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Discussion Starter #1
1989 300TE / M103 with 400K+ miles starts & runs perfect but after a while starts losing power under load; will rev fine and you could drive it home by using lower gears. Initially a year ago it would start losing power after maybe a half an hour; as of this weekend it was within 5 minutes! I pulled it into the garage assuming I could spot something but there were no obvious loose wires etc. Went to back it out and it spun over with some almost backfiring but refused to start. You would swear it had jumped timing...... but it had a new chain, tensioner and guides a few years back - no way. Finally coasted it out for the night. Next morning I go out to it and it starts right up and runs perfect so I park it well out of the way. Over the time this condition had been progressively getting worse I have replaced the cap, rotor and wires with new (REALLY needed it), swapped out the coil and the ICM with used parts (no change) and finally last weekend the fuel pump with a new Bosch (@ 400K miles it is probably due?) just prior to the final test drive. Do the cam / crank sensors fail in a heat related manner? Sure seems electrical in nature. We own 2 SLK's (1 manual / 1 auto), a '90 560SEL, '74 450SLC and a '67 230S 4-speed manual. The wagon is by far our highest mile car and the dogs will never allow us to get rid of it. Any thoughts would be appreciated; I've been doing all my own 'Benz work for 40+ years and have not come across this one; until now!
 

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Is this a model with a FUEL DISTRIBUTOR? Fuel pressure loss?
Does it burn oil? Plugs looked good?
Did you happen to run a full compression check, hot, cold, wet, dry?
Fuel filters clogging? Changed the fuel accumulator with the pump?
The misfiring sounds like Cap/Rotor, moisture issue..
 

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It's a M103 from 1989, so of course it has KE Jetronic a.k.a. fuel distributor.

First place is to start taking readings from all 3 critical fuel pressures. Without proper pressure, Jetronic no workie.

Based on the description though, it sounds like ignition with noise supressor disc at the top of my suspect list followed by cap and rotor. Ditto on verifying it has the updated style rotor driver arm.
 

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Discussion Starter #5
Is this a model with a FUEL DISTRIBUTOR? Fuel pressure loss?
Does it burn oil? Plugs looked good?
Did you happen to run a full compression check, hot, cold, wet, dry?
Fuel filters clogging? Changed the fuel accumulator with the pump?
The misfiring sounds like Cap/Rotor, moisture issue..
Compression / vacuum all good; will check fuel pressure next. Gotta get my test kit back.....
 

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Discussion Starter #7
It's a M103 from 1989, so of course it has KE Jetronic a.k.a. fuel distributor.

First place is to start taking readings from all 3 critical fuel pressures. Without proper pressure, Jetronic no workie.

Based on the description though, it sounds like ignition with noise supressor disc at the top of my suspect list followed by cap and rotor. Ditto on verifying it has the updated style rotor driver arm.
Noise suppression disc?? I did just buy a crank position sensor again on the premise at 400K it can't be a waste of money......
 

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Discussion Starter #9
Crank sensor on the way; will probably do the cam sensor as well. The car just runs so perfectly even for a while after the engine was at full temp for me to believe the fuel system was the culprit. But hedged my bet with the new fuel pump anyway. BTW, I have fuel pressure test equipment but I figured this would be easy to figure out...... Gauge set loaned out right now so if the crank sensor changes nothing I will get it back and confirm pressures when hot.
 

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I'd go with what sbaert suggested, the noise suppression disk in the distributor, they fail, and hte spark starts to jump across them. The EZK ignition modules can overheat when things get warm, especially if not properly heatsinked to the fender..
 

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Discussion Starter #11
Did 2 different ignition modules (and coils!) w/o change. Based on various others symptoms experienced from crank shaft position failures I'm betting on that next. My 40+ years experience has never heard of distributor cap, wires, plugs ever failing progressively sooner each use over a period of time especially if they are OEM parts less than a year old with the exception of a condenser in my MGA waaaaay back when. But you never know......
 

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...My 40+ years experience has never heard of distributor cap, wires, plugs ever failing progressively sooner each use over a period of time especially if they are OEM parts less than a year old with the exception of a condenser in my MGA waaaaay back when. But you never know......
Then you've got a lot to learn on these cars. These cars are hypersensitive when it comes to having clean up power and good ignition.

More importantly, OEM is not the same as OE. Case in point, a Bosch distributor cap and rotor will fail very quickly on these cars while the genuine MB branded version (also made by Bosch) goes for years without a hiccup.

Also, you could have at least taking the resistance value off your crank sensor to determine if it was suspect or not.
 

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Did 2 different ignition modules (and coils!) w/o change. Based on various others symptoms experienced from crank shaft position failures I'm betting on that next. My 40+ years experience has never heard of distributor cap, wires, plugs ever failing progressively sooner each use over a period of time especially if they are OEM parts less than a year old with the exception of a condenser in my MGA waaaaay back when. But you never know......
What gets hot when the engine warms?
Catalytic converter- when is runs poorly rev the engine to see if exhaust is fully open.
Distributor cap - OEM isn't MB. I've read about cracked caps right out of the box
Coils - heat kills coils or whatever electronic device is used in these M103 engines(ECM?).
EGR system - Could there be something in the system causing this symptom?(IDK)
Fuel Distributor - Seals, gears/bushings(?), leaks?
Radiator - sensors tripping, causing changes in air and fuel delivery.
CPS - The redneck check for the Crank Positioning Sensor is to pour cold water on it when it's hot, but that's in a no start emergency situation from what I read.
Injectors - Seals get hard and suck air around the injectors.

The 400K miles is the mystery input. Not a lot of ppl drive a vehicle for that many miles, and everything WILL fail eventually, especially crazy things like critical small parts in the fueling system, valves, seals and such.
Fuel - Air - Spark... sounds pretty simple till you add sensors that control all of that.
 

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Discussion Starter #14
What gets hot when the engine warms?
Catalytic converter- when is runs poorly rev the engine to see if exhaust is fully open.
Distributor cap - OEM isn't MB. I've read about cracked caps right out of the box
Coils - heat kills coils or whatever electronic device is used in these M103 engines(ECM?).
EGR system - Could there be something in the system causing this symptom?(IDK)
Fuel Distributor - Seals, gears/bushings(?), leaks?
Radiator - sensors tripping, causing changes in air and fuel delivery.
CPS - The redneck check for the Crank Positioning Sensor is to pour cold water on it when it's hot, but that's in a no start emergency situation from what I read.
Injectors - Seals get hard and suck air around the injectors.

The 400K miles is the mystery input. Not a lot of ppl drive a vehicle for that many miles, and everything WILL fail eventually, especially crazy things like critical small parts in the fueling system, valves, seals and such.
Fuel - Air - Spark... sounds pretty simple till you add sensors that control all of that.
Logical Position I agree with you 100%! at 400k+ if this car crumbles into a heap and smolders it has done well. But it won't 'cause we will not let it; FYI the cat was replaced a couple years ago as was the entire exhaust. We have a '98 SLK230 closing in on 300K that we have had since 68K miles. We pile miles up out here in the upstate S.C. woods.
To sbaert this is the second 124 we have had; the other was a 5-speed manual sedan. Did the cam chain / valve seals etc. a few years back and the car still does 100 smoothly shifting just before the limiter. Head has never been off and does seep a little at the front and bearings / rings untouched from new as far as I can tell. It was bought with 200K on it. I appreciate that I always have a lot to learn so thank you.
 

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My original bought TE once closer to 300,000 developed a pretty long list of to-do projects. Enough so that it's value as a daily driver was diminishing. Fortunately for me, another TE of the same yr came up for sale and had only 100,000 miles. I'm having so much fun with this car!

My ex put most of the miles on the original TE and enjoyed it, so now it's my turn with a fresher TE. Point being that you can keep these cars going indefinitely, but with all the ones still out there it's kinda silly (and given their diminished value).

You definitely have a heat related problem. The suppression disc in the dist could be the culprit and/or the crank sensor.....although with the crank sensor and heat related issues, it just becomes a no-run scenario if it's failing.....then cools down, starts again, gets hot, fails and repeats the cycle.

Sounds very much like when your engine gets warm, some spark related current is going to ground. If you've tried other EZL's then that's probably moot.

I think an OE dist suppression disc is about $50. You could pull over when the car is acting out and test the resistance (at the EZL) of your crank sensor and report back.

Kevin
 

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Discussion Starter #16
My original bought TE once closer to 300,000 developed a pretty long list of to-do projects. Enough so that it's value as a daily driver was diminishing. Fortunately for me, another TE of the same yr came up for sale and had only 100,000 miles. I'm having so much fun with this car!

My ex put most of the miles on the original TE and enjoyed it, so now it's my turn with a fresher TE. Point being that you can keep these cars going indefinitely, but with all the ones still out there it's kinda silly (and given their diminished value).

You definitely have a heat related problem. The suppression disc in the dist could be the culprit and/or the crank sensor.....although with the crank sensor and heat related issues, it just becomes a no-run scenario if it's failing.....then cools down, starts again, gets hot, fails and repeats the cycle.

Sounds very much like when your engine gets warm, some spark related current is going to ground. If you've tried other EZL's then that's probably moot.

I think an OE dist suppression disc is about $50. You could pull over when the car is acting out and test the resistance (at the EZL) of your crank sensor and report back.

Kevin
My original bought TE once closer to 300,000 developed a pretty long list of to-do projects. Enough so that it's value as a daily driver was diminishing. Fortunately for me, another TE of the same yr came up for sale and had only 100,000 miles. I'm having so much fun with this car!

My ex put most of the miles on the original TE and enjoyed it, so now it's my turn with a fresher TE. Point being that you can keep these cars going indefinitely, but with all the ones still out there it's kinda silly (and given their diminished value).

You definitely have a heat related problem. The suppression disc in the dist could be the culprit and/or the crank sensor.....although with the crank sensor and heat related issues, it just becomes a no-run scenario if it's failing.....then cools down, starts again, gets hot, fails and repeats the cycle.

Sounds very much like when your engine gets warm, some spark related current is going to ground. If you've tried other EZL's then that's probably moot.

I think an OE dist suppression disc is about $50. You could pull over when the car is acting out and test the resistance (at the EZL) of your crank sensor and report back.

Kevin
Kevin; you completely are on the same thought process as me. Interesting that our wives really love the wagons. I have the a/c hot-wired but all else still works as intended. Perfect dog car and a blast when 3 motorhead couples want to go somewhere in 1 car. I know this thing so well (no real rust) and have replaced most consumables so it has been extremely reliable over the years with reasonable effort. We have looked at others but most have been twin cams or so expensive it wasn't justifiable enough considering our other 11 cars we regularly drive. It also looks great in smoke silver over parchment with CLK 16" alloys.
 

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Kevin; you completely are on the same thought process as me. Interesting that our wives really love the wagons. I have the a/c hot-wired but all else still works as intended. Perfect dog car and a blast when 3 motorhead couples want to go somewhere in 1 car. I know this thing so well (no real rust) and have replaced most consumables so it has been extremely reliable over the years with reasonable effort. We have looked at others but most have been twin cams or so expensive it wasn't justifiable enough considering our other 11 cars we regularly drive. It also looks great in smoke silver over parchment with CLK 16" alloys.
Yeah, this one is Ice Blue Metallic and the paint fading over the yrs has only rendered the color more unusual and chameleon-isk. Sometimes green, sometimes blue depending on the light/shade effect.....very easy on the eyes...lol.

I had real 'adventures' in the old white TE. I'd get a notion to travel across country somewhere and just do it. My kids got to the point where they'd say, "Uh oh, dad's getting ready to go across country again in the wagon." They were raised in that wagon too. As sentimental as I was about the old bird, when this car came along I happily jumped ship....especially given the long to-do list on the original TE. The old girl is funneling her good parts into this one....it's a win/win.

Someday I'll splurge on some decent rims. The previous owner had some more modern rims he tried to sell me, but I didn't like them.

The twin cam TE's are better engines, but they require more knowledge to keep right. However, the HFM can work with OBD II diagnostics at least. With the TE's 3.27:1 rear, the M103 skips along nicely in town....never been a problem. Personally, the face-lifted wagons don't do anything for me. I like the lines right before those.

So yeah.....I know just where you are with your car. Familiarity with the M103 speaks volumes. The engineers figured this to be a 450,000 mile gas car with routine maintenance and a head job around 250,000 miles.

Kevin
 

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Discussion Starter #18
Changed the CPS out, let the car run for 10+ minutes checking for air leaks, loose connections etc. revving it up sounding perfect as usual then backed it out to take it up the steep driveway then up the mountain. It couldn't even make it up the driveway!. Coasted it back down and idled it back in the shop. Re-read everything you guys said drinking a couple beers while watching football in the shop and decided I would take off the recently new distributor cap off and confirm it was still looking new. Guess what? The inside of the cap had a perfect clear coat of STP consistency oil. Clean as can be. All the contacts were carboned / corroded over as was the rotor. I first liberally sprayed everything down with carb cleaner spray then used a small wire wheel brush (14mm dia.?) in the Dremel tool to clean all the contacts. After that everything was again liberally sprayed down with electrical contact cleaner then blown out with compressed air. Put it all back together with only minor irritation getting the fan clutch bolt back in (maybe that beer?) then took it for another attempt at a blast up the mountain. Perfection; problem finally solved. Pulled it back in the shop for one last look for anything I forgot like allen wrenches on the radiator top / tool tray and saw a bunch of oil on the floor and on the RH side of the engine compartment. The self leveling suspension hose had sprung not 1 but 2 leaks..... Oh well. So I assume I will need to replace the oil seal on the distributor shaft and now from evening reading on this site have my suspension hose rebuilt as it appears you cannot get them, at least not at a reasonable price. So Real1shepherd wins as the closest diagnosis and if you tell me where to send it you can have a slightly used suspension hose! Thanks everybody!
 

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There have been a LOT of running issues solved just by looking inside the distributor. So many in fact, that I just assume everyone checks in there first for power related issues. Especially since the Spanish caps carbon track and are known to give problems......the dealer cap is over $300.....both are Bosch.

I had a long thread I started on replacing that high pressure SLS/4Matic hose. I'll warn you up front that you may get some noise from using the Gates hose if you rebuild the hose yourself. Some do, some don't. So in the end, you might wanna consider the OE hose for around $100 last time I checked. I think the hydraulic place charged me almost $50 for the Gates hose blank.

Kevin
 

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Discussion Starter #20
There have been a LOT of running issues solved just by looking inside the distributor. So many in fact, that I just assume everyone checks in there first for power related issues. Especially since the Spanish caps carbon track and are known to give problems......the dealer cap is over $300.....both are Bosch.

I had a long thread I started on replacing that high pressure SLS/4Matic hose. I'll warn you up front that you may get some noise from using the Gates hose if you rebuild the hose yourself. Some do, some don't. So in the end, you might wanna consider the OE hose for around $100 last time I checked. I think the hydraulic place charged me almost $50 for the Gates hose blank.

Kevin
I'd pay the $100 just to save the time. A thread I was on said it was like $500 Euro...... NO! Wouldn't happen to have a part# and a source handy wouldja??

Mark
 
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