M129 unresponsive to tune up - PeachParts Mercedes-Benz Forum

Shab · #1 09-28-2006, 08:48 AM

Ok..1967 250 SE W111 coupe M129.

New plugs, wires, cap, rotor, points, condenser, air filter. Start her up, vroom, no problem. However, virtually no difference in running condition! Didn’t set dwell yet.

Old points were burnt and pitted, plugs fouled and spent, wires almost certainly originals, cap & rotor beat, condenser miserable looking and likely original as well.

While other things need attention, this should have produced some result at the very least yes? I know I need to change fuel filters yet and other chores but sheesh.

I did notice while running, if I remove the vac line from the distributor, absolutely no change in idle. Is this a clue to something? Seemed strange.

First thing I suspect is I am not getting robust fuel delivery and will have to test. Also a compression test. Cleaned up old plugs were jet black immediately yet bone dry after just a toodle around the block(4 0f 6) so I thought lousy spark. The other two looked same as when I cleaned them up.

Could the coil be suspect? It's looks to be the original black coil.

Any direction appreciated.

ggenovez · #2 09-28-2006, 10:14 AM

Hey Shab,

What is the running condition? what's happening exactly?

Also you mentioned that the points where burnet but didn't set the dwell. That's like your brakes are gone but didn't replace the pads...

To check the coil, remove a plug, attach it to the plug wire and make it rest on the head. then crank the engine and you should see a spark. Nice big blue is what you want.

Also, have you checked your valve clearances? I have a M130 engine that uses ball studs. when they go bad they loosen, make a clacking sounds and go lean.

Good luck!

68_280SE · #3 09-28-2006, 10:19 AM

Make sure the dwell and timing are set to spec as these MFI engines require them to be set just right for peak performance.

Check the operation of the mechanical advance inside the distributor by twisting the rotor clockwise and then letting it go. It should snap back to it original position. If it doesn't then the mechanical advance is sticking. There is a felt pad under the rotor that needs to be oiled periodically that keeps this from happening.

The vacuum retard on this engine only has a vacuum applied at idle when the throttle plate is completely closed. If somebody in the past tried to adjust the idle by adjusting the set screw the on venturi unit (throttle body), then the throttle may not be closing completely. The throttle plate must be completely closed at idle. This may cause the vacuum retard not to work. You may want to adjust the set screw on the venturi unit and adjust the all of the fuel injection linkage. Here is a link to some wonderful instructions on how to do this. http://pagoda113.com/eve/forums/a/tpc/f/3296041521/m/7246004272

Check and make sure that the cold start valve isn't leaking which is pretty common on older MFI engines.

Check to see if the thermostat in the Warm Running Device is working correctly. Remove the little air filter and then start the engine. You should feel air being sucked in and as the engine warms up it should decrease until the air stops. If it doesn't then the sliding valve inside is frozen or the thermostat is bad. I had to put a new thermostat in the WRD in my car to solve a rich running condition. Here is a like to the parts inside the WRD
http://www.sl113.org/forums/uploaded/ja17/200662802329_20046281523_InjPumpWarmUpDeviceParts_1.jpg

Since this is a M129 engine the fuel injection pump has on isolated oil supply. There is a small oil level dip stick on the backside of the pump near the idle adjustment screw. Check and make sure it has the correct level of oil. Too much or too little oil will interfere with the operation of the govener fly weights inside the pump

This is all of the information I learned while trying to get my M130 engine car to run really well and I hope it helps you!
John

Shab · #4 09-29-2006, 05:35 PM

Thanks for the info guys. I'll have a go at it this weekend.

68_280SE · #5 10-03-2006, 08:23 AM

Shab,

Any luck with the M129 engine tune up this past weekend?

John
68_280SE

Shab · #6 10-03-2006, 07:30 PM

Not yet. This past weekend was devoted to fall lawn care here in New England and at the wife's request, planting 150 tulip bulbs which next spring, we can tip toe through I suppose. I can however highly recommend the long handled bulb hole digger thingy. Best $8.00 I ever spent. Available at Lowe’s Home Improvement.

Hope to be left in peace in my garage this weekend...maybe.

Shab · #7 09-05-2007, 08:41 PM

Following up and reporting back on some instructions I received from A.D.

1) Did the CSV test, it was good.

2) Just did the fuel delivery test this evening, got 2 litres in 15 seconds.

3) Did valve adjustment, 003 / 007 all set.

4) Checked the thermo time breather on the MFI pump, functioning.

Oil change, filter, fuel filter in the engine bay.

Engine still running on the back 3 cylinders only.

Any ideas where to go next?

Tomguy · #8 09-05-2007, 09:45 PM

You didn't say you set your dwell, then timing. Remember, points changes will screw with your dwell, and a change in dwell WILL result in timing change. That 4° at the distributor your dwell might be off by? It's 8° at the crank. That's a heck of a lot to be off by, especially if it's on the bad (retard) side.

Aside from that, I don't know if you have done so or not, but have you removed your injectors and soaked them overnight in carb cleaner? You need to do that to remove varnish or blockages, even on MFI injectors. If any are rusted, that's a sign to replace them of course. Then check and make sure they all have a uniform spray pattern, and your fuel is being correctly and evenly distributed!

Shab · #9 09-05-2007, 10:50 PM

Thanks Tom. I did set the dwell/timing but now that you mention it, and how critical it is on these MFI engines it's worth revisiting.

I've been leaning at this point towards the injectors, so yup, time to pull them. Might even send them out but I'll clean first and see if that helps. I'm just praying the MFI pump isn't pooched.

I suspect blockage at the #1 injector in particular. It starts to weep at the pump after the car has been running a bit making me think it's right about the time the line to the injector is full of fuel going nowhere if that makes any sense.

Thanks again.

cth350 · #10 09-05-2007, 10:52 PM

always, always, always get the ignition "to spec" before worrying about fuel delivery.
That means, dwell, timing at speed (4,500rpm) and correct advance/retard setup is a must.

-CTH

Shab · #11 09-05-2007, 10:56 PM

Roger that.

Shab · #12 09-06-2007, 09:36 PM

Had my first go at pulling the injectors from the none firing cylinders in the M129. Soaking (3) for the night in cleaner. Look pretty fouled up as pictured. Any hints on testing? Anything one can do in the garage to see if they spray at all after being cleaned up?

Thanks!

cth350 · #13 09-08-2007, 09:18 PM

You might want to swap the three seemingly good ones for the others to see if the problem is truely the injectors.

There is a nifty hand tool for testing the injectors. If you're in NJ, I can tell you were to find one to play with at a friend's house.

In the mean time, just soak them in warm kerosene for a couple of days. Investing in a cheap ultrasonic cleaner would help too.

-CTH

Shab · #14 09-09-2007, 01:13 PM

Thanks, I think I have the injectors suitably cleaned up. I will do the swap if revisiting the ignition doesn't yield results. Thanks for the offer on the device but I'm up in Rhode Island. Much appreciated!

I just received the 2 CD workshop manual from MB. Fantastic value by the way.$27 all in. Print your pages, head to the garage. Smudge em up, print another set.

As the wise have mentioned here before, it specifically recommends going though the ignition and timing spec as the first step in troubleshooting suspected fuel issues on an MFI equiped M129.

From the manual..

Job # 00-18: "Before beginning to search for faults in the injection system, always check the ignition system."

bwostosh · #15 09-09-2007, 01:26 PM

sometimes the vacuum port gets clogged,
pull vac line and blow into throttle,
then suck to test vac diaphragm.
Either end can cause probs.

I have taken an extra hard junk fuel line and screwed the injector in and run the motor to test spray pattern Yes it will run rough on five cyls. but you can get a visual on the spray pattern and the potential drip after shutdown You can test all 6 nozzles this way to roughly eliminate problems. Otherwise a diesel shop can clean, test release pressure variation, and spray pattern. All must be within 5 lbs.