worse news 16v - PeachParts Mercedes-Benz Forum

jasondew · #1 09-24-2002, 08:42 PM

my 16v has been idling rough lately. more recently it runs rough at all rpms. it feels like it's running on 3 cylinders. i pulled my plugs today to read them. here's where it gets good--plugs 1,4,2 all read normal operation; plug 3 is oily, covered in oil. when i look down into the cylinder, 1,4,2 all look frosty black. 3 looks...guess what...oily. i'm pains me to think i might have a blown piston ring. any thoughts?

thanks

mbdoc · #2 09-25-2002, 08:00 AM

Test the engine compression & cylinder leakage first!

Has happened to me on the race car, running too lean!! Hope your engine didn't do that to you!

jasondew · #3 09-25-2002, 08:15 PM

i just had a compression test and leakdown 185,180,185,185 5%,5%,7%,5% (research for a now abandoned forced induction project). all numbers were good at that time. my mechanic will test both again and compare. i would assume it has changed for that cylinder.

i don't think i'm running lean because all the other plugs read normal to a little rich. i just changed plugs and they read as stated. the plugs i removed read the same. plus about a week before my problem started i adjusted the EHA to richen up just a bit. question: will hooking up an air/fuel meter to the o2 sensor be accurate since the senor is downstream of the precats? does the KE system have some compensation tuned in to counteract the effect of the precats.

i have another issue. while trying to determine if i have any vacuum leaks i found one. there is a nipple near the intake runner for the cylinder nearest the firewall that is sucking in air. it looks like it recently had a cover or hose on it. is there a hose that connects here or a cover or something? i can't finding anything.

thanks

#4 09-25-2002, 11:04 PM

The plug blew off the nipple on my 16v, the replacement was somehing absurd like 10 dollars, so a bit of heat shrink and a nail is sufficing. Just to make sure we are talking about the same thing though......

If the 'nipple' is uncovered, start the engine, pop the hood, and cover it with your hand. If that improves the idle situation, i'd say it needs a cover. If it doesn't improve anything, try the test at different engine speeds and tempretures.

When I tested mine, it evened out a rough idle.

Dan Rotigel

jasondew · #5 09-26-2002, 06:20 AM

i actually found this by testing with carb cleaner. that area was the only place that raised the idle when carb cleaner was sprayed. eventually i determined it to be that nipple and not other hoses in the area. i tried covering it and it did improve the idle. but, i've still got something else bad going on with this oily plug and cylinder. i should be able to get it to my mechanic this weekend for diagnosis. i'll keep everyone posted.

thanks.

#6 09-27-2002, 01:00 PM

From what I understand, that (vacuum) port on intake runner #4 is connected to 16Vs with automatic transmissions. For our manual models, it should be plugged. Mine's plugged with a 3/4" long piece of hose with a machine screw in the end. Maybe I also ought to check to see if it's holding vacuum. What's the procedure again? While running, spray some carb cleaner near the plug and listen for ???

Thanks!

Brian16V