine, inside the compressor housing has small non penetrating hole about the size of an eraser tip doesn't seem to be leaking (no air leak when under boost)

*MAF
Will trigger turbo limp mode when plugged in (no boost) due to EGR disabled, when unplugged has boost 6-9 psi but acceleration slow

*Compression test
A. Unlikely an issue as it starts up almost immediately afterglow plug cycled and after sitting overnight (70*F ambient)...however awaiting on diesel compressor tester to arrive
B. No smoke or oil consumption (after driving 300+ miles after purchasing from previous owner)

Impressions
So far all fingers points to the turbocharger delivering boost thus slow acceleration however i can't seem to wrap my mind on what about the turbo that may cause it to have performance issues and not sure on what other test I'm missing out here, I hope this isn't too much information, I did all I know to try to diagnose this problem but im still stuck, any advice or input will be appreciated.
Attached Thumbnails
1994 S350 slow acceleration diagnosis input appreciated-img_2665.jpg  
__________________
Benz's in our garage
1994 S350 357k mi

Sold
1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi


RIP SECTION

1995 E320 Special Edition [Rear ended]
1984 300SD [Head on collision]
Reply With Quote
  #2  
Old 07-11-2019, 10:03 AM
Diseasel300's Avatar
Registered User
 
Join Date: May 2016
Location: Texas Hill Country
Posts: 4,657
The turbo is only half the battle. Fuel enrichment is the other. If you have extra boost but no extra fuel to use with it, you gain no power. Since you're making 12-15PSI of boost, the turbo works. You need to figure out why you're getting no fuel. Try connecting the boost line from the intake manifold directly to the ALDA and see if you get an improvement. If you do, you likely have a problem in the lines, switchover valve, boost sensor, or elsewhere. The 3.4L is not slow, it should be like a gas car off the line. In city traffic, I'd even call it quick compared to my 300SDL.
__________________
'11 Honda Accord EX - "The Daily" 64K
'83 500SL Euro - "The Money Pit" 116K
'91 350SD - "The Diseasel Jr." 168K
'86 300SDL - "The Diseasel" 189K (Totaled 1/31/19)
The Diseasel Thread - Everything You Didn't Know You Wanted To Know
Reply With Quote
  #3  
Old 07-11-2019, 11:13 AM
WTB: 94/95 E320 Wagon
 
Join Date: Oct 2007
Location: Charleston SC
Posts: 2,675
When you disabled the EGR, on that car you need to do some other gerry-rigging to make sure limp-home mode / no boost does not happen. MB made it harder to defeat the EGR, it is not a simple block-off.

Low boost sounds like turbo /waste gate problem, maybe more work required there. Straight pipe means a blocked exhaust is not an issue, right?

After that, typical check list. Fuel filters and screen in tank, air filter, ALDA actually working, maybe re-seal ALDA or adjust / shim.
__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC
Reply With Quote
  #4  
Old 07-11-2019, 12:18 PM
Registered User
 
Join Date: Dec 2011
Location: Norwalk, CT
Posts: 163
Don't these cars have biodegradable wiring to the wastegate actuator that goes bad and the wastegate then defaults to no boost??
Reply With Quote
  #5  
Old 07-12-2019, 10:35 AM
Actros617's Avatar
Ich fahre dieseltypen
 
Join Date: Apr 2008
Location: Oklahoma
Posts: 1,105
Quote:
Originally Posted by Diseasel300 View Post
The turbo is only half the battle. Fuel enrichment is the other. If you have extra boost but no extra fuel to use with it, you gain no power. Since you're making 12-15PSI of boost, the turbo works. You need to figure out why you're getting no fuel. Try connecting the boost line from the intake manifold directly to the ALDA and see if you get an improvement. If you do, you likely have a problem in the lines, switchover valve, boost sensor, or elsewhere. The 3.4L is not slow, it should be like a gas car off the line. In city traffic, I'd even call it quick compared to my 300SDL.
It only boost up to 6-9 psi and when it gets up to 3500 rpm is when it barely gets to 10 psi, I'll see if can direct connect the manifold to the ADLA and report back. I also had a 300SDL and those things are a rocket once the turbo is spooled and boosted.


Quote:
Originally Posted by Maxbumpo View Post
When you disabled the EGR, on that car you need to do some other gerry-rigging to make sure limp-home mode / no boost does not happen. MB made it harder to defeat the EGR, it is not a simple block-off.

Low boost sounds like turbo /waste gate problem, maybe more work required there. Straight pipe means a blocked exhaust is not an issue, right?

After that, typical check list. Fuel filters and screen in tank, air filter, ALDA actually working, maybe re-seal ALDA or adjust / shim.
Correct, from what i've read MB had made it harder for one to delete the EGR a complete delete of the transducer and conversion to pressure operated wastegate is required. The exhaust is wide open no resonator or muffler and perhaps no catalytic converter ( theres 3 straight pipes welded on to the existing stock exhaust). How does one goes about resealing or testing the ADLA, and whats does the shim do?

Quote:
Originally Posted by ccrelan View Post
Don't these cars have biodegradable wiring to the wastegate actuator that goes bad and the wastegate then defaults to no boost??
The wastegate is not directly operated electronically, but also by vacuum via transducer, Air flow sensor, egr valve and a few 3 way vacuum switch over valves.
__________________
Benz's in our garage
1994 S350 357k mi

Sold
1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi


RIP SECTION

1995 E320 Special Edition [Rear ended]
1984 300SD [Head on collision]
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 10:47 PM.


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