1990 560sec Ignition advanced. - PeachParts Mercedes-Benz Forum

mikesmerc · #1 11-23-2005, 05:10 AM

Hi, can anyone out there help me to diagnose the above problem. Where exactly is the crankshaft position sensor located on this model and could a faulty one effect the timing. There is also a vacuum pipe running from the ignition control module in under the inlet manifold, where is this connected to?. There seems to be a removable section on the module where this connects, is it wise to remove this for examination?. I dont have a CAT fitted so would correct to say there isnt a lambda sensor fitted, I have looked on the exhaust manifolds and down pipes with no sign of any sensors.
Any suggestions would be helpful
Rgds
Mike

mbdoc · #2 11-23-2005, 08:37 AM

On the rear on the engine, drivers side(USA).

Timing can't be changed, pre-set program in the ignition module (EZL)

Incorrect installation of the ring gear will result in the timing being 35deg advanced OR retarded!

mikesmerc · #3 11-23-2005, 11:53 AM

Thanks for the reply MB Doc, I have traced a cable from the module to the rear of the engine before, but very difficult to see where it connects to the sensor. I presume its mounted on the bell housing, ie where the engine bolts to the gear box. I tested the ignition timing with a stobe light when warm at idle 650rpm and it read 20deg btdc., I think it should be 7-11 deg. This is resulting in backfires at start up and a hesitant acceleration. Have replaced fuel pumps, filter, distributer cap, leads and plugs. have also checked fuel pressures at cold, hot, driving and stationary.So it seems I am back to ignition problems.
I might just add that this problem occured overnite, so its leading me to believe that its some electronic wizadry has had it.
Thanks again for the help.
Any tests I can Do?
Mike

mikesmerc · #4 11-24-2005, 07:03 AM

Anyone know what the resitance reading on the crankshaft position sensor and the ignition coil should be?
Thanks
Mike

stevebfl · #5 11-24-2005, 11:36 AM

If the car is running the sensor is being recognized. Timing is not an issue of sensor performance. It is possible for intermittant misfires or worse to occur as a result of poor sensor signals or signal strength; not timing issues though.

You should have vacuum at the line to the ignition control unit. The ign controller also is dependant on engine temp. The reading comes from the two wire temp sensor. One wire is used for ignition and the other for KE.

There is a removalble plug to the ignition unit that is a coding plug for timing control. I have no info for how it varies timing.

mikesmerc · #6 11-24-2005, 12:16 PM

Thanks for that Steve, I shall leave the crank sensor alone and see if there is vacuum present when running (if I can get it started)at the EZL unit. Any quick test to check the temp sensor?
I can see there are different positions on the plugs to the EZL unit but I presume these are for adjusting timing for differences in altitude or gas grades. I have not touched these as the problem occured overnite, no previous mechanical or electrical work was carried out prior to this.
Mike

stevebfl · #7 11-24-2005, 12:42 PM

If you are having problems starting the car you could have a crank sensor problem. The temp sensor isn't likely to matter as far as starting goes.

he most appropriate way to test the sensor circuit is to probe the wire and measure the voltage. I'm not sure of the actual values but I would say that with the key on and the wire disconnected the wire shoul have close to 5v. When attached to the sensor which is a variable resistor. The values that I see in Florida are around 3v when cold and down as low as .8v or so when hot. Measuring the resistance of the sensor is a poor evaluation. When voltage is measured in a working system it evaluates all the issues: output from the controller, all connections and the value of the sensor. It does it the way the value is used by the controller and as such gives the most complete measure of the circuit.

Another simple diagnostic mechanism would be to switch the two wires. The sensor prepares the same signal for both KE and ignition, but there are two outputs that are the same. They can be switched by just switching the two single wire connectors. To be of any use, such a technique must also involve some form of precise evaluation such as watching the EHA current on KE or the exact timing of the ignition. If this is a 88 or newer model the value will have a substituted value used by the controller if the circuit is open. In other words if you just pull the wire off the controller won't think it instantly went to the dark side of the moon.

mikesmerc · #8 11-25-2005, 09:04 AM

Will check it out Steve. By the way I started her last nite and pulled the vac pipe off the ignition module and there seemed to be a healthy vacuum present in the pipe so I would assume its ok.
Thanks again
Mike

Strife · #9 11-25-2005, 09:26 AM

Quote:

Originally Posted by stevebfl

There is a removalble plug to the ignition unit that is a coding plug for timing control. I have no info for how it varies timing.

All the plug is is a resistor - it would be fairly interesting (but potentially hazardous to the rather expensive unit) to see what putting a variable resistor in its place would do with the timing. With no schematics to the unit itself, it's hard to say if its a digital, analog, or hybrid kind of device.