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 06-26-2008, 03:08 PM
Registered User
 
Join Date: May 2005
Location: Minnesota
Posts: 9
73 450SL engine misfire & vapor lock

I've got a 73 450SL that starts great when cold, but misfires significantly until it warms up. Once it is warmed up, it runs ok, but with greatly reduced power. If I stop for more than 5 minutes, it will not start until it cools down. I have been able to "coax" it back to starting when I furiously pump the gas pedal while trying to start it. I've replaced the plugs, wire, rotor, and points. I just checked the point gap and reset it to nominal. I've replace most of the vacuum lines as well. I don't believe this is electrical, but maybe an injection issue or perhaps intake manifold issue. I'm kind of at a loss as to where to go next without tearing the whole top end off. Any suggestions would be greatly appreciated. Thanks.
Steve

Reply With Quote
  #2  
Old 06-27-2008, 10:20 AM
meltedpanda's Avatar
Certified Benzaholic
 
Join Date: Mar 2003
Location: Central Ky
Posts: 6,265
fuel filter/fuel pump - status
blowing smoke - what color?
Plug tips - what color?
Timing set ?
valve lash ?
injectors - status - new/old/refurbished?
__________________
Ron
2015 Porsche Cayman - Elizabeth
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
  #3  
Old 06-27-2008, 10:29 AM
Registered User
 
Join Date: May 2008
Posts: 154
Smile

Vapor lock is from metal fuel lines. If you have any, change them to rubber, and that will go away.
Reply With Quote
  #4  
Old 06-27-2008, 11:58 AM
Registered User
 
Join Date: Sep 2004
Location: Dublin, Ireland
Posts: 385
Could be running very lean which might explain why it just about starts from cold with extra fuel being dumped by the CSV.
Reply With Quote
  #5  
Old 06-27-2008, 06:02 PM
Tomguy's Avatar
Vintage Moderator
 
Join Date: Aug 2002
Location: near Scranton, PA
Posts: 5,407
Actually, it sounds too rich. The reason I say this is because it'll start up hot but if it sits (IE: Thermo-time switch turns the CSV on during cranking) too much fuel is put into the fairly warm engine for a start.

Check your trigger points. Running poorly when cold is usually a sign that trigger (NOT breaker/ignition) points are gunked up. Clean them with something NON ABRASIVE. Fix vacuum leaks also, I bet you have a lot on an engine that old. Main culprits would be the MAP sensor hose, door locks, transmission modulator and the brake booster line.
__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k
Reply With Quote
  #6  
Old 06-28-2008, 01:53 AM
Gurunutkins's Avatar
Certified Idiot
 
Join Date: Oct 2005
Location: Seattle WA
Posts: 496
got to agree with tomguy, sounds like its too rich. if it starts fine cold then acts badly warm but you can get it to start when you pump the pedal, its probably seeing the pumping pedal as WOT and the engine computer is programmed to shut of the injectors if you crank with the pedal fully depressed (specifically to cure flooded engines!)
check everything tomguy suggests, I would also check your TPS and make sure its reading all of the way off at idle. pull a couple of plugs and see if they look sooty black or not. if they are and everything else checks out put a spark tester in line and make sure you are getting a 15Kv to 20Kv spark. it could be that your ballasts are breaking down and your spark isnt strong enough to burn all of the gas and you are also "flooding" it from incomplete combustion (this is a possibility as the coil gets weaker as it get hotter which would also fit your symptoms)
cheers
barri
__________________
61 Austin mini
67 Lotus 7
74 450sl
76 Cadillac 8.2l (501 ci)

some new cars

megasquirt conversion on:
djet 74 450sl http://www.mercdjetmegasquirt.britautorepair.com/
cis 76 450sl http://www.merccismegasquirt.britautorepair.com/

the best view is always from the point of no return
Reply With Quote
  #7  
Old 07-01-2008, 11:58 AM
Graham's Avatar
Registered User
 
Join Date: Nov 2004
Location: Ontario, Canada
Posts: 4,393
Quote:
Originally Posted by Hardhead View Post
I've got a 73 450SL that starts great when cold, but misfires significantly until it warms up. Once it is warmed up, it runs ok, but with greatly reduced power. If I stop for more than 5 minutes, it will not start until it cools down. I have been able to "coax" it back to starting when I furiously pump the gas pedal while trying to start it. I've replaced the plugs, wire, rotor, and points. I just checked the point gap and reset it to nominal. I've replace most of the vacuum lines as well. I don't believe this is electrical, but maybe an injection issue or perhaps intake manifold issue. I'm kind of at a loss as to where to go next without tearing the whole top end off. Any suggestions would be greatly appreciated. Thanks.
Steve
I had almost same symptoms, but not the misfiring until warmed up. I did have the hot start problem. Very annoying not to be able to start at all sometimes. Other times also did the pedal pumping routine, whether it worked or not!

I no longer have the problem. Most significant thing I did, was to adjust the fuel rail pressure. Mine was at about 27 psig and I bumped it up to 30. It goes to 32 psig when running, presumably because of back pressure in the return line. I now need to lean out the engine using the MPS, but without O2 meter, I have not tried yet.

Only other problem I have partially fixed, is the Aux Air Valve which also affects idle. It sticks when cold and engine idles too fast. I freed it up and it now seems OK once engine is hot. But the idle screw is still only 1/2 turn open and there is air passing through the bypass - Rubber hose is new and flexible and I can squeeze it and hear the air flowing through. Maybe I will have to resort to adding an orifice. At the moment, I start up with idle at 1400rpm and when hot it drops to 500 rpm which is a bit low and causes some stumbling. If I set it higher, the 1500 rpm cut-out kicks in and I get surging/cycling until engine warms up. I probably need a new AAV, but new ones are expensive!

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5
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 04:55 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, 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