Testing fuel sending unit on Duel tank?

[Mrcrowley]

Hey folks,

I am not sure which fuel sending unit is not working on my truck how do I go about testing them to see if one or both are gone. My truck is listed below.

[crabtruck]

May just go after it simple and unplug them one at a time at tank.
The main tank is Ppl and the secondary is DkBlu.
Both run directly to ECM.
If you were to ohm the disconnected senders
probably looking for 90ohms on a full tank and close to zero on empty.
While the senders are unplugged, grounding the sender wire that comes from ECM
should show you an empty tank

[Mrcrowley]

Originally Posted by crabtruck

May just go after it simple and unplug them one at a time at tank.
The main tank is Ppl and the secondary is DkBlu.
Both run directly to ECM.
If you were to ohm the disconnected senders
probably looking for 90ohms on a full tank and close to zero on empty.
While the senders are unplugged, grounding the sender wire that comes from ECM
should show you an empty tank

Ok I unplugged each tank and the gauge would read half full when one was unplugged when you unplugged both the fuel gauge would read zero. The rear tank still is full and you can not hear the pumps come on at all even with ear close to tanks. So next question which wire feels voltage to pump and what voltage should it be at I tested all the wires with the key in on position and the back tank read like 8 volts but not sure if it is voltage feed wire. which colored wires on both tanks are live feeds for the pumps. I am not thinking it is the main tank not i think it is the second tank in back unless the main tank tells the other tank what to do . One more question do both tanks run at same time or will one run low then the other turn on?
Also when I unplug the main tank while truck is running it will die in like 20 seconds .

[crabtruck]

Let me get back to you on this, have to run out door.
Could be senders are doing it right but balance pump not handling fuel.
Do you fill up with engine runnig ? Can cause problems with modern dual tanks,
as it tricks the ECM.

[Mrcrowley]

Originally Posted by crabtruck

Let me get back to you on this, have to run out door.
Could be senders are doing it right but balance pump not handling fuel.
Do you fill up with engine runnig ? Can cause problems with modern dual tanks,
as it tricks the ECM.

No I never did that crab.
By balance Pump you mean pump from second tank feeds main tank?

[crabtruck]

My world just got a little busier.
Tranny on the wife's car just slammed
gotta go see.

Read this for some useful related info

[Mrcrowley]

Originally Posted by crabtruck

My world just got a little busier.
Tranny on the wife's car just slammed
gotta go see.

Read this for some useful related info

Would this be a recall?

Also I found a fuel sending Assembly its says it OEM for $140.00 I called they said it would fit and looks like you need to wire it in . Could anyone give a idea if this would work? here is link

Fuel Assembly Unit Link

[crabtruck]

Thanks for asking, but the wife's car is not a recall.
The PDF I linked above was a TSB (info) not a recall.

Those pumps you linked to seem to offer 2 choices in 4 pictures.
The $140 seems to be made for California trucks although not stated.
It has a lower flow rate and different "Turb/gerotor type" action.
The $129 ones all seem the same to me with "Rollervane type" action.
Has higher (45-55g/hr) rate vs $140 (30-40g/hr)
They all seem to have the same part number from that place also.
Bigger issue I think is the module code of "TCF" vs "TCU"
And do you actually need a "TCJ"
Notice the connector types: TCJ=2wire+2wire, TCF=4wire+2wire,
and TCU=4wire only. Check this link for specifics, not recomendation:
AutoZone.com | Vehicle Selection | Year
or look up your truck @AZ HOME - PARTS - FUEL DELIVERY - FUEL PUMP

Before changing pump (an annoying and costly proceedure)
it would be good to see if they run.
Part of this is checking codes, let us know what comes up.
Light may not be currently on - no indicators, check anyways.
You may have a code saying exactly what the problem is.

You asked for this wire drawing in an earlier post. Just for clarity,
since I'm not too sure how readable it is, here's some notes.
Pumps running are dependent on two fuses and two relays.
First relay is activated by ECM by a hot signal, and then it supplies
both the main pump and the power for second relay.
The second relay is activated by the ECM with a "Gnd" signal,
which causes the second relay to get hot from second fuse
and connect it to aux pump. Both pumps share a ground.
Fuel level senders are completely seperated from gauge
as they feed their info to the ECM for processing.

There are more complicated steps you can dig into to troubleshoot,
but make sure the basics are covered before going after pump.
Are both fuses good ? (I'm pretty sure they are)
Are both relays good ? Both relays are needed for second tank
but if first tank pumps first relay is likely ok.
Is the second relay being selected by the ECM ?
Do you feel it "click"? If so pull the plug on aux tank and
check for 12v when it does.
.
2001 Chevy Silverado K3500
.

[Mrcrowley]

Hey I have 1 question for now which vehicle best compares to my 1 ton most parts places do not have my truck listed?

[Mrcrowley]

Originally Posted by crabtruck

Thanks for asking, but the wife's car is not a recall.
The PDF I linked above was a TSB (info) not a recall.

Those pumps you linked to seem to offer 2 choices in 4 pictures.
The $140 seems to be made for California trucks although not stated.
It has a lower flow rate and different "Turb/gerotor type" action.
The $129 ones all seem the same to me with "Rollervane type" action.
Has higher (45-55g/hr) rate vs $140 (30-40g/hr)
They all seem to have the same part number from that place also.
Bigger issue I think is the module code of "TCF" vs "TCU"
And do you actually need a "TCJ"
Notice the connector types: TCJ=2wire+2wire, TCF=4wire+2wire,
and TCU=4wire only. Check this link for specifics, not recomendation:
AutoZone.com | Vehicle Selection | Year
or look up your truck @AZ HOME - PARTS - FUEL DELIVERY - FUEL PUMP

Before changing pump (an annoying and costly proceedure)
it would be good to see if they run.
Part of this is checking codes, let us know what comes up.
Light may not be currently on - no indicators, check anyways.
You may have a code saying exactly what the problem is.

You asked for this wire drawing in an earlier post. Just for clarity,
since I'm not too sure how readable it is, here's some notes.
Pumps running are dependent on two fuses and two relays.
First relay is activated by ECM by a hot signal, and then it supplies
both the main pump and the power for second relay.
The second relay is activated by the ECM with a "Gnd" signal,
which causes the second relay to get hot from second fuse
and connect it to aux pump. Both pumps share a ground.
Fuel level senders are completely seperated from gauge
as they feed their info to the ECM for processing.

There are more complicated steps you can dig into to troubleshoot,
but make sure the basics are covered before going after pump.
Are both fuses good ? (I'm pretty sure they are)
Are both relays good ? Both relays are needed for second tank
but if first tank pumps first relay is likely ok.
Is the second relay being selected by the ECM ?
Do you feel it "click"? If so pull the plug on aux tank and
check for 12v when it does.
.
2001 Chevy Silverado K3500
.

Ok I found one relay under hood where would other one be located?