W116 M110 engine cranks wont fire - PeachParts Mercedes-Benz Forum

MB_Mike · #1 02-27-2011, 05:15 PM

My euro spec 280SE W116.024 with m110 engine has not been driven in 4-5 days. Today I went to start it but it only cranks.

1. I put a couple gallons of gas in to be sure the fuel gauge wasn't grossly off (showed 1/4 tank)

2. changed the cap and rotor with ones off a running 280.

3. changed plugs for W9DC (just did this about 4-5000 miles ago with NGK equiv.) all but one were black and sooty.

4. couldn't hear fuel pump running so I swapped it out with the other running 280 fuel pump (still couldn't hear it and reused crush washers so fuel was spraying out)

5. checked the fuses, just because.

The last few months my starter has developed a terrible flat spot (it has gotten progressively worse) and it now takes many many turns of the key to get it to catch. Also most recently I have had to pump the accelerator a little bit to get the car to fire.

I am sure there is lots of info on this site, but truthfully, I am exhausted from laying out in the cold ALL day and troubleshooting what I have so far.

Thanks in advance for any suggestions

thorsen · #2 02-27-2011, 05:51 PM

Whenever I am in that position I spray some starting fluid and try to start it. If it starts and runs briefly, that means the ignition system is working and you need to look at the fuel system. If it does not try to start, I immediately suspect the ignition system.

WANT '71 280SEL · #3 02-27-2011, 05:52 PM

If you can't hear the fuel pump running, and you know it works, but it's not coming on, then you need to look into the FP relay. Good news is that it should be easy to locate and R&R. Often it just needs to be resoldered or have the contacts cleaned.

Best Regards,

David

P.S. Sorry I don't know where the relay is on this car though I'd imagine it's on the firewall like most other Mercs.

cth350 · #4 02-27-2011, 07:23 PM

Ditto what Thorsen said.

I have a fuel pump relay bypass for situations like this (presuming starter fluid gets you running for 2 seconds). Basically 20 feet of wire with a fuse and a momentary switch (dead man style) in-line on the +12 wire. One end of the wires has aligator clips for the battery and the other end has eyelets for the fuel pump.

With the M110 motor the fuel pump is cut off based on wiring under the hood. If you disconnected the wires at the fuel distributor (or have some other wiring fault), the pump won't run.

-CTH

MB_Mike · #5 02-27-2011, 07:40 PM

I just went out and swapped fpr's and still nothing. I didn't spray starter fluid in the intake but my brother did spray carb cleaner I think, lol. IDK if that is supposed to do anything but it didn't.

Hmmm. What's next?

79Mercy · #6 02-27-2011, 08:01 PM

Pull off the number 1 spark plug wire, stick a plug in it, ground it to the motor and crank the engine. Do you have any spark??

alabbasi · #7 02-27-2011, 08:24 PM

Mike,

There are a couple of things that you can try here.

For fuel:

1) Pull off the fuel line that feeds the fuel distributor (17mm) and direct it to a bottle.
2) Turn the ignition on and you should see a shot of fuel come out of that line.

If not, then the fuel pump is not working. Check either the pump or the relay.

Ignition:
1) If the system is getting fuel, then the next step is to check the ignition using the instructions that 79 Mercy provided.

Good luck.

79Mercy · #8 02-27-2011, 08:56 PM

Another thing to remember on this car is that your fuel pump doesn't come on when you flip the key on. The pump only gets power when the starter is engaged, the the starter is engaged the pump continues to run...

alabbasi · #9 02-27-2011, 08:58 PM

I'm not sure about that. The pump engages as soon as I turn the ignition on with the 6.9 and with the SL's. On the SL's, there was a blue plug mounted near the air flow meter. If you disconnect it, the pump will run continuously.

79Mercy · #10 02-27-2011, 09:12 PM

Thats d-jet. The fuel pump runs for about 3 seconds when you first flip the key on.

K-jet is different, it only runs when the starter is engaged.

alabbasi · #11 02-27-2011, 10:30 PM

Unless the ones that I have messed with have been rigged differently, that's not the case. I emptied out my gas tank in the 6.9 about a week ago after the check valve on the end broke by but turning the ignition on and letting it all pump out.

On the older SL's, there is that blue plug which once disconnected, will run the pump continuously.

kraakevik · #12 02-28-2011, 10:13 AM

With the "flat spot" on the starter the long timing chain on the M110 may have jerked around enough to have skipped a cog or two on the exhaust or intake camshaft.

After all else you've already checked I'd suggest you take off the valve cover and rotate the engine carefully clockwise as you face it with a socket wrench on the crankshaft nut and make sure the camshaft index marks line up precisely at TDC.

If they're out there's just enough room to readjust the chain on the sprockets if the cam fingers and chain adjuster are removed.

I've had good luck in removing the starter, rotating the crank fifteen degrees or so and replacing the starter to ensure that the ring gear has fresh teeth to mesh on the compression stroke.

Good luck and let us know how you fare, if you would

Tim Kraakevik
kraakevik@voyager.net
Four M110's