Fuel gauge with full tank reading empty/ flashing low fuel light. Engine dyes two miles later. (1 Viewer)

[obe12]

99 100 series new fuel pump for E85 fuel two months old. No previous issues…
Stop for gas 1/2 tank, top off and leave. Fuel gauge reading full then went empty and low fuel light was flashing… so odd. Stop / shut down restart and same fuel gauge go up, then down and low fuel light flashing. Ok, sender issue I am thinking old truck, continue my drive home. Two miles later after this it stalls out. At the time just leaving the intersection, and coast to a stop, flasher on, attempted off on key restart. Starts, gauge now reads full and no flashing low fuel light. Drive home 2-3 miles fine.

Unplug the wiring harness in front of the tank left side while running, trying to see if this connection might be the issue. Car dies, fuel gauge goes low and low fuel light steady on. NOT FLASHING. Hum.
Cycle key restarts and no issues.

Have a gremlin now…

Why flashing low fuel light? Sudden stall

Obviously intermittent… issue likely electrical. But what?

 

[GOLIGHTLY]

Almost sounds like a worn wire, intermittent short or something, but that would likely trip a fuse right? Try shoving some dielectric grease in the connector?

EDIT: Just trying to think what’s going to hit the sender and the pump simultaneously. An intermittently bad sender would just affect the gauge I would think

 

[kevgentile]

The circuit that feeds the section of the combination meter (instrument cluster) receives its power source thru the No.1 igniter relay.
The only thing I can think of at the moment that would have a 2 fold effect on both shut down and a fuel light. The only thing is that the fuel level sensor is not tied into the same circuit, so I may be barking up the wrong tree but it's worth looking at.

 

[kevgentile]

Looked back thru the wiring diagram, the level circuit also ties into the combi meter so I'd check the power source of that circuit...IG 1 relay

 

[obe12]

The fuel low level was a steady off - on flash … about 3/4 -1 sec interval. I expect it to be on or off not flash. When I open the fuel sender - fuel pump harness it shows low on the gauge, low fuel light on steady on cluster. The sender doesn’t have an actual low fuel separate sensor to trigger the light, function of the fuel sensor to gauge that triggers it I believe. My older older pickup had an actual low fuel sensor and lamp activated by that alone.

Do see that on this cruiser.

I was hoping another have seen this behavior before.

Thanks
tex

Also the fuel pump is a separate system all
Together. I don’t remember when it stalled if the check engine lamp illuminated. My bad

Was more concerned not getting ran into

When I simulated opening the circuits the check engine lamp illuminated.

Tex

 

[obe12]

The fuel low level was a steady off - on flash … about 3/4 -1 sec interval. I expect it to be on or off not flash. When I open the fuel sender - fuel pump harness it shows low on the gauge, low fuel light on steady on cluster. The sender doesn’t have an actual low fuel separate sensor to trigger the light, function of the fuel sensor to gauge that triggers it I believe. My older older pickup had an actual low fuel sensor and lamp activated by that alone.

Do see that on this cruiser.

I was hoping another have seen this behavior before.

Thanks
tex

Also the fuel pump is a separate system all
Together. I don’t remember when it stalled if the check engine lamp illuminated. My bad

Was more concerned not getting ran into

When I simulated opening the circuits the check engine lamp illuminated.

Tex

Hi all and thanks for the leads.


Worked out what I think is wrong with the cruiser

Studied other people reports of suspected fuel pump failures and quit running symptoms … with no CEL. Or DTCs.

One voltage drop through the fuse to control relay, the path then runs to the rear of the truck left rear side inside to a fuel pump Ecm leaves there and drops through the body at the front of the fuel tank with a connector , then a pigtail to the top of the gas tank.

Members has said quit running and no start , no fuel and change pump still no fuel

Either fuse connection or wires through the body to the plug corroded from moister ans caused connection issues to the pump, one have a broken wire at the point where the wires can through the body.

Not one had a fuel pump Ecm issue, some experienced this after changing the fuel pump, aka like I did… possibly the fuel pulling more current being hi flow..

Plus I disturbed the connection point where others have had issues.

So, measure voltage at the main fuse and while running at the actual pump connector on top of the tank.

Look for a voltage drop while wiggling the wires and suspected connector plug.

Common to both fuel gauge and fuel pump is this connector… at the body and on top of the gas tank. Completely separate circuit. Share the connection plugs, and sender pump housing.

The flashing lamp, I am believing the cluster ecm loosing some connection to the sender. The gauge sends it one power hi to the gauge, and provides it on signal ground low and reads the potential return as signal return. I think when it looses like the hi to the gauge nothing is returned and sees resistance between signal and low it see this as an error. Or hi low circuit is there and open return. Either way a leg of the three wires is open. Therefore low fuel light flashes detected error.


With the history and age of this truck I bet the issues is pour connection …

Ordered the special grease for plugs to clean and hopefully apply to this connector and solve my intermittent issues.

Thanks again

Tex

 

[GOLIGHTLY]

Good ol dielectric grease

 

[nissanh]

I struggled this gauge sensor located inside the tank for about a year. Suddenly it shows empty and reserve light on for a full tank of gas. I drove like that for a while while maintaining the trip meter. fill up every 200-250 miles.

For the last few months, the issue didn't come back on. The gauge works as it should and I did nothing.

 

[obe12]

I struggled this gauge sensor located inside the tank for about a year. Suddenly it shows empty and reserve light on for a full tank of gas. I drove like that for a while while maintaining the trip meter. fill up every 200-250 miles.

For the last few months, the issue didn't come back on. The gauge works as it should and I did nothing.

I am impressed you get 200-250 miles on a tank. At sea level I average 10 mpg in town… 12.5-14 hiway. About 200 in town is it. We’ll 99 Landcruiser 33 inch tires, and 70-80 mph on the freeway.

Tex

 

[nissanh]

I am impressed you get 200-250 miles on a tank. At sea level I average 10 mpg in town… 12.5-14 hiway. About 200 in town is it. We’ll 99 Landcruiser 33 inch tires, and 70-80 mph on the freeway.

Tex

Mine is all stock with 265 75 16 AT tires (Discount tire Pathfinder A/T) e rated. I get 12.5 to 13 in city and highway about 15.5 to 16.5 at 73+ MPH. I comfortably do 225-250 miles before each fill up and I never hit reserve light ( I believe I can do 300 but don't want to take any chances in West TX lonely roads!. I used to get max of 12.5 MPG highway (same tires, and stock) when I first bought it. Did regular oil service and most importantly replaced 4 coil packs that were non-OEM. I got Sequoia Toyota OEM coil packs (junk yard) and new set of plugs. OEM air and fuel filters.

 

[obe12]

Mine is all stock with 265 75 16 AT tires (Discount tire Pathfinder A/T) e rated. I get 12.5 to 13 in city and highway about 15.5 to 16.5 at 73+ MPH. I comfortably do 225-250 miles before each fill up and I never hit reserve light ( I believe I can do 300 but don't want to take any chances in West TX lonely roads!. I used to get max of 12.5 MPG highway (same tires, and stock) when I first bought it. Did regular oil service and most importantly replaced 4 coil packs that were non-OEM. I got Sequoia Toyota OEM coil packs (junk yard) and new set of plugs. OEM air and fuel filters.

Mine has the 33 inch tires and 2 inch lift, with off road front bumper. It seems lift , larger tires all go towards lower gas mileage. The power seem a lot less compared to my v8 runner same engine non VVTI engine. I eventually did part time 4x4 kit in the transfer case, along with a 10% underdrive kit, plus low range gear set in the transfer case. The drive ability really improved … better acceleration and tip in the gas pedal at 70-80 and can accelerate without downshifting. 60-65 MPH in 3000-5000 feet got 15 mpg. Interstate hiway through New Mexico 75-85 12.5 average.

More wind load with the lift, and larger bumper I am sure doesn’t help.

I run on e85 primary now, with replacement hi flow fuel pump. 1.79 per gal over 2:39 is nice. The increased fuel burn is really 9 ish in town instead of 10. Still about 1/3 bucks cheaper in gas over 180-200 miles. Not a lot at all but the e85 runs a lot better than 87-88 octane.

I have a supercharger coming to boost the engine to travel in the mountains pulling large 11.5 foot tall trailer 18x8.5 feet 7500 lbs.

The e85 with the supercharger goes hand and hand.

Now fuel pump change, recommended unplugging the pump via body connector to depressurize the fuel system to disconnect the fuel lines from the fuel pump.

I exchanged the pump about 2 months ago. Now this last two days a gremlin came in, flashing low fuel light, and two miles later stalled out.

Cycle key, fuel gauge came back, low fuel light turned off, and started. Drive home 2/3 miles.
Suspect the connector under the body in front of the tank I disconnected to depressurize the lines.
This may have compromised my electrical connection to both the sender and pump.

Tex

 

[obe12]

Ok everyone here we go…

Removed the rear seats and access panel to my Fuel Pump. Used my back probs to stick connections to my fuel pump power and ground.

Start truck, see little less than 8 volts engine running. Wait a min I think, loss of power to pump voltage drop. Go to truck ground and power 13.2 volts not really in the supply line, ground to ground there it is. Ok, trace back through intermediate connector at the body outside the vehicle and check car side of the connector, same loss. Hum
Shut off truck, go back across pump wires at pump, start and while starting get 13.2 and run 8 ish volts, so the fuel pump ECU must be varying the ground to change power at pump. I de pin the connector ground and jump ground lead to pump to chassis ground and have 13.2 volts. However it runs pump key on engine off .. not idea .. incase of roll over or accident pump stays running key on.

Now to say when I pulled on the connector to remove the plastic side anchor pin, he truck died with little to no movement of the connector, bingo found my issue. Unplugged it and did the voltage testing. De pinned each fuel sender wire one at a time. Only the opening the yellow green wire caused my flashing low fuel lamp. I could replicate this too. Loss of connection on this one circuit causes low level fuel light to blink as it did that day.


There is corrosion on the ground wire of the pump through this connector.

The plan, cut connector out, replace it with outside sealed connector with new pins and seals.
Ordered from Lexus V8 .com, Timmothy.

Now the voltage drop on ground…. With aftermarket pump hi flow pump going Supercharged. I need to address this.

Maybe a relay triggers by ground control of the fuel pump ECU to take pump to ground and run 13.2 volts. When ECU opens ground, it open replay to stop pump. Or figure what signal the ECU sends to the fuel pump ECU and use this signal to build a box to ground the fuel pump to run on hi.

Last, I took a jumper and jumped the two terms on the relay on the fuse box and pump supply voltage have about a 1 volt drop, next use jumper to battery to these terms and and still have .9 volt drop. To pump , compared to battery pos term. Hat about .1 volt drop through the fuse and relay when connected. It’s some for sure. Not a lot. I see this across the actually 20 amp fuse. Taking voltage reading at top of fuse. The fuse itself is that drop.

Now any one experience this lower voltage at the pump via fuel pump ECU? By design or a fault ?

Tex

 

[jerryb]

wow, those are some dirty terminals.

you have a fuel pump resistor, far as I know. Verify you do and rule that out. Short the pins at the connector. It's in series on the ground.

 

[obe12]

wow, those are some dirty terminals.

you have a fuel pump resistor, far as I know. Verify you do and rule that out. Short the pins at the connector. It's in series on the ground.

If my year 99 cruiser has a resistor in line on my fuel pump ground or power it isn’t in the Wiring Diagram for my year, However Some later models do.

The Pump wires directly to the Fuel Pump ECU both lower and ground legs, through this pictured mid harness connector.

The Fuel Pump ECU is powered directly by the 20 am known issue EFI fuse through a 4 pin relay. The power side of the relay also splits off to the Main ECU and the load side of relay power when tripped closed the fuel pump ECU with no resistors in line. There are two other wires to the Fuel Pump ECU they one comes from an inertia switch and another from the main ECU. This signal is unknown if it’s analog off on, or a digital square wave frequency signal to possibly trigger fuel pump ECU low / hi?
This fuel pump ECU is located in the back left side panel under the interior panel. Now I have a Gear Up air down complete drawer system. It will have to be removed to gain access to this fuel pump ECU.

I have a couple of duel trace scopes to look at the signals to this ecm once I gain access to it.

Since I saw full battery voltage to the pump while cranking then drop when running to the pump I suspect this voltage drop is by design of the fuel pump ECU. Now I am not sure on this just suspecting until I actual probe and look
At these signals to the Fuel Pump ECU. More things to discover.

Another “Super cruiser” he has low fuel pressure on his 2007 at boost until he did the resistor bypass in the fuse box to keep pump on HI.

I don’t see this provision on my year make and model.

 

[obe12]

If my year 99 cruiser has a resistor in line on my fuel pump ground or power it isn’t in the Wiring Diagram for my year, However Some later models do.

The Pump wires directly to the Fuel Pump ECU both lower and ground legs, through this pictured mid harness connector.

The Fuel Pump ECU is powered directly by the 20 am known issue EFI fuse through a 4 pin relay. The power side of the relay also splits off to the Main ECU and the load side of relay power when tripped closed the fuel pump ECU with no resistors in line. There are two other wires to the Fuel Pump ECU they one comes from an inertia switch and another from the main ECU. This signal is unknown if it’s analog off on, or a digital square wave frequency signal to possibly trigger fuel pump ECU low / hi?
This fuel pump ECU is located in the back left side panel under the interior panel. Now I have a Gear Up air down complete drawer system. It will have to be removed to gain access to this fuel pump ECU.

I have a couple of duel trace scopes to look at the signals to this ecm once I gain access to it.

Since I saw full battery voltage to the pump while cranking then drop when running to the pump I suspect this voltage drop is by design of the fuel pump ECU. Now I am not sure on this just suspecting until I actual probe and look
At these signals to the Fuel Pump ECU. More things to discover.

Another “Super cruiser” he has low fuel pressure on his 2007 at boost until he did the resistor bypass in the fuse box to keep pump on HI.

I don’t see this provision on my year make and model.

This power / gauge intermittent issues lead me to discover the lower voltage to fuel pump. The OEM pump maybe by design to run at this lower voltage and last. The aftermarket hi flow pump design for e85 may not like the lower voltage over time.

Tex

 

[jerryb]

The reason I said that was this pic below.
I couldn't remember at the time. I had looked years ago. I was pointing it out just in case.
This picture could be wrong also, but even the 80s had them.

 

[obe12]

The reason I said that was this pic below.
I couldn't remember at the time. I had looked years ago. I was pointing it out just in case.
This picture could be wrong also, but even the 80s had them.


View attachment 3514317

Yeah mine is different…

However different source I found this : low / med / Hi commands from ECU is based on voltage sent to the Fuel Pump ECU. This supports my theory of why I saw batt voltage on start and lower voltage engine running / idling.

Tex

My truck doesn’t have a fuel pump relay. It does have a Fuel Pump ECU .

 

[jerryb]

yup, another reason not to bother.

 

[2001LC]

Good job, finding the bad wire housing block.
I had one intermittent AHC problem. Where I found external wire house block not sealing well enough. Resulting in increase resistance and low voltage, when wet/soak. These bad wire housing, can be hard to find.

Fuel pump resistor bypass, is what I think was done, on that 2007 you referred too. Bypass was so fuel pump received a constant full pass though of volts, as if engine at high RPM. Which keeps fuel pressure/flow, at max, at all RPMs.

Fuel pump resistor, in this 03. Is recognized by its heat sink, on RH fender-well. Note: some variations, based on year.

Side note: Dielectric grease, does not improve connection. It helps seal out moisture and oxygen, reducing chance of oxidation/corrosion inhibiting connection.

 

[obe12]

Good job, finding the bad wire housing block.
I had one intermittent AHC problem. Where I found external wire house block not sealing well enough. Resulting in increase resistance and low voltage, when wet/soak. These bad wire housing, can be hard to find.

Fuel pump resistor bypass, is what I think was done, on that 2007 you referred too. Bypass was so fuel pump received a constant full pass though of volts, as if engine at high RPM. Which keeps fuel pressure/flow, at max, at all RPMs.

Fuel pump resistor, in this 03. Is recognized by its heat sink, on RH fender-well. Note: some variations, based on year.

View attachment 3514365View attachment 3514358View attachment 3514357
View attachment 3514370

Side note: Dielectric grease, does not improve connection. It helps seal out moisture and oxygen, reducing chance of oxidation/corrosion inhibiting connection.

Some news to report, the replacemen Sequoia ECU replacement in place of my 99 ECU can be flashed either way, Relay or Fuel Pump ECU.

I run a teat today on my Fuel Pump with my DC power supply, at 7.8 volts 6 amps, 10 volts 8 amps, and 13.5 Volts 10 Amps. My AEM E85 capable FP is rated at 43 psi and 13.5 Volts.. Its voltage ran ge is 6-18 volts. I am going to reach out to AEM and ask can I supply low, medium and Hi Voltages and not compromise Pump life. My 387600 mile OEM pump lasted years operating this way. My plans is E85 and Supercharger 7-8 PSI boost, with 365 CC injectors, Air Fuel ratio wide band gauge, with Hi Flow E85 capable fuel pump with Adjustable Fuel pressure regulator. Supercharger Elate supplied is on its way and due hopefully before the New Year.

If AEM fuel pump allows Low, Med, Hi operation, I have to make sure no fuel lean out conditions will happen under boosting 7-8 PSI at Sea Level. The new injectors 365 CC should help keep the required fuel pressure down.

I will update once I know more.

Tex