M103 woes, FIXED.

[tomatoes4all]

Hello all, I have come to the end of my ability getting my daily driver 1989 300e back running properly. I'm quite methodical by nature and like to do things right and don't believe in ''she'll be right" and that has worked for me for many years (my hobby is wrenching on hydraulic suspension 1960's Citroens, so methodical perseverance is a learned virtue). I hope the collective brains trust of OZBeNZ is able to point me in the right direction. Here's the issue:

Poor idle, frequent stalling when braking, especially when approaching a roundabout. I replaced fuel injection relay, no more stalling. Still a poor idle, especially when warm. I removed the idle control valve, which was the original dated 10/1989 and was hanging up even after cleaning, so I replaced that as well as the hoses to and from the idle control valve. Idles nicely when cold, but stalls when warm, after erratic idle. This points to either a faulty coolant temperature sensor or fuel accumulator (next to fuel pumps). Coolant temperature sensor reads correct and shows the right resistance with varying temperatures. Replaced fuel accumulator, car starts immediately, but still no cigar. Running very rich too, so checked duty cycle, which pointed to a dead oxygen sensor as it probably was the original as most parts were on this car. Unplugged the oxygen sensor, duty cycle goes to 50%, so closed loop. Idles better when cold, but still very rich. I also found an incorrect installation of the air/fuel intake boot (the big rubber one) when I replaced the idle control valve hoses, with one side sitting on top of the intake manifold instead of over the throttle body. Removed all and sundry, reinstalled the boot and had high hopes of having found the culprit. Well, not so fast, terrible over-fuelling when warm, cold idle good, but almost impossible to restart when warm. Black smoke type of over-fuelling.

When I bought the car 3 years ago (120,000 km) I did a full replacement of all consumables and then some: distributor cap, disc, seal, rotor, spark plugs, wires, injectors and seals, brakes, shocks front and rear, replaced all fuses with copper ones, all filters and fluids etc. I’m convinced the fuel system and ignition system are spot on, I have also replaced both fuel pumps and filter lately. So, I have a 1989 300e that is in very good condition and has 135,000km on it, but is undriveable. Being located in Western Victoria, about 3 hours away from any W124 competent work shop in Melbourne is an additional handicap. Before I give up on this car and very reluctantly send it to the great wrecking yard in the sky would anyone have any hints on what to check next? Suggestions gratefully received. Thanks, Erik.

[Bartman4800]

Maybe I missed it in the quite elaborate list of parts you replaced, but have you replaced the seals around the injectors?

They are easy to replace and cheap but when they go hard the engine idles poorly.

Kent Bergsma has some videos on this, explaining it in detail


Good luck, Bart

[tomatoes4all]

Hi Bart,
Thanks for your reply. Yes, I replaced the injector seals too, they were more like bakelite than rubber when I pulled them out. Cheers, Erik.

[Ivanerrol]

Get underneath and give your cat a whack with a piece of 2x2. See if there's any noise.

KE Jet

Have you checked your EHA for leakages? Any fuel smell?
There's a throttle position sensor on the side of the throttle body - they wear out and can cause poor idling and poor economy.
Have you had the fuel pressure checked?

I'm assuming you have non resistor plugs and good ignition leads.
There's a round plate under the distributor. If it hasn't ever been replaced - they break down and ignition voltage gets leaked to ground

135,000 is a good mileage. It's worth getting right

[John Green]

Two things:

1) disconnect the ke-jetronic module and go for a drive. See what happens. The ke-jetronic system is just a fancy k-jetronic system where the electrical side of things just fine tunes it. You may have to artificially increase the idle speed as the idle motor will no longer be working. This will help you separate issues with the electronics of the ke-jetronic system with the more mechanical aspects of the system.

2) check the air flow meter potentiometer. You should be able to google the procedure, if it goes open circuit anywhere near idle that could be the issue.

[tomatoes4all]

Thanks for your responses. The EHA is not leaking, the cat is still solid, I had replaced the distributor inner plate and seal as part of my stage zero approach, as well as the correct spark plugs and wires.
However, a quick test of the air flow sensor output (running engine and plug partially plugged in to be able to get a reading) last night shows 1.1 V between pins 1 and 2, a 60% deviation on the required 0.7 V. Moving the sensor up and down just a fraction (those Torx 15 screws are a pest to get to!) shows a wildly fluctuating voltage and a change in idle speed. I'll remove the sensor today and clean the carbon tracks as well as the "fingers" behind it and see if this helps; I might need to buy a new sensor as I'm sure it's still the original one that Helmut or Heinrich used on the assembly line in 1989. Also, I'll need to buy a new oxygen sensor, it seems there are genuine Bosch ones for about $140. But first things first.
I'll report back on progress, thanks for pointing me in the right direction, Cheers, Erik.

[KimB]

Erik, the M103 is a great motor as others will agree.

Unfortunately, I cannot comment on what may or may not be wrong and I'll leave that for others to do as they already have.

Be patient, you are on the the right track and the issues will soon be sorted and your W124 will be purring like a newborn kitten!

Cheers,
Kim

[tomatoes4all]

Well, I am happy to report that adjusting the air flow potentiometer to 0.7 V has done the trick! It was 1.1 V when cold and increased to 1.4 V when the car would warm up. After removal and cleaning of the carbon tracks on the sensor it looked still very new, new as in recently replaced. After reinstallation and adjusting the car runs like never before. Thanks for the technical expertise John, Bart and Ivanerrol and encouragement Kim, it's much appreciated. To go from wanting to park the car somewhere public late at night with the keys in the ignition to having a well running car, without spending a single dollar, is an excellent result. Thanks again all, Erik.

[CraigB]

Great news! Thanks for all your reporting and follow up and all learnt something.

[KimB]

Yahoo! The M103 PURRRRRRRRRSSSS on!

[Ivanerrol]

I tried to buy an original one of those potentiometers.
Couldn't find one. Ended up buying a cheap PRC one on steal bay. - Couldn't get it adjusted it all.
Found another one at a wrecker of a relatively low K car - Japanese import.

It would have been nice to see a M103 with a modern injection and ignition system.