Crank speed sensor - '93 300TD

[balge59]

hi
engine is 603 912 non-turbo, RHD UK model, 3.0 six-pot. Can't actually find that engine code at all in that PDF, I have been using the basic diagram.
Car has ELR, kickdown and OVP relays and what I assumed was the ABS ECU? behind the relays?
Does that do the tickover as well then?
Sounds like I need to ID this set up better. Whats the easiest way to ID the diesel system?

I will get the number off that ECU. Would the VIN help?

Car also has the partial remains of an aftermarket Diavia a/c system on it which confused the hell out me initially.

cheers guys

 

[Alex Crow]

ELR alone controls idle speed, have a look again at the excellent pdf poster by number cruncher - page 17 onwards.

you have identified the control units correctly. i suspect that talk of ECUs is confusing you - the elr could be called a module, control unit, ecu, brain or even (incorrectly!) a relay. so ignore the abs ecu/module/control unit - there are only two in your picture that require attention as has been said. look at the schematic in the pdf and you will see how simple the system is in essence, as long as the control unit has voltage, earth, temp sensor signal, crank signal and connection to the solenoid it will work. if your engine number does not match i suspect that the pdf is for us market engines, but still the same system.

 

[balge59]

ok! - I think...

Won't be able to get to the car for a bit, at least I will be able to check it now!
The elr gets its power from the OVP then,
earth is wired in to it,
coolant temp sensor tested ok (gauge is really low all the time though...)
crank speed signal I can test (now I know where to look - cheers!)
connection to the solenoid - ermm is that the 'actuator' on the fuel pump?
(initially thought you meant the starter motor..)

Beginning to make sense now, cheers for all the assists!

 

[balge59]

update

Right, managed to find the connector and the sensor!
The connector was stuffed in amongst all the soundproofing (?) in front of the wiper motor - also found that the cable had apparently been caught during assembly and was tangled round behind the bracket thing in the middle of the pic, and the bottom half of the wire was bowstring taut and showing signs of crushing....
So I get the belly pan off and pull the sensor out easily enough (much easier from below even with airbox off), 'de-stressed' it, cleaned it up and retested - still fails.
Think I might try replacing the wire, in case its broken internally - unless it's 'special'? specific resistance or something? If that doesn't work does anyone have a part number and a good supplier or is it straight to MB?

 

[television]

No special wire on these circuits, just standard

 

[balge59]

cool, I thought it looked stock stuff but you never know...I will try and keep to similar weight wire and hope for the best, if a rewire works I will be a happy bunny...
hmm, if not, would an '88 230TE use the same sensor by any chance? didn't think to look when I was at the garage..I suppose the diesels use one because there's no ignition circuit so it seems unlikely now I think about it?

cheers!

 

[television]

The sensor also does the injection timing so I still do not think that it is the fault

 

[balge59]

Not convinced it's all that's wrong myself but at least it'll be a step in the right direction, entirely possible that the relay - uhhh ECU, ELR - whatever it is! is duff too but I cant find a test scheme directly for that, only by eliminating the other components and wiring in the circuit - if everything else tests good it must be the ELR lol!

cheers!

 

[television]

It has been known for someone to change the radio and kill off the signal to the RPM gauge

 

[balge59]

hmm I may not have mentioned in this thread, car seems to have aftermarket a/c - not working, and wiring all to pieces - wonder if I should go round and make sure all that stuff is completely disconnected in case there's a problem? Judging by the 'workmanship' I've seen today, this car's been through the hands of a right muppet....

cheers!

 

[Number_Cruncher]

The sensor also does the injection timing so I still do not think that it is the fault

No, the injection timing is purely mechanical. All the sensor does is to provide an input signal for the idle speed controller. The engine will run well without the sensor, but just won't tick over very smoothly.

 

[Number_Cruncher]

>>Think I might try replacing the wire, in case its broken internally - unless it's 'special'? specific resistance or something?

The wire will be coax, so, to maintain the continuity of the screen, you could use something like a BNC or perhaps SMA connector which you then heat shrink to protect from moisture.

 

[dieselman]

Perform a continuity check on the wire and sensor before replacing anything. with the engine running the sensor should generate a small voltage which rises with revs.
I thought the sensor fed through an amplifier on these engines, if so check that as they can suffer dry joints.

 

[balge59]

@Number_Cruncher - you mean I need some kind of screened wire, or just a screened connection if there is a break? Shrinkwrap is a good thought, will have to get hold of some.

@dieselman tested the resistance and Voltage - got 0.1V (think it should be 5V?) ticking over, didn't seem to rise with engine speed - resistance got either 0 or 1 - can't remember which :Oops: but not 2kOhms anyway - I'm just hoping to repair the wire if poss as it looks quite bad...worth a try!

cheers

 

[Number_Cruncher]

Yes, typically, the screen of the cable is connected to earth, and the signal is passed on the central conductor.

The cable itself will be a bit like the coax you find on telly aerial leads, but a bit smaller diameter.

If you carefully cut into the cable, exposing but not actually cutting the central conductor, between where the damage was and the sensor itself, you should be able to measure the resistance between the screen and the central conductor - this will tell you if the sensor itself is OK, and if it's worth trying to salvage.

As this sensor isn't actually needed to make the engine run, I don't see any real problem in having a go at mending it rather than fitting a new one - it's not safety critical in the way that a crank angle sensor on a CDi engine would be.

Unless you go to expensive extremes, the connectors for coax cables tend not be suitable for underbonnet use, so, it's necessary to protect them. Heat shrink might be OK, or you could also pot the connection in epoxy, and heat shrink while the epoxy isn't fully cured.

 

[balge59]

hmmm, ok think I get you, if I can repair it I will - BUT, bit of googling found this

http://www.auto-parts.spb.ru/cat/cats/m.mycat?Form

found a part number, A 010 542 22 17, which lead me to these

http://truckpartsmb.com/product/0105422217/

so I've emailed to see if its compatible with my VIN -looking forward to some good news tomorrow!

cheers!

 

[television]

No, the injection timing is purely mechanical. All the sensor does is to provide an input signal for the idle speed controller. The engine will run well without the sensor, but just won't tick over very smoothly.

Thanks I forgot that this car has 2 sensors

 

[Number_Cruncher]

Thanks I forgot that this car has 2 sensors

I don't think it will have.

I hope the explanation below will help - perhaps DM could fill in any gaps if I have missed anything

Engines like my '95 E300D and earlier, the fuel injection is *purely* mechanical (they're very old fashioned). Once the engine is running, you could remove *all* the vehicle electrics, and *all* the vehicle's vacuum system, and the engine would still be running. With a few odd exceptions, this is true for all pre W210 diesels.

All the crank angle sensor does on older diesels like mine is to give an input for idle speed control (the engine will idle without it, but, not as smoothly), and to provide signals for the rev counter, and signals to allow the EGR to switch on and off at various engine speeds. On my OM606, the signal is also used to provide the speed signal to switch the intake manifold resonance flaps.

It's only on the engines in W210s and CDi engines where the crank angle sensor has any real input into fuel injection. The indirect injection diesels in the W210s have more electronic control on them, and have electrical cut off valves, and electrical control of the fuel rack position, but, they are mechanically timed. On CDi engines, the crank sensor, as well as providing engine speed information also provides crank angle information for the timing of injection events.

 

[television]

Thanks Number Chruncher,,I do not answer that many diesel post

 

[Alex Crow]

number crucher is correct by george! and a good post.

there ARE 2x crank sensors on many such cars, and this om603 might have 2x, but the front one does nothing - it is wired into the round diagnostic port and nowhere else. on some odd models (eg w116 with diesel engine) the front crank sensor is used as a signal generator for the rev counter, but as far as i know no uk market mercedes ever used the front crank sensor for any more than a signal to the round diagnostic connector for 'tuning' purposes.