Dear Plug Whisperer (pics inside)

[Bleu Omdurman]

What's wrong with this picture? I don't know enough about plugs but here are a couple of pictures of the plugs from my 1999 MB SLK 230.

The other day I had a loud pop from my engine compartment. The engine started vibrating much more than normal. I decided to pull the plugs as it was the easier of a few options I have as I try to figure out what happened.

Notice that two of the plugs have oil on them. The second from the right/bottom was not even tight. I just got this back from a "B" Service at the dealership.

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[DeanG]

The insulation looks to be a nice even tan. The oil seems to be more on the outside of the plugs. The wires and engine seem to be a bit grungy.

Clean everything, put anti-seize on the threads and torque the plugs to spec. Then see how it runs.

[choi0706]

those plugs aren't that great..

do a compression test..

[RoadDad]

Originally Posted by DeanG

put anti-seize on the threads and torque the plugs to spec.

If you put anti-seize on, your torque specs will not be valid.

[Quicker]

was there oil in the plug wells before you removed the plugs? it could determine if the oil is coming from the outside in (like a valve cover leak) or from the bottom up (like poor compression).

[Bleu Omdurman]

Thanks for the notes guys.

I just torqued everything and the car still runs rough. It almost seems like a cylinder is not firing correctly. When I rev the engine, everything seems fine, nice and smooth. At idle, it is very choppy and the tach bounces more than it should. By that I mean it bounces about 75 rpm with a low of about 700 and a high about 800. Normally (i.e. before this) the motor hums around 850.

As a side note, I found my power steering fluid to be low. But so far all the fluids look fine.

So this next part is hard to describe. You know how if you put your hand down behind the exhaust you feel a little puff puff ? Ha, laugh now. Well, anyway, that "puff puff puff puff" is more of a "puff, skip, puff kinda hard, puff". Wash rinse and repeat.

Your thoughts are appreciated and welcome. Again, this is not on my Lotus or on a 2ZZ. Its an 1999 SLK.

Thanks,

Trevor

[Quicker]

usually that would point to a vacuum leak of some sort - which is pronounced at idle. You should be pulling about 18-22hg at idle (roughly -10 PSI). maybe the pop you heard was a mis-fire and it knocked something loose or popped a small hole in a line.

You can test your manifold vacuum with a gauge.

[Demonized]

Like Choi said, compression test, takes 15 minutes if that.

And figure out where the oil came from.

And like quicker said, it could have been a vacuum or pos pressure hose of sorts that popped a little hole, that you heard.

[choi0706]

on one of my old hondas, which needed a new spark plug oring.. if it seeped some oil, it would cause 1 cyl to miss.. could be what you're seeing.. try cleaning up the plug and wire..

this is after doing a compression check, and finding normal results..

[MikeinAlexandria]

Those plugs look like old technology and designed more for long life than performance. I would look up your car on SparkPlugs.com, check your local auto parts store to see how they compare in price, and replace those plugs with Iridium versions. I changed out the plugs in the Lotus with only 15,000 miles and it made quite a difference... the plugs were four years old and had been discontinued.

If the car still isn't running well, check the plug wires, and of course try to see where that oil is coming from!

[Overlander23]

Could also be time for new plug wires... if they're old... and plug wires (as opposed to a coil-on-plug design).

I've had an old set of wires cause a misfire on a cylinder before.

(Ooops... what he said ______^ )

[Mr.C]

Originally Posted by Overlander23

Could also be time for new plug wires... if they're old... and plug wires (as opposed to a coil-on-plug design).

I've had an old set of wires cause a misfire on a cylinder before.

(Ooops... what he said ______^ )

+1
I had that happen more than once im my Miata.
The wires short out thru the insulation to the zylinder head rather than transmitting the power to the plug. It always seemed to be most noticable at low rpm's.
Once it happened on a road trip, and I just wrapped the defective wire with tape in order to make it home without ruining my cat.
I let the engine idle and pulled one plug wire at a time. The one that didn't make any difference was the defective one.

[Bleu Omdurman]

Can some one refresh me on how to do a compression test? I have access to the compression test tool (screw on type). Takes two people doesn't it?

On the plugs, I'd prefer long life in this car over performance.

[Tracktimeplz]

Originally Posted by Bleu Omdurman

Can some one refresh me on how to do a compression test? I have access to the compression test tool (screw on type). Takes two people doesn't it?

On the plugs, I'd prefer long life in this car over performance.

disconnect injector plugs(Or pull Fuel pump fuse) remove sparkpluG(as in one at a time) screw tester into hole, turn over 5 revolutions, check, repeat.


If your car doesnt start afterwords, just replace the fuse or plug the injectors back in


Oh, and did you say your power steering fluid was low?? Did I miss sarcasm or?

As a side note, I found my power steering fluid to be low. But so far all the fluids look fine.

[TimMullen]

Originally Posted by Tracktimeplz

remove sparkpluG(as in one at a time) screw tester into hole, turn over 5 revolutions, check, repeat.

Actually, you should remove all the plugs, then test each cylinder one at a time.

If you test one with three plugs still installed, your starter is going to have to overcome the resistance of all four cylinders - you get a better reading if the engine can turn over freely (spin faster). Leaving the extra plugs in, will also cause the battery to "wear down" quicker (again giving misleading results).

[RoadDad]

Originally Posted by Bleu Omdurman

Can some one refresh me on how to do a compression test? I have access to the compression test tool (screw on type). Takes two people doesn't it?

On the plugs, I'd prefer long life in this car over performance.

You do not necessarily need 2 people. You can do a compression test alone in one of two ways. Either you need to see the gauge face (see * below) from in the driver's seat as you turn the engine over (pretty hard to do in the mid-engined cars but not so difficult in front engined cars - I place the gauge facing the cockpit and peer under the propped hood) or you need a remote starter. Either way is fine if you can do it.

In detail, to do the compression test you should start by cleaning the area around the plugs before you remove them with compressed air if you have it.

As Tim states, remove all the plugs.

Either block the throttle wide open if you are using a remote starter or press the go pedal with your foot to the floor if in the cockpit (again, pretty hard to see the gauge face from the mid-engined or rear engined car seat, but front engined is usually doable). The throttle needs to be wide open or you will not get an accurate reading.

Install the compression gauge in the #1 plug hole.

Crank the engine over at least, I say, 7 times while watching the guage. *The reason to do this is to watch how quickly the compression builds up. It should build up quickly in a healthy engine. Low compression on the first stroke, followed by gradually increasing pressure on successive strokes could indicate worn piston rings. A low compression on 1st stroke which doesn't build up during successive strokes may be leaking valves or a blown head gasket (or a cracked head). Deposits on the underside of the valve heads can also cause low compression. If your gauge doesn't hold the highest compression reading automatically (which most do) you will need to watch closely to see that highest reading.

Write down the highest compression reading and your take on the compression build up for each cylinder immediately as you finish it.

Repeat that procedure for each cylinder.

Compare your readings to the specs for your car and to each other (i.e., cylinder 1 to 2, 3, 4 etc.)

If you have low compression, you can add some engine oil (about three squirts from a plunger-type oil can) to each cylinder through the spark plug hole and repeat the testing.

If the compression increases after the oil is added, the piston rings are worn. If the compression doesn't increase significantly leakage is occurring at the valves or head gasket.

If one cylinder is about 20% lower than the others with a rough idle there may be a worn lobe on the camshaft.

If you find that your compression is way down (compared to specs) or varies greatly between cylinders you may want to do a leak down test.

You do not need an expensive Snap-on tester. If your local AutoZone, or Advance Auto doesn't have loaners, try Harbor Freight. They have one for under $10 that is just fine. They also have one that is IIRC about $40 with quick connects, more sizes of plug hole connectors (for 2 stroke engines and the like), etc. The $10 one has the same gauge and works just fine with most cars.

Good luck.

EDIT: And again, if you do put anti-seize on the plugs (I wouldn't) do not torque them to the recommended values as those values will be "too high" unless the spec'ed values are for lubed plugs.

[Bleu Omdurman]

Quicker nailed it.

I was feeling around for a pressure leak thinking blowing. Right next to my head as I was torquing the plugs to spec, was a disconnected line that runs from the trottle body to the ABS. At least it looks like it does. I kind of lose track of the routing at one point.

Anyway, I reconnected the line and all is well. The car purrs like a supercharged kitten... whatever that is.

Thanks for help gentlemen.

Trevor