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1988 560sl
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7 Posts
Discussion Starter #1 (Edited)
1988. It gets gas up to the FD @ a rate of 35oz/30sec, but not out the FD. Spark is good. Could this be an electrical prob? If so what?



-Also, the car died (a few mo. ago) in the middle of running, and was normally having a high idle, but the day it died it ran seemingly *perfectly* but there was a 'groaning' noise from the front of the car ( it may have been the FD), so I was told to get a new FD. I got a supposedly working used one and just put it on, and it still won't run...which makes me think it could be electrical? Let me know what you think, any help is GREATLY appreciated:) .

(fuel pressure test results below vvv)
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
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1988. It gets gas up to the FD @ a rate of 35oz/30sec, but not out the FD. Could this be an electrical prob? If so what?

-Also, the car died (a few mo. ago) in the middle of running, and was having a rough idle, as well as a 'groaning' noise from the engine (I think it was actually the FD), so I was told to get a new FD. I got a supposedly working used one and just put it on, and it still won't run...which makes me think it could be electrical? Let me know what you think, any help is GREATLY appreciated:) .
You really need to do a CIS fuel pressure test. but can you hear fuel being injected when you push down the sensor plate with the key on.
 

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1988 560sl
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Discussion Starter #3
You really need to do a CIS fuel pressure test. but can you hear fuel being injected when you push down the sensor plate with the key on.
...I pulled an injector and hooked it up while trying to start, to see if it was clogged -no spray- then realized gas wasn't getting to the injector after loosing the line, so there's no fuel being injected...
 

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1988 560sl
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Discussion Starter #4
Hopefully some more input will come tomorrow :)


And thanks to everyone's input past present and future :)
 

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Always Remembered RIP
1979 280sl 4 sp w/ac 1957 MGA 1998 volvo xc/70 2004 F150
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6,050 Posts
Is this something new? Is the car new to you? How long was it sitting? Did you have the key on and manually press down on the damper? Can't help without info.
 

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1988 560sl
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Discussion Starter #6 (Edited)
Is this something new? Is the car new to you? How long was it sitting? Did you have the key on and manually press down on the damper? Can't help without info.
Mercedes are totally new to me, I've had the car for a while, been sitting dead for months...more like a year actually, it's been very frustrating to work on, especially with this vague mercedes cd manual... I don't know what you mean by 'damper' ...thanks for the help, will post back when I know what to do.
 

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Always Remembered RIP
1979 280sl 4 sp w/ac 1957 MGA 1998 volvo xc/70 2004 F150
Joined
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6,050 Posts
The damper is the air intake, the suction of the pistons as the car turns over causes the damper plate to open and start the flow of gas to the injectors. If it's stuck closed - no gas. Two things, one fill in your profile so we know where you are and the type of car (yes I saw it in the first post, but it will show in all your posts so people don't have to read everything to find out wat kind of car were talking about), second spend some tie reading up on the fuel system in the EG107 at the top of the post.
 

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1988 560sl
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7 Posts
Discussion Starter #8
`88 560SL being fuelish

Yeah, this Bosch injection system is a little different than my Holly 750 double pumper with mechanical secondaries ;-) The car runs just fine if you hand feed it, just not on it's own. I can push the damper down with my finger, then it returns back up on it's own. I'll try the key on, damper down, listen for the fuel maneuver tomorrow. Need fitting for pressure test, if you really think it's needed. Btw, odo has 109k on it, with a bit of a rattle on cold start ups...so I have that to look forward to. But she's so pretty.
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,232 Posts
Yeah, this Bosch injection system is a little different than my Holly 750 double pumper with mechanical secondaries ;-) The car runs just fine if you hand feed it, just not on it's own. I can push the damper down with my finger, then it returns back up on it's own. I'll try the key on, damper down, listen for the fuel maneuver tomorrow. Need fitting for pressure test, if you really think it's needed. Btw, odo has 109k on it, with a bit of a rattle on cold start ups...so I have that to look forward to. But she's so pretty.
Perfect time to do a timing chain, rails and oil tube fittings. That's what is making the rattle on cold start.

Without a fuel pressure test you are guessing. You can have correct fuel flow from with 1 pump inoperative but pressure will be lower than the cracking pressure of the injectors.
 

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1988 560sl
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Discussion Starter #10
OK...

cranking/starting fuel pressure is 90 psi ...and it holds at ~45psi not cranking.

this was done on the input line of the FD / the left hole....lmk what these #"s mean, and if there's any other type testing I should do and make sure that what I did was correct...

to confirm...yes the damper is cracked open(~1/8'') while trying to start.


P.s. I had an injector pulled (very front right) and its line open while doing this, and no flow...wet, but barely a drip.
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,232 Posts
OK...

cranking/starting fuel pressure is 90 psi ...and it holds at ~45psi not cranking.

this was done on the input line of the FD / the left hole....lmk what these #"s mean, and if there's any other type testing I should do and make sure that what I did was correct...

to confirm...yes the damper is cracked open(~1/8'') while trying to start.


P.s. I had an injector pulled (very front right) and its line open while doing this, and no flow...wet, but barely a drip.
There is an upper chamber pressure and a lower chamber pressure. Looks like you only checked upper chamber. Lower chamber pressure should be ~ 6 PSI less. Non cranking key off and out should hold 49PSI for at least 1 hr.

Did you check the feel of the plunger with key on and also with key off and out.

3000 mile guess is dirty plunger in fuel distributor. Remove fuel distributor and remove plunger and and plunger barrel. Be careful O rings are a PIA. I don't know where to buy these things anymore so clean and replace carefully.
 

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1988 560sl
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Discussion Starter #12
Many thanks for your reply.

Before I go through that, I now remember that the distributor came to me with a note from the post office saying it was dropped, and the package (a plastic bag...geez...) was pretty ripped and messed up...could this possibly mean the dist. is broken?
 
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