EZI unit problem

[MersMadness]

Having spent an absolute fortune on a 1994(M) 500SL my local Mercedes dealership has run out of ideas. The car will, for no apparent reason, suddenly misfire and jerk as if all electrics have been cut out. More embarrasing you can be at traffic lights or a roundabout and the engine will die without notice. Quite dangerous is the person behind you thinks you are going. You need to constantly watch the rev counter to ensure that you still have a running engine.

Work done so far: Air mass sensor changed. New servo unit. New fuel pump and filter. New distributor heads and rotor arms. New crankshaft sensor.

The Mercedes dealership now thinks I may have a faulty EZI unit, but will want £1,250 odd to replace it. Having already spent £2,000 I am beginning to wonder whether I will be throwing good money after bad. Any members had similar problems or know of a cure? Will appreciate any help.

 

[television]

You can learn a lot by the way it stops.
When it stops are all of the warning and ignition lamps on without you touching anything, just like they are on key possition 2.

How easy does it re start.

malcolm

 

[golfcarmad]

My C280 did similar-I suggest you look at yr loom.don't be surprised to find each and every wire split every 2-6 cms.It is a notorious problem on some mercs-straight 6's especially.sorry dont know config or yr car-but peel soom covering back and have a look.I also had my ECU tested-as that was original diagnosis,no fault found-cost 30 quid for test-worth it I think

 

[television]

My C280 did similar-I suggest you look at yr loom.don't be surprised to find each and every wire split every 2-6 cms.It is a notorious problem on some mercs-straight 6's especially.sorry dont know config or yr car-but peel soom covering back and have a look.I also had my ECU tested-as that was original diagnosis,no fault found-cost 30 quid for test-worth it I think

This 94 car should be clear of any wiring issue in this country, though anything can happen.

malcolm

 

[MersMadness]

You can learn a lot by the way it stops.
When it stops are all of the warning and ignition lamps on without you touching anything, just like they are on key possition 2.

How easy does it re start.

malcolm

Re-start is immediate with no problem. However, cant say I have noticed any lights come on. May be because I restart immediately and not giving the lights a chance to come on. Thanks for your help, your advice most appreciated

 

[television]

Re-start is immediate with no problem. However, cant say I have noticed any lights come on. May be because I restart immediately and not giving the lights a chance to come on. Thanks for your help, your advice most appreciated

The reason that I say this is because the most known fault fo this is the Ignition switch, most of us with SL129 have had to replace the swich.

Another faulty common part is the fuel pump relay, they go dry soldered.with this component the engine could well hesitate just befor it dies.
they can be opened up and blanket soldered by any TV eng;

these are the two most common problems with this fault on a 129, I will still think about it tomorrow.

malcolm

 

[MersMadness]

Thanks Malcolm, The best way to describe the sudden cut out is as follows. With a light throttle it feels like a gearbox problem. A slight jerk as if the auto box is not functioning properly. However, give it a bit of throttle, to see off an annoying Golf GTi for example, and the jerk is sudden. Doesn't always happen, can go miles without problems, then 2 or 3 times within a few miles. Sudden cutting out in traffic is the biggest danger. My wife who mainly drives the car has received many rude gestures and aggresive horn use when this has happened. Sleep well, Regards Gerald.

 

[MersMadness]

I have just spoken with my wife. She tells me that the Ignition lights do NOT come on when the engine stalls in traffic. Does this sound like a faulty ignition switch? Have Merc Macclesfield taken me for a glorious and expensive ride?

 

[MersMadness]

Thinking about Televisions reply regarding a faulty ignition switch. Is there any way that this can be tested. For example could the wiring be easily bridged so that the key postion is irrelevant for the purpose of testing the car. Without checking with Merc, but previous experience tells me, that I would probably end up changing all the locks, or having an ignition key and seperate door/boot key

 

[jberks]

but previous experience tells me, that I would probably end up changing all the locks, or having an ignition key and seperate door/boot key

MB can supply a new ignition barrel to match the original key, but in any case, I believe you can swap the 'key barrel' component over and simply replace the electrical parts, so no need for a 2nd key or lock change.

If the ignition lights don't come on then to me that's the tell-tale. The ignition circuit has been switched off by the failure. If it was an engine issue, then as soon as the engine stopped, the charging light would come on at the very least, but if the ignition circuit has gone off then it will behave as if you've turned the key.
As a test, find something that only works with the ignition on (fan, cig lighter?) and monitor them when it dies. If the key is on ignition but they die too, that would be proof enough for me. (Plus as Malcolm says, its a known weak spot on the SL129).

 

[MersMadness]

Thank you very much. It is so nice to visit a forum and receive so many ideas, and expert opinion. The trouble is everyone has been blaming various expensive engine components, and at the end of the day the problem, as with most problems is very simple. It is a shame that my Merc dealership were unable to ask the right questions, and solve the problem at the beginning. I sometimes wonder if all they can do is service cars under 3 years old. It seems a shame that they have all this expensive factory diagnostic equipment, but not the knowledge to think a problem through before they set about on expensive and unnecessary work. Perhaps they should read this forum!!!

 

[television]

Thank you very much. It is so nice to visit a forum and receive so many ideas, and expert opinion. The trouble is everyone has been blaming various expensive engine components, and at the end of the day the problem, as with most problems is very simple. It is a shame that my Merc dealership were unable to ask the right questions, and solve the problem at the beginning. I sometimes wonder if all they can do is service cars under 3 years old. It seems a shame that they have all this expensive factory diagnostic equipment, but not the knowledge to think a problem through before they set about on expensive and unnecessary work. Perhaps they should read this forum!!!

The main problem is getting mechanical engineers to get their head around electronics. The electronic trade is something that you love doing, without the basic training, and by that I mean several years at component level, the problems out there will exist. When a person understands that a simple ressistor or condenser can each be used in around 25 different ways to do different things, then we might start getting somewhere.

A mechanic at MB or any other outlet can change pieces all day long, eventually he must get to the faulty bit, but he is not picking up the tag.

Malcolm