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Topic: Intermittent No Start and Fuel Return Line (Read 2071 times) previous topic - next topic

Intermittent No Start and Fuel Return Line

1984, Mercury Cougar, 3.8L
After playing with this intermittent no start forever (6 to 9 months at least),
it finally failed today where I could do some troubleshooting.
While everything checked out OK again,

I did find I could repeatedly restart the car by disconnecting the fuel return line at the throttle body -- but -- with the fuel return line connected It  would always fail to start.

Initially I thought some type of back-pressure issue , but having the return fuel line connected and removing the gas cap still kept the NO-start condition.

I always though the return line just dumped into the tank at the top.

Question:
Anyone have any ideas why disconnecting the fuel line would help a no start?

Intermittent No Start and Fuel Return Line

Reply #1
I would think if your fuel pumps were up to snuff you would have gas coming out of that disconnected return.
"Did everything checking out" include checking the fuel pressure?

Intermittent No Start and Fuel Return Line

Reply #2
X2, gas shuld squirt out of the return. How's the fuel pressure?
Quote from: jcassity
I honestly dont think you could exceed the cost of a new car buy installing new *stock* parts everywhere in your coug our tbird. Its just plain impossible. You could revamp the entire drivetrain/engine/suspenstion and still come out ahead.
Hooligans! 
1988 Crown Vic wagon. 120K California car. Wifes grocery getter. (junked)
1987 Ford Thunderbird LX. 5.0. s.o., sn-95 t-5 and an f-150 clutch. Driven daily and going strong.
1986 cougar.
lilsammywasapunkrocker@yahoo.com

Intermittent No Start and Fuel Return Line

Reply #3
Softtouch and Haystack always great to get your feedback.

Pressure is definitely OK.  Volume is Ok to slightly low.
FWIW:
Finally had a no-start in the garage after running vehicle for about 20 minutes.
Got my 13 / 14 code again -- so said a few choice words -- and ordered a new distributor (reman).
Took awhile to get it (several hours) so vehicle had cooled down and figured it would start again with old distributor still in.
Still no-start.
Put in new distributor and TFI and again no-start.
A friend came by and said try this and crawled underneath and banged on the bottom of the fuel tank.  Vehicle started just once.
Tried it a couple more time and still no-start.
Out of frustration decided to do a fuel volume test (had checked pressure eariler (40 psi but not volume) and pulled the return line.
Turned over engine and started right up.  Was surprised.
Tried several more times: return line connect (no-start)  Return Not connected (start) 
Put in the old distributor and TFI and repeated return line change out. 
Results same as with the new distributor and TFI.

========================
This is why I'm confused.
If the in-tank pump sock is being blocked with junk, I could understand I may get good pressure but little or no volume.
But with pressure good and volume pretty much OK, the only thing I can think of is that the return line must be clogged
somewhere downstream from the trottle body.

I've never touched the return line or any fuel line other than at the trottle body connection == or -- fuel filter replacement.

========================
Just went out few minutes ago, 6:30AM here, after letting vehicle sit overnight.
As usual started right up and ran great.

==========================

Thinking out loud, maybe the return line through the throttle body (where I'm checking volume) isn't the problem -- BUT -- the rest of the return line going back to the tank.
By disconnecting the return line this would leave this part of the line open to the tank.
Any chance some kind of vacuum is being created -- but -- this is supposed to be a pressurized system.

QUESTION:
Any ideas?

Intermittent No Start and Fuel Return Line

Reply #4
Just a question. Did you check the volume and pressure. Removing the return line and checking return fuel should be a given is.  If no  fuel is returning back to the tank that is a RED FLAG. How about the regulator??? Just asking are you Throttle body or multi port???  The return line should be blown back with air to see if it is clogged and be careful and use very low pressure. I find it fascinating that it starts with the return line disconnected. I cant figure why this is happening. This is the type of trouble one needs hands on to figure out. Good luck but i would think it is fuel related at this point. My guess is delivery.
I spend money I don't have, To build  cars I don't need, To impress people I don't know

HAVE YOU DRIVEN A FORD LATELY!!

Intermittent No Start and Fuel Return Line

Reply #5
Mr. Renzo thats for responding.
Fuel Pressure is 40 PSI with Key ON and pump energized.  After Start right at 39 PSI.  Hold above 30 after shutdown for at least 30 seconds.
Volume is around a 1/3 quart for 10 seconds.  Volume was checked with the return line removed at the connector.
All this is in spec per shop manual.

Per shop ford has a value at top of tank used to bring vapors to carbon canister.
The fuel system is pressurized so this value must open and close otherwise gas would be pushed into the canister.
Not sure what triggers this value opening (need to do some reading), but wondering if this value is not opening which is creating a back pressure
somehow into the return line and giving a false reading to the pressure regulator..

So (shot in the dark therory):
1)  taking a pump pressure at the inlet, you get what your supposed to.
2)  With the return line disconnect the pump is pushing the volume required.
3)  But as pressure builds up in the tank while running it starts creating a backpressure
such that the regulator stop putting out the correct amount to the injectors.
4)  Removing the return line would relieve this pressure.
5)  Not sure why a quick restart with line reconnected gives no start unless tank pressure builds up very quickly
    to fool the pressure regulator.

 Not sure how to test this???

Intermittent No Start and Fuel Return Line

Reply #6
The fuel tank should not pressurize.
The vent valve in the tank is normally open all the time. It should only close if the fuel in the tank gets too high and the float in the valve closes it. It should also close if the car rolls over.
A plugged return should cause the pressure to go too high. It would be the same as a stuck closed regulator.
Are you checking the pressure at the Schrader valve?
Is the pressure there different with the return on/off?

Intermittent No Start and Fuel Return Line

Reply #7
Softtouch:

Quote
The fuel tank should not pressurize.

This is somewhat confusing.  When the low pressure pump sucks the gas , the low pressure pump and subsequent high pressure pump
are adding pressure (till 39 psi -- regulated --which we are measuring at the shrader value) in order to force the gas through the fuel lines.
This same pressure (39) should be what is also forcing the  gas back to the tank. 
This pressure needs to either be relieve somewhere -- or -- the tank would be pressurized.

So the question is:  "where is this pressure being relieved??  I know the gas cap is vented and we have the
carbon canister vent, but doesn't seem these would relieve that much pressure.  Obviously, I'm missing something?

Added:  Per 24-50-6, the carbon canister is able to relieve the pressure. 

Quote
The vent valve in the tank is normally open all the time.

Saw shop they want you to put max 2.5 psi up line to check vent value.  (p24-50-8) with gas cap removed.

Quote
Are you checking the pressure at the Schrader valve?

Yes

Quote
A plugged return should cause the pressure to go too high.

Makes sense, but would not the pressure regulator control this so the max would be 39?

Quote
Is the pressure there different with the return on/off?

Will verify tomorrow and post here.


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Seems other Fords have this issue:  http://www.automotiveforums.com/t942138-hot_soak_start_rough_idle.html


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These are the results:
Return Line on CFI and Gas Cap Off:
KOEO (energize after overnight)
...... 34 1/2 PSI
...... After 5 minutes  33 PSI
KOER
...... 40 1/2 PSI
...... after 5 minutes  39.75 PSI

Return Line Disconnected -- Gas Cap On
KOER  39.5
After 5 minutes 39 1/4

Intermittent No Start and Fuel Return Line

Reply #8
The return is how it is regulated. If your regulated to 39psi, then any fuel over that goes back through the return line.

It might be possible your pump isn't able to push over 39psi.
Quote from: jcassity
I honestly dont think you could exceed the cost of a new car buy installing new *stock* parts everywhere in your coug our tbird. Its just plain impossible. You could revamp the entire drivetrain/engine/suspenstion and still come out ahead.
Hooligans! 
1988 Crown Vic wagon. 120K California car. Wifes grocery getter. (junked)
1987 Ford Thunderbird LX. 5.0. s.o., sn-95 t-5 and an f-150 clutch. Driven daily and going strong.
1986 cougar.
lilsammywasapunkrocker@yahoo.com

Intermittent No Start and Fuel Return Line

Reply #9
OK the rollover valve stays open to the canister as noted above. But the gas cap is also a pressure vacuum instrument as well. So i dont think it is a venting issue. To check that just remove the gas cap and see if that corrects the issue. I dont think it will.

Try this is the in tank pump working?? And i am going to assume the rail pump is because of your pressure readings. I have a suspicion your in tank pump is not working. If memory serves me the rail pump is not self priming. It has to have the booster pump operating to feed the rail pump. So at this point check the low pressure in tank pump for volume and pressure. I have a feeling it is shot. Just a GUESS.

Your pressures are OK. So the return system is OK. If in fact the return was plugged it would in fact act as a stuck closed regulator and pressures would go through the moon. Once again you have a supply issue and only thing is the in TANK pump sock fuel filter or the pump. I remember some time ago we had an issue with a SAAB that has 2 pumps and the in tank pump was shot and caused a similar ISSUE. Good Luck Tom
I spend money I don't have, To build  cars I don't need, To impress people I don't know

HAVE YOU DRIVEN A FORD LATELY!!

Intermittent No Start and Fuel Return Line

Reply #10
Thanks guys:

Tom:
Regarding the in-tank pump.  Will try and check soon.  But my thoughts are that the inline (high pressure) pump would NOT work if the in-tank pump was out completely.
I could see where having trash in the tank could create intermittent issues.
However, I would expect also some time of running problem -- intermittent cutoff / stalling--  since that trash would be sucked to the sock while running.
At shutoff the trash should be released from the sock and float back to the bottom of the tank.
Overnight might help it settle more, but since no running issues, seems odd to me sock would be the issue.

Intermittent No Start and Fuel Return Line

Reply #11
Yes i know what you mean. But i have seen lift pumps go bad from time to time and cause strange issues. If memory serves me and i am not 100% on this. I think the in tank pump is rated at 6-8 PSI. That feeds the booster Rail pump. Just a thought you might want to replace both pumps with a single 255. If you have to drop the tank any way WHY NOT??? This way you kill 2 birds with one stone. Just an idea!!! Once again this is one of those hands on issues. It is hard to shoot a trouble like this from a LAP TOP. ;);)
I spend money I don't have, To build  cars I don't need, To impress people I don't know

HAVE YOU DRIVEN A FORD LATELY!!

Intermittent No Start and Fuel Return Line

Reply #12
Quote
I think the in tank pump is rated at 6-8 PSI.

Yes I know it is pretty low pressure based on test instructions.  Haven't found a rating in shop -- yet

Quote
you might want to replace both pumps with a single 255
.

Never would of considered it.  Thanks for the thought.

Quote
this is one of those hands on issues.

Don't disagree, but most auto is.  Based on my searches, a LOT of FORD vehicles seem to have no-start or stalling issues that are Very difficult to resolve.
One solution I found of interest (see my internet link in post) -- just from a troubleshooting point to keep in back of ones mind --references a master mechanic in MN as I recall, who claims stalling can occur from clogged radiator fins.
Could possibly see this in MN where may have road mud, salt, etc which is thrown into the radiator by other vehicles and "may" give false readings to the ECT.
But I'm sure a lot of $$$$ were / are spent trying to resolve stalling before this particular solution is found to resolve the stall problem, if it is found by any given mechanic.

Intermittent No Start and Fuel Return Line

Reply #13
Just drop the tank already and eliminate that part.  Its free and won't cost you a dime other than your time.  The intank pumps fail and part of the time they will not have enough go to overcome the return line if there is any kind of restriction.  Disconnect the return line at the tank now that you have it dropped and disconnect it in the engine bay and blow compressed air through it to ensure it is clear.  Another way it to support the tank under the car with the fuel pump still in the tank and hooked up and see what you get coming out of the return line.  This can be achieved with several turns of the ignition switch.  The other thing to look for is the rubber hose between the pickup and the intank pump to see if it is cracked or in bad shape.  This affected another member here.

Darren

83 351W TKO'd T-Bird on the bottle


93 331 Mustang Coupe - 368 rwhp

Intermittent No Start and Fuel Return Line

Reply #14
Thanks all for input.

Took for several test drives and finally got it to fail again..  Confirmed in my mind I have some type of fuel problem
Removing the return line allowed a restart (glad I brought along a hose, bottle and necessary tools as line needs to be off while cranking.  Without gas is squirting everywhere -- great with a hot engine!!!).

Still don't see what the return line has to do with anything????

But at least I now have a plan and a few things to test.
Now what to do with a full tank of premium!!