EFI / Fuel smell / fuel pressure drop

[pcf_mark]

Short story to give you all the details as they may inter-relate:

1995 5.0 stock EFI controlled by Megasquirt
New frame mounted pump from an 88-90 F250
Sealed cap - I know this because on a hot day the fuel expands and the air rushes in when I go to fill it
Return line is plumbed into the filler neck
The regulator is about two years old bought it new.
Cold start and driveability are awesome no complaints.

Two symptons I need some advice on:

When I shut the truck off the fuel pressure drops to zero very quickly. If it sits hot for 20 minutes or so it runs very poorly for a few minutes until it stabilizes. During this rough running period it smells very rich. I thought this was the fuel pressure dropping and the fuel in the rails boiling and pushing the fuel out the return line and the engine trying to run on a fuel / air coming out of the injectors. I can't pinch my return line as a test because all my lines are oem plastic. Should I replace my regulator since the fuel pump (and internal check valve) are new or could I have a leaky injectors?

When it sits in a small garage over night the fuel smell is noticeable. With a sealed EFI fuel system how can this be?

Are these two things related and can I test for something?

Maybe I have a leaky injector or injector seal that is causing the fuel pressure to drop, fuel is boiling and fuel is getting dumped into a cylinder when sitting?

 

[904Bronco]

Still running the 68 tank?
1st guess... I am thinking that the tank is venting to the outside, since EPA requirements were minimal back then?

 

[NYLES]

injector stuck?

 

[pcf_mark]

Yes stock 68 tank I do not think it is vented based on how it holds pressure when it gets hot. I did replace the short rubber piece feeding the fuel pump out of the tank too. But I did not replace the filler hose piece. Hmmm.

If I had a stuck injector I do not think it would run right and it runs fine. I tuned with a wide band and I can get it to run lean a stuck injector would run super rich right? If it was stuck how would I check for that? Maybe take the rail and all injectors off the engine assembled and cycle the key to power up the fuel pump (but not crank!)?

 

[NYLES]

pull plugs look fer a soaked one

 

[jim3326]

Put a vented cap on and see if that solves the problem. Sounds like fuel starvation since you have a vacuum when you pull the cap. The tank has to get air in some way.

 

[NYLES]

Put a vented cap on and see if that solves the problem. Sounds like fuel starvation since you have a vacuum when you pull the cap. The tank has to get air in some way.

Just run it without a cap see what pressure does when turned off

 

[DirtDonk]

When I shut the truck off the fuel pressure drops to zero very quickly.

You're monitoring this on a good pressure gauge? Permanently mounted type, or one you stick on the schraeder valve when you need to? How quick is quickly? A few seconds?
Things that come to mind for a quick loss of pressure are:
1. Leaking pump
2. Leaking line(s)
3. Leaking injector(s)
4. Failing regulator.
And as we know from experience these days, new does not mean good.

If it sits hot for 20 minutes or so it runs very poorly for a few minutes until it stabilizes. During this rough running period it smells very rich.

I wonder if it's flooding from multiple leaky injectors? Seems odd, but I supposed it could happen. How old are they? Original to the '95 and of unkown-ish mileage?

Should I replace my regulator since the fuel pump (and internal check valve) are new or could I have a leaky injectors?

Again, new doesn't mean good. But the regulator is certainly the easiest of all the suspects to change. I just hate to throw money at it if it's not the problem.
I'm not sure how to test that half of the system without blocking off a line though. Since you can't pinch, maybe someone else has a suggestion. And are you sure you can't pinch off plastic lines?

When it sits in a small garage over night the fuel smell is noticeable. With a sealed EFI fuel system how can this be?

Because it's NOT actually sealed and that was always the problem. Sealed systems don't have sealed caps. A truly "sealed" system like on modern EFI vehicles uses a cap with a one-way vent only, and the charcoal canister system to collect the vapors and then reintroduce them to the engine when it's running.
Your old pre-'70 cap (is this a '68 as 904 was asking?) is actually a truly vented cap. Not only does it let the air in to take the place of the used fuel, but any over-pressurization is just going to send excess fumes out into the atmosphere. The fact that it wooshes when you open the cap means that it's not doing it's job consistently. Maybe it's also not allowing air to flow in to the tank either during those times?
As suggested, remove the cap completely while you're testing (but not in the garage!) and see if the issue repeats.
Is this trouble you're having consistent and repeatable? Or does it do it on it's own sweet time?

Good luck.

Paul

 

[pcf_mark]

I'll try to add info / answer questions

You're monitoring this on a good pressure gauge? Permanently mounted type, or one you stick on the schraeder valve when you need to? How quick is quickly? A few seconds?

Using a quality gage but yes installed on the schrader fitting. 39 psi running at idle. Shut engine off (hot or cold) it drops to zero within a few seconds.

I wonder if it's flooding from multiple leaky injectors? Seems odd, but I supposed it could happen. How old are they? Original to the '95 and of unkown-ish mileage?

Yes these are the old un-serviced originals. The o-rings even! They were hard like rocks.

Again, new doesn't mean good. But the regulator is certainly the easiest of all the suspects to change. I just hate to throw money at it if it's not the problem.
I'm not sure how to test that half of the system without blocking off a line though. Since you can't pinch, maybe someone else has a suggestion. And are you sure you can't pinch off plastic lines?

The plastic lines seem so stiff that pinching them they would not return to the original shape. Maybe I could put a short section of rubber in at the T into the filler hose.

It is VERY consistent. Every time I shut it off I have to cycle the key two or three times to get the fuel pressure up then it fires right up. If I just try to crank it it cranks 5-6 seconds then starts. Hot start is also very consistent. Spits and stutters like vapor lock or running out of gas for a full minute or two then once it burns through it no problem. The rush of air when I open the cap is less consistent - sometimes when I run it low sometimes when it sits in the sun.

I am sure it is nothing too serious just a headache but worthy of fixing.

 

[pcf_mark]

I took a very close sniff around the truck after driving and letting it sit indoors. The smell is definitely from the rear near the fuel tank / filler area. If it was an injector I think it would smell upfront near the intake or out the tail pipe (on opposite side of the filler)

I wonder if the regulator is bypassing and the smell is the fuel dribbling back to the tank via the return line and then sitting in the filler hose close to the cap.

 

[EFI Guy]

All of your symptoms except for the fuel smell at the back sound like a pressure regulator with a leaky diaphragm to me. Pull the vacuum line off of the regulator and see if there is any sign of fuel in it.

 

[pcf_mark]

I took the vacuum hose off the regulator with the engine off and it smells like gas. I assume this mean the regulator is leaking? I also noticed it is not sitting perfectly flat on the rail. Both are leading me to replace it.

At the rear near the tank after a very close look it appears the smaller fill hose - which I have a T in for my return line - is HEATER HOSE! My smell may be fumes leaching out of this. Odd that I can get pressure in the tank if it sits in the sun. I am going to replace the filler hose and the overflow hose.

I'll get back to y'all thanks!