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Die Bosch D-Jetronic war 1967 die erste Großserien elektronische Einspritzung der Welt. - Bosch's D-Jetronic was the first mass-production electronic fuel injection.

Stumbling when revving

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3 Wochen 1 Tag her #21665 von Pcircle
Stumbling when revving wurde erstellt von Pcircle
Hi there

I am expreriencing a problem on my ‘72 450 SL (US spec). It has begun to run slightly rough, primarily in idle both when cold and warm. Also when I give the throttle a quick “jab” the engine seems to stumple and almost stalls. When I depress the throttle more slowly, the engine runs fine and revs without any problem.

I have verified dwell (32 degree), timing (5 degree ATDC) and fuel pressure (2 bar). I have also verified that all injectors are firing.

I have turned the the ECU knob all the way counter-clock wise and that has made the rough idle go away, but the stumbling when quick revving the engine is still there, so turning the ECU knob may only be a quasi treatment.

Any ideas?

Best, Peter

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3 Wochen 1 Tag her #21667 von Dr-DJet
Dr-DJet antwortete auf Stumbling when revving
Hi Peter,

either there is an issue with ignition timing or more likely you have an issue with false air. Rheostat helps to correct in idle only. That is what does not let the engine rev up if mixture is basically wrong. Other options are wiring harness and injectors.

Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107

Workshop D-Jetronic 20.7. (ER), K-Jetronic 31.8. (F)

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3 Wochen 23 Stunden her #21668 von nordfisch
nordfisch antwortete auf Stumbling when revving
Hi Peter,
maybe the TPS enrichment-signals are missing.

Regards
Norbert

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3 Wochen 22 Stunden her #21669 von Dr-DJet
Dr-DJet antwortete auf Stumbling when revving
Hi Norbert,

not likely as it would not create such a bad mixture that car would not want to rev up. Remeber that we often recommend to drive without TPS connected to verify that stumbling does not come from TPS.

Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107

Workshop D-Jetronic 20.7. (ER), K-Jetronic 31.8. (F)

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Bitte anmelden oder registrieren um das Bild zu sehen.

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1 Woche 6 Tage her #21693 von Pcircle
Pcircle antwortete auf Stumbling when revving
I have re-checked the fuel pressure and it is right on 2 bar. All injectors are clicking without misses.

When idling there is no problem, but as soon as I put it in gear (reverse or drive) it begins to stumble and almost dies. When in gear it practically has no power and barely accelerates.

When disconnecting the air temperature sensor the idle is practically the same, but now the engine acts normal when I put it in gear and accelerates.

Does it sound like I need to chase a vacuum leak/false air? 

/Peter

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1 Woche 6 Tage her #21694 von Pcircle
Pcircle antwortete auf Stumbling when revving
....I may be on to something. I just measured resistance on the engine temperature sensor. The area around the sensor was 53 degrees celcius and it measured 480 ohms. Even with a +/- 15% tolerance that appears to be too small a resistance. I measured both with/without connector plugged in and that made no difference.

I will measure the resistance again tomorrow when the engine is cold and see what resistance value I get there.

/Peter

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