Author Topic: 1975 450SE Big Service  (Read 7130 times)

TJ 450

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Re: 1975 450SE Big Service
« Reply #15 on: 29 November 2009, 08:59 AM »
Hmm, if it ran fine then it must be an electrical problem I reckon.
Good luck with the second opinion, but I hope the dealer services older models frequently, or they might not know what they're looking at. 8)

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

Big_Richard

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Re: 1975 450SE Big Service
« Reply #16 on: 29 November 2009, 03:04 PM »
injectors don't just decide to work randomly - theres 8 of them.

You'd have more chance in winning the lottery than getting 8 injectors to miraculously start working or failing all at exactly the same time.

This problem reeks of electrical to me.

Isn't there a ground connection to the injector harness that frequently goes bad ?

oscar

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Re: 1975 450SE Big Service
« Reply #17 on: 29 November 2009, 03:50 PM »
Damn good point.  There's two earth points for the injectors whereby the two banks are separately grouped and attached to the top of the manifold. So one dodgy earth would affect 4 injectors.  Look for the two gangs of light tan wires. Even if the bolts are tight, loosen them, clean the connectors and surfaces, reattach.  For the ECU I can't remember which pin or where the earth comes from or goes to.
FWIW, I doubt any of this has to do with the MPS unless it's a continuity problem to its contacts.   Inside the MPS the electrical components are easily tested with a MM and resistance ratings.  And there's no way it's a vac leak there. Once that issue arises there's no "comes and goes" aspect to it.

I was hoping someone was going to suggest an Italian tune-up.  Find your inner hoon brett. 8)  I don't blame you if your hessitant but little story, I just came back from a charged run down the highway, it's the first time I've reached my rev limiter. Usually I get a bit of smoke during high revs just before the gear changes but today I kept the foot to the floor on the kickdown switch switch and after 4 sets of changes from 1st to 2nd and 2nd to 3rd post rev limiter kicking in.  The thing stopped smoking during high rev changes, there's no smoke on the overrun and the motor sings and idle is smooth.  Incredible really.  It's as though the Fonz slammed his fist on top of the motor and said "eyyyyh" and all was well. :D




1973 350SE, my first & fave

brettj

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Re: 1975 450SE Big Service
« Reply #18 on: 29 November 2009, 05:06 PM »
I gave the motor an Italian tune up last week and unknowingly was followed by a state police officer who surprisingly did not pull me over! He must have been a fan of the W116!

I drove the car home from work today and it ran fine again! At a light the idle is still a bit rough but the sputtering issue didn't occur. I did not do any stop and go  driving though. When you start and shut off the car frequently within a short time frame that is when the warm stalling problem occurs and the rough idle issue seem to get much worse.  I also agree that perhaps there is an electrical problem but I'm also thinking that perhaps one or more of the injectors are sticking and the gunk clogging the injector may have burned off. Remember this car sat in my uncle's garage for three years rarely started. Maybe all the old crud in the gas tank clogged the injectors. Is that a logical assumption?

Here is a list of the motor related parts and services undertaken on my car:

Valve adjustment, compression test, all vacuum hoses, connectors and check valves replaced in engine bay, all three switch over valves replaced, new radiator hoses, breather hose near air slide, flame filaments, air slide, MPS replaced. New fan belts, spark plugs, spark plug wires, new distributor, distributor wire, rotor, points, distributor cap and coil and timing reset. New cold start valve, thermotine switch, water temp sensor, air flow sensor and all other related temp sensors replaced. New water pump, alternator, heater valve, air filter, oil pan and gasket, both valve cover gaskets, throttle control switch. New fuel pressure regulators, fuel pump, damper, filter and all braided hoses for the fuel system and new filler neck for the gas tank. New oil cooler liner lines for the transmission, trans tune up and filter and a new trans vacuum modulator valve.  New battery and all relay cubes replaced in the fuse box and under the dash. All fuses in fuse box also replaced. Throttle linkage  rebuilt and throttle body cleaned with throttle cleaner. New thermostat and coolant recovery tank, radiator cap.

I don't think I missed anything but there has been even more work done on the suspension,  steering and exhaust system of the car. So as you can tell, I hate to sell this car as its almost brand new!

Would you happen to have a picture of the electrical harness wiring you spoke about? Do I clean the connectors with regular Emery paper?

Thanks,
Brett
« Last Edit: 29 November 2009, 05:09 PM by brettj »

oscar

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Re: 1975 450SE Big Service
« Reply #19 on: 29 November 2009, 06:46 PM »
From your list ... "Throttle linkage rebuilt."  Maybe coincidence here and I'd hate to sound too optimistic but both groups of injector earth wires connect to throttle linkage brackets which connect to the manifold.  At least one bank and maybe both were taken off and reattached during the linkage rebuild. See below. PB turn away, I don't want you to see how filthy my 350 engine has become.  ;D

The bolts and injector earth wires are circled.  I'd loosen them, take them off, emery paper I'm not sure.  I would but that's just me.  I reckon maybe steel wool or a plastic scourer with WD40 would be less abrassive and protect any plating that might be on them that's supposed to improve electrical conductivity and also less abrasive on the manifold and brackets.  I don't think this will help the ongoing warm stall but hopefully will fix this other lack of power/stall issue.  Who knows, good luck. ;)  The rest of the harness
I'll have to look for pics and deal with that later.




1973 350SE, my first & fave

s class

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Re: 1975 450SE Big Service
« Reply #20 on: 30 November 2009, 02:14 AM »
Something else missing from your list.  Remove the battery, remove the battery tray, and underneath on the inner fender sheet metal is a screw terminal strip with a variety of lugged wires going to it.  Undo these one at a time, clean, reattach. 

'76 6.9 Euro, '78 6.9 AMG, '80 280SE, '74 350SE, '82 500SEL euro full hydro, '83 500SEL euro full hydro , '81 500SL

TJ 450

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Re: 1975 450SE Big Service
« Reply #21 on: 30 November 2009, 02:40 AM »
For contact cleaning, a pencil eraser is an invaluable tool. ;)

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

brettj

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Re: 1975 450SE Big Service
« Reply #22 on: 30 November 2009, 03:00 PM »
Thanks for the info and pictures. I'll give the contacts a cleaning and see what happens.

brettj

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Re: 1975 450SE Big Service
« Reply #23 on: 30 December 2009, 08:31 AM »
Just following up here. I cleaned the contacts and the car doesn't run much differently. I put in some fuel injector cleaner, took the car out on the highway and ran her at high speeds. The motor is running much smoother but is still rough at idle and once in a while still does the warm stall thing.

I spoke with Tom at the MB Classics Center. Explained my issues with this car and he suggested changing the spark plugs which I'm going to do and to change the fuel injectors. Tom stated that the injectors should be changed every 100,000 miles. My injectors are original and Tom feels that they are long over due for replacement. So I've broken the bank and ordered new injectors and everything that goes with them. Hopefully this make a difference. I'll keep you posted.