Urgent info required please.................. - PeachParts Mercedes-Benz Forum

#1 01-22-2003, 07:55 AM

'87 300E , UK model,

Can some1 tell me where the overun cutoff switch for the injection system is located ?

Thanx in advance

mbdoc · #2 01-22-2003, 08:09 AM

The fuel pump relay controls the RPM cut-off & that is behind a plastic cover just behind the battery.

#3 01-22-2003, 08:29 AM

MBD,

Thanx 4 that , but I am now confused

I have a wiring diagram that shows the overun cutoff and fuel pump relay as separate parts , so do I take it that both these devices are in a single unit ?

Also , maybe you can comment on this , this car has a problem with intermittent cutting out which seems to be worse in damp/wet weather and is accompanied by an increase in fuel consumption , in your experience could the overun cutoff switch be responsible ?
I have checked the other obvious stuff , like ignition wires etc.

Thanx

stevebfl · #4 01-22-2003, 10:46 AM

It sounds to me that you are talking the decel cut-off function. If you are worried about it causing the problem disconnect the eHA and see if the problem goes away. If it doesn't that isn't your problem.

moakesr · #5 01-22-2003, 10:53 AM

There is a microswitch activated by the throttle linkage, that feeds the info back to the ECU.

Take off the air filter housing, and you should see it.

Is that what you are referring to?

Richard

#6 01-22-2003, 12:38 PM

Thanx guys,
Moaksr,
Yup I know the switch u mention , is that it ?

Steve,
I'll check that , is there anything else that typically causes this sort of problem ?

BFN

moakesr · #7 01-23-2003, 06:59 AM

Hi,

I believe that microswitch is the one you are looking for.

Test it with a multimeter, and make sure it 'clicks' at the appropriate moment.

What are the symptoms...?

Richard

#8 01-23-2003, 07:07 AM

Symptoms are as I have mentioned above.

Thanx

G

moakesr · #9 01-23-2003, 07:28 AM

My car stalled a couple of times in the cold weather a few weeks back.

I took the idle air valve off the car, cleaned it up, sprayed some WD40 onto the slide valve, followed by some light machine oil.

No problems since, but then it might be a co-incidence.

Richard

#10 01-24-2003, 04:03 AM

OK,
I have disconnected the EHA and overun cutoff switch and this has removed the cutting out problem.
Firstly , what problems will be caused by disconnecting the EHA ?

Second,
Does this now point a finger in a particular area in order to locate the cutting out fault ?

Thanx

G

stevebfl · #11 01-24-2003, 07:54 AM

You disconnected two devices and got results. I can tell you that the EHA is the over riding device as the decel switch only participates in the control of the EHA. So..... You must use the test harness and watch the EHA current when the event occurs. You will, based on above, probably see a -60ma decel cutoff function.

If when both are reconnected (and you watching the current) you again have the fault then remove just the decel switch.

There is a test sequence for the decl function on the CD. I don't remember it. but I know what it looks like and the decel switch is part of it.

#12 01-27-2003, 01:27 PM

Hi Steve,

OK , procured a test harness from Mercedes , results as follows :-

Normal running , 30ma at cold start , about 1-2 ma when warm at idle, minus 5>6ma during normal acceleration , 0 > 2 ma at cruise.

(no cat on this car)

Have tried with and without the decel switch connected and the fault occurs regardless , approx -60ma on decel followed by a massive 250ma approx surge at the point the fault occurs.
After the engine cuts it is then reluctant to start , two things affect this , 1/ holding the throttle flat to the floor , the engine will then restart with some hesitation 2/ disconnecting the test meter , so effectively disabling the EHA , the engine will then immediately restart.

What do I check next ?

Thanx

Gary

stevebfl · #13 01-27-2003, 02:15 PM

You say the current goes to 250ma! Is this minus or plus? Not that it matters as this is way wrong. Unless you have some sort of short to another circuit the control unit sounds like a likely culprit.

#14 01-29-2003, 11:37 AM

Hi Steve,

Have been playing with the car in the workshop , meter connected to test harness on the EHA , air cleaner off (just for info) , decel switch connected.
The fault can be induced even with the car static by just jiggling the throttle for a while .
I have observed the following :-
When the fault kicks in (engine suddenly runs very rough) , the current goes +60ma and if opening the throttle is attempted the engine will stall as the current goes about +110 to +125 ma.
If you are very delicate with the throttle it is possible to prevent the stall but the current then fluctuates at about +110 to + 125 ma , if the throttle is left alone the fault continues with the current at +60ma. During the fault I have jiggled wires etc with no effect.
The fault will then decide to persist or just clear of it's own accord.
I have also noticed that sometimes during idle revs will increase without me doing anything then just fall back , didn't notice the current during this event.

Any ideas ?

Thanx

Gary

stevebfl · #15 01-29-2003, 12:22 PM

This amount of current can only represent some interpretation of cold start enrichment. I had that happen on an 88 420SEL. Periodically it would just die for the customer. After driving for some time watching the EHA current it did it too me. and I saw the exhaust look like a diesel. Current ran up and down around 100ma.

I have to say I found the answer by accident but I guess it was concept driven. I inclose a picture of the connector behind the fuse box that includes the wire that goes to the starter from the KE controller. The green was evidently carrying enough potential from one of the other circuits to convince the controller that starting was taking place. I think anything but a ground potential will do this. The wire is normally grounded through the solenoid wiring when not starting the car. I was following this circuit when I took apart that connector. Cleaning it solved the problem.

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