The previous owner of this car had water put in its gas tank which stopped it dead and the car sat for over a year. I purchased the car and have done the following: removed and cleaned the gas tank, replaced gas tank filter, replaced both Bosch fuel pumps, fuel filter and fuel accumulator, flushed out the lines and fuel cooler, flushed and dried out the fuel pressure regulator and distributor, cleaned and flushed the fuel injection lines and replaced all of the injectors with new Bosch injectors. Upon start up the engine ran very rough, smoked heavily and wanted to run at high RPMS and would not idle back. I installed a used junk yard fuel distributor and fuel pressure regulator. Restarting the engine it seemed to run better but still smokes heavily and still will not idle. I think the smoke is unburnt gas from over fueling? Not sure where to look at this point. My intention is to get the car to a Mercedes repairman but wanted to at least make it drivable to get there. Any thoughts would be greatly appreciated. Thanks Woody

I should have given more details about the car, its a 1986 Mercedes 560 SL

The idle is electronlically controlled by a relay and a frequency valve. The relay gets its power from the over-voltage protection (OVP) relay. If any of these three are bad, the engine will have a high idle.

The mixture may be rich because the o-ring on the FD's plunger is bad, fuel pressure too high, bad oxygen sensor, mixture mis-adjusted.

If it were in my garage, I would go after the mixture problem first.

- check system and control pressure, correct as needed
- check coolant sensor resistance
- check o-ring in FD
- replace oxygen sensor and try to set mixture by duty cycle method

If you do a search, you will find lots of information on these components and how to check them.

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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

Thanks Chuck, where would I search for diagnostic info? Also the o ring you mentioned that might be leaking on the FD, is that the big o ring (about 2 1/2" diameter one that seals the FD to the air intake? Thanks Woody

You can use the Search function on this Forum, buy the CD, or get an Alldatadiy subscription for the car. You should also sign up for a free subscription to the EPC at

https://epc.startekinfo.com/epc/home.jsp

There are two o-rings, one on the piston itself, and the second that seals the FD to the air intake.

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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

Thanks Chuck I will subscribe to that forum. I did swap out the EHA valve with another one but no change. Are there any adjustments that could be off in changing out the FD with a unit from another engine? Woody

At this point it may be best to have your SL towed to a shop with a scope/CO meter so the injection can be set to a baseline after which it will be possible to accurately diagnose your rich condition.

Make sure to check the electrical system for the FI. also check routing and condition of all vacuum lines. Many driveability (or in your case, un-driveability!) complaints arise from simple failures such as relay grounding or broken/blocked vacuum lines.

Are the donor fuel supply components known to be functional, removed from a running engine?

Just for the heck of it - check the thermostat, thermo time switch and all temp and throttle sensors, as well as the throttle linkage.

good luck, it's most likely not serious and, will easily be running correctly soon.

The fuel distributor was suppose to have been taken off a running engine but I have no way to verifi that. I did go through and cleaned all connections on sensors, after which the smoking exhaust cleaned up but the engine still won't idle. Tried adjusting the fuel mixture adjustment but it made little difference except that I could make the engine very hard to start but could not affect the high RPM. Have signed on with Alldata and will try to test some of these sensors but it looks like you need some special test equipment to do some of the test. Like the Idle speed control which apparently is a prime suspect has a test procedure which requires special euipment. Is there a way to test to see if the fuel distributor oring leaks?

I'll throw in my $0.02. On my 1989, started it one time, idled fine. Next time would not idle down. Turned out the throttle position sensor buried in the V of the engine went bad. Replaced it and the problem went away. If you have a Mercedes engine service manual, it says how to easily check it with a basic ohmeter at the wire connection located at the left top front of the engine.

If the mixture problems have cleared up (meaning it's not running super-rich), and the remaining problem is a high idle, then the problem is air, not fuel. This can be caused by one more of the following:

- defective idle valve. Does it click when you touch it with battery voltage?
- defective idle relay. Are you getting voltage at the valve?
- throttle linkage binding. Disconnect at front pivot, see if it improves, peer down at throttle plate with good light to see if anything is jamming the plate.
- "false air" from a vacuum leak. Double check all vacuum hoses and connectors on the engine. Plug the cabin vacuum outlet at the back of the intake manifold. Be sure the injectors are tight in the cups. (You did replace the seals, didn't you?)
- "false air" in the idle air system. Check all the idle air hoses for cracks.

If you isolate the problem to the relay/valve, you can make the car driveable by removing the valve and putting a washer with an outside diameter matching the inside diiameter of the hose in the hose to restrict the air flow. I have also used a piece of dowel with a hole drilled in it.

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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

Thanks for the post guys, I feel like I am making some headway now that the exhaust is clear. Will have a look at the throttle position sensor and yes Chuck I did replace the injector seals, will check over the vacuum hoses and throttle linkage. Not sure I know where the idle valve and idle valve relays are located, are the idle hoses you spoke of attached to these? I have signed on with Alldata and was able to log in once and have not been able to gain access to the site again for some reason. So I am not real sure where all these relays and controls are located. I had purchased a Mercedes w126 CD on ebay which was suppose to cover my car but it requires some antiquated software to run it and the only way I can retreive information off it is to blindly open up stuff which appears to be of pretty poor quality. Hopefully I can get back online with Alldata so I can learn were these things are on the engine. I will look into what I can and post back, Thanks for help Woody

The idle valve is the cigar-shaped gizmo right right at the front of the intake manifold. It has an inlet that goes down into the manifold, and an outlet that feeds the black rubber idle air tubes that criss-cross the intake and have small outlets in the manifold that feed each cylinder.

The idle relay is in the relay farm on the right side of the passenger footwell. You have to remove the underdash panel and maybe the glove box to get to it. It should have PN 006 545 85 32 on it.

The relay monitors the RPM via the signal from the ignition unit, and adjusts the air flow to the idle valve to regulate the idle. Higher voltage, less air, lower idle. It's actually on-off pulses, but it can be measured as voltage.

If you go under the dash, look for the OVP relay, the only one with a fuse on top of it. Make sure the fuse is good. The OVP relay powers the idle relay and the other engine electronics.

It's very common for the valve and the relay to fail as a pair. The valve goes TU and allows the idle to go up or "false air" gets in. The relay puts out ever-increasing amounts of voltage trying to keep the idle down and finally fries itself.

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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

I was searching the forum for the source of a chattering or clicking that is coming from my passenger footwell, but i am having a difficult time determining what relay is causing the problem.

Fastlane shows the following Relays for sale:
Fuel Pump, Overload, 'relay...', Seatbelt Warning, Turn Signal, and Wiper.

In some posts, including the one above, there is reference to an idle relay and over-voltage protection relay. I know my SL is a different beast than the vehicle discussed above. So, can i assume that there I do not have Idle and OVP relays?

Also, how do i determine what is chattering? The sound presents only occassionally, and I haven't linked it to any action or conditions. Also, it sounds like removing the dash to access this panel is non-trivial. I'd rather not do it more than once, and I'd rather not have this part removed while I try witness the noise.

Is the first step just to pull the panel, and clean any/all relays in view? Then wait to see if it clears up?

Thanks for your suggestions.
Regards,
Justin

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Justin Ford
'84 380SL
'05 Jeep Grand Cherokee

Your car has an idle relay. It's not in the relay farm, it's more in the center of the passenger footwell on the firewall. You can access it by removing the lower dash panel. Some places call it an "idle control module." It is solid state, and I don't think it's the clicker.

It is very simple to remove the under-dash panel, and if you're lucky, you may be able to isolate the noise.

BTW, if you are going to work on the car, you really should get either the CD or an AllDataDIY subscription, and sign up for the free Mercedes EPC.

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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

Thanks Chuck, I am going to work on the car saturday and check out your suggestions and will post back. Woody