Running out of fuel at 40-45 mph.

[1970pelle]

I drove the truck Tuesday where I needed to get it to highway speeds. I quickly found out it would not go over 40-45 mph without bogging out. If I lifted my foot off the gas pedal and let the engine recover it would and I could go at speeds below 40 mph. It never stalled out when coming to a stop. It just seamed to not have the volume of fuel to power the truck at higher speeds.
I checked the clear fuel filter and it always has fuel in it, completely full. I checked my new fuel lines for any loose clamps, kinks anything out of sorts. Nothing found. I am running dual tanks and there switching as designed.
No gas smells or leaks on the ground or intake manifold. I do have a fuel gauge before the carb, a good one Auto Gauge(oil in the gauge). I'm thinking of mounting a GoPro under the hood and watch fuel pressure. But I'm pretty comfortable that I have a bad new fuel pump, because it recovers quickly. And my engine vacuum doesn't drop completely off when condition occurs.

What do you think ?

[TexasJeff]

I will bet you your fuel filter is clogged, I have a very similar problem, but the only fuel filter I have is the one inside the carb, I removed the filter and it drove fine. I got to the parts store as quick as I could then replaced it, has run fine ever since.

[1970pelle]

I wish it would be that easy. I'm not running a filter inside the carb. Just one in the line after the fuel pump, and its clear. I'm planning on changing it out, even tho it looks very clean. But I have been fooled before by a bad filter. I always check the basic and simple things first, before jumping into a driveability issue. I have seen guy get buried in jobs, to find out it was one of the three basics. Spark,Fuel,Compression.


Ken

[Dead Parrot]

+1 on check fuel filter.

Any gas smell in the oil or worse, the oil level is increasing?

Check the suction line between the tank switch and frame.

[rich weyand]

Make sure the fuel tank is vented, and that the vent is working.

One method is a vent line from the vapor canister. Another is a vented gas cap.

If the vent system was removed, and the non-vented gas caps remain, you can have problems.

One way to test is to remove/loosen the gas cap and see if the problem resolves.

[ironroad9c1]

make sure you reinstall a new filter in the carb, I currently have the carb off my latest van , and its full of **** from the tank, and it had a filter before the fuel pmp.. and no filter in the carb. try a fuel pump for a 1986 GMC g20 with the 305, its the big one more volume

[Gregski]

what type of in line fuel filter are you running, the big ugly see through plastic one (that works) or the sexy glass and metal chrome one that does what you describe, ha ha

[bhc41051]

My 75 was doing the same thing; It felt like it was starved for fuel at 45-50 mph. I was checking fuel filters, caps, hoses, the switch for the duel tanks. I was sure it was the NOS AC-Delco fuel pump I had recently installed. I was getting ready to pull the pump when I noticed the flapper on the air cleaner was closed, it was about 75 degrees out and the truck was at operating temperature. I unhooked the vacuum line and capped the port on the carburetor. I took the truck out for a test drive and it ran fine. I later replaced the sensor on the air cleaner which fixed the problem with the flapper.

[1970pelle]

Here is the style fuel filter. I'm also running a K&N 14 X 3 air filter with a K&N filter top. So I have to use with lack of air.
Tomorrow I'll have time to mess with it, I post my findings. Thanks for all the Help.

Ken

[1970pelle]

I had a lot of honey does this weekend. So not a whole lot done with the truck. I did mess with it tonight. Removed fuel filter and gut it apart, no signs of being blocked or plugged. I replaced the fuel pump, again with a brand new one. I had replaced the pump when the crate engine was installed. I visually checked fuel lines from both tanks, steel and rubber. Fuel caps, all clamps tight. The vent is open, even tried it with a bolt in it blocking it off. Ran it on the right tank.
I have the same issue, I have changed it slightly. Still there still falls on its face at 40-45 mph. But now recovers quicker.
Tomorrow I'm planning on checking my Distributor out and see if I don't have a ignition module issue or pickup coil. Its all brand new stuff.
So there search continues.

[1970pelle]

I pulled my fuel tanks this afternoon, man I love southern trucks. Did it all with hand tools, everything broke loose without any fussing. What I found was interesting, both tanks where very clean on the inside and out. But the intake socks where black in color. They didn't slide of the sending unit so I cut them off as close as possible. I opened up the left side sock you can not see any light through it, completely plugged solid. The right side the same, blow air through the sending unit ports no blockages. I plan on replacing all the rubber hoses and hose clamps. I cleaned both tanks out and painted the outsides, a nice shade of black. So tomorrow afternoon we should have a report.

KA

[gramps77]

I had the exact same issue with mine, same setup too with dual tanks. I found that my fuel line had swelled internally choking the driver side tank. Replaced all my fuel line and no issues since.

[Jeepwm69]

I had a fuel line that slightly kinked when I reinstalled the tank after rewiring the sending unit. Straightened out the line and it has been fine since.

[1970pelle]

It turned out to be quite the job cleaning,painting and reinstalling my gas tanks. The left side(drivers side) went right in place. The right side was a fight the whole way. Even using the holes in the frame to loosen the straps. But I finally wrapped it all up, after lifting the bed up a few inches so I could get to the hose connects. Even with my skinny arms it was to tight with the bed down. So since all my bolts all come loose by hand, I lifted the bed. Made the job a bit easier.

Took the truck to get some gas in both tanks, ran good to the gas station. Ran good for a few miles, hitting 55-60 mph no problem. Then after a stop lite, it started staving for gas again. This time at 25mph, but would recover much faster. So I still have a blockage somewhere. I'm going back up to the carb, everything else has been replaced or serviced.

Ken(a little bit grayer than before)

[1970pelle]

Anybody want to buy my truck? Man I'm starting to hate it, or hate working on it. Everything I have done so far chasing this lack of fuel issue has not completely fixed the problem. It has effected it, or changed when the condition occurs.
After reinstalling the VERY clean gas tanks and sending units. Replaced the short rubber lines at the 6 way tank switching valve. The truck would now run great for 15 miles, also we are having 100 degree temp days here. Once it hits around the same place each day15 miles, it starts the fuel starving deal and dieing. If I let the truck set for a half hour it will start and make the rest of the way home 5 miles. And then completely die at the house, fuel gauge reading zero.
So I wrapped the fuel line where the headers come the closest. After doing this it won't go over 25 mph without running out of fuel. So I must have disturbed something. So I'm going to try a different fuel source and line to the pump. Meaning a fuel tank in the bed and a new line to the pump. And see what happens. I'm stumped on this thing, Its something I'm over looking.
We'll see what happens.


To add. I did replace the fuel pump, with a brand new unit. That pumps 40 GPH, the pump I removed was only 6 months old also, had maybe 250 miles on it. I had finally found my receipt.

Ken

[1968k20]

Originally Posted by 1970pelle

Anybody want to buy my truck? Man I'm starting to hate it, or hate working on it. Everything I have done so far chasing this lack of fuel issue has not completely fixed the problem. It has effected it, or changed when the condition occurs.
After reinstalling the VERY clean gas tanks and sending units. Replaced the short rubber lines at the 6 way tank switching valve. The truck would now run great for 15 miles, also we are having 100 degree temp days here. Once it hits around the same place each day15 miles, it starts the fuel starving deal and dieing. If I let the truck set for a half hour it will start and make the rest of the way home 5 miles. And then completely die at the house, fuel gauge reading zero.
So I wrapped the fuel line where the headers come the closest. After doing this it won't go over 25 mph without running out of fuel. So I must have disturbed something. So I'm going to try a different fuel source and line to the pump. Meaning a fuel tank in the bed and a new line to the pump. And see what happens. I'm stumped on this thing, Its something I'm over looking.
We'll see what happens.

Ken

I'd be looking at the fuel pump.

['76 Big Block]

I noticed (from your photos) that you have what looks to be a brand bew Edelbrock carburetor, but didn't see anywhere in your threads that the float levels have been checked and verified.
I also didn't see if you were having the problem during hard acceleration, or just cruising along.
Since you've replaced pump and filter, I would start looking at carb issues----even new ones can be defective/improperly adjusted.
I experienced the same symptom on my big block, I replaced fuel pumps and filters several times before digging deeper and finding my issue was the shredded sock filter in the tank. It would run fine after sitting, but starve when accelerating or just cruising.
Since you've eliminated the sock filters, I'd look at the carb.
Good Luck!

[cadillac_al]

"fuel gauge reading 0" You mean the fuel pressure gauge? New tanks and lines; is it possible your elec fuel pump is mounted too high? Grasping at straws now. Is a mechanical pump not an option?

[1970pelle]

I have had the carb apart, and everything was set to spec. And nice and clean.
I'm running a stock style fuel pump driven off the engine. Yes the gauge I'm watching is a fuel gauge by Auto Gauge with oil inside to help with needle bounce.

As far running as cruise speed or highway speeds, I have never had the chance to do that yet. If you read my whole thread I can never get past 45mph. And for the few times I did, it was on back road two lanes.

I have even change out the HEI distributor module,coil,rotor and cap. The wires where the first things swapped but a different reason, the red MSD wires looked better.

My 12 volts going to the Dist. is there and constant. I have good engine and body grounds, and plenty of them.

No exhaust restrictions, new headers,new exhaust pipes and mufflers.

I have a vacuum gauge installed in the A-pillar pod, and it reads correctly till the issue starts. Then once it starts the loss of power engine vacuum drops off with engine speed. As I lift my foot off the gas pedal and allow the engine to catch up, sometime it will recover and the vacuum will build back up. Other times it will still struggle act as starving for fuel, if I don't pump the gas pedal it will stall. But in the end it does stall and won't restart till the engine has been allowed to sit for about a half hour.

I'm going to blow air through the fuel line again today. And then see about making up a fuel tank in the bed with a new fuel line to the fuel pump. And go from there.

Ken

[cjthompson]

0 pressure thing doesn't support this, but have you checked the regulator?

Had a motorcycle that had the same problem once upon a time. Ended up being a rats nest in the air cleaner. Sounds like you've had yours off a few times though messing with the carb.

[geezer#99]

Liquid filled gauges sometimes go to zero when they get hot.
Do you have a fuel regulator?
Do you have a heat spacer?
What's your vacuum at idle and in cruise before it acts up?
What's your timing curve like? Initial? Mechanical? Vac advance?
Do you have a breather on the passenger side valve cover?

[cadillac_al]

I think I would trust the gauge and 0 means 0. Other than the 0 fuel pressure the symptoms sound a lot like a clogged catalytic converter but you have a free flowing exhaust. Two different fuel pumps and same issue, the fuel tanks aren't getting vented somehow. I think you are on the right track my trying a tank/fuel can in the bed plumbed to the pump. Good luck.

Maybe a pic of your fuel pump setup would show something that we could debate. Do you have it mounted as low as possible in the frame rail?

[1970pelle]

Fuel pump is in stock location, lower right front corner of the block. Has 3 lines, 3/8 line is fuel supply, 5/16 line is return to fuel tank, 1/4 line is a vent line.

I do not have a blocked vent line. I do have a vent line run and its mounted to the side of the core support and runs to the top of the support. There is a space in the support near the radiator that you can hide a hose in. I have the open end of the vent higher than the fuel tanks.

I don't have a air filter blockage, I'm using a 14X4 K&N air filter with a K&N filter top. So there is no lack of air supply.

No I'm not running a spacer between the carb and intake. I thought about it, but with the air gap intake manifold didn't feel I needed one. But willing to give one a try, I have the clearance for one.

I have breather's in both valve covers

I'm using a HEI distributor, with a adjustable vacuum advance. I have to go check my notes on how I set the timing.

Engine vacuum at idle setting still 15. Running down the road at 40-45 with my foot out of it almost 20. Now remember I'm at sea level in some places below. So I usually have more vacuum than needed.

I keep my stuff clean & neat. I have done everything asked, but it doesn't hurt to check again.

[cadillac_al]

I am under the impression that you are running an electric fuel pump. I don't remember and don't see it mentioned except for the 40 gph. If it is electric and in the stock location, that is a long way to pull fuel.

[cjthompson]

Just read an forum on hot rodder about those liquid filled gauges causing problems at operating temperature. I'm sure it's in here, but have you tried running it without the gauge or icing it down?

Go to about page 4....

http://www.hotrodders.com/forum/fuel...s/92844?page=4