W124 Erratic Misfire

[Wheelbarrow]

I'm posting this because my solution might just help others and I did not find it in other posts!

Just about a year ago my 1990 230TE (190,000 miles) started to hiccup every so often. It gradually got worse. Checking the various forums it appeared that it could be anything (or everything ).

First off was to check the distributor cap and rotor arm. These showed wear. They were replaced and all was well for a while. Problem came back. An independent specialist checked over the ignition and fuel injection. Spark strength was weak, and the mixture was weak (set spot on for a catalyst, my M102 engine does not have one, so he set the fuelling to the correct level) but nothing obvious causing the misfiring. It was fine for a while. Spark plugs were fine (new at last service) so I decided to change the coil next (it turned out that I actually had a 190 coil fitted instead of correct spec – this had been done by a main dealer some 10 years ago :-? following a similar problem!). With the new coil she drives much smoother and more eagerly, but after a few weeks the misfire starts again.

Ok back to forums, find OVP, fuse OK, pull relay disassemble – find dry joint. Fix. Brilliant – for a while – then misfire comes back. Fuel Pump Relay checks out ok, fuel pump is ok, fuel filter is ok. Other posts now hint at vacuum leaks, temperature sender, cold start valve or ECU. Start with the easy stuff.

I discover the area around the temperature sender, etc is a bit grimy. I clean this off with petrol (in well ventilated area!) and continue to clean whole area under the air filter while I’m at it (checking the vacuum system visually as I go).

As dirt is dislodged by the brush I notice some brown coloured wires moving. Where do these go – I check the wiring diagram. They are the earth wires for the temp sender, cold start valve and the KE-Jetronic . Wires are removed, contact surfaces cleaned and refitted (with a spring washer!). Put everything back together. That was a month ago.

No more misfires car driving like a dream .

So if anyone else is having misfires with a W124 and an M102 check for loose wiring under the air filter!

 

[roofless]

well done. it's good to see you posting back with a up date

 

[LNM]

Spot on post !! I've spent the last three days going through the motions of the usual suspects on the M103 enginen in mine. I noticed a tiny little sparky spark bit (looking in the dark) on one of the coil connections. Undid it, looked at it sternly, and put it back and checked for leaking electricity. Saw none and the car now starts like its just come off the production line, but I'll be having a look at those sender wires tomorrow.. because the connection that was apparently sparking was sound and the wires were too..

Fingers crossed !!

 

[television]

The interesting part of wheelbarrows excellent post is that all of the firms like auto data do say check the sensors first as they set up the whole engine

 

[power-steering]

very handy information there

 

[charlfourie]

Thanks for the post,
I'll keep it in mind if anything like that starts happening with my w124.

 

[Mercedes 190E]

Hmm...the cold starting in mine has been getting worse lately. I'm going to check the suggested connectors.....

 

[LNM]

King lead (geddit....?) was leaking small blue pieces of electricity wherever it touched a metal component. It can be made to jump gaps too with the help of a wooden chopstick to move the lead about. whatever, this can't be a good thing.

I've no recollection of how old that one is to be honest as I really can't remember having changed it. I suppose I must have done, because I've bought OE lead sets in the past.

I'm assuming that this leakage, whilst clearly to earth, might still give any electronics in the old goat some extra trouble to contend with.

If anyone is in doubt over the build quality of OE leads and why they can work out at over a tenner each, take an old one to bits using a stanley knife, hammer, screwdriver, vice and a pair of pliers. You'll need all those tools for the job... nuff said.

Interesting article, I never knew so much design went into these things.....

http://www.magnecor.com/magnecor1/truth.htm

 

[television]

LNM yes it is a complicated subject

 

[Wheelbarrow]

To you all,

What a wonderfully friendly lot you are - glad the original post was useful.

She's still going strong!

Wheelbarrow