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W124 Ramdom Misfires When Starting

Perhaps some of you can help me in solving this puzzle. Car is an euro 230E, engine M102, KE Jetronic, a 14 years old beatiful, reliable machine.

During the first start in the morning, wIth low ambient temperatures (below

15°C / 60°F, winter), the starter turns the engine 4-5 times and then the car starts normally, very clean.

However, on mornings with higher ambient T° (spring / summer), as soon as the starter motor turns the engine over just 1-2 times, there are a couple of misfires (sputtering for a second), after which though the car starts fine.

When the engine is warm or hot, sometimes the misfires are there, sometimes not. When I turn the engine on a short while after turned off, there is no misfire. When I step up the pedal, the situation seems to improve a little.

The injectors are new, so they are not leaking (I guess, before I changed them the misfires were present).

Could this be a vapor / accumulator problem, preventing the first ignitions?, even if the misfires happen at first startings (only with high ambient T°), when the motor is very cold and the fuel lines are supposedly empty?. Is it possible to have fuel vapor in the fuel lines or in the intake in the mornings?

Although the car idles fine, I suspected an air leak leaning the mixture, but the misfires are occasional and if there is a leak, the air would be always present. I also was thinking about a leaking cold start valve, however I dismounted it and was an entire afternoon looking if some drops came out, nothing. The ignition parts and fuel filter are almost new.

I would appreciate if someone suggest me an idea or a possible suspect, or what to test.

The car always starts, and has plenty of power.

Thanks for any help or advice. MMansilla

Reply to
MMansilla
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When you changed the injectors did you check the engine wiring harness? It is not such a problem on the 102 engine but if you were playing with injectors it may be something to look at. I dont suggest taking it apart again unless you have a wiring harness available.

Reply to
macdrone

When you changed the injectors did you check the engine wiring harness? It is not such a problem on the 102 engine but if you were playing with injectors it may be something to look at. I dont suggest taking it apart again unless you have a wiring harness available.

Reply to
macdrone

I had something similar in a E320. Perfect cold start but delayed hot start after 30 minutes had passed, otherwise OK. Cracking the throttle open, even a bit, caused the hot motor to start instantly. Exhaust reeked of fuel. Cause: the #6 fuel injector was leaking after shut down.

I found the culprit when changing spark plugs. Cold engine, wet #6 spark plug - covered with fuel. One new fuel injector cured the problem.

You already changed the fuel injectors so perhaps they can be ruled out. That leaves the fuel pressure regulator which is a spring loaded valve with a vacuum hose connection to the intake manifold. With engine shut off, detach the vacuum hose from the regulator. If fuel drips from the regulator the cause has been found, replace it. That fuel entering the intake manifold has the same effect as a leaking fuel injector - "flooding" the motor.

Reply to
T.G. Lambach

Thanks for your responses.

I inspected visually the wiring harness. There are some minor cracks in the black rubber isulator that covers a couple of wires, but I don´t know how to check it porperly, so I can´t say more than that. It is possible that the ECU is receiving / sending wrong voltages when the car is starting due to the condition of the wires. Thinking about it, it is also possible that the engine T° sensor is defective and sending erroneous voltages to the computer when the car is starting. I´ll try to test it.

If that is not the case, then I guess something is leaking. It is not the regulator though, I did the test suggested and it is dry. As for the injectors, the sparks plugs were dry, however now I'm thinking I didn't wait enough time with the engine off and cold, for a drop to go down from an injector to the spark plugs.

I believe I got to focus on the fact that the misfires are tied to the temperature. The more the air temperarure around the car in the mornings, or the engine T° the rest of the day, more misfires on startings. I don´t know how to go beyond that though.

Reply to
MMansilla

here are some minor cracks in the black rubber isulator that covers a couple of wires, but I don´t know how to check it properly

Use an ohm meter for this is most likely the problem's cause.

Reply to
T.G. Lambach

I'm going to try it. I have a good multimeter, though I'm afraid that the electrician is not so good.

Thanks for your help.

Reply to
MMansilla

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