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Old 06-19-2018, 09:55 PM   #1
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C' 5.9 lift pump pressure alarm?

I have a 2002 Freightliner/Thomas with a Cummins 5.9 engine.

I have heard that the lift pump is poorly sized for the engine, and is likely to fail sooner or later (this bus has been through about five of 'em per the records).

The bus mechanic who sold the bus to me said the school district put in a low pressure sensor on it.

But I don't know if they did, how it looks in the cab, or what the pressure is. I borrowed a fancy gauge from the car parts store... and couldn't find the Schrader valve.

Here's a photo. I'm guessing they popped off the Schrader valve and installed a sensor - and the green piece is the connector for the wire into the dash.

If I have that right, I should be able to ground that (single) wire with the engine on, and get a light or a buzzer in the cab, right?



In the image I've labeled what I think is the sensor, and its connector ("B"), and where I think the Schrader valve was.

...and if you're still with me, is Connector "A" a water-in-the-bowl sensor?

Thanks!
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Old 06-20-2018, 08:28 AM   #2
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I would say B is the added sensor and A is the WIF sensor.
The block off plate is the optional fuel heater and there's an O-ring in there that can leak.
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Old 06-20-2018, 08:32 AM   #3
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Originally Posted by 2kool4skool View Post
I would say B is the added sensor and A is the WIF sensor.
The block off plate is the optional fuel heater and there's an O-ring in there that can leak.
Thanks, Don! And that would be a "short to ground if the pressure is too low" sensor, right? (It feeds out only one wire.) Thus if I shorted it to ground while the bus was running I ought to get the alarm or light in the cab. Thoughts?

BTW, my wife and I are still praying for Mary. Thanks so much for posting her progress. We care.
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Old 06-20-2018, 08:42 AM   #4
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Quote:
Originally Posted by Dapplecreek View Post
I have heard that the lift pump is poorly sized for the engine, and is likely to fail sooner or later (this bus has been through about five of 'em per the records).
Not so much poorly sized. They'll work if you place it back by the tank below the fuel level. It just wasn't really designed to pull fuel long distances under a vacuum. Airtex has an upgrade that works better, same cost as the carter it replaces, and is all that I'll install now. I never jumped on the fass, bullydog, aftermarket pump train, mainly because of cost.

Quote:
Originally Posted by Dapplecreek View Post
The bus mechanic who sold the bus to me said the school district put in a low pressure sensor on it.

But I don't know if they did, how it looks in the cab, or what the pressure is. I borrowed a fancy gauge from the car parts store... and couldn't find the Schrader valve.
Cummins(or maybe it was bluebird, not sure) had a campaign that installed a pressure switch that would set a trouble code and illuminate the check engine light if pressure went below 3 psi. I thought it was installed in the banjo fitting on the side of the injection pump but it's been a while since I've looked at one that closely.

Quote:
Originally Posted by Dapplecreek View Post
Here's a photo. I'm guessing they popped off the Schrader valve and installed a sensor - and the green piece is the connector for the wire into the dash.

If I have that right, I should be able to ground that (single) wire with the engine on, and get a light or a buzzer in the cab, right?



In the image I've labeled what I think is the sensor, and its connector ("B"), and where I think the Schrader valve was.

...and if you're still with me, is Connector "A" a water-in-the-bowl sensor?

Thanks!
You might have found it. Ground the wire and see if a light comes on. Use a 1 amp fused jumper wire to do it just to be safe.

Connector a is the water in fuel sensor. The black piece above all of that is the fuel filter heater. The black piece on the back side of the housing is the bowl drain which is a common leak source.

When you change the filters you're supposed to turn the lid so it's open, drain the fuel and then remove and install the new filter.
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Old 06-20-2018, 08:50 AM   #5
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Yes, "ground completion" is what I would call that circuit. I know our 5,9 has a low fuel pressure sensor there OEM, it shows as "fuel filter" on the dash. After market usually has a small LED somewhere.

Thank you!!
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Old 06-20-2018, 08:54 AM   #6
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...Cummins(or maybe it was bluebird, not sure) had a campaign that installed a pressure switch that would set a trouble code and illuminate the check engine light if pressure went below 3 psi. ...
Egad: it only fires at 3 PSI? I've heard it said that the pressure should never be under 10 PSI!
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Old 06-20-2018, 09:04 AM   #7
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I think that's what it was. Certainly wasn't 10 because in stock configuration with the carter pump at idle the it will barely get 10.

I've seen that spec on every dodge forum imaginable. Idk if I've ever seen it from cummins though, so I can't validate it. If I have time, I'll go through the old manuals and see if they have one.
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Old 06-20-2018, 09:14 AM   #8
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I could also imagine the "10" spec being from folks who spent a gob of money on a new lift pump and want to justify it.

Still, I don't want to lose my injection pump.
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Old 06-20-2018, 09:15 AM   #9
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https://www.bluechipdiesel.com/diagn...ift-pump-issue
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