Fuel Drain Back

[Andrew in SE GA]

I know this topic has been beaten to death on this forum but I don't know what else to do.
I have a 1997 TJ 4.0. It has had 3 fuel pumps (the last 2 were delphi) and a new set of injectors and it still has a fuel drain back if it sits for more than 24 hours.
I have also changed the Schrader valve on the fuel rail, the CPS sensor, and many other parts.
If this jeep sits for more then 24 hours turning the key on and off 10 times will still not make it start immediately, it still sputters to a start.
After that it runs great!
Does anyone have any advice other than to replace the fuel pump again?

 

[NashvilleTJ]

I know this topic has been beaten to death on this forum but I don't know what else to do.
I have a 1997 TJ 4.0. It has had 3 fuel pumps (the last 2 were delphi) and a new set of injectors and it still has a fuel drain back if it sits for more than 24 hours.
I have also changed the Schrader valve on the fuel rail, the CPS sensor, and many other parts.
If this jeep sits for more then 24 hours turning the key on and off 10 times will still not make it start immediately, it still sputters to a start.
After that it runs great!
Does anyone have any advice other than to replace the fuel pump again?

Did you replace just the pump, or the entire assembly?

 

[Andrew in SE GA]

Did you replace just the pump, or the entire assembly?

The whole assembly 3 times

 

[Woodrow]

Have you verified the fuel pressure is good (around 47 PSI IIRC) when running and drops when it sits with a gauge?

 

[Andrew in SE GA]

Yessir. Pressure is good. When running but drops slowly over 24 hours

 

[NashvilleTJ]

The check valves on that delphi assembly could very well be causing the problem - assuming there are no leaks on the engine side. I know the OEM fuel assemblies are no longer available, and the aftermarket stuff is not good. Rather than continue to play Russian roulette with new assemblies, one option would be to add a fuel line check valve on the fuel line back close to the tank.

But the fact that you say cycling the key 10 times does not make it start, tells me there may be something else going on. If everything is working properly but the check valves, it should start normally after about 3 cycles.

 

[Andrew in SE GA]

Could I add a check valve to the rubber hose that comes off the top of the pump? Do you have one you recommended?

 

[NashvilleTJ]

Could I add a check valve to the rubber hose that comes off the top of the pump? Do you have one you recommended?

Yes, that location would work. No recommendations for a check valve, but I’m sure you can find one for 5/16” line (assuming you are still stock there) over on Summit.

 

[Tob]

Have you replaced the fuel pressure regulator assembly that sits on top of the pump? I believe that has a check valve in it as well that can fail.

 

[jonny jeep]

Could I add a check valve to the rubber hose that comes off the top of the pump? Do you have one you recommended?

Do not do this.

Others have done this in the past and the increase in pressure due to heat soak can cause hoses to pop off. The result can be fuel leakage and TJ turning to ashes.

 

[macleanflood]

I put a $60 or so Brute Power pump assembly off Rock Auto in my 97 last year and zero issues.

Throw a cheap pump assembly at it and see what happens.

-Mac

 

[NashvilleTJ]

Do not do this.

Others have done this in the past and the increase in pressure due to heat soak can cause hoses to pop off. The result can be fuel leakage and TJ turning to ashes.

You need to explain this one, as I have never heard of this: how does heat soak cause hoses to pop off?

If hoses are popping off due to pressure, they are not installed correctly. Also, how is this any different than having the stock check valve right there on top of the fuel pump assembly?

 

[jonny jeep]

It's just something I remember from my years on forums over 25 years of TJ ownership. I think at least one jeep, maybe more has burnt down after fuel leaks caused by heat soak where external one way valves were fitted.

I've also seen somebody post the same thing recently in another thread which came to mind when I read this thread.

Maybe hoses didn't pop off, maybe they just leaked. Hard to tell after a vehicle's burnt down.

 

[Moglocker]

It's just something I remember from my years on forums over 25 years of TJ ownership. I think at least one jeep, maybe more has burnt down after fuel leaks caused by heat soak where external one way valves were fitted.

I've also seen somebody post the same thing recently in another thread which came to mind when I read this thread.

Maybe hoses didn't pop off, maybe they just leaked. Hard to tell after a vehicle's burnt down.

Shouldn’t be any different than the one that is in the pump,I would at least install this just to see if it fixes the problem,

 

[jonny jeep]

Above the pump is the fuel filter/pressure regulator. If pressure is held at the pump, but increases due to heat soak, the pressure regulator allows over pressure fuel to drop back into the tank. If an in line check valve is added increased pessure cannot bleed off and increases chance of leaks.

 

[forstmeister]

I put a $60 or so Brute Power pump assembly off Rock Auto in my 97 last year and zero issues.

Throw a cheap pump assembly at it and see what happens.

-Mac

Any issues with this pump yet? I am looking at the same one for my 97 that crapped out last night

 

[macleanflood]

Any issues with this pump yet? I am looking at the same one for my 97 that crapped out last night

No issues!

-Mac

 

[MO 02 X]

A week and 200 miles ago, I replaced my fuel pump assembly with a delphi. (02 4.0 with 150,000 miles)

Overnight fuel pressure goes to 0. One prime cycle with the key = 42 lbs. 3 minutes later = 30 lbs. 10 minutes later = 24 lbs. (I did not start the engine.)

Same experiment but with starting engine. running = 54 lbs steady. shut off immediately = 48 lbs. 30 seconds later = 40 lbs. 3-4 minutes later = 30lbs. 10 minutes later = 16 lbs.

So...consistent results. Delphi check value most likely issue? Should i look for other issues before replacing it, again?

BTW...this started by chasing extended crank times. 3-4-5 seconds then always start and run. My crank times are virtually unchanged whether I key prime and have fuel pressure or not. But thats for a different thread.

Jeep totally useable this way so maybe isn't hurting anything anyway. IDK

Thanks.