DMCH New Pump/Sender - Suddenly, sender malfunction?

So, as the title says... I have (and have been running for years) the "new" DMCH combo unit in my tank. Pump has had its share of issues (on the 2nd or 3rd one now I believe?) but yesterday it pulled a new trick on me. For no reason, after a nice long drive with no issues, the gauge went to 0 and the fuel light came on. I know I had 3/4 of a tank. Opened the tank (removed the stainless plug where the old sender goes) and verified that the tank was indeed full. Checked the electrical connections at the combo box logic unit, which I know is futile since the light was on so there's clearly power there - solid. Went to a gas station and topped up that 1/4 tank to see if maybe it would shake something loose - no dice. Pump is running A-OK, no issues there.

I haven't yet removed the pump body from the tank, as with a full tank of gas that is going to be a messy proposition. Anything else I can or should try in the meantime? I tried to see if I could discern the position of the float through the sender plug hole, thinking maybe it got pushed to the bottom somehow, but I can't seem to see it.

What gives?

This unit has sort of been more trouble than it's worth - for what it cost I could have had two replacement Bosch pumps and $250 worth of liquor... an appealing prospect given the amount of times I've had to R&R this thing.

You can check for corrosion in the connectors since you do use the factory connectors and I have the same fuel pump to and I've had it now for a year but I remove the factory connectors and installed weather pack connectors for a better connection because my connectors didn't look all that great. You can try that?

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Originally Posted by Christian Dietrich

You can check for corrosion in the connectors since you do use the factory connectors and I have the same fuel pump to and I've had it now for a year but I remove the factory connectors and installed weather pack connectors for a better connection because my connectors didn't look all that great. You can try that?

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I disconnected and reconnected the two pigtails, which should be enough to clear any minor corrosion on them, but it didn't help. I feel like the issue must be inside the sender or logic box itself.

So you have no problems starting the car but you're just not getting any kind of a signal to the gas gauge in the cluster? If that's the case you probably could have a problem with that plug-in Logic box

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Originally Posted by Christian Dietrich

So you have no problems starting the car but you're just not getting any kind of a signal to the gas gauge in the cluster? If that's the case you probably could have a problem with that plug-in Logic box

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Yep, car starts and runs no problem. Just the gauge and light show zero. No other gauges affected. It's either the logic box or the float/sensor mechanism in the tank itself, I agree...

That is bizarre. I wonder if the float is getting physically stuck in the down position? Probably difficult, if not impossible to see via the old sender hole.

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Originally Posted by burch

That is bizarre. I wonder if the float is getting physically stuck in the down position? Probably difficult, if not impossible to see via the old sender hole.

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Yeah, it's possible. I wonder if the float itself broke off the arm, the metal arm isn't buoyant and would sink if the float was damaged somehow. No idea how that could happen, though.

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Originally Posted by jawn101

Yeah, it's possible. I wonder if the float itself broke off the arm, the metal arm isn't buoyant and would sink if the float was damaged somehow. No idea how that could happen, though.

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Probably the more likely scenario than the float sinking.

It may be possible to view the float arm by looking through the old Sender cover removed. You may be able to use an inspection mirror and flashlight to view the arm or the plastic pivot that the metal wire clips too.


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I figured it out. This high-quality GM part decided it wasn't quite up to the herculean task of floating lazily in a pool of warm liquid and took it upon itself to simply fall off.

Removing the pump allowed me to see the problem instantly and reach in to the tank (kids, don't try this at home) to find and retrieve the part. After letting everything dry off I reinstalled the brass bushing into the plastic collar it had worked out of and put the pump back in. Gauge is fine now.

http://dmctalk.org/attachment.php?at...4&d=1497907214