D-Jet running rough at idle, losing power above 2500RPM

1973-1980 : 280S, 280SE, 280SEL, 300SD, 350SE, 350SEL, 450SE, 450SEL, 450SEL 6.9
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tyrrellnick
B Class
Posts: 22
Joined: Tue 17 Jan, 2017 2:22 pm
Model you own: w116

D-Jet running rough at idle, losing power above 2500RPM

Post by tyrrellnick » Sun 20 Aug, 2017 11:03 pm

Hello all. I have a '75 280SEL M110 D-Jet.

My injector trigger points failed last weekend, but it wasn't the points themselves, rather the earth wire attached to the plate in the assembly detached. Roadside solder job temporarily sorted it out, but then the problems really started!

Took the dizzy off to make a more permanent fix, but stupidly forgot to mark the rotor button position. I don't have an extensive workshop at home, so lots of stuffing around.

Long story short, lots of cursing, flooded engine etc, finally got her going again today but new symptoms appeared and I'm hoping someone can help me diagnose?

Allowing of course for me to get the advance perfect again (and therefore idle speed etc), riddle me this:

1. Rough idle (not inconsistent or lumpy, just rough as though it's consistently not firing on all cylinders);
2. Doesn't hesitate when I press accelerator like it used to when injector points had their connection issue;
3. Bring up to 1,500-2,500RPM and she sings. Smooth as silk;
4. Out on the road, when I tried to clear her throat, thinking a bit of carbon had built up, she goes all feathery above about 3,000RPM. Just loses power, very little acceleration, engine somehow sounds a bit 'lighter.' Maybe less exhaust noise, has to explain, but 'feathering' is the best I can describe. Above 4,000RPM it's a bit smoother again.

Really frustrating, as before the trigger points went she was running absolutely beautiful. Had her re-timed perfectly etc, and was just fantastic. Now, really disappointing. Hope someone has an idea.

Please bear in mind I'm not an expert.

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Chai
OZBENZ moderator
Posts: 618
Joined: Fri 04 Nov, 2005 11:49 am
Model you own: w107
Location: Melbourne

Re: D-Jet running rough at idle, losing power above 2500RPM

Post by Chai » Fri 25 Aug, 2017 10:47 pm

Hi,
Assuming you've correctly slotted the distributor back into the engine block, did you check the ignition advance after the installation?
Was the gap for the contact points touched?
Chai
1974 450SLC

tyrrellnick
B Class
Posts: 22
Joined: Tue 17 Jan, 2017 2:22 pm
Model you own: w116

Re: D-Jet running rough at idle, losing power above 2500RPM

Post by tyrrellnick » Sun 08 Oct, 2017 12:34 pm

Hi Chai, the dizzy is back in the right spot. I just tried adjusting slightly and now the point at which the 'feathering' /hesitation/power loss occurs is slightly higher, more like 3000rpm instead of 2500rpm. So perhaps it all comes down to timing? If I keep adjusting slightly perhaps the symptom will disappear?

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