My 1986 560SL is driving me crazy. The problem is that it has good performance when the engine is cold, but as soon as it warms up the performance is extremely poor. When the engine is cold the intake manifold vacuum is at 10 inhg and the enrichment ma is in tolerance, as the engine warms up my vacuum falls to 7-6 inhg and the enrichment falls to well below tolerances. All fuel pressures look good.
I have replaced the temperature sensor, ignition control module, airflow pot, fuel pressure regulator, fuel distributor, fuel pump, fuel filter, distributor, all new fuel injectors, exhaust system, o2 sensor, and overload protection relay. I also changed out the K-jetronic control module

My question is where do I go now?

David
1986, 560SL

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Dave

Try a leak down test to pinpoint the problem!

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1988 560SL
Black Pearl/Palamino

That's not much vacuum. If it started suddenly, I would look for a broken hose, fitting not connected, or maybe a problem in the brake booster.

What is the vac guage in the instrument cluster reading?

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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

the intake manifold vacuum should be 15-19" at hot idle in neutral. Something is seriously wrong--either cam timing is off (bad chain guides allowed chain to jump a tooth?), ignition timing way late, or engine is seriously ill. I am presuming you have checked for vacuum leaks--it would be a big one to drop the vacuum this low.

Run a compression test--both dry and, if low then with 1 teaspoon of oil added to each cylinder in turn, cranked 5-sec and then read the pressure.

Thanks for the help. The dry compression test is as follows:
1-115, 2-120, 3-120, 4-115, 5-130, 6-105, 7-120, 8-120.

Vacuum readings from manifold.

Idel 700RPM 7 then stablises at 12
open throttle 4 , very unstable
at 400 RPM vaccum goes to 20 and runs smooth

Thanks for any and all advise

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Dave

Pretty hard to evaluate the problem with absolutely no testing having been done.

Since money is no object why not do it the cheap way and pay a professional.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician