What could cause a low fuel pressure situation

[det0326 179]

Mike,

Don't worry Ive already took care of it. The open Buckets were for pictures. In fact I've already used the fuel in my truck and daughters Jeep.

 

In regards to those droplets, it has always puzzled me. It happened so long ago, but it's something I always remember.

 

Tomorrow I will test the line by capping one end and blowing air through the other.

Visibly I checked the entire line and could not find a problem.

 

Prayers1 I do declare you have some odd problems with your classic. On second thought if it was sucking air I believe it would have did it with the

289 also. With everything being new I am dumb founded and all out of suggestions but will keep on my pea brain and if I think of anything I will sure let you know.

Dave

[sportsroof69 13]

I would cut that sock off the sending unti, and just use a good pre pump filter. 3/8" line is plenty to support your power level, but I'm not sure about your gas. That's odd.

[prayers1 153]

Before going further I decided to pull the metal fuel line off the car. I found a tiny circular hole about the size of a toothpick that faced upwards towards the floor, there was dry gas on the topside of the line and not visible when bolted up. I took a prong and pierced it, I think it still had a thin shell, so maybe air came in but gas didn't flow through.

 

I had nothing in the area to cause that hole, so I wonder how it got there, it was a new line.

 

All in all, do you think that would be the cause of my problem?

 

[det0326 179]

Before going further I decided to pull the metal fuel line off the car. I found a tiny circular hole about the size of a toothpick that faced upwards towards the floor, there was dry gas on the topside of the line and not visible when bolted up. I took a prong and pierced it, I think it still had a thin shell, so maybe air came in but gas didn't flow through.

 

I had nothing in the area to cause that hole, so I wonder how it got there, it was a new line.

 

All in all, do you think that would be the cause of my problem?

 

 

Yes it could, being on the suction side of the fuel pump. Was this hole in the area where you saw a few drops of fuel in the past. This really makes you wonder where they get the stainless to make these lines. You wouldn't think that would happen to a good grade of stainless. Edited this reply I was assuming you replaced the line with stainless but if it is non stainless line this hole could be from rust that previously got started from the other tank.

Dave

Edited August 25, 2014 by det0326

[prayers1 153]

Not Stainless, but is new, about 1 1/2rs old. Can't wait to put the new line in, but I have to run to my daughter Volleyball game.

 

Any other ideals or is this the problem.

[LoneWolf2U 136]

Yes that could be main source of trouble. Air will enter the system thru dry and cracking rubber hose without leaking fuel out.

So it could be the cause of the contamination too.

[Brian Conway 264]

Been following along here to see what you guys come up with. That first oil pan sample of gas was some really foul looking stuff. It seems your fuel pump is adequate and of course holes in any part of the system is not good. jmlay posted early on about flip gas caps and venting. As has been mentioned after market flip gas caps have no provision for vents. The OE stock gas tank filler tube has a small ' dent ' that serves as a vent. Does your filler tube have this dent ? Brian

[prayers1 153]

I have the original gas filler tube and not detent. I did notice that the little aftermarket screw on cap has a center hole with a push in valve. So I'm guessing that's for ventilation.

 

I put everything back together including a new fuel line and still the pressure will drop to 3 and at one time 2.

 

The drivability is great except for punching it. It seems it takes a long time to build rpms, but when it gets there the pressure drops.

 

I'm at a lost.............Why did I build this Cleveland.......................................

[det0326 179]

I have the original gas filler tube and not detent. I did notice that the little aftermarket screw on cap has a center hole with a push in valve. So I'm guessing that's for ventilation.

 

I put everything back together including a new fuel line and still the pressure will drop to 3 and at one time 2.

 

The drivability is great except for punching it. It seems it takes a long time to build rpms, but when it gets there the pressure drops.

 

I'm at a lost.............Why did I build this Cleveland.......................................

 

Prayers I feel for you, chasing a problem like this can be frustrating the only thing I can think of at this point is have you confirmed the float adjustment is set to manufacture specifications, I know this is not the psi problem but it could maybe be the problem at higher rpm's and the stumbling if floats are set really low. Have you confirmed a good steady fuel stream from the carb booster pump when throttle is opened, while this want cause a pressure drop either it will cause a stumble when the throttle is punched really fast but want cause a power loss at higher rpm's tho.

Edited August 26, 2014 by det0326

[det0326 179]

Prayers I did a little research on line and in a couple of places I read that 2 or 3psi at high rpm's WOT is normal, and 6psi at normal driving and idle is also normal. So what it seems like is 2 or 3psi is not starving the carb of fuel delivery but the carb could be starving the engine of fuel through carb adjustments like float level and etc. I could be wrong but I think you should focus on the carb at this point maybe.

Dave

[LoneWolf2U 136]

I have the original gas filler tube and not detent. I did notice that the little aftermarket screw on cap has a center hole with a push in valve. So I'm guessing that's for ventilation.

Don't think so, but could be wrong. It should say if its vented.

 

I put everything back together including a new fuel line and still the pressure will drop to 3 and at one time 2.

At high rpm and fuel demand pressure is not the problem, Flow is.

Your top end drop off could be jets size in the carb.

 

The drivability is great except for punching it. It seems it takes a long time to build rpms, but when it gets there the pressure drops.

Once again your lag time may be carb or ign related.

 

I'm at a lost.............Why did I build this Cleveland.......................................

 

You built the C for fun with your right foot. You just need to dial it in.

[det0326 179]

You built the C for fun with your right foot. You just need to dial it in.

 

Thats is a true statement Mach1rider. I get frustrated sometimes at mine but then realize hey this is suppose to be fun and wait a day or two and start back fresh.

dave

[prayers1 153]

I agree with both of you. but today I just pulled it into the garage, disconnected the battery and walked away. This is very frustrating.

 

I spoke to just about everyone. It seems best to put an electric pump in. I really hate to do something like that.

 

I'm gonna put the RobbMc Mech pump www.robbmcperformance.com back on (the parts store one I'm using has a 5/16 outlet that I put a 3/8's fitting on), I'm also gonna take the fuel filter off by the carb inlet and try that. Those are the only thing left that I can think of as causing a restriction.

 

I have been advised by others to take the sock filter off the sending unit, you all know that's a lot easier said then done. But, what do you think about that. I keep think, the Boss 302's all FE motors, etc.. had the filter on the sending units with no problems.

 

I spoke to Quick Fuel and they said it definitely not a carb issue.

 

I've been told by others that you need 5psi at WOT.

Edited August 27, 2014 by prayers1

[434josh 10]

I have never had any luck running less than a 110gph pump. Usually try for 140 or better.

If you still have pressure, your pump is still supplying more fuel than the carb is using however if the pressure is dropping, the carb is starting to out run the pump. Even with a carb, you need some fuel pressure. 6psi is plenty for most carbs but 4 or less doesn't cut it.

 

I think your problem is more the pump but the parts store filter could also be an issue. The under hood pic showed a filter that looks like something from autozone or a similar store.

I would suggest a good filter that is rated to flow a decent amount. You have no idea what the parts store filters will flow.

[jmlay 80]

I dug out my NOS pop open gas cap for comparison. Ford stopped supplying the spring, etc... to make the pop open as original, they did supply a vented cap. The cap is clearly marked as vented as well as you can blow/suck air through the vent. Comparing my cap to prayers1 I would venture to guess his is vented to. A pucker test would tell for sure. ;-)

[LoneWolf2U 136]

Ok one last post here as beating a dead horse is not my idea of fun.

From a Built 351Cj owner running a stock fuel pump on a engine pushing 500+ at the crank, I don't see what the pressure problem is here.

Pressure means there is a restriction somewhere as this is not fuel injection but naturally aspirated. Breaking it down the pressure rises when the floats shut off the flow of fuel. With the float lowered it allows fuel to flow and pressure drops. This is indicated by your gauge that is happening as it is running 6+ at idle and less at wot.

 

I would look at the float levels first as once stated low floats will starve it for fuel, the bowls need a set amount to feed the engine at speed which allows the pump to keep up with demand. The rising rpm means the pump is working faster moving more volume and should match the need.

If the levels are not correct from start it will never catch up.

 

I know little about Quick fuel carbs, But they look like Holley.

I'm running a 750 on the 351(yes it could be larger but not as streetable from the been there file) and a 770 on the 390 in the truck.

Both needed to be set up for the engine it sits on.

While it took a slight more fiddling for the 351 vs the mild 390 they both run like scalded dogs, No flat spots or lag in rpm run up.

I can go from putting along at idle to foot on floor with tires lighting up.

 

So my check would be carb then ign check to fine tune it.

As for the lag time you have, If I recall you went from stick to auto.

This IMHO is where your not feeling the rpm climb like before.

have you tried running thru the gears manually to get the rpm band up.

Your build should at least run the mid 5k range without too much trouble if its tuned right.

[prayers1 153]

To answer some questions:

 

Quickfuel is almost identical to Holley, they tweaked a little bit. My fuel bowls have clear sites on both sides, front and back. The levels are a little bit above 1/2.

 

I had one of those Jegs 6an filters at first with the quarter size screen. I switched to a parts store reg filter to see if things would change.

 

Aftermarket pop off gas gas has a vent in the center.

 

Questions

Should I take the filter off the sending unit?

 

I'll try it w/o the filter after the pump.

 

I'm trying to figure on how to get a video showing what it is actually doing.

[det0326 179]

To answer some questions:

 

Quickfuel is almost identical to Holley, they tweaked a little bit. My fuel bowls have clear sites on both sides, front and back. The levels are a little bit above 1/2.

 

I had one of those Jegs 6an filters at first with the quarter size screen. I switched to a parts store reg filter to see if things would change.

 

Aftermarket pop off gas gas has a vent in the center.

 

Questions

Should I take the filter off the sending unit?

 

I'll try it w/o the filter after the pump.

 

I'm trying to figure on how to get a video showing what it is actually doing.[/quote

 

 

Just me but as clean as your fuel and sending unit assembly looked I would not take the sock off. I think everything from the tank to the fuel pump is fine. I am with Mach1rider on the pressure too I think that what you are seeing on the gauge is normal. You can add electric pump but you will probably need to also use a regulator because if you get to much pressure with needle and seat you could cause a flooding problem if the pressure over rides the needle and seats ability to close the fuel off. At this point I don't know what the problem is either but I am wondering now if it is even fuel related. As Mach1rider stated if you go through the shifts manually will it act the same. If you hold it in 1st gear manually does it flatten out at higher rpm's?

Dave

[prayers1 153]

OK, now with the new fuel line, I put back in the RobbMc fuel pump and the Jegs filter.

My floats were a little higher than 1/2.

 

I took it for a test run. The lowest pressure got was around 3.25, most of the time around WOT it was 3 1/2 -4. At cruising around 6.

 

The car felt a little stronger and it didn't feel like it was starving. The video I took was done in DRIVE, I was trying to view the gauge and road at the same time, so I couldn't see what my shift points were,. You can see when I let up the pressure went back to 6.

 

There was no hesitation, stumble, backfire or breaking up. Initial is 14, Mech 24 and total 38 all in a 3000.

My advance starts around 1200

 

I'm wanting to change the advance to 800, Initial at 16, Mech at 20 for 36.

What do you think?

 

So, is this a good reading or should I have more pressure at WOT?

 

[prayers1 153]

Here's another run with a better view of the gauge

 

On both videos depending on your CPU you might have to allow it to load then view again.

 

 

 

Edited August 30, 2014 by prayers1

[det0326 179]

Here's another run with a better view of the gauge

 

On both videos depending on your CPU you might have to allow it to load then view again.

 

 

 

 

So its running OK now other than maybe tweaking your timing. I did some research the other day when you were working on this and I read links that were really conflicting. Some say it should never go under 5psi and others say 3psi is fine. So it just depends on where you are reading. If it is running ok at higher rpm's now I guess it must be OK. So just putting the other pump back on fixed your problem? In the video after the tires barked and finally grabbed it sounded like rpm's flatten out for a sec. but it could just be the way the video sounded.

 

Dave

[Zipppo 11]

I don't know if this will help. I lived in the Philippines and I know when it gets hot and really humid at times Vapor Lock can be an issue. One other thing I have seen is if there is any rubber hose in the system to the carb. it collapses restricting fuel flow. Lastly a low, no spark condition has caused stumbling.

Anyway just tossing a couple of ideas out there to try and help.

Hope it resolves as this stuff can be well just really makes one lose confidence in the car.

[prayers1 153]

Hi Zipppo, Nice to see a Mustang fan in the Philippines!

 

I thought about the collapse rubber fuel line myself, especially the hose from the line to the pump. I was trying to give enough slack so that the torque of the motor wouldn't pull the line. I wonder if suction on that side can also be a concern.

 

I've been looking into other type of fuel lines from line to pump and pump to carb.

 

Any suggestions?

[Zipppo 11]

Old school Earl's Plumbing or as I have steel braided aircraft grade been on since 91.