taj khan

Hi Guy', Got a major problem. I own a 1989 500se auto, 2 weeks ago, went to the shops, sat back in the car, turned the key and the car won't start. Tried many times, engine turning but just won't start. Had to get it lifted to a garage. after a diagnostic check, 1 guy Say's its the Ignition control module unit and a second opinion told me it's the ecu !!!

The car used to drive superb, no major problems but this has just put a blank in my mind was driving well the day this happened then all of a sudden it refuses to start.

any suggestions or anything i can do to check to see what the fault is or if anyone has ever had the same experience then please tell me what it was.

Thanks

Goatman

Sounds like you've been told what it is. Electronics are like that. One minute they're there, the next they're not.

taj khan

whats the most common electrical fault in the W126 to prevent it from starting ?

elolson

Who gave you the 2nd opinion? Where did you take it, a competent mechanic would be able to isolate one from the other.

TMAllison

Where are you located?

Out of my element on gassers, but know enough to know it doesnt have a ECU and that its not a year/model we got here in the USA. Also know it does not have an ECU so wouldn't bother replacing that. Might be OVP, KE or CPS related.

Start with the basics:
1) Confirm spark.
2) Confirm fuel.

taj khan

I had 2 seperate mechanics come out and diagnose the problem ! thats what got me confused as to what the main problem is. I am based in the UK !

taj khan

HI, I am based in the UK, Glasgow. It's a European model that i have. You said it could be either the OVP, KE or CPS related, can you tell me what the short words stand for because i think that the guy's who i am getting in to see the car are going to try and rip me off. There are only a handful of these models in Glasgow and i know some people are going to take advantage of this hence if i have an idea other than the Igniotion module then i'll be 1 step up ! get what i mean.

The car is NOT sparking but the fuel is coming through !

TMAllison

The dealer is always qualified to diagnose and/or repair it; at times they are the lesser of evils.

OVP = Over Voltage Protection relay
CPS = Crank Position Sensor (yours may be old enough it doesnt have one.)
KE is the injection system which you claim is working.

taj khan

Thanks for the info, Kind of you. I am going to check it out later and will keep you posted.

elolson

I am thinking ignition control module or something else on the electrical side. Even if the ECU (Lambda control unit,aka KE) is bad the car will still run. It's basically mechanical fuel injection with an electrical trimmer (frequency valve controlled by the ke unit with feedback from the O2 sensor).

I am assuming you have checked the coil and all the wires are plugged in? Was the car engine dying out of the blue now and then before it finally quit? Maybe at stop signs just shutting off, etc.

taj khan

.

HI, Thanks for your email. the car was running perfectly then it just decided not to start. Drove to the shops, turned the ignition off, when i got back in to start it, it was turning but wouldn't start !!

I have checked the coils and the wires over and over again, I was told about 3 things and 1 of them is the Over Voltage Protection relay which i am going to do tomorrow.

2 independent mechanics have told me it's either the Ignition control module unit or the Ecu, i am kind of ruling both of them out as for some odd reason i feel like i am getting ripped off every time they come and as soon as they see the car, the only thing that's running through there brains is £££££. I approached the dealer, for them to check the fault i need to get the car lifted and get it taken across the city.

If you or anyone else can advise me of anything else then please do keep me posted.

Thanks

taj khan

Hi, Just to let you know, My W126 still off road. Have changed the Distributor cap as it had a crack in it, rotor arm, Ignition coil and i managed to get a hold of a Ignition control module unit, all changed as advised by a mechanic BUT the god damn thing still won't start !! He is standing scratching his head and so am I. Where do i go from here. The car has been put back on a diagnostic machine and it's not reading anything. This is driving me nuts now. Any advice will be great.

spicyguy2005

Just to share with you my previous experience with car stopped unexpectedly. Everything was fine most of the time, but suddenly I ran into the situation that the car lost power on the highway and may even stop abruptly. Many times the car will die right at the stop sign. I will not be able to get it to start back right away, but if I wait about 10-15 minutes and try to restart I will be able to start it after keeping it cranking for a while.

I had a couple mechanics looked at it, but there seems to have no solution because by the time I got to them, everything is just fine. Fuel system is fine, spark plug is working OK. After reading a few threads I suspected that it may be defective Crank Shaft Position Sensor (CPS). After changing this part, all the problems are gone.

You case may or may not be the same as mine.

BENZITCH

Have you tried the fuel pump relay?

There is a way to jump past the relay to see if that will allow it to start.
I don't know of it but mbca.cartma.net you might find the answer on how to jump the fuel pump relay.

These are from USA models.
Component
Location
Symptom
Fix
Yr/Model
Notes

Fuel Pump relay
back firewall, rt of brake booster near ICU
First hard to start, then it won't start. Wiggling relay got it started.
Resoldered solenoid to circuit board.
1)85 500 SEC
2)91 560 SEC

Bart Henderson

Check your fuel pumps.

Older big engined models run two fuel pumps in series. If you run your fuel low a lot this can cause one or the other to overheat with time and seize up.

The fuel actually also acts as a coolant.

In any event simple wear and tear can do it.

Get under the car and hook up a battery charger direct to your pump/pumps. If they spin, they good, if only one or the other or none spin.

There's your problem.

S Khan

Hi Taj. Just wondering, did you over come the problem? I have the exact same problem with mine & have changed everything you mentioned & now my mechanic is also scratching his head

taj khan

Hi S khan,

Sorry for the late reply...
After much debating and spending a good few pounds, turned out to be the crankshaft position sensor !!!

After i changed that then HOORAY the car started...

I did however change the ignition control module too but i really to this day think that was not really that important but was a desperate method to get the car started...

Since then to this day, its purrrring all the way...

I am in need of the rear chrome for the bumper so if you have a complete set or know of anyone then please let me know...

Many thanks...