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 > Vintage Mercedes Forum

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 08-29-2021, 05:07 PM
Registered User
 
Join Date: Aug 2007
Location: Middle Haddam, CT
Posts: 297
A few words about D-jetronic

I've owned a 1972 W109 4.5 with Bosch's first generation electronic fuel injection system for 14 years. I have learned that the engine will "run" even when certain parameters of the system are not what they should be, but it will never run WELL unless everything is right. I recently found to my surprise that mine was faulty in several respects and now it runs better than it has in 14 years! So here's a summary of the things that have to be spot on for the 4.5 (and preceding 3.5) to run flawlessly at all temperatures.
1) Start by checking the compression. If you have a problem here, you'll be wasting your time and money on the rest of this list until that big ticket item is fixed.
2) Cam timing. Stretched cam chains will throw off the cam timing.
3) Ignition timing and points. Pierre Hedary swears by the stock ignition system on these cars, and the fact that the system is "sort of" electronic in that the points themselves operate at low voltage means they will last a lot longer than ordinary points. (Nevertheless, the fiber cam follower is subject to wear if not kept greased)
4) Clean and flow matched fuel injectors. Its hard to tell if yours are up to spec unless you've already addressed this, AND you know the ones you have were done by reliable experts. I thought my rebuilt injectors were good until I found out they weren't.
5) Good and clean trigger points. They weren't made to last 60 years. They, too, don't carry a lot of voltage, but, like regular ignition points, they also have fiber cam followers that will wear out if neglected and chances are lubricating them has been overlooked some time in the last 60 years. And the points themselves are all but impossible to access to "trim" the contact points. Furthermore, they are subject to oil contamination from crank case pressure forcing oil up the distributor shaft, in consequence of which regular cleaning with electric cleaning spirits is advisable even if they are otherwise sound. The are available new from Mercedes Classic, but they are expensive. I tried to determine if mine were "good enough" by measuring the height of the fiber cam followers and spraying the electrical contacts, but finally sprung for new ones so now I KNOW they are right.
6) Correct ignition wires and non resistor plugs.
7) Good fuel pump and fuel pressure regulator set to 30 lb.
8) Properly functioning manifold pressure sensor (MPS). It turn out the one in my car was from a VW! That MIGHT not have mattered if it was working right, but it wasn't.
9) Proper functioning auxiliary air valve. This purely mechanical devise manages cold start air flow and closes as engine temperature rises. Unless it doesn't. It can be tested in hot water on the stove, and is repairable with a new heat expansion element and a good tutorial on YouTube If it doesn't close properly.
10) Check all connections that could cause a vacuum leak, and indeed any old rubber connectors should be replaced. Even truer of all rubber fuel connectors including the eight little short ones from the fuel rail to each injector.
11) Water temperature sensor and air temp sensor must function properly.
12) The Throttle Position Sensor (TPS) has to be operating properly. The contacts can be cleaned and perhaps "touched up" with fine abrasive paper or steel wool (make sure all residue is removed). The setting of the TPS is adjustable and a slight movement on the adjustment ark matters. Trial and error worked for me. It should be somewhere near the middle of the adjustment ark.
13) The big, ancient, primitive Engine Control Unit (ECU) has to be up to snuff, and as I recently learned, all of the electrical connections to it have to be sound.
And that's all there is to it...

__________________
Berfinroy in CT
Present vehicles:
1973 300 SEL 4.5
1959 Rolls Royce Silver Cloud I
Past vehicles;
1958 Bentley S 1
1976 ex-Max Hoffman 6.9
1970 300SEL 2.8
1958 Jaguar MK IX
1961 Jaguar MK IX
1963 Jaguar E-type factory special roadster
1948 Plymouth woody
1955 Morgan plus 4
1966 Shelby GT350H Mustang
Reply With Quote
  #2  
Old 08-30-2021, 01:26 PM
cth350's Avatar
Registered User
 
Join Date: Dec 2000
Location: Long Island, NY
Posts: 4,073
A great list.

Missing the item For:
- Ensure that there are no vacuum leaks.
Might restate the last one as two points by including:
- Ensure the wire harness is sound and the ground points are clean and tight.

Might actually do some of the checks in a different order based on ease of doing so. But that's quibbling.

-CTH
Reply With Quote
  #3  
Old 08-30-2021, 02:18 PM
Registered User
 
Join Date: Aug 2007
Location: Middle Haddam, CT
Posts: 297
CTH350:
"- Ensure that there are no vacuum leaks."
See my #10.
"- Ensure the wire harness is sound and the ground points are clean and tight."
Good point.



-CTH[/QUOTE]
__________________
Berfinroy in CT
Present vehicles:
1973 300 SEL 4.5
1959 Rolls Royce Silver Cloud I
Past vehicles;
1958 Bentley S 1
1976 ex-Max Hoffman 6.9
1970 300SEL 2.8
1958 Jaguar MK IX
1961 Jaguar MK IX
1963 Jaguar E-type factory special roadster
1948 Plymouth woody
1955 Morgan plus 4
1966 Shelby GT350H Mustang
Reply With Quote
  #4  
Old 08-30-2021, 05:40 PM
meltedpanda's Avatar
Certified Benzaholic
 
Join Date: Mar 2003
Location: Central Ky
Posts: 6,197
And that's all there is to it...

great list , I consider myself pretty knowledgeable about the ol Djet system, your last line was perfect ....and comical ( in a good way)
__________________
Ron
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace
Reply With Quote
  #5  
Old 08-30-2021, 11:21 PM
cth350's Avatar
Registered User
 
Join Date: Dec 2000
Location: Long Island, NY
Posts: 4,073
Quote:
Originally Posted by berfinroy View Post
CTH350:
"- Ensure that there are no vacuum leaks."
See my #10.
-CTH
[/QUOTE]

The vacuum leak musta been between the keyboard and the chair.
-CTH

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 05:44 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2021, 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