I need to find out the correct plug lead to cylinder orientation for a 1994 S500 W140 V8. Csn==an someone please help?

limited info generic answer check wires and make sure they are in good shape and are on correctly ,driverside front close to rad #1,and then2,3,4 [same side]and pass. side front 5,6,7,8 [if only 6cyl you have 123and 456? https://www.justanswer.com/car/1ewpk-firing-order-1996-mercury-grand-marquis-v8-4-6l.html

Which engine do you have in the vehicle? They fitted them with an in-line four cylinder and a V6. The firing orders are different for each version. I'm assuming the distributor has NOT been removed and is set correctly!
**Note, Take your time to make sure you get this right!**
The Four cylinder is the standard 1,3,4,2, firing order with number One being the nearest cylinder, (spark plug), to the belts and pulleys on the engine. Use the plug leads as a guide as they should be four different lengths. The longest plug lead to the spark plug furthest away, shortest to the nearest spark plug.
With the distributor cap removed make sure the engine is at Top Dead Centre for cylinder One. Check where the metal tip on the rotor arm is pointing as this is where the plug lead for Number One should go.
Refit the the distributor cap and insert the lead for the Number One spark plug into the hole nearest where the rotor arm tip was pointing. Now refit the remaining 3 plug leads in the Correct Order, (1,3,4,2,) into the remaining 3 outside holes in a CLOCKWISE direction. The centre hole should connect to the coil pack lead.
A V6 engine uses the same setup BUT a different firing order. (See photo). 1,4,2,5,3,6. In the photo numbers 1 and 4 are nearest the belts and pulleys.
Set your distributor as you would for the four cylinder engine, fit plug lead one and going CLOCKWISE fit them as the 1,4,2,5,3,6 sequence.

im sure the timing cover at front of the engine
http://www.importecwarehouse.com/Mercedes-Cam-Camshaft-Position-Sensor-Front-of-Eng-p/mb0021539528.htm

The thermostat is located in front of the engine, between V cylinder banks, for Audi A8 V8 4.2 Quattro Automatic. See pictures below:




Remove the thermostat housing (2 bolts) and the old thermostat. Note the orientation of the old thermostat (vent valve facing UP). Clean both thermostat housing and block surfaces and remove all traces of old gasket material. Install the new thermostat vent valve facing UP.

Please do rate my response. Thanks!

This issue may be cause by a restricted catalytic converter on that side of the vehicle and quite possibly will only affect one cylinder. The other option is a vacuum leak around that particular cylinder.I have seen the converters cause this a few times. Why it's only one cylinder it affects is beyond me logically speaking it should affect the whole bank on that side sometimes it does affect multiple cylinders on the same bank.I guess it may just depend on how restricted it is.

you can always get a second opinion

The part that you unscrewed from the spark plug is what allows the plug cap to snap onto the plug. Screw the little adaptor back onto the spark plug - and the plug cap should then snap into place with a little pressure.

if you look on top of the cylinder heads there are a number leads say you have a V8 there will be 4 leads on each cylinder head total of 8 under the where the leads go into the engine are the spark plugs

crank sensor,cam sensor,ignition module,coil pack,or the computer itself

firing order is 1-3-4-2, cylinder number 1 is closest to the timing belt