85 500SEL Great Crank w/ No Start (Crankshaft Position Sensor)? - Mercedes-Benz Forum
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post #1 of 30 (permalink) Old 04-06-2019, 12:18 PM Thread Starter
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85 500SEL Great Crank w/ No Start (Crankshaft Position Sensor)?

The other day the car was running fine and then when I went to start it the next morning to go to work, all it would do was crank, but no start. After I got home from work, I looked at it a little more and realized I wasn't hearing the hum of the fuel pumps when turning the key through the positions. Removed and checked the FPR ( not really knowing what to look for) and jumped the 7/8 pins (fuel pumps activated). Ordered/installed a new relay, fuel pumps came on much more noticeably than before, but still no start. By this time, I had ran the battery down so I took it to get charged. Picked it back up, re-installed, got a really great crank, but still no start.

When doing some research into possibilities, I noticed the crankshaft position sensor kept coming up as a pretty common issue w/no start; however, I also saw that Gen1 79-85 motors didnt use this sensor as part of the ignition system.

Any experience/suggestions with what the culprit may be?

Replaced recently:
Rotor, cap, plugs, wires, OVP w/ new fuse, battery, fuel accumulator and filter, all fuses.
(all OEM parts)
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post #2 of 30 (permalink) Old 04-06-2019, 12:35 PM
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Correct, there's no CP sensor on the gen1's other than one for diagnostics.

Look into the aluminum EZL, confirm the connectors are clean, confirm you get fuel and spark. The "green" wire to the ezl is known for causing no starts, also if your battery has a wire going to the terminal clamp, check that too.

Also check your OVP fuse.
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post #3 of 30 (permalink) Old 04-06-2019, 02:59 PM Thread Starter
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Originally Posted by bondavi View Post
Correct, there's no CP sensor on the gen1's other than one for diagnostics.

Look into the aluminum EZL, confirm the connectors are clean, confirm you get fuel and spark. The "green" wire to the ezl is known for causing no starts, also if your battery has a wire going to the terminal clamp, check that too.

Also check your OVP fuse.
well. when I checked for fuel from one of the injectors going into the top of the FD while my wife cranked a bit, there was nothing coming out whatsoever.

So i did run some seafom in it a few weeks ago, of course i got the extra shake to the idle thing for about a week but then that went away. the day before it decided to stop working the gas pedal had gotten stuck all the way down once while driving and once when starting the car (had to turn the car off and use my hand to unstick the pedal before restarting).

After work, I was adjusting the Fuel/air mixture (got all shaking to cease) and noticed when it was idling and i would give it some gas, the rpms would first go down, the engine would stop for a half second, and then the gas i had just gave it would take effect and raise the rpms.

When I was done with adjustments, i parked it in the garage only to find the next morning the fuel pump relay was now bad.

When the pumps do their pre-engagement before turning the key they sound as if they are running good and there is a strong smell of fuel after cranking, but nothing at the injector on the FD.
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post #4 of 30 (permalink) Old 04-06-2019, 03:14 PM
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How did you introduce the Seafood into the engine? Via intake or via gas tank?

FD adjustments can definitely cause non-starting, but the fact you get no gas at the injector points to a fuel delivery issue. If you sea foamed the tank, probably caused some gunk to clog the line going to the FD.

Where do you see the strong fuel smell? At the engine or back at the tank?

Of course you can rule out ignition by spraying starting fluid and seeing if it will fire.
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post #5 of 30 (permalink) Old 04-06-2019, 03:28 PM Thread Starter
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Originally Posted by bondavi View Post
How did you introduce the Seafood into the engine? Via intake or via gas tank?

FD adjustments can definitely cause non-starting, but the fact you get no gas at the injector points to a fuel delivery issue. If you sea foamed the tank, probably caused some gunk to clog the line going to the FD.

Where do you see the strong fuel smell? At the engine or back at the tank?

Of course you can rule out ignition by spraying starting fluid and seeing if it will fire.
Lol. thats what my wife said too that it was the adjustment that did it, and then i asked her to explain the no from injector part.

Put the seafoam in through the gas tank and the smell is around the engine bay/ front, no noticeable smell around the pumps.

I might just run and grab some starting fluid to check the ignition aspect.

this would happen as soon as i get the idle shake resolved.
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post #6 of 30 (permalink) Old 04-06-2019, 07:09 PM
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J Benzo

This sounds eerily similar to an issue I just had over the last few days. I have an 84 500SEL, so we may have very similar engines. This is going to sound stupid, but is there gas in the tank? That was ultimately, I think, the main culprit in my situation. I will thank you to not judge me (broken gas gauge)
In my defense, I also managed to trace the fuel flow from the tank, through the FD, to the WUR, but not back to the FD. In addition to adding gas to my gasoline powered engine, I also disassembled the WUR and cleaned it really well. There was, I think, some build up inside the WUR that was restricting the flow back to the FD as I had a hard time blowing through the "inlet" hole of the WUR. After cleaning and reassembly, and gas in the tank, she fired right up.
I would suggest adding 5 or 10 gallons of fresh gas and try disconnecting the fuel line from the FD to the WUR and see if the fuel is getting through the FD. Then hook it back up, and disconnect the inlet fuel line (the big fitting. Mine was 14mm) on the WUR and see if fuel is getting there. Then hook it back up and disconnect the outlet fuel line (the small fitting. Mine was 12mm) on the WUR and see if fuel is getting through the WUR. Then hook it back up, follow that return line back to the FD, disconnect it and see if fuel is getting back to the FD. Then hook it back up and disconnect the main fuel return line from the FD back to the tank and see if fuel is getting all the way around the "circuit". While that main return line is disconnected, it might not be a bad idea to blow some air from your compressor back through the return line into the tank to see if it is restricted. You should hear bubbling in the tank. Remember, you are working with gasoline, so safety first. Also, it's not necessary to crank too long, just long enough for your helper to verify gas is coming out of whatever fitting you have disconnected into the towel that is being held over the open fuel line to avoid spills.
I really don't know what I am doing, but this is what I did to track down my problem. I hope it works for you too.

Good luck!

Jason
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post #7 of 30 (permalink) Old 04-06-2019, 10:18 PM
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Do you know if you have a spark or fuel - need to establish this first.

As you mentioned you have a wife , have her crank the engine while you check for spark - this can be done in many ways:

You can disconnect the a lead connection on one of the spark plugs and using an old one, ground it and check for spark. Make sure to have a good ground.

Another option is to use the "main", coming from the ignition coil - disconnect at the distributor cap, ground and check for spark.

After this checks out, check for fuel.

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post #8 of 30 (permalink) Old 04-07-2019, 10:12 AM Thread Starter
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Quote:
Originally Posted by InOverMyHead1* View Post
J Benzo

This sounds eerily similar to an issue I just had over the last few days. I have an 84 500SEL, so we may have very similar engines. This is going to sound stupid, but is there gas in the tank? That was ultimately, I think, the main culprit in my situation. I will thank you to not judge me (broken gas gauge)
In my defense, I also managed to trace the fuel flow from the tank, through the FD, to the WUR, but not back to the FD. In addition to adding gas to my gasoline powered engine, I also disassembled the WUR and cleaned it really well. There was, I think, some build up inside the WUR that was restricting the flow back to the FD as I had a hard time blowing through the "inlet" hole of the WUR. After cleaning and reassembly, and gas in the tank, she fired right up.
I would suggest adding 5 or 10 gallons of fresh gas and try disconnecting the fuel line from the FD to the WUR and see if the fuel is getting through the FD. Then hook it back up, and disconnect the inlet fuel line (the big fitting. Mine was 14mm) on the WUR and see if fuel is getting there. Then hook it back up and disconnect the outlet fuel line (the small fitting. Mine was 12mm) on the WUR and see if fuel is getting through the WUR. Then hook it back up, follow that return line back to the FD, disconnect it and see if fuel is getting back to the FD. Then hook it back up and disconnect the main fuel return line from the FD back to the tank and see if fuel is getting all the way around the "circuit". While that main return line is disconnected, it might not be a bad idea to blow some air from your compressor back through the return line into the tank to see if it is restricted. You should hear bubbling in the tank. Remember, you are working with gasoline, so safety first. Also, it's not necessary to crank too long, just long enough for your helper to verify gas is coming out of whatever fitting you have disconnected into the towel that is being held over the open fuel line to avoid spills.
I really don't know what I am doing, but this is what I did to track down my problem. I hope it works for you too.

Good luck!

Jason
Jason,
There is definitely fuel in the tank, I put a 20 in it a day or so before this happened and only drive it maybe 20 miles a day, so there is still about a quarter tank left. No judgement from me lol. Iím in the military and we have people all the time that look at the fuel gauge before taking a vehicle for a mission and end up stranded somewhere because they didnít take the extra 30 seconds it takes to go knock on the externally mounted fuel tank. Interesting that you mention he WUR, about 2 days before this happened I had disassembled and cleaned the WUR. I am not sure what the issue is at this point but I only have about a month or so to get it resolved so it is somewhat frustrating.
-Jason (JBenzo)
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post #9 of 30 (permalink) Old 04-07-2019, 10:24 AM Thread Starter
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Originally Posted by bondavi View Post
How did you introduce the Seafood into the engine? Via intake or via gas tank?

FD adjustments can definitely cause non-starting, but the fact you get no gas at the injector points to a fuel delivery issue. If you sea foamed the tank, probably caused some gunk to clog the line going to the FD.

Where do you see the strong fuel smell? At the engine or back at the tank?

Of course you can rule out ignition by spraying starting fluid and seeing if it will fire.
Quote:
Originally Posted by S320L1999 View Post
Do you know if you have a spark or fuel - need to establish this first.

As you mentioned you have a wife , have her crank the engine while you check for spark - this can be done in many ways:

You can disconnect the a lead connection on one of the spark plugs and using an old one, ground it and check for spark. Make sure to have a good ground.

Another option is to use the "main", coming from the ignition coil - disconnect at the distributor cap, ground and check for spark.

After this checks out, check for fuel.

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Bondavi,

So maybe I am just not smart, which connections on top of the FD donít actively supply fuel on crank? The line I checked did not; however, there was definitely some fuel on the spark plug that I removed when checking for spark.

S320L1999,
So when I was checking for spark, I pulled the spark plug from its position, reattached it to the lead coming from the cap, put it up to a ground, and had my wife crank and there was no spark. I was going to try it using the lead from the coil but couldnít figure out a good way to ground it (with the connection being a female type).

The coil is the original.
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post #10 of 30 (permalink) Old 04-07-2019, 11:11 AM
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Ok, so you have an ignition related issue, not fuel, or at least, not only fuel.

Next step, remove the lead wire that connects the distribution cap to the coil and see if you are getting spark from the coil.

If this fails, you can start narrowing it down by checking the resistance and voltage at the coil and verifying the resistance of the CPS (disconnecting the round connectors going into the EZL).

Tell us what you find and we continue from there.

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