[W126 Coupe] 87 560SEC (euro) running problems

[Mister McGoo]

Al,
Restricted exhaust would cause steady drop in vacuum but so would retarded ignition timing.   MacBain's suggestion would fit.  A faulty coil will heat and take spastic fits (or simply pack in) and of course is connected to the Ignition Control Module.  Randomly confused ignition, lower RPM, lower vacuum and lower oil pressure.  You have access to a coil to swap in?  Cheaper than the Module for sure! ($2,000+)
-Bellamy 

Date: Tue, 7 Jun 2011 11:47:21 -0500
From: alal30319 at gmail.com
To: mbcoupes at mbcoupes.com
Subject: Re: [W126 Coupe] 87 560SEC (euro) running problems

Bellamy

Thanks for responding, the vac and oil pressure drops only during the miss and they come right back (in the case of the oil pressure, it actually drops on every miss and comes back). When driving, the oil pressure is pinned at 3 bar. Engine temp is around 80.


The car has dual manifolds going into a two in two out cat in the center of the car.

I'll try disconnecting the 02 sensors and see what it does. 

With best regards

Al Abbasi



On Tue, Jun 7, 2011 at 11:19 AM, Mister McGoo <eelploot at hotmail.com> wrote:






alal30319...name?
With the limited information, ideas are somewhat shots in the dark.  The "economy" gauge acts as a poor excuse vacuum gauge but a vacuum test is a good place to start.

I assume that the oil pressure drops at idle because the RPM's drop somewhat due to the missing.  Or does the oil gauge read something LESS than 3+bar at higher RPM when driving?  What about engine temperature... is it abnormally high at the same time?

The fact that the vacuum drops as the engine heats up possibly indicates a restricted exhaust system.  Does the [euro] car have catalytic converters?  [assume yes with 02 sensors?] Twin exhaust? [like earlier euro 500 & 380?]  Or secondary cat in single system??

-Bellamy

Date: Tue, 7 Jun 2011 10:51:26 -0500
From: alal30319 at gmail.com
To: mbcoupes at mbcoupes.com

Subject: Re: [W126 Coupe] 87 560SEC (euro) running problems

Jay

Thanks, the plugs are good and on tight. I would not expect it to be the plugs because if it was a bad one, you would usually see a constant miss. In this case, it can be smooth on startup, but then act out after a drive which is why i'm thinking that it may be o2 sensor or computer related.




On Mon, Jun 6, 2011 at 6:18 PM, Jay Hirsch <j.hirsch at mac.com> wrote:


Just a suggestion



Pull the plugs  and put them back in making sure each one is in fact screwed all the way in



Jay H

On Jun 6, 2011, at 5:59 PM, alal30319 at gmail.com wrote:




> All



>



> I posted this on a couple of forums but i've not been able to get any tangible answers so I thought I would cross post here:



>



> Here is my scenario:



>



> When I bought this car, I got it to run like a scalded ape. It was fast and smooth. I replaced the plugs (NGK non resistor), plug wires, coil, rotor and crank position sensor.



>



> Recently, I had a bad miss which I've been trying to chase down. I initially thought it was a bad fuel distributor or injectors caused by bad gas, so I pulled the injectors and checked them. Some of them were a little weak so I replaced all 8 and got the car to run very well at idle. But after running the engine for a while, it would develop a miss on and off and you'd see the oil pressure gauge drop when it does.





>



> After a long drive, the miss would get worse and become more constant.



>



> I've been able to disconnect the electrical connection to the EHA and get the car to idle better.



>



> I've checked for vacuum leaks but could not find any. The vacuum gauge on the dash is pinned to the left until the car develops a miss and then it will move towards the center (about 1/2 way between far left and center).





>



> I swapped out the EHA with another that I had on shelf but this did not change the symptoms.



>



> I suspect that it could be the O2 sensors, or the computer trying to lean out the mixture but I am not sure how to test these.



>



> I'd be grateful for your thoughts.



>



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The MB Coupes Website!

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Postings remain property of MB Coupes, L.L.C.




The MB Coupes Website!
W126 SEC Mailing List
Postings remain property of MB Coupes, L.L.C. 		 	   		  

The MB Coupes Website!

W126 SEC Mailing List

Postings remain property of MB Coupes, L.L.C.



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Postings remain property of MB Coupes, L.L.C.
 		 	   		  
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