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#1
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Surging at idle
Hi, guys!
Things were good for a while but looks like gremblins attacked again- when idling, out the blue,my car will surge as if somebody stepped on the gas pedal and than rpms will drop off again, and after a few seconds the whole thing repeats itself. There is no pattern to it except that it happens only when car is just sitting idling. For the heck of it I replaced both fuel filters but it made no difference. Any ideas? |
#2
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If there is some way to pinch off the Fuel Return from the Fuel Injection Pump and doing that improves the situation I would say you have a Fuel supply Pump or Pressure Relief/fuel Bypass Valve issue.
Air leaks in your fuel inlet can cause odd problems. You might try getting a container of Diesel and some longer Fuel Hose hooked up the the Fuel Supply/Lift Pump inlet and see if runing it off of the Fuel in the Container improves things. Is there any difference if the Fuel Tank is full or the Car is parked with the Fuel Tank higher than the Engine? If the Fuel Fill Cap is off is there any difference?
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84 300D, 82 Volvo 244Gl Diesel |
#3
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thanks Diesel911 for all the suggestions- I will check them out as soon as my daughter comes back home with the car. Until than one more observation- the weird surging goes away with even the slightest pressure on the accelerator. It seems to effect the car only at the "pure" idle stage.
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#4
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Is the Idle speed within the normal range.
If there is some room to raise the idle speed that might Help. While it is hard to say without some real evidence what you said about giving it a little fuel and raising the RPM is so far still consistant with an Fuel Supply issue or an Air leak. Some speculation: On the 617s in the manual they have a minimum Vacuum where you T into the Fuel Inlet right before it goes into the Fuel Supply Pump. If the Fuel Supply Pump suction (vacuum) is low raising the speed would increas the vacuum and kind of mask the issue. Somewhat the same with a small Air leak. At idle speed a tiny bit of Air could get into the Fuel Injection Pump Housing and form a bubble. When the Bubble is big enough it will pass and cause rough running. When that Bubble is gone another will start to form. Raising the rpm may causes enought Fuel volume to push the Air out of the Fuel Injection Pump Pressure/Overflow Valve. Now that I think about it there are some Threads with Idle issues where the Members believed that there Delivery Valve O-rings were somehow allowing Air to get in; but their was no external leaks. They changed the Delivery Valve O-rings and Crush Washers and the problem went away.
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84 300D, 82 Volvo 244Gl Diesel |
#5
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Another observation I did not mention in my previous post: one of the return lines is leaking. Would that have anything to do with fuel supply/air bubble theory?
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#6
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it looks like the car in question is an '87 300d.
Do a search on ELR. |
#7
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Quote:
As jt20 indicated, I do not know what the ELR is so I cannot comment on that.
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84 300D, 82 Volvo 244Gl Diesel |
#8
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Good call! I did the search and one of the members had a link to the procedure for testing and adjusting idling speed. One of the very first steps was to unplug and plug in the 2-pin coupling at actuator. Seems to have helped a lot. The black nob with numbers that is supposed to change the idle speed does not do much no matter what setting is on. Maybe that's the ticket?
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#9
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How much fluctuation in RPMs is occurring?
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1982 240D, sold 9/17/2008 1987 300D TurboW124.133 - 603.960, 722.317 - Smoke Silver Metallic / Medium Red (702/177), acquired 8/15/2009 262,715 and counting |
#10
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Quote:
Also the setting does not "click in" and take effect until you push the knob back down and reseat it. Pulling the knob up and turning it changes very little until you push it back down again. After the re-push is when the change occurs. So if you're twiddling the dial and nothing is happening, it may be because you simply aren't putting the knob back into position. Or it may be malfunctioning. I've got weird idle problems on my SDL with the same engine. If I let the engine fall from 2000, 2500 rpm or more -- sort of like "gravity" pulling the idle down -- the *sensation* even though I KNOW this is a horrible way to describe it -- the sensation is as if the falling idle built up so much momentum that it crashes PAST the idle stop and almost kills the engine at 500 rpm or so and then bounces back up to 630 where it belongs. This is intermittent, seems to be exacerbated by hot engine temperature or especially hot ambient temperature, and I haven't managed to track it down for years. I've started several threads about it over the years as a new description occurred to me and never got far. |
#11
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Quote:
My idle does audibly fluctuate, however not enough to register on the tach...it's very subtle.
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1982 240D, sold 9/17/2008 1987 300D TurboW124.133 - 603.960, 722.317 - Smoke Silver Metallic / Medium Red (702/177), acquired 8/15/2009 262,715 and counting |
#12
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Well, when there was a problem, the difference was obvious: from low idle to sudden surge that normally would have taken a good whack at the accelerator, and than back to the idle.
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#13
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Quote:
My voltage regulator was failing, and the cycling voltage was changing my idle. BTW this was with a new red-top Optima, which wasn't enough to absorb the fluctuation (over 14v).
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Gone to the dark side - Jeff |
#14
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I asked this same q on BW, someone mentioned looking if your shut off switch was moving up and down with the rythm and if so that I might be the shut off.
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http://superturbodiesel.com/images/sig.04.10.jpg 1995 E420 Schwarz 1995 E300 Weiss #1987 300D Sturmmachine #1991 300D Nearly Perfect #1994 E320 Cabriolet #1995 E320 Touring #1985 300D Sedan OBK #42 |
#15
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My stop lever does bob up and down quite a bit. I could easily believe it's the problem, but I thought other than being vacuum operated, they were foolproof. Can you make a "which pieces to replace" suggestion without our derailing this whole thread? The entire shutoff mechanism? A spring somewhere? I've never seen the guts of one.
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