M103 Misfiring/fouled plugs issue.... - Page 2 - PeachParts Mercedes-Benz Forum

Ivanerrol · #1 01-10-2009, 03:09 AM

The leads are copper so the resistance is close enough to zero, however the ends plugs (the plug ends) should be between 900 and 1100 ohms. If they are Beru then the ohmage is actually printed on them (at least they are on mine). The distributor cap also has built in resistance. Check this cap and the rotor and make sure they are good. Dissy caps are known to develop small cracks in them so clean it out well and do a very close inspection.

There is a DYI sticky on this forum that shows how to change out the valve seals. If you have upwards of 120,000 miles (180,000 km's plus) and then depending on the use of vehicle, the valve seals are in line for replacement. If the car has been left for long periods between runs the seals can dry out so (this can explain why M103 engines with relatively low mileage seals require replacing - previous owners include little old ladies who only drive the car to church on Sundays or once a month).

If you have upward of 160,000 miles on the engine it's time for a head pressure test. Possibly valve seals, stems and head gasket are due. Although this is a little expensive if you intend on keeping the car for a few years this would be money well spent.

Bigdaddybenz · #2 01-10-2009, 05:50 AM

Definitely VALVE SEALS!!!! Been there, done that!

George560sel · #3 01-10-2009, 06:30 AM

This is from my service manual.
Model 124, test data for engine at normal operating temp

minimum compression pressure at (normal compression) approx 12 bar, (low compression) approx 7.5 bar.

Allowable difference between cylinders max 1.5 bar

ignition cable w/ spark plug connector 700-1300 ohm.

babymog · #4 01-10-2009, 02:09 PM

The compression test is a 1hour job on a 103. Once the plugs are all out, a remote-start switch in one hand, a rubber-ended compression gauge in the other, hold the rubber tip in each spark plug hole as you crank, quick and easy compared to the diesel version. Some things are actually easier with the gassers!

If you haven't already been following the thread, this: My 300TE Head Gasket Thread (yes pics!) one has a couple of nice photos of the M103 valve and rocker assembly.

pawoSD · #5 01-10-2009, 03:12 PM

Problem with doing the valve seals myself is that I have none of the following:

All special tools
Shop air supply (or any air supply)
confidence in doing it.

Anyways, today I re-gapped the plugs properly (my guess job was a bit off on most of them) None were really much dirtier than last time, so thats good...

Replaced distributor rotor and cap/cover, rotor was singed and scary looking, the cap was coroded and burnt, and the carbon tip was worn....only 2 of the tips measured properly on the ohm-meter!

I haven't started it yet, but I will be going out and doing so in a few minutes....I'll report back any improvement.

pawoSD · #6 01-10-2009, 05:48 PM

Well, it still ran with a miss/crappy. So out of frustration I slapped in the old champion resistor plugs that came in the car when I got it. Well what do you know, fires right up and runs smooth/powerful. No miss at all.

Explain that!!!

I just bought some el-cheapo "copper core classic" splitfire brand plugs....I am going to see how it runs on those......they were $1.29 each, I'm going to go gap them to .034" and throw them in and see how it runs.

Why does it seem to run better on the resistor plugs? Makes no sense.

dang50 · #7 01-10-2009, 06:23 PM

I'm afraid if you check www.splitfire.com Copper Core classic plugs are resistor plugs. Everybody says non resistor is the way to go. The dealership can provide them for less than platinums and you'll have the recommended plug in there. Also the exact proper heat range may be coming into play with other than recommended H9DCO.
I worked at a car parts store in the '80's when platinums came out and in Bosch plugs one platinum plug would replace up to 4 different heat ranges in the copper core. We had plenty of people bring platinums back because they wouldn't run right with the application being used.
Dan

pawoSD · #8 01-10-2009, 10:59 PM

Quote:

Originally Posted by dang50

I'm afraid if you check www.splitfire.com Copper Core classic plugs are resistor plugs. Everybody says non resistor is the way to go. The dealership can provide them for less than platinums and you'll have the recommended plug in there. Also the exact proper heat range may be coming into play with other than recommended H9DCO.
I worked at a car parts store in the '80's when platinums came out and in Bosch plugs one platinum plug would replace up to 4 different heat ranges in the copper core. We had plenty of people bring platinums back because they wouldn't run right with the application being used.
Dan

Well, it runs excellent on them, so I'm leavin' them in for now. The non resistor bosch plugs got all sooty and gross after barely 1500 miles and wouldn't run right even after I cleaned them off. (Sputtering and missing). Threw in these $1.30 apiece china plugs, and she's running awesome, and tons of power/rev's freely and smoothly. I'm a believer. So until it stops running smoothly, I'll be keeping them in it.

Oh, and it got 11mpg on the Bosch plugs on the last fillup. The mpg's continuously fell each fillup when using those plugs. Makes no sense.

The exhaust even smells normal/not oily or gassy with the splitfire plugs.

And I don't think it needs valve seals yet, it doesn't put out the slightest bit of blue exhaust, even if you rev it up in 2nd, coast, then hit the gas again....nothing. Oil consumption is less than a qt per 1000 miles.

Hit Man X · #9 01-11-2009, 01:57 PM

M103s don't tend to smoke much during oil consumption from what I have seen. Don't judge anything by simply that. Mine doesn't, 260k and the head hasn't been rebuilt.

Keep the oil weight around 0/40 or 5/40. Plenty of film at high RPM and quick pressure on cold starts.

Have you pulled the old cap/rotor yet? They don't last that long as the M103 is a high rev car... just like the rest of the accys. With a poor arcing setup...

Do you have a lazy injector or many?

Do the stem seals to rule them out, under $20 and a few hours. Plus you get a new valve cover gasket and oil cap seal then to help idle vacuum. Also the upper timing cover always leaks, go ahead and replace the seals while it's apart, then toss on new cap/rotor.

Your PO sounds like a moron, so you get to basically replace everything and start fresh to get a solid base.

babymog · #10 01-12-2009, 01:10 PM

... and Don should know, chances are he's done "a few".

johnathan1 · #11 01-12-2009, 01:39 PM

I used to just replace the spark plugs on my M103 every 2 months or so.