Hey guys--

So recently I deleted the return line from the fuel filter header and in it's place put a pressure gauge so I could glance at it whenever and always have a good reading. (here's a picture of the header, it's not mine, but the line marked "check valve/return line" is the one I deleted)
https://www.ford-trucks.com/user_gal...d=217555&.jpg=

It's a sweet mod, but now I see that i'm getting terrible fuel pressure from my(new last year) lift pump. It maxes out at 3psi only sometimes, at mid-rpms. The rest of the time it's reading 0-1psi.
And she reads higher more consistently with cold fuel, but still not more than 3psi.

Ok so I have crappy inlet pressure to the IP.
Today I accidentally broke off the barb on the return line "T" that the IP outlet hose goes to. So I put the hose into a bottle and figured I could drive some distance like that, but NO the IP outlet filled up most of a 1-liter bottle in maybe 10-15 seconds. (with no more than 3psi inlet pressure)
I had a similar issue once years ago and it took MILES of driving to fill up most of a 20oz bottle.
What gives?!?!? Is my IP becoming a sieve and that's why I have bad fuel pressure? Or is it normal to have that kind of flow through the IP and my lift pump is somehow partially bad?

Thanks guys, I'm not sure what to replace. It drives fine for now but low inlet pressure seems to be messing with my timing quite a bit. Or my IP is crap and it's messing with it's own timing.

-Joshua

 

fuel pressure should be 7psi and delivery should be 1/3 pint in 10 seconds cranking. not running.
if you pull the FSS wire off what is the pressure when cranking?

 

The IP return is supposed to be somewhat restricted, with a check-ball inside which keeps the housing at 5PSI, no matter what. The Cold Advance solenoid bypasses this and drops the pressure to 0. I'd pull the top cover and make sure that's all intact.
Note that the IP has it's own low-pressure 'boost' pump, so it will easily have more PSI going to the main pumping elements than is coming in -- up to 130PSI, actually.
The housing, however, is supposed to only have a small orifice filling it up(the "vent wire" assembly), so a ton of fuel may not be right. I don't know.
I'd make sure the housing check-ball is actually working.

 

Thanks guys for the replies.
I'm totally aware of the fuel pump testing procedures, but brain farted on actually doing them as I was so concerned about the flow coming out of the IP. I've had timing/fuel curve issues with this IP for a long time as detailed in other posts.

Lift pump Tests:
#1 Fuel pressure:
FAIL. 4psi max. And won't hold it unless at mid-range rpms. Anything else is 0-1psi.
#2 Flow rate:
Pass. I had well over 1/3pint(5.3oz) in 10 seconds of cranking out of the schrader valve. This was with cold fuel, not sure if the test calls for a hot engine or not.

The only thing left for my personal understanding of the pressure test is to verify that the gauge i was using works, by testing with a different gauge. I'll try to do that today.

Macrobb- thanks for the tips on the check ball, etc. I've never had the cover off any pump so maybe it's a good time to explore that.

 

if you spend some time looking at stanadyne tech info you will find that the nominal fuel pressure for proper operation is 1/2 lb. the return line from the top of the filter housing, is to remove small bubbles that are pumped from sloshed fuel in the tank, as the engine consumes between 6 and 8 oz's of fuel per min at cruz speed on the highway, the vast majority of fuel the lift pump pumps returns to the tank after passing thru the small orifce in the brass outlet on the filterhead, and cooling the exterior of the injectors along the way. the fuel pressure of the system is determined by the pumps springloaded pressure valve built in to the lift pump, some manufactures used differing set points, 1-4 is fine the ip employs a transfer pump that raises the internal pressure's to alow the high pressure metering system to do its job, when you let of the peddle at high rev's the extra pressure is relieved thru the return on top of the ip, and it to returns to the tank. you may see a increase in fuel pressure when cold as the fuel is thicker when cold. and the CFFF changes. (cold fuel flow factor). adding pressure to a stock ip WILL negatively affect the advance curve of the ip.....

 

https://docs.google.com/file/d/0B4F4...p=docslist_api

Dunno if this link will work but I got a second gauge set up simultaneously while cranking. it reads .75 psi higher than the liquid filled gauge I installed, but taking the average of the two it's still way under spec. Again with cold fuel, once hot it would be much lower.

 

As long as the flow is sufficient, the pressure should actually not be an issue -- the stanadyne DB2 pump can run gravity-fed with no issues. The key, however, is consistency -- a fuel supply which starts out at 8 PSI and drops to 1 under heavy throttle(like an electric pump that's undersized) /will/ mess with timing slightly.

 

Ok an update, came home the other day and popped the hood to check out my fuel pressure. This time the fuel was warm from driving.

It was 0 no matter what RPM I revved it up to.

So I went to NAPA and got a new pump.

Cold pressure reads almost the same as before, but reads 5psi at idle and instead of the pressure dropping fast and coming back up around 2K rpm this time it dropped off linearly, slowly as the RPM climbed.

Here's the kicker-- hot psi is exactly 0. At all RPMs.

Isn't the Schrader valve pressure measured before the fuel travels through the filter?

 

It should be after.

I'm thinking something broke on the IP solenoid cover -- I'd pull it off(mind the leaked fuel) and investigate the check-ball and cold-idle solenoid.
With the solenoid activated, it should have no backpressure; with it off, you should have 5 psi in the housing.

 

Actually Josh Bear is correct, the Schrader valve is before the filter.
Trust me on that one, I just replaced the fuel heater o-rings and checked out how things run.
Fuel goes into the filter header, there is a passage over to the Schrader valve and an opening that lets the fuel drop into the fuel heater. Once the fuel passes through the fuel heater it can drop into the filter. The fuel then comes up through the center of the filter into a passage that feeds the fuel return fitting, vacuum sender (for the fuel filter light), and the fuel outlet to the injector pump.

 

I forgot to post but I did take the cover off and looked around. I could only visually check if stuff was working, and I didn't really know what to look for. Both my FSS and high idle solenoids work perfectly as far as I can tell.
I even took the return elbow off and could see the ball you're talking about, power on and power off for the high idle solenoid opens and closes the passageway.

If I'm missing something, let me know.

Thanks for the verification! It wouldn't make a ton of sense to measure pressure after the filter as a test of the pump, cause if your filter was clogged then you'd end up replacing a pump for no reason.

Poop. How do I check that the housing is holding 5psi?

-Joshua

 

Idle the truck while cold. You should hear the clatter go away somewhat when you pull the wire off the cold advance solenoid, and come back when you put it back on.
If it's doing that, I have to assume that part is good.