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Old 05-21-2019, 03:53 AM
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97 C280 Fuel rail bolts torque

I'm replacing fuel injectors on my friend's 97 C280 (M104.941) I can't find torque specs for the 5 bolts holding fuel rail. There is nothing in WIS on this, I only see 25 Nm for intake manifold bolts.

Is it safe to assume that fuel rail bolts would be the same 25 Nm?

First time I work on this engine but, it looks like fuel rail bolts are part of intake manifold bolt pattern… I wouldn't want to over or under-torque this if that's the case.
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Old 05-21-2019, 06:12 PM
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The M104 is in my 97 SL320 and 97 C280 so I should remember how this is built up. Do the injector rail bolts go into the plastic manifold or aluminum? If aluminum then 25 nm / 18 ft-lb should be fine. If steel inserts embedded into plastic, I'd go 12 nm / 9 FT-lb. Pretty much a bit past heavy screwdriver tight so the insert isn't damaged.

Are you chasing a problem by changing the injectors? Be aware that ignition coils / wires / boots fail on this engine and will cause a miss fire. When this occurs, the computer will shut off the injector to the offending cylinder after 5 or so seconds so raw fuel does not melt the catalyst.

The 97 M104 in an SL or C is unique in that it was the first and last year for a M 2.0 / M 2.1 engine computer, electronic shift trans , metal key with an RFID chip. The M104 did continue in the S320 until 99.
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Old 05-21-2019, 07:15 PM
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They are the same as the intake manifold bolts.
90 300TE 4-M

Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
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A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
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90 300CE 104.980
Milled & ported head, 10.3:1 compression
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Old 05-21-2019, 07:18 PM
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Thanks for the info.

Can the coil cause misfire on one of it's cylinders but not the other? I have misfire on #1 an # 5 but not on 6 or 2. I'm not familiar with this engine so I went all in with parts roulette… injectors, coils and spark plugs.
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Old 05-22-2019, 06:58 AM
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This uses a " waste spark " system where each end of a specific coil has a spark plug. When one cylinder has an a/f charge on the compression stroke, the other is on the exhaust stroke both plugs fire.

Going from memory, the pairing should be 1 / 6 , 2 / 5 . 3 / 4. Is your 1 / 5 pairing a typo?

Be aware that just changing spark plugs can temporarily mask a failing coil so first swap coils and see if the problem follows. You don't have much choice to move plug wires around so use an ohm meter to test.

Another oddity I haven't figured out. At least in the aftermarket, the 97 C280 takes a different coil part number than the 97 SL320 / 97 E320.( or some similar odd split ) Both use the same basic M104 engine and both use the Bosch ME 2.0 / ME 2.1 computer.
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Old 05-22-2019, 03:49 PM
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Originally Posted by 97 SL320 View Post
Going from memory, the pairing should be 1 / 6 , 2 / 5 . 3 / 4. Is your 1 / 5 pairing a typo?
No it's not a typo. I have cylinder 1 and 5 misfire codes, confirmed by shutting off injectors with SDS. You are correct coil pairing is 1-6, 2-5 and 3-4.

My knee jerk reaction was to replace injectors, which at 135,000 miles probably not a bad idea regardless. I still have 1 and 5 misfire with new injectors so I ordered 3 new coils and 6 spark plugs. Wires look new but given what I learned here this will probably turn out to be bad #1 and #5 wires/ boots.

I also found some oil on spark plugs/ boots… mostly 1 and 5… which surly must be coming from spark plug hole seals under valve cover.

As much as I hate just throwing money/ parts at the problem… in this case, given the age and milage I don't feel too bad about it.
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Old 05-22-2019, 07:43 PM
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Yep, Having a good injector spray pattern can be an overall help.

Changing the coils / boots / plug wires seems to be required maintenance at the mileage you have. Between the SL and C I think I've changed 3 coils at 124,000 ish and 164,000 respectively.

Changing the valve cover gasket is super easy once you have pulled the coils. When you put the coil cover back on, watch the small white plastic vacuum line that runs down the passenger / exhaust side of the coil well. It is super easy to get this line pinched if the clips are broken and you will get an AIR pump trouble code. This line connects the diverter valve ( between the exhaust manifolds ) and the solenoid valve ( under the front plastic engine cover )

Early M104 engines had a EGR valve that hooked to one exhaust manifold and the cylinder head , the later ( 96? for sure 97+ ) had only the AIR diverter valve and an electric AIR pump.
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Old 05-23-2019, 07:24 PM
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Thanks for the tip, yes I noticed that vacuum line but wasn't sure what it is for… I'll be careful with it.

I don't like to use aftermarket parts with these kind of gaskets so I found Genuine MB (104-010-21-30) at my local dealer… opening bid from them $106.56, negotiated down to $62.00… still you've got to be kidding me. Well, that's before I asked for 12 bolt seals… $13.50 a piece, negotiated down to $7.00… holy ****, $84.00 for 12 rubber O-rings I could get for $10.00. I'm not even sure how important these bolt seals are but, I don't like to take chances with un-known aftermarket parts when labour is involved.

On my SL500 (M113) I've already replaced 4 coils before 100,000, I should probably replace remaining 4 (original MB) but, finding bad one on this engine is pretty easy so I'm not concerned.

Swapping coils on M104, to find a bad one, is like playing chess… screw it… 3 new ones and be done with it.

Spark plug wires for this 97 C280… I can't find Bosch set anymore, MB NLA… I only see Karlyn-STI set. Are these any good?

The wires I have in there are Bosch Ultra-Premium 7mm copper core. They look new, clean contacts. Resistance rated @ 2K Ohms… tested with multimeter @ 1.9K Ohms
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