Fuel Range.. how far past zero can you go?

[LH Lead Foot]

This topic about running low fuel, bothers me a lot. If you want to know what empty looks like, yes, take an extra fuel can and go for a drive, make note. But never do this as part of normal practice. 

As stated, it cools the pump and lubricates it, while suppling an un-aerated volume of fuel to supply correct pressure to eliminate misfire. While passenger cars fall into a different DOT / CARB category, trucks follow a year or two later with the same components for the most part. Now, we have the expense "Bucket" type fuel pump assembly. It has two designs that started in 1997 to meet misfire regulations and the manufactures screamed until the misfire counter was relaxed.

First Design, has a simple umbrella one way valve on the bottom of the plastic bucket. This allows fuel into the bucket to surround the pump and avoid misfire as this is an emissions no no.

Second design: This has a small high pressure bleed on the pumps outlet. This tiny fuel volume travels to a brass jet on the base of the bucket. Its is used to create the venturi effect, to create a vacuum on the bottom sock type screen. But it fills the bucket for reasons above, put passes though a second sock-type filter on the pump itself. This type by design will draw all of the fuel it is exposed to regardless of the amount of fuel, turns or movement. They even include a float to release fuel if too high inside the bucket on many designs, plus, with return type fuel systems, the return fuel is dumped into the bucket, not the tank. (I will try to post photos). 

Every time you refill the tank, you may get a little fine dust with your fuel. With tank size, average fuel MPG and the current mileage on the vehicle can estimate the number of re-fueling events the vehicle has seen. This dust is not in all fuel, but many gas stations will have a small amount and adds up in your tank. The fuel pump is not a garbage disposal, and this dust wears the pumps vanes and commutator plates & brushes over time. 

If you experience a pump failure, three tab & a pocket screwdriver will allow the bucket to slide off, just enough to look inside. It is the bottom of the bucket, while the tank is the source. GM eSI direct the technician to inspect the pump. If debris is present, the tank must be removed and cleaned. This is getting rid of the remaining fuel properly, but washing the tank with the hottest water you can get. Rock and agitate the tank to help remove the debris, wipe clean and air dry, then install the pump assembly and tank. This information is in the diagnostic flow chart for a reason. 

Shops, big and small plus dealers that follow this procedure have reduced fuel pump failures almost completely. Delphi or ACDelco is the only pump I would ever install. Checking the terminals, replacing the inline filter and normal R&R best practices will help eliminate you or your customer from have to default to tennis shoe mode.

Below are photos I took or diagrams and screen shot with amp clamp & scope.

#1 E85 armature on the right.

#2 G-Rotor pump

#3 Rusted roller vane pump

#4 New Turbine used 20 years

#5 Venturi Vacuum Valve on New Bucket Types

#6 Worn Commutator plates / Plastic shown is the BLK

#7 Worn Fuel Pump Amp clamp wave pattern

#8 Good Fuel Pump wave form Pattern

 

Hope this Helps all who drives / This is GM stuff / I can not speak for others

[Silverado4x4]

5 hours ago, diyer2 said:

Not hear say IMO, fact.

The fuel also lubricates the pump, directly related to cooling it.

 

If you replace your vehicles every 3 or 4 years run it down if you can't find the time to fill it up.

 

I do fills at half a tank, or 1/4 when on the road.

 

When I was buying a fuel pump at the dealer for my 93 Silverado the service guy asked how many miles were on the truck. When I told him the mileage he replied you don't run your gas tank low do you.

 

Our Honda has a 105 K miles with the original fuel pump.

 

Funny you said that as my 96 I had I use to run the tank down just before (E) and my pump went up don't remember the mileage maybe around 20,000 and a friend of mine that runs the shop at the dealership ask me the same thing then went on saying about the fuel in the tank what it does for the pump other then pumping fuel.

[LH Lead Foot]

Regardless of what you drive or the year it was made, a simple check online at fuel pumps will show you the type of fuel pump you have.

 The type used for 50+ years, attaches to the tank at the top with a metal ring. Ok so far. When you pull it out, you find a ground wire & one for the fuel sensor. There is a float that swings just like new ones, but could be "Bent" if you want to cheat a LOW TANK READING. It's up to you if you want that, but if your son or daughter runs out of fuel, the big "E" on the dash should scare them and avoid you getting the phone call at 3AM "Dad, I ran out of gas". (Leave 3 -4 gallons in there and don't tell them)

This is a top referencing tank sender, wire wound resister for 0 - 90 ohms for the gauge. As the "EFI" badge started to show up on the trunk lid on certain models, like a whole 13 PSI that goes to a little hose squirter under the air cleaner. Wow. No carb! This is lovingly called a "Pump on a Stick".

Now, with 60 PSI being normal rail pressure, and the pump jumped to $450+ and came in a big box with a plastic bucket, rubber feet on the bottom with springs...basically all kinds of new weird stuff. Now, during installation, you get the flange cleaned of gravel, sand, dirt, corn cobs and place the O-ring in placed, you found out it have to be pushed down to get the ring started. This is bottom referencing. Then, a few years later they added a pressure sensor and the CEL light was on all of the time a few days after someone put gas in it. Welcome to clock run, computer driven EVAP systems. The sensor measures inches of water. Yep, H2o. Running down the road, the computer turns on the purge valve when the engine is warmed up and you're at highway speeds, the PCM uses PWM to open the purge valve to pull in gas fumes of hydrocarbon vapors, causing an exothermic event in the carbon canister. The PCM monitors fuel trim by the 02 sensors to keep the engine from running rich. Oh yes, the canister gets warm during purge. The poor old fuel tank vent solenoid, sits there under the rear fender, allowing dirty dusty air to enter the canister, letting air in so vapors can pass thru the canister to empty and burn those fumes. After all, you paid for them and engines like fuel in vapor form, not liquid. The canister is tied by the gallons of fuel it will hold. 

Now, I said time clock, EVAP, purge, all kinds of crap that some techs to this day don't completely understand. Yes, depending on the vehicle, but about every 6 hours of engine run time, it will trigger an EVAP test. The purge is opened, the tank gets vacuum, the vent valve closes and it watches the pressure sensor drop until it hit 8" h2o. It closes purge and the tank & hoses are sealed. Right? Well if the cap is hanging, or did not click, or the vent valve is full of dust & dirt, you know, under the truck behind the fender. No dust or dirt ever goes there. Then as the timer count two minutes and the sensor show less that 12" of h2o, you pass. If it fails, it saves a screen capture of all of the engine / EVAP PID's for future viewing. (A TECH2 will show 5 fail records captured in history) It is a type 2 failure so the CEL does not come on...until it fails the second test, then light! But wait, If it fails a large leak, the cap maybe loose, so engineers got clever and said, Hey, we can tell the driver using the information center. 

I know shops, DIYer's and farmers that take the tank valve, maybe relocate it, but wrap it in foam and put two white socks over it with a little tape maybe. Plus to run EVAP, the tank can not be full or completely empty, therefore it has to be between 90% to 10% before it runs the test. This is why the "Check Gas Cap" message does not come on when you get home and see the cap hanging there after filling up that morning. The cap has changed as well. Yes, it still allows air to enter the tank so it does not flatten out, but they change the pressure release from 1 PSI to 2 PSI. 

Sulphur is bad, so it attacked the ceramic card with the silk-screened resistor ink that contains silver, to turn into silver sulfide. The sender would not read very well and some people ran out of gas while showing full. In "some" models they changed the reading from 40 ohms full, to 280 ohms full. It remains that way today, 40 ohms empty & 280 ohms full. Some vehicles have to have the PCM reprogrammed to fix this reading, plus the speed at which it reads. People complained that when the had 1/4 tank and turned off the interstate, it would go to empty. So new programming changed the re-fresh rate of the sender to once every 12 seconds and only 20% of the last reading at any given time. So the ceramic card has ink with gold, nickel and other stuff. This make the type of fuel sender important too. I don't think some brands know about this, or sell the updated goodies.

My experience is aftermarket brand copy the first design from the manufacture. If it changes to "Second Design", you are not getting it unless you purchase a Delphi or ACDelco.

The photo's below should tell you to inspect the fuel pump, sock filter, inside the plastic bucket...then make a decision. If this junk is in there, and you do not remove the tank to clean it with hot water and agitation, then you will have a repeat failure real soon. Not fun!

It's ok...This is only about 3 or 4 reasons why you get a code or check engine light. There is only 389 or more to go though and understand. It all easy! Welcome to OBD-II and enable criteria. 

What my point? There is a lot of stuff going on back there, when it comes to fuel pumps and the wires, gadgets and junk hanging off or around the tank. Learning may have occurred. It's not your grandfathers fuel pump anymore! 

Have a nice day! Retired ASE Master Tech / Since 1978

 

#1 Modular Reservoir Assembly Fuel Pump

#2 Fuel Sender Ceramic Card /certain metals other than silver.

#3 Fuel Tank Vent Solenoid / Turned in under warranty at dealer

#4 Dirt & trash in MRA type Fuel Pump / turned in for warranty

#5 Dirty E85 Corroded Fuel Pump / Not SS E85 Pump Housing

Edited April 10, 2019 by LH Lead Foot
spell check sucks with mechanical words.