Brian_I.

Hey guys, I changed my plugs today (along with the distributor cap and rotor) and noticed something. Four of the plugs came out with the tips slightly wet and were black but two were completely dry and not really black at all. The two dry ones were towards the front end of the engine (closest to the headlights) and the back four were the wet ones.

One thing I did notice was that the last two (the dry ones) were much harder to loosen and remove. Almost as if they were over-tightened when installed.

Any thoughts? According to some sites, both are characteristics of a rich fuel mixture and a few other things. What do yours look like when pulled? Just a bit of background, these plugs haven't been changed in the past 3 years and I've been through two O2 sensors so they could have been messed up from that.

Saijin_Naib

I know when my car had the cap/rotor issue as well as the spark plug wire issue, it would stall and foul plugs like, every 3 months. They'd come out gummy. This may also have been because we were using Bosch Platinums instead of copper, not sure my m104 likes those.

RobertG

It could also mean that the injectors maybe dripping fuel after shutdown, check your fuel rail pressure for drop after shutdown.

Brian_I.

The ones I pulled out were not the same as the ones I put in. I will look again to see if they were platinums. Now that I know how easy it is to change I will definitely remember to do that on any new (used) car I buy, if ever.

Hey Robert, could you elaborate on this? I'm assuming this is something that must be done at a special shop or something?

RobertG

The fuel rail connects and feeds fuel to the injector, it stays pressureized after you shut the engine off.
To test for leaking injectors hook up a pressure gage to the fuel rail(manifold) and take note of pressure loss (if any)after you shut the engine off.

RobertG

Do you experience hard starts?

Brian_I.

No, it starts up fine. It's just when it idles it seems like the RPM's drop too low, although it hasn't actually died out at all. Maybe I'm just paranoid because my trust in the car is low right now.

To make things worse, the car kinda vibrates while it's running which I was told was because of the "engine mounts" (?). Since that isn't something I can change myself I left it alone.

rayhennig

Hello Brian, I seem to be stalking you, don't I?

My M104 engined 300 had 6 exotic plugs supplied by MB dealer parts dept and they were ****e. They cost over 100 Euro and the car was never right.

I bought a set of 6 cheap Bosch copper plugs type F8DC4 for about 25 Euro and everything was fine until my rotor arm problem cropped up and I've harped on about that ad nauseum.

Try the cheap, simple things first and don't waste cash on Platinum or assume you have costly injection problems until there's hard evidence.

RayH