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Discussion Starter #1 (Edited)
Hello,

Ive been having major problems with my 300SL, its a M104 32 Valve with CIS fuel injection. Vehicle currently has 125,000 km. When I go to accelerate away from a stop the vehicle has zero power with the A/C on. It will not even get out of its own way when the AC is on, with it off it will move but then the no power problem is only intermittent. I have taken the throttle actuator and throttle position sensor out and looked at all the wiring and it looks great! This car doesnt have the throttle actuators like the M119 engines or later M104 where the throttle motor is on the side of the throttle body. This car has a stand alone actuator under the intake manifold with a linkage that goes out to the throttle body. That said when the problem acts up its as if im not giving it any throttle when I go from a stop I have to put the pedal to the floor so it can crawl through the intersection. Even when parked and revving the engine up with the linkage under the hood it takes a long time to rev up. Its as if something is holding it back. I had a code for oxygen sensor and replaced that today and it didnt help one bit. Ive tested EHA, and the potentiometer, both are well with the specifications range. Ive checked the distributor cap, rotor and insulation piece behind the rotor for cracks or carbon tracking and nothing is to be found. Ive tried new coil and spark plugs but no luck!

Parts that have been replaced
Fuel Injections
Camshaft position sensor
Distributor Cap + Rotor
Coil
Spark Plugs
Oxygen Sensor
 

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2009 S550, 1973 Avanti II, 2008 Silverado LTZ
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I had the exact same problem with my 91 300SL with the 104 motor. The bad news is, I never found the problem! I changed injectors and thought that it helped, but it didn't cure it. It would do it sometimes with the A/C off, but with the A/C on it was just plain dangerous!
I suspected the fuel distributor, but never did confirm that, I just sold the car instead.
I've heard this complaint enough times to think there is an inherent problem with that model, but I've never heard a good solution for it.
 

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Discussion Starter #3
Oh god, well I like the car, I just want to pin point the problem and not keep throwing parts at it, could be EZL or main ECU for what I know. I do have this mysterious 2 pin plug by my fuel distributor with no where to go. I find this very odd............This connector looks like it piggy backs the EHA too...
 

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Greek God of the R129
SL500-500SEL-190E
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Put a fuel gauge on, check for pressure and volume.
I suspect regulator, fuel pump problem.
Could also be a fuel filter. ;)
Tap on the MAS module see if it reacts.

Regards,
aam.
 

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2005 SLK350, 91 300SL with Pano Top, 04 S500, 2015 Tesla Model S
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2,084 Posts
A 300Sl straight six has 24 valves.
I fought this same problem 3 years ago for over two months. After spending lots on parts and replacing every sensor under the sun it turned out to be a frazzled EZL.
And in hindsight it was my own fault, I charged the dead battery without disconnecting it first.
 

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Discussion Starter #6
checked fuel pressure, pressure is good and doesnt fluxuate when the problem is there. Problem goes away if you pull over and cycle key - EZL would make sense - any way of checking something like this?
 

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2009 S550, 1973 Avanti II, 2008 Silverado LTZ
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mrelbe, I checked out some of your adventure in the Benzypaloosa. Looks like a good (if somewhat wet and chilly) trip!
 

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Discussion Starter #9
Im starting to think it is the EZL but correct me if im wrong but the ezl is designed to retard timing during the shifts, when the car acts up the shifts are definatly harder than usual. I will price out a ezl tomorrow, any checks i rm on this ezl?
 

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2005 SLK350, 91 300SL with Pano Top, 04 S500, 2015 Tesla Model S
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Try to find a good used one. When you install it, make sure that you have a good layer of thermal compound on the back to make contact with the inner fender metal to dissipate heat.
 

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Discussion Starter #11
hi, i replaced the main coil wire a couple weeks ago now, it seems better but no where near 100%. the complete falling on its face as if i wasnt even pushing the pedal hasnt appeared but the poor throttle input is still there. I cant seem to find a used EZL, is there any place that rebuilds them? I took it out a couple weeks ago just to inspect didnt see anything obvious when I put it back in it ran great for about a day then started having problems again. Ive also now noticed when it acts up its as if it surges ever so slightly around 2-2500 rpm right when the trans is about to shift like the EZL is trying to attempt to retard for shifting but it doesnt know what its doing? Some very very odd symptoms, I almost wish something would just fail so I dont end up thowing parts at it...
 

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Greek God of the R129
SL500-500SEL-190E
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checked fuel pressure, pressure is good and doesn't fluctuate when the problem is there. Problem goes away if you pull over and cycle key - EZL would make sense - any way of checking something like this?

I found pressure to be good & doesn't fluctuate?
Good as what?
What was the pressure and volume?

What happens under load?

Is the vacuum advance working???

Want help, provide the WHAT'S...

Regards,
aam.
 

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Discussion Starter #13
ahh, i will have the re-check fuel pressure to get the exact numbers. Another small detail ive noticed when the problem happens ill be cruising along at part throttle maintaining a consistent speed the fuel economy gauge will read 10l per 100km, then out of no where the RPM's will decrease ever so slightly and the economy gauge reads that im getting 20km per 100km so now it feels like the engine is under excessive load and the economy gauge is pinned to the right as if im at wide open throttle I have to give it more throttle to maintain that speed I was travelling at. This is all while the climate control is on EC or off. If i put it in neutral shut off the key and re-start sometimes its back to normal 300SL performance other times the problem wont go away. I did notice when i had the fuel pressure gauge hooked up and driving the car i would have the same thing happen but fuel pressure would not fluctuate i just cant remember what those numbers were. I will hook the gauge back up later and drive to and from work with it on and see what happens.
 

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Discussion Starter #15
okay well what ever is going on its getting worse. I'm thinking its an EZL I had the problem act up when the car was in park and if i increased RPM's to 2000RPM I could see with the hood open the engine shake back and forth and feel/hear the misfires coming through the exhaust. If i increase engine speed via the linkage under the hood, rev engine to 2000rpm and unplug the vacuum advance line going to the EZL nothing happens. I then shut the car off, re-start and make sure that it isn't misfiring at 2000RPM I then try again, disconnect vacuum advance and sure enough RPM's decrease not sure by how much but its noticeable. I'm getting vacuum with or without the problem so its not a vacuum leak there is something wrong with this EZL. Just took the car out for a 30km drive along the highway WOT from a stop to 120KPH acceleration is NOT smooth what so ever. Engine hesitates can feel the engine struggle then comes back to 3/4 power then struggle again then back to power. This all happens between 5000-red line do to this the shifts are horrible!!! Im trying to locate another EZL but this is very very hard. Dealer wants HUGE money for it.
 

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Discussion Starter #17
okay, thank god a local shop had a M104 EZL which is identical to mine. The car runs MUCH better...so far anyhow. I put a nice layer of electric grease on the back so no way to over heat. Full throttle acceloration is much improved except for that 5200RPM blip...next im going to steal the cam advance mechanism off my C220 see if it helps. Both part numbers are the same already verified that.
 

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Discussion Starter #18 (Edited)
Okay swapped cam adjuster mechanism, it seems slightly better the C220 i stole it off of has around the same KM as my SL, when i took my SL one off i noticed the plug was full of oil, looked on the back of the adjuster and there is no silicone there what so ever, i believe someone has been in there before from the factory they had a ring of silicone around the magnet portion. I will double check fuel pressure tomorrow but can you guys think of anything else that would adjust around that rpm 5000-5500 RPM. Would EHA adjust pressure?

Doing some reading as well and maybe i should replace the crank position sensor. Correct me if im wrong, CPS sensor takes pulse readings for the ME, fuel injection system. Maybe its having a problem around that RPM range.
 

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Discussion Starter #19
Okay problem is back, car is sluggish! I drove a 1992 300SL same M104 as mine same amount of miles and his car felt like driving a new car. The power was incredible. The car actually felt light felt like how a SL is supposed to feel. The acceloration seemed effortless. Ive tried a good used EZL that made it slightly better but not fixed, I tried a cam advance magnet which needed replacing anyhow due to oil leaks and that didnt make a difference either. Ive tried a new EHA valve and that didnt make a difference either. Ill have to check fuel pressure tomorrow. I can get the problem to really act up if i WOT around 50KM so it down shifts to second gear, once it shifts it hesitates then has power to accelorate. :mad::mad::mad:
 

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I feel your pain! That's why I eventually sold my 300SL and bought my current SL500. It cost me $2000, but I upgraded by 7 years and 2 liters!
Well worth it, in hindsight!
 
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