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7.3 IDI idling at 100RPM

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Northern Red, Jun 24, 2020.

  1. Northern Red

    Northern Red Registered User

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    Hey everyone, new to this forum, I’ve got a ‘94 f350 with a non turbo 7.3 IDI, 127,000km on it.

    She shakes more than I think is normal at idle and my tach shows 100RPM at startup, MAYBE 300rpm during high idle (slight bouncing of the needle as well) when it’s cold and it seems to lag some when I press the accelerator to come up to speed, but once I’m driving it has a normal response.

    What do you guys think? I haven’t adjusted anything, but apparently the previous owner “advanced the timing a little bit”.

    Not sure if the photo helps, but maybe someone will notice an adjustment needed.

    image.jpg
     
    Selahdoor likes this.
  2. franklin2

    franklin2 Full Access Member

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    I would not go by the factory tach. Mine doesn't work right either until it warms up a little bit. Been that way since I bought it years ago.
     
  3. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    I don't think that our engines can run at 100 RPM. I think that Wes said that a good starter will spin it at 300 RPM. Your tach isn't reading right. There can be several different things that can cause a tach to not work right, but the most common one is the pick up. That's the one that has wires plugged into it in the housing that your injector pump bolts to. It takes a 1" open end wrench to unscrew it.
     
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  4. WAID

    WAID Full Access Member

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    Yeah the tachs can be pretty wonky. Mine works for a whilea then suddenly decides everything is about 1000rpm slower than normal. Funny how my manual transmissions goes from cruising at 2500rpm suddenly down to 1500rpm without slowing the truck.
     
  5. Northern Red

    Northern Red Registered User

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    I’m finding that’s the case with pretty much every gauge on this cluster, when I first bought it she showed zero oil pressure, and crazy high temps, I’ve replaced both of those with aftermarket ones and both were totally inaccurate, thanks guys, good to know it’s not the only truck with wonky readings
     
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  6. WAID

    WAID Full Access Member

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    I'd really be wondering about grounds if it is the whole cluster like that. All my gauges and lights work except the tach intermittently. I don't really rely on the tach for shifting, the engine has pretty good audio feedback for shift points, so I haven't really prioritized troubleshooting it.
     
  7. dan-o

    dan-o Registered User

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    My tach seems to affect the transmission on my 89 7.3 idi. The other day it acted like the torque converter would not work in drive, it would act like it was low on fluid. The tach was reading 0.
    When the tach started working a few minutes later, the truck shifted fine!!! I ohmed out the pickup, it was within range. Go figure?
    There is a Youtube video from a guy named Ramirez that gives good information on the tach sensor troubleshooting. If I figure out how to load the link, I will.
     
  8. franklin2

    franklin2 Full Access Member

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    Your truck has a EECIV computer to run the transmission. It does have a rpm signal that does come from the tach sensor.
     
  9. franklin2

    franklin2 Full Access Member

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    Here's a diagram with the transmission control wiring at the bottom.
     

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