No engine run at 1/8 tank

[Bitsyncmaster]

I've been doing a lot of engine idle testing software changes on my idle ECU. I had run the tank down to 1/8 tank and this morning I could not keep the engine running after start. I tested a stock ECU and another ECU of mine with the old software and same problem. Added 5 gallons to tank and it ran fine.

So has anyone else seen this problem? It could be my level sender has gone bad and I was out of fuel. Or maybe my Tahoe fuel pump works like that.

I will have to investigate this problem later. I'm to busy working that software now. I wonder how my software testing results have failed because of that fuel problem.

[Timeless]

I have experienced that with low fuel in the tank. OE gauge reading close to 1/4 really equates to my car having VERY low fuel. I fill up when at ~1/4 to not risk running out of fuel. One stop recently I added 11.8-12 gallons with the gauge needle reading just about at 1/4 exactly.
Car has DPI pump setup.

[mhanch]

Stock pump and guage and I can run down to almost empty - but i rarely ever do.

[AugustneverEnds]

I have the OEM spec pump and the DGo sending unit. I regularly run it down until the low fuel warning light illuminates without trouble.

[Helirich]

Mine will run, but runs poorly.

[Citizen]

So has anyone else seen this problem? It could be my level sender has gone bad and I was out of fuel. Or maybe my Tahoe fuel pump works like that.

Two thoughts on this:

1) You might try removing the 5 gallons by siphon into a 5 gallon container (so you know when you?ve removed exactly 5 gallons) and verify the tank gauge is indicating 1/8 full, where it was when you noticed the problem. Then, open the top of the tank and run a clean, straight, metal rod or tube down to the bottom and out again, and observe where the wet mark is (do not pickup a stick off the ground to use for measuring, like believe it or not, I?ve seen some people do?I know you already know not to do that ?.).

You might find, as you indicated, that at 1/8th tank indication, you were actually out of fuel (or have only a trace left, enough to maybe start and run for a moment until the pump can?t pick up any more fuel). Thus, your indicator is inaccurate.

2) I too have a GM product (though not a Tahoe) that experienced the almost exact same symptoms. I could always start it, but it wouldn?t keep running unless I kept pumping the gas pedal every 10 seconds or so. After verifying fuel level and replacing a number of fuel related parts, and verifying my exhaust wasn?t plugged up (possibly by critters building a nest in there), all to no avail, I finally replaced the fuel pump as a last resort. And you guessed it, it started right up and ran perfectly.

It seems the fuel pump, while not completely dead, was in the process of failing and could not even pump enough to keep the engine idling without pumping the pedal. So after verifying there is more than just a trace of gas in the tank, then verify you have proper, continuous fuel pressure.


My lesson learned: Start with the fuel pump.

Good luck.
Thomas

[Timeless]

Two thoughts on this:

It seems the fuel pump, while not completely dead, was in the process of failing and could not even pump enough to keep the engine idling without pumping the pedal. So after verifying there is more than just a trace of gas in the tank, then verify you have proper, continuous fuel pressure.

My lesson learned: Start with the fuel pump.

Good luck.
Thomas
FWIW my DPI setup is new - installed in August 2022. My fuel gauge reads differently vs. stock setup.

[Bitsyncmaster]

Thanks for all the replies.

I will find out why this happened when I get time to do testing on the pump. What I will do is just put the return hose in an empty tank and power the pump until the flow stops from the return line. It should stop when the pump can not produce 75 PSI since that is what my PPR is calibrated for.

[cis6409]

Mine has oem set up and runs right down to the low warning Light no problem.

Looking at the integrated pump sender pics set up I can't see how it can suck fuel from the baffle location at the back of the tank where the oem one sucks from.
It can only suck from directly underneath itself??

I used to have that same issue when I ran the old Hervey aluminum baffle set up which could only source the fuel from Directly underneath the pump itself..
I had to keep filling up at 1/4 tank otherwise it would splutter or die which got frustrating so I switched back to oem set up and everything was fine again. Back to full capacity and no more range anxiety..

[Bitsyncmaster]

Mine has oem set up and runs right down to the low warning Light no problem.

Looking at the integrated pump sender pics set up I can't see how it can suck fuel from the baffle location at the back of the tank where the oem one sucks from.
It can only suck from directly underneath itself??

I used to have that same issue when I ran the old Hervey aluminum baffle set up which could only source the fuel from Directly underneath the pump itself..
I had to keep filling up at 1/4 tank otherwise it would splutter or die which got frustrating so I switched back to oem set up and everything was fine again. Back to full capacity and no more range anxiety..

That is good thought of why this may happen. Does the tank sit at an angle?

[cis6409]

That is good thought of why this may happen. Does the tank sit at an angle?

No, the tank doesn't sit at an angle in the chassis I believe , but the combination of the baffle design/size, and location towards the back of the tank means it can always keep a minimum amount till its empty and stops fuel from sloshing around and escaping the reach of the pump suction

[MrChocky]

No, the tank doesn't sit at an angle in the chassis I believe , but the combination of the baffle design/size, and location towards the back of the tank means it can always keep a minimum amount till its empty and stops fuel from sloshing around and escaping the reach of the pump suction

Yes, that said, my car had to be < 1/8 of a tank to be shipped (on an actual ship), and the shipper had trouble starting the car when it was on an angle to be removed from the later truck. That's an early car too, so I don't know if there were design changes later on. I also live in a
very hilly area, and the reading is really iffy if you spend time stopped on a hill. To that end, I have the DM sender; which helps a great deal, unless you happen to stall as well (it's wired to the radio power supply).

[Bitsyncmaster]

It would be best if the tank was higher in the front. You would want extra gas climbing a hill. Going down hill would not make much draw and even if it stalled you can pull over since your still moving.

[Michael]

Newer cars have the pump sit in a low cavity in the tank to offset fuel starvation on hills, curves, etc. The old design used a return line directly in a crude "above ground" capsule. When you add the new design pump you eliminate the low fuel safeguards and can easily starve the pump given the right circumstances.

It also would not surprise me that some gauges may register differently with different types of pump sending units. I just live with it and consider 1/4 tank time to look for a fuel stop.

[Timeless]

More info from yesterday:
With the stock gauge reading 1/4 the fuel tank took 10.58 gallons. [DPI pump kit]

[Delorean Industries]

We tell owners, especially those with EFI, that 1/4 should be considered the lowest level the tank should see. With fuel slosh and integrated pumps not having an external baffle further back in the tank, this can be a problem. Two gallons in the base of the tank is a very small amount.

[Bitsyncmaster]

Here are my notes when I tested my new pump sender. Note if you top the tank up to the filler you get 14.75 gal. I have to run my empty test again since I had that problem starting the engine at 1/8 tank.

I started with an empty tank and put in two quarts of gas. I'm surprised when I ran the pump I got a little flow from the return line with just two quarts of gas in a clean tank.

Note: pump current at 12.6 volts

Empty 39.8 ohms
2 Qt 39.8 ohms 4.8 amps
4 Qt 39.8 ohms 4.6 amps
6 Qt 48.0 ohms 5.5 amps
8 Qt 55.9 ohms 5.5 amps
10 Qt 63.7 ohms 5.9 amps
12 Qt 71.3 ohms 6.1 amps
14 Qt 78.4 ohms ?
16 Qt 85.8 ohms 6.5 amps
18 Qt 93.4 ohms 6.6 amps
20 Qt 101.3 ohms 6.6 amps

I had filled an empty 5 gal jug with 5.0 gal at the gas station and I had ? Qt. left (my error or pump error)

5 Gal 101.4 ohms 6.8 amps
22 Qt 112.8 ohm 6.7 amp
24 Qt 112.7 ohm 6.8 amp
26 Qt 120.3 ohm 6.7 amp
28 Qt 127.8 ohm 6.8 amp
30 Qt 133.9 ohm
32 Qt 140.2 ohm
34 Qt 151.8 ohm
36 Qt 158.0 ohm
38 Qt 157.8 ohm
40 Qt 170.4 ohm

Had about 4 oz left from my 5.00 gal fill up can

10 gal 170.5 ohm
42 Qt 176.7 ohms
44 Qt 182.4 ohms
46 Qt 188.3 ohms
48 Qt 200.5 ohms
50 Qt 206.7 ohms
52 Qt 218.2 ohms

53 Qt 218.3 ohms
54 Qt 223.9 ohms
55 Qt 229.0 ohms
56 Qt 234.3 ohms
57 Qt 234.3 ohms
58 Qt 243.6 ohms
59 Qt 243.8 ohms overflowed 6 inches above top of tank

[Bitsyncmaster]

Just some more thought on this problem. If your running low front suspension and stock back like mine, that makes the problem worse because your tank is tilled forward. Someday I do plan to lower my rear suspension a little.