An interesting problem - Misfire, surging... MADNESS - PeachParts Mercedes-Benz Forum

Breckman99 · #1 02-12-2006, 04:53 PM

All right - I've been working on the OM617 for many years now professionally and as a hobby. Normally there is no problem that has phased me, but listen to this one:
Car is running perfectly - absolutely smooth, great power ect ect. Tank is about 1/4 full so I stop in at a local service station and fill her up with diesel and a large shot of Power Service.
About 18 miles later I notice a slight vibration at idle while stopped at a light. Strange I think... About two blocks later I stop again. HUGE vibration and pronounced misfire. Well now! That’s no good! I pull into a mall parking lot to inspect the situation. Nothing I can gather from a visual, no strange knocks ect.
I drive the car back home, and decide to park it until the weekend.
Weekend: Valve adjustment, filters, oil, and adjustment of the rack damper pin.
Note when I replaced the filter I filled it with my "special blend" injector cleaner. When I had the car on the lift looked over all mounting points ect, all was golden.
When I started the car again the misfire was still present even while running off of the juice. That’s slightly discouraging. The car still has beautiful power, and anything above idle is smooth as silk. After fiddling with the rack damper for awhile I was able to get low idle smooth (in D) but just above it, IE slowing down and free idle is still very rough.
My thoughts so far are:
1. Bad fuel
2. Bad fuel knocked something loose and clogged an injector or IP
3. IP is dying
4. I’ve had the IP timing at about 15 (using AB method) just because these run better at high elevations at that setting. You don’t think the chain has stretched that much that it screwed my timing? (should have checked this when doing valves)

Haven’t yet had time for a compression check, but the running characteristics in all other ranges makes me think this probably has nothing to do with it. I don’t have any spare injectors with me right now or I would try swapping those out. While I was doing the valves I pulled the injectors and they had quite a bit of soot around the pintle. It is very hard to isolate the misfire as it is so random you can’t tell if you just caused it by cracking a line ect. Any ideas or similar experiences?

Brian Carlton · #2 02-12-2006, 07:02 PM

Too coincidental. Bad fuel.

Rig up a can and run it on the can fuel for a bit and see if it clears up.

Breckman99 · #3 02-18-2006, 05:20 PM

Yup. Turned out to be the fuel. Two tanks later and all is well!