[W126 Coupe] W126 losing power

[Dick Spellman]

Hi Tom,

Change the plugs to the prescribed NGK or Beru.  The OEM Bosch W7 or 
9DCO (I can't recall) may still be available at your local MB dealer.  
All are single electrode plugs and offer the correct resistance for the 
ignition system.  The Bosch Platinum +4's are NO GOOD on your engine 
regardless of what the parts store may have said.  Presumably you used 
OEM cap and rotor, not aftermarket.  Plug and coil wire leads should be 
Karlynn or OEM.

A quick check of the coil supply voltages as per the manual is a good 
idea to rule out a weak coil.

Fuel pressure gauges (StarProducts Lindhurst, NY $80~) would allow you 
to check the system and differential pressures which should be something 
like 5.3 bars system with a differential of 0.40.  Just as a comment, a 
common tweak to the differential pressure is to adjust the screw on the 
EHA so you get 0.45 diff. for improved performance.

You could road test with a minimum 12ga. stranded (soldered tips)  
jumper wire on the fuel pump relay socket to rule out an ailing FPR.  
The jumper is needed in any case for the fuel pressure tests with 
gauges.  A write-up on using the Star gauges for a 300se (same set-up as 
your 380) is on Steve Nirvig's web pages.

The gauges will also let you know if the system has any leaks such as 
the control piston seal or accumulator.  You don't mention replacing the 
fuel filter this could be fouled and restrict flow. What's the 
age/mileage on the 380's single fuel pump?  This too could be weak.

Of course, a VOHM meter preferably with dwell angle (Sears $30) 
connected to thediagnostics outlet (see Dan Landiss's write-up) would 
allow you to accurately tune the air/fuel mixture at idle and at 
2500rpm.  This critical setting cannot be done manually.  This same 
meter will let you test the EHA's current once the engine has warmed 
up.  Where the factory spec'd O2 is in place and new you should be okay 
and not need to meter this in the passenger footwell.

Have you disconnected and blocked off the air pump?

Good luck,
Dick
diyr

  On 7/30/2011 6:13 PM, Tom Brophy wrote:

>

> I  a have 1985 380se, with a 1984 500sec Engine. the compression is 

> within 5lbs of the fuel filter.  factory spec on all cylinders.

>

> I have a loss of power under load [going uphill] or quick 

> acceleration, otherwise car runs smooth at a constant speed, but 

> dropped 4-5 mpg. failing smogou see if the system pressure is dropping 

> misserably - CO emissions. replaced catalytic converter 2 years ago.

>

> I'm fairly sure whatever is causing the power loss is at the root of 

> my smog woes, the emissions are about 10x higher than 2 years ago.

>

>

> What I have done --

>

> new spark plugs bosch platinum, [tested plug wires] new cap & rotor, 

> new fuel injectors w/seals, new dir replacement bosch O2 sensor, 

> checked timing adjusted fuel mixture [manually], cleaned idle control 

> valve. replaced ECU [salvage] when nothing else worked.

> even at a richer mix I still have a problem under load and the engine 

> stalled on the dynamometer. someone suggested it might be the 

> catalytic, and I loosened the exhaust to create a good leak before the 

> catalytic and the engine still stalled when I put it under load by 

> applying the brake and reving the engine slowly to about 1100 RPM.

>

>

> Any suggetions?

>

>

> Tom

>

>

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>

>

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