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1996 (01/96) Mercedes Benz E320 W210 Inline6 140,000 miles
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Discussion Starter #1
Hello! My 1996 e320 cranks but won't start. Thanks to these forums, I've been able to troubleshoot and fix several issues, but now i am stuck. I've replaced the original fuel pump and filter, and just recently replaced the crankshaft position sensor. All parts replaced were OEM except the MAF which i also replaced. I've also resoldered the relay control module. Im getting 60 psi on the fuel rail, i can see the 5th relay(fuel pump) on the RCM engages when i crank. The car will start sometimes but immediately shuts down, or it will shut down a block down the road. I did do 2 battery resets(unplug positive cable for 2 mins) and a trans reset(key 2nd position, hold gas pedal) . I know i need to test for spark to make sure its not faulty wires. Any ideas out there on what this might be. I can't tell you its been serviced correctly, but when it runs, its a very nice smooth ride, and alot of the parts on the car are original. I cant see any damaged wiring anywhere. The RCM i resoldered is 23yrs old and may need to be replaced. The copper relays are a little dull and wore out, but they work. I'm hoping there is something i am missing before i buy a new RCM.

Thanks for your time!
Tim
 

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1998 E320 base sedan @ 160kmiles
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6,011 Posts
I would buy a new relay module (K40). It is not only the solder joints that go bad, it is known that the contacts can wear out on the engine control and fuel pump relays. Maybe if you can get a used one from a car that is known to have run fine.

Sometimes the crankshaft position sensor wire (coaxial cable) gets damaged due to engine heat, insulation degradation issues over time.
 

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1996 (01/96) Mercedes Benz E320 W210 Inline6 140,000 miles
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14 Posts
Discussion Starter #3
Ty mrboca. My original problem was stalling after it sat too long in traffic or waiting in a fast food line too long. Its intermittent. I have checked the cps wiring and no visible damage. I will search for a new k40 relay and update what happens. I've learned so much from these forums. Thank you!
 

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1996 (01/96) Mercedes Benz E320 W210 Inline6 140,000 miles
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14 Posts
Discussion Starter #4
Rcm ordered, and i DID check my RCM again. I cleaned the little contacts on the relay with emery cloth and added a little more solder to the back and it fired right up at least to get it home. Fuel pump is 5, ecm is 3? Just curious which ones do what. 6 is pretty shiny and i was thinking of trying to switch them. 6 auxillary fans??
 

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1998 E320 base sedan @ 160kmiles
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6,011 Posts
Rcm ordered, and i DID check my RCM again. I cleaned the little contacts on the relay with emery cloth and added a little more solder to the back and it fired right up at least to get it home. Fuel pump is 5, ecm is 3? Just curious which ones do what. 6 is pretty shiny and i was thinking of trying to switch them. 6 auxillary fans??
The attached shows the schematic for your K40. Relays K3 and K2 (rightmost in the diagram feed the ECU (N3/4).
 

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Registered
1996 (01/96) Mercedes Benz E320 W210 Inline6 140,000 miles
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14 Posts
Discussion Starter #6
I replaced the K40 RCM with same issues. Sometimes fuel pump turns on and sometimes i have no spark.

I've replaced...
Fuel pump and filter
Maf sensor
K40 relay control module
Crankshaft position sensor

Symptoms are intermittent stalling not starting, could be cold or hot, during troubleshooting, sometimes no spark or sometimes no fuel pump. I got 60 psi at rail after replacing pump, ive gone through 3 different cps. (First one was not oem) i did a throttle reset and battery reset. It started right up, drove around the block with new life in it. Parked it and 10 mins later it wont start. Fuel pump didnt turn on right away, when it did finally turn on no spark.
 

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1996 (01/96) Mercedes Benz E320 W210 Inline6 140,000 miles
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14 Posts
Discussion Starter #7
Troubleshooting is leading me to cps again. What would keep killing the cps?
 

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1998 E320 base sedan @ 160kmiles
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6,011 Posts
Troubleshooting is leading me to cps again. What would keep killing the cps?
Wiring / connector issues, possibly. Make sure that the wiring is in good shape (coax) and the connectors at both ends are fine and no moisture. Make sure that the moisture seals are in good shape in the connector(s).
 

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1996 (01/96) Mercedes Benz E320 W210 Inline6 140,000 miles
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14 Posts
Discussion Starter #9
I noticed my coil packs are a little rusty and worn out. Spark plugs look good. Is there a smart way to troubleshoot this? I followed the wiring back to the RCM and besides a little dirt, it all looks good. I double checked the cps and it still looks brand new. When you say coax, do you mean the connection at the cps?
 

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1998 E320 base sedan @ 160kmiles
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6,011 Posts
I noticed my coil packs are a little rusty and worn out. Spark plugs look good. Is there a smart way to troubleshoot this? I followed the wiring back to the RCM and besides a little dirt, it all looks good. I double checked the cps and it still looks brand new. When you say coax, do you mean the connection at the cps?
Yes, the cps wiring. Someone had the same problems as you did, and it turned out to be a damaged wiring between the CPS and the ECU. The CPS wiring to the ECU does not go to K40 relay module. If the car runs fine when it starts, it has nothing much to do with the coils and spark plugs. The ECU looks for valid impulses from the CPS. If the signal is weak or intermittent, it will not let the fuel pump / injectors and ignition to fire up.
 

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1996 (01/96) Mercedes Benz E320 W210 Inline6 140,000 miles
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Discussion Starter #11
Ok I'm going to focus on that wiring. Can i throw a multimeter on it to test if it is getting signal? I followed it to a connection in the spaghetti behind my k40 relay, then it goes down. I don't see any visual signs of deteriating. Should i unwind the black fabric tape? Could the short be deeper?

In the meantime, I'm going to just order the cps wiring.
 

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1998 E320 base sedan @ 160kmiles
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6,011 Posts
You can measure the resistance of the CPS which should be around 800 to 1200 Ohms, and the signal from it should be more than 2.5V with Voltmeter SET TO AC scale when cranking.

Typically the measurements are done from the ECU connector end (where the CPS wiring terminates at the ECU connector 1 (pins 29 and 30 if your car was manufactured before 6/96). Please provide the manufacturing data from the driver door pillar.

I would jiggle the CPS wiring and see if it makes any difference in starting. I would not replace it without confirmation that it is the problem, as it may cause more issues when you handle the very old and fragile wiring.

If you have a scanner that shows the rpm, I would monitor the rpm during cranking. It should read more than 200. The ECU gets the rpm data from the CPS signaling, but I am not sure if the rpm data is available during cranking. it is worth the check.

BTW. Many of the problems are due to weak battery conditions. Have you recently got the battery checked ? This is not just measuring the battery voltage but checking the actual capacity with a proper meter.
 

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1996 (01/96) Mercedes Benz E320 W210 Inline6 140,000 miles
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Discussion Starter #13
Ok that helped out alot. I did find a short in the cps wiring near the engine mount, but i cannot find a replacement online. I think you are right about a weak battery. That will be the next on my list.

Where can i find cps connector wiring? Nothing on ebay, rockauto, or amazon.
 

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1998 E320 base sedan @ 160kmiles
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6,011 Posts
It is a coax cable. I do not think it is sold individually, maybe as part of an upgrade harness. You may try junk yards, or try to repair it (splice a new cable, end to end). The wire must have insulation that can withstand heat and chemicals (oil, ATF, antifreeze, etc, in case of a spill).
 

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1996 (01/96) Mercedes Benz E320 W210 Inline6 140,000 miles
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14 Posts
Discussion Starter #15
There are only 2 wire harnesses in the world for this car priced at $1000. I think I will have to repair it myself since a junkyard wire will most likely be damaged in the same way. I'm hoping to find a solution that benefits all who own these cars. I just need to find the correct gauge wire and splice it at the old connectors. Thank you mrboca! Btw 01/96 is the manufacture date. Pins 29 and 30 on ECU seem to be correct for cps. Would the wiring diagram show the correct gauge for the coax cable?
 

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1998 E320 base sedan @ 160kmiles
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6,011 Posts
There was someone whom I helped about a year ago with the same problem. We discussed his issue with the CPS cable with a series of PMs. Since then, I deleted the old P messages. As far as I remember, he managed to get the cable replaced with some coax he obtained from somewhere. He tried non-coax cable (two conductor), and it worked but he decided to use coax for obvious reasons (noise immunity). The diagram shows the gauge of the green core is 0.5 mm which is equivalent to 22 awg. If you use a lower gauge (thicker conductor), it will not hurt, actually you will have slightly stronger signal. The core wire (green) goes to pin 30, and the shield (black) goes to pin 29.

Unless you are an expert in splicing, I would not recommend fixing the problem with tape etc. One can cut the damaged part out and splice a coax of similar gauge, but how reliable it would be is the question. If you splice a cut cable service coax and it goes bad, you lose cable service for a while. If it happens with the CPS coax, you will be stranded somewhere you may not like..
 

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1996 (01/96) Mercedes Benz E320 W210 Inline6 140,000 miles
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14 Posts
Discussion Starter #18
I didn't plan on splicing a small section, i thought just covering the crack with tape might fix it, but it probably wouldnt last and i am definitely sick of being stranded lol.

22 awg is what i was looking for. I plan on replacing the whole wire. The unknown challenge is splicing the nee wire at the cps connector and the 2 pins at ecu. I will post pics if this works.
 

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1996 (01/96) Mercedes Benz E320 W210 Inline6 140,000 miles
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14 Posts
Discussion Starter #19
Ok here we go. This is what I've learned about coaxial cables. Rg6 is 18 awg, rg59 is 20 awg, and rg62 is the 22 awg which is my goldilocks coax, "just right". I'm sure any of these will work. Riser rated coax is not rated for heat, plenum rated coax is.

Rg62 plenum rated coax is what i need. They sell rg6 (18awg) riser rated pretty much everywhere. The plenum rated is sold in large spools(1000ft for $350 US dollars).
 
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