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  #1  
Old 06-05-2008, 02:57 PM
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Cool Will not rev above 1200rpm

I bought this '77 450SL after it had been stored for 6 years. After removing and cleaning the fuel tank, replacing the fuel pump, filter & in tank screen, checked injectors, replaced nozzle holders & O rings the engine will not rev above 1200 rpm. I have let the car idle for extended periods with injector cleaner in the fuel, no change. Have replaced faulty vacuum lines. I did the fuel delivery test listed in my Haynes manual, 1 liter in 30 seconds, got about 2/3 liter, replaced pump-same results. The new pump came with an external check valve. The original had none. I did not install the valve because I could not adapt it to the banjo fitting on the car. I have checked the timing. I think it may be fuel pressure related but don't have the gauge to check it. Sounds like it is fuel starved when trying to accelerate. Short of trailering it 80 miles to my nearest MB garage, what should I check next on my "getting old fast" DIY project?

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  #2  
Old 06-05-2008, 05:09 PM
AUBluTiger
 
Join Date: Jul 2007
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did you have an opportunity to run the car prior to you making these changes...just trying to eliminate if this is a problem that existed before you replaced all these parts, or if it is perhaps something that resulted after.
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2006 Audi A4 "Audrey"-daily driver
1976 MB 450SL "Marlene"
2000 Jetta VR6 "Julia"-traded at 220k miles
1997 Jetta 2.0Trek "Blanche"-traded at 450k miles YES 450,000 miles
1986 Prelude "Gladys"-died at 120K miles
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  #3  
Old 06-06-2008, 09:54 PM
300SDog's Avatar
gimme a low-tech 240D
 
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And did you check ignition spark and distributor advance? I had similar prob with twincam m110 and turned out to be stuck distributor advance.
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'80 300SD/ w116
'79 240D 4-spd
'71 750cc Guzzi

previously owned:

'83 240D 4-spd
'77 280SEL 4-spd
'74 280/8
'72 250/8
'65 220Sb 4-spd
'63 220Sb 4-spd
'63 190c 4-spd
'61 220Sb 4-spd
'60 190b 4-spd
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  #4  
Old 06-06-2008, 09:58 PM
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Is it running on all 8?
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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

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  #5  
Old 06-07-2008, 01:45 AM
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as its a 77 it will be cis. have you checked that the air sensor plate is moving freely? when you open the throttle the vacuum (or the air movement to fill the vacuum in the manifold!) should pull the air plate down and in so doing cause the piston to move in the fuel distributor and squirt in more fuel. if its been sitting a while that little piston and the fine slots that the fuel flows through can get clogged and stuck and you idle fine but cannot do anything else. try holding the throttle linkage open and pushing down on the air sensor plate when its idling and see that the plate moves freely and the engine revs up. if it doesn't its something other than the fuel distributor
cheers
barri
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  #6  
Old 06-07-2008, 06:43 AM
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The car would not run at all when I got it. The fuel that had been left in the tank was "solid" and the pump bound up, I got it running after replacing the fuel system parts. I will check for spark advance, thanks for that tip. It is firing on all 8. The air sensor plate is moving but with some resistance. If I hold the plate down about 1/8 inch & open the throttle linkage I can increase the rpm's slightly. Any further movement of the linkage will stall the engine.
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  #7  
Old 06-07-2008, 09:05 AM
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Did you try to run it on the old fuel?

If so, you may have a severe varnish issue that can lock up the intake valves.

When old fuel is allowed to set in the system, fuel system cleaner will not be sufficient to purge the CIS system of all the varnish deposits.

Methinks you still have a way to go before you have sufficiently cleaned the FI system.

Jim
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  #8  
Old 06-07-2008, 09:26 AM
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I don't have alot of experience with the CIS system on your car, but maybe your fuel distributor-metering unit (the part that moveable air-plate is attached to) is also jammed up with 'solid-fuel'.
Many years ago, a friend had a '76 Saab with CIS FI and his fuel distibutor was destroyed after his air-filter caught fire. He replaced it with a used one that had been sitting a long time and turned out it was plugged up with varnish. The car wouldn't even fire. We eventually found a good working used fuel distributor, but not until my friend had burned out his starter!

Happy Motoring, Mark
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  #9  
Old 06-07-2008, 09:38 AM
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I think maybe you are concentrating on the wrong end of the engine. You might check the exhaust system for a restriction. I don't know when they started installing catalytic convertors but if yours has one it could very well be clogged or there may have been critters living in the muffler who brought in lots of nest material and clogged it up. This sounds to me like a classic exhaust restriction issue.

If you strongly suspect it is a fuel delivery system issue you ought to be able to bypass it by spraying gumout directly into the intake and get the car to run on it temporarily. If it won't rev up on gumout then I don't think it is a fuel problem.
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Last edited by nhdoc; 06-07-2008 at 09:44 AM.
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  #10  
Old 06-08-2008, 02:54 PM
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The sensor plate should move w/o resistance. You can try removing the fuel distributor and cleaning and oiling the piston. Be sure to replace the o-ring.

Also, there is is a filter in the inlet hose fitting on the FD that can be cleaned or replaced (entire fitting, from a dealer).

If this doesn't work, you will probably need a rebuilt fuel distributor.
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #11  
Old 06-08-2008, 07:36 PM
250 Coupe's Avatar
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The clearances in the fuel distributor are measured in microns. Solid fuel is fine for rockets and such but not so good in a CIS system.

If you need info on the CIS system, check out the library at w116.org. I know it's the wrong chassis but I don't think there is all that much difference in the FI system.

Michael
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  #12  
Old 06-12-2008, 10:35 PM
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I checked out the vacuum advance and EGR valve with a vacuum pump, they seem to be moving alright. The sensor plate in the FD moves freely with engine off, has some resistance when engine running. Will check the cat converter next, I did check the screen at the FD inlet, it was clear.Thanks.
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  #13  
Old 06-19-2008, 07:06 PM
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I finally got around to removing the catalytic converter. The engine will now rev up, I didn't let it go above 3000rpm, if I spray fuel into the air intake. I also hooked my shop vac to the removed exhaust system at the tail pipe end, blocked off the other tail pipe ( muffler removed) and placed my hand over the inlet side of the cat converter and felt no suction. I guess this points to a plugged cat converter.
My next step is to remove the fuel distributor, I have removed the "plumbing" and the 3 screws holding the fuel dist. but it won't budge and I don't want to force it. Am I missing something or has it "grown in place" after 30 years. My Haynes manual is somewhat vague in this area.
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  #14  
Old 06-28-2008, 07:08 PM
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I have removed the FD. It looks fairly clean from what I can see. I removed the pressure regulator control piston, it is clean. The control plunger also. There is an allen head screw that threads into the side of the PR body. The end of this screw is cupped. What is the purpose of this screw. My next step will be to disassemble the FD. THE only thing I have been able to find on this is to do it upside down so parts don't fall out. I do remember seeing a thread on this last year but can't locate it now. Any tips?

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