tgroup

When testing for faults in the MAS Engine Systems Control (Pole 14 on the 16 Pole X11/4) I get no flashes at all. Clear of faults is supposed to be shown by 1 flash. Actual faults by additional flashes. Why would this test generate no flashes? There is 12V at MAS terminal 30.
This can drive a guy nuts! Any help is welcome.
Thanks.

bobterry99

The MAS controller is faulty.

tgroup

Thanks, Bob. I came to the same conclusion and ordered a new MAS. If that doesn't do it I will probably send the EZL for testing and, if necessary, for rebuilding. There is an outfit in Florida specializing in testing and rebuilding Mercedes EZLs. (I find that the various, used electronic control units sold on Ebay are frequently defective.)
Thanks again for your advice.
Harry

tgroup

Hi Bob,

I installed the new MAS. It was advertised as new and the correct part number (012 545 48 32. Instead, ProgRama sent a rebuilt unit with a different part number (011 545 83 32) which they claim to have rebuilt to the original part number specifications. On installing the new unit I tested socket 14 (MAS) and obtained a constant light, as opposed to the proper no light and then flashes for faults. Do you think the new unit may be shorted or otherwise not compatible?

Thanks,
Harry

bobterry99

That is another part number for your vehicle's MAS and is compatible.

On my car when I make connections the LED (light) is on. Still, if I ground the diagnostic socket for 3 seconds the light blinks-out a code, and then it stays on continuously.

tgroup

Bob,

Thanks once again for the information.

Harry

tgroup

Hi Bob,
I replaced the MAS but still no joy. With ignition on, the check engine light does not come on; Pole 14 (MAS) has a steady light and flashes code 1. Pole 8 (EZL) flashes code 17, crankshaft position sensor - which has been replaced; Pole 3 (EIS) has a steady light with no flashes. Seems the check engine light not coming on when the ignition is turned on and the constant light on Pole 3 indicate a problem, but I'm out of ideas. Your thoughts on what the problem might be would be greatly appreciated.
Thanks,
Harry

bobterry99

If the problem is the one described in your other thread, Harry, then the problem may be with the RPM signal the MAS gets from the ignition controller. To test that possibility I suggest you remove the MAS and jumper together sockets #1 and #2 of its connector. This will cause the fuel pumps to run unconditionally with the ignition key in position 2.

tgroup

Hi Bob,
I did as you suggested and the pumps ran, however, how does that explain the check engine light not turning on? (In reading further about the circuit, it seems that the EZL (ignition controller) simply passes through the RPM signal to the MAS which then distributes it.) In any case, I'll send the EZL to Florida for testing and will let you know what happens.
Thanks,
Harry

bobterry99

The check engine light is a separate issue, Harry. You may have a faulty fuel injection controller.

Over by the ignition controller is a round diagnostic connector. With the key on I suggest measuring the voltage between sockets #2 and #3. Typically you should read 7-8 volts -- zero volts suggests a faulty controller, but prior to condemning it you would remove the electrical connector to the controller and verify it is being powered: with the key on there should be 12 volts on socket #1.

If normally the engine starts but immediately quits but starts and runs with the MAS bypassed, then you probably have a faulty EZL.

tgroup

Thanks again, Bob. I've sent the EZL for testing. Should get a reply sometime this week.

tgroup

bobterry99

That's not good. You may have a power supply problem or a faulty injection controller.

I would remove the connector to the injection controller and see that it is powered by measuring voltages on the connector. The layout of the connector sockets is shown here. With the key on you should have 12 volts between socket #41 and #19 (ground) and between #1 and #19.

To me that seems to be a good measurement.

A defective EZL was indicated by a specific set of circumstances: with a new MAS normally the engine starts but quickly dies, and with the MAS bypassed to force the fuel pumps to run unconditionally the engine starts but does not die.

tgroup

Hi Bob,
You seem to have uncovered the problem. I tested the connector to the injection controller and it has 0 voltage at either #41 or #1 and ground #19. So, thankfully, at least it may not be a faulty injection controller. Do you know where the power is supplied from to the connector? Could it have something to do with the check engine light not coming on?
As always, thanks for all your excellent advice.
Harry

bobterry99

Yes.

Since the fuel injection controller is not powered, either the over-voltage protection relay (OVP) or its fuse are likely bad. The OVP is located near the MAS. It is square with a red top and a clear plastic cover. If the fuse is okay, then unless the OVP is less than 10-years-old I would just replace it with no further testing. The date of manufacture should be printed on the side of the OVP.

tgroup

Hi Bob,
The OVP was bad just as you surmised. When I installed the new OVP, the fuel injection controller got power and had one flash on socket 3 (16 pole diag.) On socket 14 (MAS) the light is steady and flashes once more brightly. The only problem is the ignition controller (socket 8) which flashes code 17 (crankshaft position sensor). The sensor had the correct resistances, but while cranking the sensor did not produce a steady AC voltage, but one which fluctuated, never exceeding 300 mv. The specs require a voltage greater than 400 mv. So I installed a new position sensor, but the AC voltage still fluctuates and does not reach 400 mv. Socket 8 still flashes code 17 (I did remember to clear the code after installing the new sensor) and the car still doesn't start. I tested for spark at the coil and at one of the plugs and it seems OK.
Your suggestions are appreciated. Thanks.
Harry

bobterry99

I suppose the engine was not running when you read code 17, Harry. Ignition codes are supposed to be read with the engine running as detailed here.

Since you have spark, I would be looking for fuel. One way is to have a fuel line on top of the fuel distributor cracked-open. Run the starter and see if fuel emerges. Another test would be tor remove a fuel injector from the head, re-attach it to its line, and observe fuel spray while the starter cranks.

tgroup

Hi Bob,
I was using the method for testing the crankshaft position sensor described in a CD for Mercedes purchased on the internet . It says the AC voltage generated by the CKP is tested at cranking speed. Your information about running the engine for the test must be correct. Where can I get the same manual you're using?
In any event there is no fuel supplied at the fuel distributor. I hear the pumps go on momentarily, but then nothing. When I first began to diagnose the problem, I thought the pumps were malfunctioning so I installed new fuel pumps. No joy. I bench tested the old pumps and they seem to run OK.
The MAS is newly rebuilt, so is the EZL. The fuel injection module reads no fault with the new OVP. When I changed the pumps I also installed a new fuel filter, making sure that the arrow pointed in the direction of flow.
So what could be preventing the fuel pumps from running? Is there a fuel shut-off incorporated in the alarm system, or somewhere else? (The car is jacked up quite a bit on its right side, but the fuel tank is half full.)
Again, many thanks for your help.
Harry

bobterry99

All of the diagnostic manuals are online, Harry. See here.

There is no shut-off. The pumps are powered from the MAS controller, and it uses three signals: the ignition switch in the run and start positions, and the engine running status from the EZL ignition controller. When the ignition switch is turned to the run position, the MAS powers the pumps for a second or two. It also powers the pumps while the switch is in the start position and while the engine is running.

I would remove the MAS controller and measure voltage on socket #12 of its connector with the ignition switch in the start position. It should be 12 volts DC; if not, then the ignition switch, the transmission neutral-safety switch, or wiring is faulty.

tgroup

Hi Bob,
The voltage at #12 socket (MAS connector) with the starter cranking is 10.5 volts. Then I bridged sockets 1 and 2 and the pumps ran, even with the ignition switch in off position. Ran pumps for about 30 seconds with fuel line disconnected at fuel distributor, but still no fuel pumped out at all. Do you have any ideas on what could be the problem? Could there be an obstruction in the fuel tank outlet or in the fuel line itself?
Thanks again for all your advice.
Harry

bobterry99

To see fuel the air flow meter flap must be deflected. That occurs if you crank the engine; alternatively, with the air cleaner housing removed you can deflect it with your hand.

tgroup

Hi Bob,

I ran the test with the air flow meter flap deflected and still no fuel. The fuel flow diagram shows the pump pressure inlet to the fuel distributor is the one without the fuel pressure regulator which is mounted on the outlet. Is that correct?
If I'm testing the proper fuel line, what could the problem be? Should I disconnect the line and check for obstructions? Could it be the back flow valves on the fuel pumps, or some other problem with the pumps, or an obstruction in the tank? (They were very cheap replacement pumps, not Bosch.)

Thanks again,
Harry

bobterry99

Yes, Harry. So with the MAS removed and the pumps jumpered to run I would check that a strong flow of fuel is being supplied to the distributor either subjectively by observation or by verifying that 1 litre is delivered within 40 seconds. If the flow is weak, then I suppose there could be an obstruction somewhere, but I would suspect the pumps.

With the pumps running I also would crack open the return line and check that fuel leaks. If there is no fuel, then the pressure to the distributor is weak, or I suppose there may be a blockage within the distributor.

tgroup

Hi Bob,

I jumpered the MAS and checked the fuel flow with the pumps running. Strong flow at the fuel distributor inlet and also at the fuel pressure valve outlet. Then I checked for fuel at an injector. No fuel is getting to the injector. Does this mean the problem is with the fuel distributor, or the fuel pressure valve? Is there a way to test which it is?
What would you suggest at this point? I really appreciate your taking the time to analyze this problem.

Thanks again,
Harry

bobterry99

Did you deflect the air flow sensor plate, Harry? If not, then no fuel will flow to the injectors. But if you did, then I presume there is something wrong with your fuel distributor. In that case a Benzworld member who goes by "H.D." can give you far better advice than me.