TBI question.

[Crookedaxle]

When not running, does a '93 454 TBI motor return fuel to the tank as long as the key is on or does it time out after a while? Where does the return line dump the fuel in the tank when it returns? At the top or the bottom?

The reason I'm asking, is I think I have some phase separation going on in my 1/3 full tank of ethanol gas. I went to start it last week when it was about -10F out. It started fine, ran for about 5 seconds or so and then died. I had it outside for a couple of days with the air cleaner off and the butterflies open and tried to start it on a couple of occasions when it was a bit warmer. It never fired. After that I pulled it inside, pulled all the plugs and blasted the throttle body with air after bumping the engine over to a new location every couple of hours over the past weekend. I've got good spark and both injectors are firing. I put new plugs in. Nothing. I'd repeat pulling all of the plugs and then blasting it with air and letting it sit. I've done this a few times. The last time I tried to start it I cranked it over for 30 seconds or so. A few of the plugs were wet, didn't really smell of gas and would hardly light when I put a lighter to them. It's 45F or so inside. That's when it occurred to me that maybe I got a bad tank of gas with some water in it and it separated over night on me when it was cold. It would also make sense why it started fine and died after 5 seconds when the alcohol/water reached the TBI.

So, I dumped 2 containers of isopropyl in the tank along with 5 gallons of non ethanol gas. Tonight I'm going to disconnect the fuel line and pump out the bottom 2-3 gallons in the tank. Hopefully it's mostly alcohol/water. Then I'd like to circulate the tank to get any remaining water/alcohol all mixed back together with some good gas and hopefully started. The good news is, I can now swap out all 8 plugs in about 5 minutes.

 

[Ken K]

Yeh, cold a hell +3 in Omaha as well, but you said it will start, run for 5 seconds, then die. Does it do this all of the time? Even a little warmed inside? The two second prime with key-on, engine-off should be heard. Keeping it going after it starts is IAC position, injector on time, ECT reading and intake air temp (IAT) all work together to adjust A/F to rich enough to keep running. Do you have access to a scan tool that will show engine PID's key-on, engine-off? This would help with diagnostics. Also MAP is never considered and does double duty. Key-on. Engine-off, it takes a reading for altitude...so close to 98kpa, while running, drops to 38-44kpa. I have seen them stuck at 98kpa meaning your altitude is above 12,000 feet.
(Most Likely) I have seen many "No start / Dies " cold from the EGR control. Unplug it. If it uses an electric solenoid to open / close for vacuum on old school EGR, they freeze inside with moisture. The control valve sticks open allowing vacuum to open EGR as soon as it starts. I replaced them, but if removed, warmed up and place in low humidity area, could help fix it. Hell, leave it unplugged for a while. The EGR keeps internal cylinder temperature lower to reduce if not eliminate NOX.
But, in the mean time, unplug it a retry. This will keep blood pressure down.
If it won't stay running, you can also, if you stay back far enough to keep your eyebrows and spray starting fluid, carb spray while a budding is cranking, and this works, the look for fuel supply issue. Pressure is about 13 PSI, 1/2 pint in 30 seconds (16 fluid oz container) This is true for carburated, injected, large or small CID, old or new. The exception is high end dragsters engines, as they spray fuel like a large garden hose, measured in gallons per second.
If it runs while warmer, old school test is a timing light, hooked to battery and any plug wire...shine light on injectors cone-like spray. I will help you see the shape and condition of the actual spray pattern. As for ethanol, a gallon will hold & absorb or dissolve about 6 tablespoons of water. So, it is chemically changed into a liquid and remains this way. (Don't know about real low temps / hell, propane remains liquid and won't turn to gas at -48)
1 gallon of "Methanol" will hold, absorb or dissolve up to 13 table spoons of water. The problem is, it's highly corrosive to fuel pump, lines, O-rings and internal injector coatings. Never recommended.

System pressure can leak down over time, but usually not to zero. The regulator hold the return, fuel pumps internal check valve keeps fuel draining back from supply. Line fitting, O-rings and injectors are the only other places to leak down. Look for wet places within 5-10 minutes after shut down or dies. Place a line with working fitting on regulator into a safe container and watch it while running, then shut off. It should not continue to drip or stay wet. All of these items are just variations of a check valve, and just a little dirt / dust / debris will keep them from completely seating.
You just have to find which one is the culprit...or "Root' cause.
Best of luck. ASE Master tech since 1978 / Retired

 

[Ken K]

Whoops... Taking a sample of fuel off the bottom of the tank is best, yet place it in a safe clear container and let sit for 24 hours. Separation of water, and various amounts of ethanol will be obvious. I have a "J-Tool" that samples fuel and using frequency, show the exact amount of ethanol in the sample.

(Ethanol is less dense than gas, so the E85 devices uses and produces a higher frequency the more ethanol is found. In the GMT800, the ethanol sensor produce a higher peak frequency and the second measurement is time between pulses is for temperature.
A previous design, used no sensor and was dropped from production. The PCM would see a refueling event of 2 gallons or more, then watched the 02 sensors, while disabling fuel trim for 5 or 6 miles of highway driving to get new fuel into the combustion chamber at temperature, then adjust injector on-time. You can figure the problems that came with this)

If E85 is sold in your area, it is easy to pump some amount of this into a vehicle not designed to run on that percentage. It requires way more ethanol to get the same amount of power, compared to gas. I bugs me with a fuel that sells for says 30% less, but has to burn 30% more to run the same. This equation only changes when you get at or above 100% ethanol.
I had 1 customer in 1984, who got about 90% ethanol in his tank at the gas station, where it quit running a few miles from. The mix is done at the fuel distribution center, before the tanker was filled. I guess they where a few beads short of a full abacus.

 

[Crookedaxle]

Yeh, cold a hell +3 in Omaha as well, but you said it will start, run for 5 seconds, then die. Does it do this all of the time? Even a little warmed inside? The two second prime with key-on, engine-off should be heard. Keeping it going after it starts is IAC position, injector on time, ECT reading and intake air temp (IAT) all work together to adjust A/F to rich enough to keep running. Do you have access to a scan tool that will show engine PID's key-on, engine-off? This would help with diagnostics. Also MAP is never considered and does double duty. Key-on. Engine-off, it takes a reading for altitude...so close to 98kpa, while running, drops to 38-44kpa. I have seen them stuck at 98kpa meaning your altitude is above 12,000 feet.
(Most Likely) I have seen many "No start / Dies " cold from the EGR control. Unplug it. If it uses an electric solenoid to open / close for vacuum on old school EGR, they freeze inside with moisture. The control valve sticks open allowing vacuum to open EGR as soon as it starts. I replaced them, but if removed, warmed up and place in low humidity area, could help fix it. Hell, leave it unplugged for a while. The EGR keeps internal cylinder temperature lower to reduce if not eliminate NOX.
But, in the mean time, unplug it a retry. This will keep blood pressure down.
If it won't stay running, you can also, if you stay back far enough to keep your eyebrows and spray starting fluid, carb spray while a budding is cranking, and this works, the look for fuel supply issue. Pressure is about 13 PSI, 1/2 pint in 30 seconds (16 fluid oz container) This is true for carburated, injected, large or small CID, old or new. The exception is high end dragsters engines, as they spray fuel like a large garden hose, measured in gallons per second.
If it runs while warmer, old school test is a timing light, hooked to battery and any plug wire...shine light on injectors cone-like spray. I will help you see the shape and condition of the actual spray pattern. As for ethanol, a gallon will hold & absorb or dissolve about 6 tablespoons of water. So, it is chemically changed into a liquid and remains this way. (Don't know about real low temps / hell, propane remains liquid and won't turn to gas at -48)
1 gallon of "Methanol" will hold, absorb or dissolve up to 13 table spoons of water. The problem is, it's highly corrosive to fuel pump, lines, O-rings and internal injector coatings. Never recommended.

System pressure can leak down over time, but usually not to zero. The regulator hold the return, fuel pumps internal check valve keeps fuel draining back from supply. Line fitting, O-rings and injectors are the only other places to leak down. Look for wet places within 5-10 minutes after shut down or dies. Place a line with working fitting on regulator into a safe container and watch it while running, then shut off. It should not continue to drip or stay wet. All of these items are just variations of a check valve, and just a little dirt / dust / debris will keep them from completely seating.
You just have to find which one is the culprit...or "Root' cause.
Best of luck. ASE Master tech since 1978 / Retired

Well, you sure bent over backwards to NOT answer my two little simple questions.

 

[someotherguy]

When not running, does a '93 454 TBI motor return fuel to the tank as long as the key is on or does it time out after a while? Where does the return line dump the fuel in the tank when it returns? At the top or the bottom?

Simply.. engine not running, ECM/PCM will operate the fuel pump relay for just a few seconds (except trucks equipped with "hot fuel module", these run...20 seconds?) and then shut off. TBI return line dumps just a couple inches under the top of the sending unit.

Richard

 

[Crookedaxle]

Simply.. engine not running, ECM/PCM will operate the fuel pump relay for just a few seconds (except trucks equipped with "hot fuel module", these run...20 seconds?) and then shut off. TBI return line dumps just a couple inches under the top of the sending unit.

Richard

OK, thanks. So will the pump pump gas out of the disconnected fuel line into a 5 gallon jug as long as there is minimal back pressure on it or will it still shut down after after the "few seconds" prime? I'm assuming the ECM/PCM only primes for a few seconds when it sees pressure and if it doesn't see pressure will continue to run the pump therefore letting me pump some out of the tank. Is this the case?

 

[Schurkey]

Fuel pressure has nothing to do with fuel pump prime. The ECM runs the pump for two seconds.

You want to run the fuel pump, you need to power the fuel pump bypass wire, or jump the relay, or crank the engine to keep oil pressure up.

Adding "2 containers of isopropyl" does NOTHING that the ~10% alcohol in typical E-10 isn't doing.

You are NOT going to "mix in" water that has separated unless you dump a shitload of alcohol into the tank. Better to REMOVE the water.

"I" would be trying to run the engine on aerosol carb cleaner or a squirt-bottle of gasoline--verifying that the engine will run if burnable fuel is provided. If it runs, you've cleared all the mechanical issues including spark and fouled plugs, leaving only "bad gas".

At that point, yeah, I'd be using the fuel pump to empty the tank so the tank can be dropped and cleaned out properly. Don't forget to replace the fuel filter, and probably the sock on the electric fuel pump when you're done de-contaminating the tank.

 

[Crookedaxle]

Fuel pressure has nothing to do with fuel pump prime. The ECM runs the pump for two seconds.

You want to run the fuel pump, you need to power the fuel pump bypass wire, or jump the relay, or crank the engine to keep oil pressure up.

Adding "2 containers of isopropyl" does NOTHING that the ~10% alcohol in typical E-10 isn't doing.

You are NOT going to "mix in" water that has separated unless you dump a shitload of alcohol into the tank. Better to REMOVE the water.

"I" would be trying to run the engine on aerosol carb cleaner or a squirt-bottle of gasoline--verifying that the engine will run if burnable fuel is provided. If it runs, you've cleared all the mechanical issues including spark and fouled plugs, leaving only "bad gas".

At that point, yeah, I'd be using the fuel pump to empty the tank so the tank can be dropped and cleaned out properly. Don't forget to replace the fuel filter, and probably the sock on the electric fuel pump when you're done de-contaminating the tank.

Thanks for the info on the pump.


"Adding "2 containers of isopropyl" does NOTHING that the ~10% alcohol in typical E-10 isn't doing."


Not true at all. Ethyl (as used in ethanol gasoline), methanol and isopropyl all carry different amounts of water in gasoline before separating out of the gas. And guess why I only use isopropyl in my vehicles. Because it suspends the most water. And I am pumping out the tank tonight (at least a few gallons), that's why I asked about the functionality of the pump in the first place. I just added the isopropyl and non ethanol gas to suspend the rest of the ethyl alcohol in the gasoline (if any) that hasn't separated out. Ethyl alcohol will carry very little water before separating from gasoline. It doesn't take much, which is why it happens in the first place. It's not like there is 2-3 gallons of water in the tank. I'm guessing it was 10 gallons in the tank so that makes 1 gallon of ethyl alcohol mixed with maybe 20-30 ounces of water laying at the bottom of my tank that I keep sucking up trying to start it. It ran fine on the rest of the tank before the weather got a little cooler and it separated out overnight so that's why I am fairly confidant I didn't pump a bunch of ethanol/water into the truck when I filled up 2-3 days prior. If I did, I would have stalled out a few miles from where I filled up.

It has fired a couple of times when I put a splash of gasoline down the TBI and gave it a couple of shots of either.

 

[someotherguy]

If you want to use the pump to empty the tank, you can power it with jumper wires to the 2 pin connector you'll find running down the driver side of the firewall towards the frame rail, or you can jump pin G on the diag connector (bottom left pin) which will energize the pump relay.

Richard

 

[Crookedaxle]

If you want to use the pump to empty the tank, you can power it with jumper wires to the 2 pin connector you'll find running down the driver side of the firewall towards the frame rail, or you can jump pin G on the diag connector (bottom left pin) which will energize the pump relay.

Richard

Thank you!