Fantabox

New Member
Joined
Mar 31, 2021
Messages
10
Location
Snohomish, Washington
Hello Everyone,

My name is Patrick. I live in Snohomish, Washington (pronounced Snow-Home-Ish). I have owned this Jeep before I even had a license. My grandfather bought it new.

The Basics:
1993 YJ 2.5L with 95K miles

My Actions Prior To The Issue:
- Changed the oil & filter
- Cleaned the fuel tank thoroughly
- Replaced the fuel pump & filter/ regulator in the fall of 2020
- Replaced spark plugs & cables
- Replaced the serpentine belt
- Replaced the coolant, thermostat, gasket, coolant lines, and flushed the heater core (not in that order)

The Issue:
Oil in the fuel tank, which caused the new fuel pump to quit. I DID NOT put engine oil in my fuel tank.

Other Information:
The Jeep was running very rough after replacing the fuel pump (and the items listed above). Loping and struggling to run smoothly. My suspicion was the fuel injectors were bad. The Jeep had not been running for nearly 5 years, so I replaced everything other than the injectors (hoping they were okay since I didn't see any build-up on them when removed). When I decided to replace the injectors I wanted to drop the tank again since the fuel pump was no longer functioning (still had power to the unit), remove the old pump assembly, and make sure I hadn't broken any wires or accidentally grounded the unit artificially.

Once I dropped the tank and removed the assembly I noticed a dark sheen on the fuel level indictor. I removed some fuel from the tank and instantly recognized the abundance of oil within the fuel. I have never seen oil get into a fuel tank before, and am not sure what caused the issue. The tank was cleaned prior to this, and new fuel was used (approximately 3 gallons). There was nothing in the tank to cause this prior to me re-installing the tank the first time.

My Questions:
1. Has anyone seen this before?
2. What causes this?
3. Is there a solution, or am I looking at major investments?
4. If you suspect this isn't engine oil in the fuel, then what could it be?

I can provide photos of the oil in the fuel, but I assume the more seasoned mechanics have encountered oil in fuel before.

Thank You!

Patrick
 

jeepjoe43

YJ Enthusiast
Joined
Dec 4, 2020
Messages
242
Location
Black Canyon City, AZ 85324
Hello Everyone,

My name is Patrick. I live in Snohomish, Washington (pronounced Snow-Home-Ish). I have owned this Jeep before I even had a license. My grandfather bought it new.

The Basics:
1993 YJ 2.5L with 95K miles

My Actions Prior To The Issue:
- Changed the oil & filter
- Cleaned the fuel tank thoroughly
- Replaced the fuel pump & filter/ regulator in the fall of 2020
- Replaced spark plugs & cables
- Replaced the serpentine belt
- Replaced the coolant, thermostat, gasket, coolant lines, and flushed the heater core (not in that order)

The Issue:
Oil in the fuel tank, which caused the new fuel pump to quit. I DID NOT put engine oil in my fuel tank.

Other Information:
The Jeep was running very rough after replacing the fuel pump (and the items listed above). Loping and struggling to run smoothly. My suspicion was the fuel injectors were bad. The Jeep had not been running for nearly 5 years, so I replaced everything other than the injectors (hoping they were okay since I didn't see any build-up on them when removed). When I decided to replace the injectors I wanted to drop the tank again since the fuel pump was no longer functioning (still had power to the unit), remove the old pump assembly, and make sure I hadn't broken any wires or accidentally grounded the unit artificially.

Once I dropped the tank and removed the assembly I noticed a dark sheen on the fuel level indictor. I removed some fuel from the tank and instantly recognized the abundance of oil within the fuel. I have never seen oil get into a fuel tank before, and am not sure what caused the issue. The tank was cleaned prior to this, and new fuel was used (approximately 3 gallons). There was nothing in the tank to cause this prior to me re-installing the tank the first time.

My Questions:
1. Has anyone seen this before?
2. What causes this?
3. Is there a solution, or am I looking at major investments?
4. If you suspect this isn't engine oil in the fuel, then what could it be?

I can provide photos of the oil in the fuel, but I assume the more seasoned mechanics have encountered oil in fuel before.

Thank You!

Patrick
Hi Patrick,
This smacks of human error, I'm not aware of anything mechanically that would do this,
First question, has the vehicle been driven or loaned out, or otherwise out of your control?
Does someone else know where the keys are? Like Kids or Grand-kids, who may have snuck it out?
Does it smoke when it runs?

I'm an old small engine mechanic and I have seen anti-freeze in the gas tanks of lawnmowers.
This has happens when dad tells his boy "Gas is in the plastic can". The kid doesn't know what can...
Just saying this just doesn't sound like it's the Jeeps fault. I could be wrong...
Reasoning it out, I just can't find any other reason for it.
Your running problems sound more like water than oil.
Could also be a broken tank, though I suspect you would halve found that the first go-around.
I can only postulate with the information I have, and my own experiences.
 

cas

Member
Joined
Nov 11, 2020
Messages
28
Location
NY
I've been trying to come up with some really wrong scenario... like when I bought mine, the evap line from the tank was run up to the vacuum port on the EGR valve,. lol But anything I came up with, besides being far fetched, would require serious, obvious long term issues and even then probably wouldn't do it. #1 cause is probably an accident., as stated above. #2 cause would be the same action, on spite.

I'm thinking it must have been a LOT of oil, or some really heavy stuff.

(While not the same oil, I ran a blazer on 2 cycle mix for a year without issue, and not pouring pre-mix into the tank, but adding oil to the tank)
 

Flyer58

YJ Enthusiast
Joined
Apr 12, 2020
Messages
366
Location
Magnolia, Texas
I'm thinking the same thing that it was fueled with diesel or some other pre-mix from a gas can.

The only other hose in close proximity is a vent hose from the rear axle which vents up near the tank but even if if got connected to the tank it would be a stretch to see how differential oil could get into the tank.
 
OP
Fantabox

Fantabox

New Member
Joined
Mar 31, 2021
Messages
10
Location
Snohomish, Washington
Hi Patrick,
This smacks of human error, I'm not aware of anything mechanically that would do this,
First question, has the vehicle been driven or loaned out, or otherwise out of your control?
Does someone else know where the keys are? Like Kids or Grand-kids, who may have snuck it out?
Does it smoke when it runs?

I'm an old small engine mechanic and I have seen anti-freeze in the gas tanks of lawnmowers.
This has happens when dad tells his boy "Gas is in the plastic can". The kid doesn't know what can...
Just saying this just doesn't sound like it's the Jeeps fault. I could be wrong...
Reasoning it out, I just can't find any other reason for it.
Your running problems sound more like water than oil.
Could also be a broken tank, though I suspect you would halve found that the first go-around.
I can only postulate with the information I have, and my own experiences.
I was hoping the issue would have been caused by me, but I never removed any vacuum lines, I am the only key-holder, used new fuel from a new container, and when it was running there was zero blue smoke from the tail.

I'm at a complete loss on this issue, and have NEVER experienced this ever.
 
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Fantabox

Fantabox

New Member
Joined
Mar 31, 2021
Messages
10
Location
Snohomish, Washington
I've been trying to come up with some really wrong scenario... like when I bought mine, the evap line from the tank was run up to the vacuum port on the EGR valve,. lol But anything I came up with, besides being far fetched, would require serious, obvious long term issues and even then probably wouldn't do it. #1 cause is probably an accident., as stated above. #2 cause would be the same action, on spite.

I'm thinking it must have been a LOT of oil, or some really heavy stuff.

(While not the same oil, I ran a blazer on 2 cycle mix for a year without issue, and not pouring pre-mix into the tank, but adding oil to the tank)
I was tossing around some fairly irregular theories in my head. Including a vacuum line from the differential, EGR port, injector was allowing oil bypass into the fuel return line, etc etc etc.

Nothing makes sense on this, and my only course of action is to clean out the tank...again...and see if I can replicate the issue.
 
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Fantabox

Fantabox

New Member
Joined
Mar 31, 2021
Messages
10
Location
Snohomish, Washington
I'm thinking the same thing that it was fueled with diesel or some other pre-mix from a gas can.

The only other hose in close proximity is a vent hose from the rear axle which vents up near the tank but even if if got connected to the tank it would be a stretch to see how differential oil could get into the tank.
I thought about this too, but it seemed TOO FAR STRETCHED even for my imagination. Glad someone else is pondering these types of possibilities.
 
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Fantabox

Fantabox

New Member
Joined
Mar 31, 2021
Messages
10
Location
Snohomish, Washington
Thank you for the replies thus far. I will keep this post updated as I venture out into the unknown with this issue. NEVER seen this, even when I was a mechanic, and I was hoping someone had a known fix.
 
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Flyer58

YJ Enthusiast
Joined
Apr 12, 2020
Messages
366
Location
Magnolia, Texas
Ok one last shot in the dark. When you say you cleaned your fuel tank are you sure the tank was clean and dry before reassembly? I washed out mine too and there was a lot of water remaining inside even after shaking it upside-down for a while. I had to reach in with a sponge and paper towels then let it sit in the sun and dry out.

I'm also thinking it may not be oil but some type of bacterial growth from water condensation in the gas.
 
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jeepjoe43

YJ Enthusiast
Joined
Dec 4, 2020
Messages
242
Location
Black Canyon City, AZ 85324
Thank you for the replies thus far. I will keep this post updated as I venture out into the unknown with this issue. NEVER seen this, even when I was a mechanic, and I was hoping someone had a known fix.
I have another theory, that it may be antifreeze. Admittedly, I have never observed the behavior of gas/antifreeze mix.
The Polyethylene Glycol could separate from the water and create a rainbow slick on top of the gas.
While water always sinks to the bottom of the tank.
Your running symptoms sound like water, particularly the lack of blue smoke.
To me this sounds like either an act of malice, or ignorance, not on your part of course.
Do you have a locking gas cap?
 
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Fantabox

Fantabox

New Member
Joined
Mar 31, 2021
Messages
10
Location
Snohomish, Washington
Ok one last shot in the dark. When you say you cleaned your fuel tank are you sure the tank was clean and dry before reassembly? I washed out mine too and there was a lot of water remaining inside even after shaking it upside-down for a while. I had to reach in with a sponge and paper towels then let it sit in the sun and dry out.

I'm also thinking it may not be oil but some type of bacterial growth from water condensation in the gas.
The tank was fully cleaned out nearly two weeks before being re-installed. It was bone dry.
 
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Fantabox

Fantabox

New Member
Joined
Mar 31, 2021
Messages
10
Location
Snohomish, Washington
I have another theory, that it may be antifreeze. Admittedly, I have never observed the behavior of gas/antifreeze mix.
The Polyethylene Glycol could separate from the water and create a rainbow slick on top of the gas.
While water always sinks to the bottom of the tank.
Your running symptoms sound like water, particularly the lack of blue smoke.
To me this sounds like either an act of malice, or ignorance, not on your part of course.
Do you have a locking gas cap?
The Jeep is always in our garage/ shop and I am the only person out there. This entire issue is perplexing, and I am not 100% certain what caused the issue.
 
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Fantabox

Fantabox

New Member
Joined
Mar 31, 2021
Messages
10
Location
Snohomish, Washington
I plan on working on this issue starting on Wednesday. The strategy will be to get the new pump hooked up, but inside a clean bucket with new fuel, and the return line will dispense into another clean bucket. That way I know new fuel is going into the lines, and I can separate any tainted fuel from the fresh fuel.

If anyone has a better way to do this I am all eyes.
 

Flyer58

YJ Enthusiast
Joined
Apr 12, 2020
Messages
366
Location
Magnolia, Texas
I plan on working on this issue starting on Wednesday. The strategy will be to get the new pump hooked up, but inside a clean bucket with new fuel, and the return line will dispense into another clean bucket. That way I know new fuel is going into the lines, and I can separate any tainted fuel from the fresh fuel.

If anyone has a better way to do this I am all eyes.
Sounds like a very good plan. Let us know what comes out.
Somewhere in here you'll find a way to jumper the fuel pump relay so you don't need to start the engine.
 

Gary747

Member
Supporting Member
Joined
Nov 7, 2020
Messages
38
Location
Lancaster, CA
My YJ is the 1990 version, converted to fuel injection (got rid of the carburetor) and I have observed something that I ask others to comment on. Whenever I open the gas cap to refuel, I experience tank pressure relief as the cap loosens... the tank is pressurized as I drive. The lower the fuel level, the more pressurized "air" volume in the tank and the bigger the "hiss" is as the cap comes loose. I've always liked this, as this pressurized fuel lessens the work required from the fuel pump to move gasoline to the injector rail. I've already been challenged that it's really a vacuum and that I am misinterpreting the direction of pressure relief. BUT, I can guarantee that the tank is pressurized and that the relief airflow blows OUT of the gas filler port.

I have always felt that the pressure comes back to the fuel tank from the charcoal filled evap canister in the emissions system, but I'm not positive. But since this thread concerns oil or other contamination getting into the fuel tank, I can definitely say that on my Jeep, there is a positive energized flow conduit INTO the fuel tank. So my recommendation is to think about this when tearing into your tank, that there may be an unfiltered by-pass in your fuel pump or emissions system allowing contamination to enter. If your tank no longer holds pressure (vacuum or positive), consider loose filler hose clamps and an open (broken) rollover anti-leak valve (located behind the right rear wheel well on my Jeep).

Please, though, remember to post what you find... many come here looking for advice but we often don't hear how it comes out. These unusual problems are a pain for you, but a learning opportunity for everyone.
 
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jeepjoe43

YJ Enthusiast
Joined
Dec 4, 2020
Messages
242
Location
Black Canyon City, AZ 85324
My YJ is the 1990 version, converted to fuel injection (got rid of the carburetor) and I have observed something that I ask others to comment on. Whenever I open the gas cap to refuel, I experience tank pressure relief as the cap loosens... the tank is pressurized as I drive. The lower the fuel level, the more pressurized "air" volume in the tank and the bigger the "hiss" is as the cap comes loose. I've always liked this, as this pressurized fuel lessens the work required from the fuel pump to move gasoline to the injector rail. I've already been challenged that it's really a vacuum and that I am misinterpreting the direction of pressure relief. BUT, I can guarantee that the tank is pressurized and that the relief airflow blows OUT of the gas filler port.

I have always felt that the pressure comes back to the fuel tank from the charcoal filled evap canister in the emissions system, but I'm not positive. But since this thread concerns oil or other contamination getting into the fuel tank, I can definitely say that on my Jeep, there is a positive energized flow conduit INTO the fuel tank. So my recommendation is to think about this when tearing into your tank, that there may be an unfiltered by-pass in your fuel pump or emissions system allowing contamination to enter. If your tank no longer holds pressure (vacuum or positive), consider loose filler hose clamps and an open (broken) rollover anti-leak valve (located behind the right rear wheel well on my Jeep).

Please, though, remember to post what you find... many come here looking for advice but we often don't hear how it comes out. These unusual problems are a pain for you, but a learning opportunity for everyone.
Too true...