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  #1  
Old 06-30-2007, 06:11 PM
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Location: ontario canada
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Question I am ready to give up. Help!

1986 560SL
The nasty job of replacing my fuel pumps without a hoist accomplished nothing.
The car starts right up, but still idles rough and won't rev above 3000 rpm in Park. Anything more than about 1/2 throttle causes it to bog down. It can't hardly move under its own steam.
Recap...
- Problem started with car idling and accelerating a bit rough.
- Ran a couple cans of injector cleaner. No change.
- Replaced plugs (one was fouled), checked wires etc. No change
- Did compression test. All ok.
- Damaged EZL ignition module by stupidity. Replaced it and coil. No change.
- Tried another can of injector cleaner. No change.
- Situation suddenly deteriorated. Car undriveable.
- Replaced fuel pumps. Checked for blockage. No change.

I hate to take my hobby to a pro but I am stymied. My next guess would be a faulty fuel distributor but my diagnostic abilities are obviously crappy and those devices are expensive.
Any help out there?
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  #2  
Old 06-30-2007, 08:47 PM
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There's nothing wrong with having some work done by a professional.
I'm a pretty adaptable guy and can figure out most things that come my way but there comes a time where I simply pay someone who knows more than me to fix something.
In the long run you may actually save money. Someone who works on these cars everyday may diagnose the problem more acurately (possibly with better diagnostic tools as well) while you might be changing good (expensive) parts.
Let us know what it was when it's all done so we can learn from it.
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  #3  
Old 07-01-2007, 12:34 AM
88Black560SL
 
Join Date: Oct 2004
Location: NC
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If you want to continue on yourself the next thing you need to do is a fuel system presure check. You need a special gage for that. Most likely this is your fuel distributor or pressure regulator or injectors. Dont rplace any of these without proper testing.

John Roncallo
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  #4  
Old 07-01-2007, 11:42 AM
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Quote:
Originally Posted by Roncallo View Post
If you want to continue on yourself the next thing you need to do is a fuel system presure check. You need a special gage for that. Most likely this is your fuel distributor or pressure regulator or injectors. Dont rplace any of these without proper testing.

John Roncallo
I bought a universal pressure tester but couln't get it hooked up so I returned it.
I think I'll take the car to the shop next week.
Thanks everyone for your responses.
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  #5  
Old 07-01-2007, 12:40 PM
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Location: Falls Church, VA
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Before you send the car away or start buying expensisve parts, here are some low cost basic health checks you can make:

Fuel starvation

You replaced the fuel pumps, but did you change the filter? In addition to a fuel pressure test, I suggest a volume test as well. You basically run the fuel return line from the FD into a container, and run the pumps for 30 seconds - you should see about a liter of fuel in that time. If you don't get this, find the constriction (filter, accumulator, line).

Timing advance

Connect a timing light to #1, and see where the timing is at idle. Slowly advance engine speed, and watch to see if the timing advances up to a max of 32-34 degrees

Spark plug wires

With the engine idling, connect the inductive pickup to each wire in turn. Pull the trigger and observe that you are getting spark to that cylinder. Replace wires or plugs as needed. You may have fouled plugs, which would indicate a bad injector.

Basic mixture

Connect a DMM or analog dwell meter to pin 3 on the diagnostic socket. At hot idle you should see an off-on ratio of 40-50%, or dwell of 42-45 degrees. Correct mixture as needed, but first check O2 sensor as it is usually the culprit in a bad reading.

EGR valve

Connect a Mityvac to the vacuum port on the valve. With the engine idling, put vacuum to the valve. The idle should go rough. If it does not, the EGR valve may be stuck open causing a massive vacuum leak. Alternatively, the control system may be allowing vacuum to the valve and opening it when it shouldn't

Vacuum leaks

Double-check every line and connection.
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Chuck Taylor
Falls Church VA
'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

Last edited by ctaylor738; 07-01-2007 at 12:48 PM.
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  #6  
Old 07-06-2007, 02:25 PM
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The official verdict is a bad fuel distributor. Provides fuel to only 5 cylinders at idle, starves all 8 at higher rpm. It's a wonder the car runs at all.
Thanks to all for your interest and assistance.
I will conclude the thread when a new FD has been installed.
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  #7  
Old 07-06-2007, 02:33 PM
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Quote:
Originally Posted by dugald View Post
The official verdict is a bad fuel distributor. Provides fuel to only 5 cylinders at idle, starves all 8 at higher rpm. It's a wonder the car runs at all.
Thanks to all for your interest and assistance.
I will conclude the thread when a new FD has been installed.
Outstanding! It's always a relief when you know what's wrong. Now you can get her running and enjoy that beautiful car.
Sometimes it's worth paying someone just get it done and over so you can drive it.
FD's not cheap but I guess it could have been something even more pricey.
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  #8  
Old 07-23-2007, 05:09 PM
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My indy installed the rebuilt fuel distributor today and tuned the mixture etc, all in just over an hour. I think it would have taken me a whole day.....to do it wrong.
Car runs fine. Pulls like an electric locomotive. I am delighted.
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  #9  
Old 07-23-2007, 07:43 PM
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Quote:
Originally Posted by dugald View Post
My indy installed the rebuilt fuel distributor today and tuned the mixture etc, all in just over an hour. I think it would have taken me a whole day.....to do it wrong.
Car runs fine. Pulls like an electric locomotive. I am delighted.
Nice!
enjoy your car now.
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