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1987 560SL - story - CA vehicle Passed SMOG 8.18.15. Had a…

1987 560SL - Long story...
1987 560SL - Long story - CA vehicle Passed SMOG 8.18.15. Had a buyer for car, CA requires a passing SMOG test withing 90 days of sale of vehicle, failed smog 1.23.16. mechanic tried several unknown solutions to pass but to no avail. The car was running very rough after the inspection. It seemed like a fuel problem. I replaced both fuel pumps & filter. Had very good pressure @ the fuel distributor. Still not running right. pulled and cleaned all injectors & replaced all injector seals & components. Then I thought that it was a vacuum problem because when I accelerated it the vac would drop. I replaced all the air distribution hoses, vac connectors, throttle body boot, boot strap & intake gaskets. vac was better but still could not drive it up hills without it stalling. Had it towed to a local Mercedes/BMW/VW shop. They ran a diag. Findings #1 & #6 not firing, ran compression check OK, pressure to injectors 36PSI, they replaced the fuel pressure regulator. Now it would idle properly but still would not accelerate properly. They thought that it was a probably vac issue. I drove it home very gingerly and almost needed a tow thru the hills. Now I have run smoke tests when the engine was cold. Found several leaks & repaired or replaced components. Now when I start the car, it starts immediately & idles & 800 RPM and the vacuum reads 0 until the water temp gets to 80 C. then the vacuum starts dropping as I accelerate. I ran another smoke test while the engine was warm found few leaks at the air distribution connections & a larger one at the throttle body linkage connector. The air distribution hoses are an easy repair but the smoke seems to be coming out of the throttle body arm itself. Is there a way to repair the leak without disassembling the engine again? I am very sorry for the dissertation but this has been driving me just a little crazy & would like to sell the car as soon as possible.
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Answered in 28 minutes by:
4/26/2017
Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 55,104
Experience: Bosch Certified Master Tech. Over 35 years experience.
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Hi, my name is***** never mentioned anything about the fuel distributor. A faulty fuel distributor and incorrect fuel mixture adjustment are the likely causes of your running issues. Usually a mechanic will incorrectly adjust the mixture to compensate for a bad fuel distributor. When they incorrectly adjust the mixture it won't accelerate properly.
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Customer reply replied 1 year ago
A couple of questions. Do I need to do anything about the throttle body vac leak? Is there a machine or set of tools that can test the fuel distributor? Can it be rebuilt by me or a knowable mechanic?
Small vacuum leaks at the throttle body are not a big concern. FYI, it is normal for vacuum to drop to zero on wide open throttle. Vacuum at idle should be approx 18" mg. Another possibility for your poor acceleration is a plugged catalytic converter.
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Customer reply replied 1 year ago
I will check the cats ... please answer me on the fuel distributor questions
Thanks
The FD is not really rebuildable. Your best bet is a good used fuel distributor. Your two misfiring cylinders can be due to low flow from the FD to those two cylinders. With the fuel mixture correctly adjusted the lines to those cylinders are moved to another port on the FD to see if the miss follows the lines or stays with the cylinder. If it follows the lines your fuel distributor is bad.
Marty
Marty, Mercedes Technician
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Experience: Bosch Certified Master Tech. Over 35 years experience.
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Customer reply replied 1 year ago
I will troubleshoot the FD in the morning. I have a great exhaust system mechanic available & get his input in the cats
Thank you very much for your input

Just to be clear. When you swap lines at the FD you want to check to see if the cylinder that is now connected to #1 or #6 port is now misfiring. If it is it means that you are not getting good fuel delivery from that port and the FD needs to be replaced. You will need to bend the lines slightly to swap them at the FD. I actually have made up some flexible fuel lines that I use to perform this test.

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