Fuel Line Suction Issue

[CRW-FK5]

Checking the fuel pump suction at the inlet of the pump and again at the inlet of the hose that connects to the fuel sending unit I get a huge difference.  I am drawing around 17" at the pump and less than 1" at the tank.  Is this much loss typical?

[cdr]

disconnect the pressure side of the pump when you are testing the suction side, be careful where the gas shoots out, put a rubber line on it. if a mech pump has pressure resistance it wont pull much vacuum.   & you have to crank the engine a lot to draw a vacuum in that long of a hose. the pump is designed to move fluid not air.

[cdr]

now,, tell us what is wrong with the car, dies ? wont start? runs great now that the fuel filter is in the correct location?

[CRW-FK5]

now,, tell us what is wrong with the car, dies ? wont start? runs great now that the fuel filter is in the correct location?

Ha.  Same issue as in other thread even with filter corrected (now between carb and pump).  I even switched to standard filter with only inlet & outlet just to see if that made any difference, which it didn't.  Car runs great below around 2,800 RPM, but falls completely on its face above it with A/F ratio reaching around 17.  Tried about everything fuel related, some things more than once.  Running out of options.

[firefighter3931]

It's possible that the in-tank foam sock on your pickup has clogged. How old is the fuel system in this car ? Have you measured fuel pressure with the engine under load ?


Ron

[c00nhunterjoe]

What ron said. You are skipping the basic steps as we asked several times in your other post. You need to check fuel pressure at wide open throttle under load and see if it maintains or drops. If it drops, you need to measure your pushrod next.

[CRW-FK5]

It's possible that the in-tank foam sock on your pickup has clogged. How old is the fuel system in this car ? Have you measured fuel pressure with the engine under load ?


Ron

Sock was missing on the sending unit.  Fuel lines are original.  Hose between sending unit and metal lines just replaced.  Fuel pressure during cranking is 4-5 psi.  Not checked under load but I am assuming it would not drop below that, correct?

[CRW-FK5]

What ron said. You are skipping the basic steps as we asked several times in your other post. You need to check fuel pressure at wide open throttle under load and see if it maintains or drops. If it drops, you need to measure your pushrod next.

Please back up your statement that I'm "skipping the basic steps as we asked several times in your other post".  I have measured the push rod and it is fine (3.21").  I have measured A/F ratio at suggested rpm range of 3,500 and provided detailed A/F readings from them which showed lean.  No where do I see request for pressure check at WOT.  The car won't even run at WOT.  So keep your condescending comments to your self.  I can do without it.  If you have some advise, then provide it. 

[funknut]

It's possible that the in-tank foam sock on your pickup has clogged. How old is the fuel system in this car ? Have you measured fuel pressure with the engine under load ?


Ron

Sock was missing on the sending unit.  Fuel lines are original.  Hose between sending unit and metal lines just replaced.  Fuel pressure during cranking is 4-5 psi.  Not checked under load but I am assuming it would not drop below that, correct?

It seems almost certain you have a restriction somewhere in the fuel system.  You previously stated that you can run at 3500 RPM with no engine load, but in gear under load you have issues.  The point of checking that was to rule out some electrical issues. The engine needs more fuel when loaded, so when it leans out under load, it means you're not getting the fuel you need.

Taking a fuel pressure reading at the carb at WOT will more than likely show too low.

Everything you have checked so far points towards a fuel delivery problem.  Once you confirm (or disprove) with a pressure reading it's a matter of working back through the fuel system to find the restriction.

Good luck.

[CRW-FK5]

It's possible that the in-tank foam sock on your pickup has clogged. How old is the fuel system in this car ? Have you measured fuel pressure with the engine under load ?


Ron

Sock was missing on the sending unit.  Fuel lines are original.  Hose between sending unit and metal lines just replaced.  Fuel pressure during cranking is 4-5 psi.  Not checked under load but I am assuming it would not drop below that, correct?

It seems almost certain you have a restriction somewhere in the fuel system.  You previously stated that you can run at 3500 RPM with no engine load, but in gear under load you have issues.  The point of checking that was to rule out some electrical issues. The engine needs more fuel when loaded, so when it leans out under load, it means you're not getting the fuel you need.

Taking a fuel pressure reading at the carb at WOT will more than likely show too low.

Everything you have checked so far points towards a fuel delivery problem.  Once you confirm (or disprove) with a pressure reading it's a matter of working back through the fuel system to find the restriction.

Good luck.

Yes.  I have isolated the problem to fuel delivery at higher loads.  The A/F readings are strong evidence of that, and was excellent advise by XH29N0G in a previous post.

You stated that taking a fuel pressure reading at the carb at WOT will likely show too low.  The question I have is how low is too low?  When I measure pressure at pump exit (with engine idling) I get 4-5 psi (which I've stated previously).  So my assumption is that this pressure would not drop off at higher RPM's resulting in at least this amount at WOT.  I also assume (based on literature from Edelbrock) that 4-5 psi is sufficient to supply my engine at moderate load conditions like cruising at 3,500 RPM's.  Are these correct assumptions or not, I wonder.

Regarding confirmation of this condition with a pressure reading (at WOT I assume), this cannot be done.  The engine simply will not produce power at WOT, and with the extreme lean readings I am getting under conditions like that I would not even consider confirming it.  It is not good on an engine.

[cdr]

NEVER ASSUME , hook up a pressure gauge & drive the car & see what the pressure does when you nail it.

[c00nhunterjoe]

NEVER ASSUME , hook up a pressure gauge & drive the car & see what the pressure does when you nail it.

Careful, you are going to get yelled at now.

[c00nhunterjoe]

What ron said. You are skipping the basic steps as we asked several times in your other post. You need to check fuel pressure at wide open throttle under load and see if it maintains or drops. If it drops, you need to measure your pushrod next.

Please back up your statement that I'm "skipping the basic steps as we asked several times in your other post".  I have measured the push rod and it is fine (3.21").  I have measured A/F ratio at suggested rpm range of 3,500 and provided detailed A/F readings from them which showed lean.  No where do I see request for pressure check at WOT.  The car won't even run at WOT.  So keep your condescending comments to your self.  I can do without it.  If you have some advise, then provide it. 

Before you go running your mouth, i had the initial reply on your 1st topic that said check fuel pressure, then again said it in that topic, and it has been mentioned since by others, yet you still havnt done it, and yourself just said that you "assume" its fine. So if you want to assume it instead of checking it, quit bitching at me.

[CRW-FK5]

What ron said. You are skipping the basic steps as we asked several times in your other post. You need to check fuel pressure at wide open throttle under load and see if it maintains or drops. If it drops, you need to measure your pushrod next.

Please back up your statement that I'm "skipping the basic steps as we asked several times in your other post".  I have measured the push rod and it is fine (3.21").  I have measured A/F ratio at suggested rpm range of 3,500 and provided detailed A/F readings from them which showed lean.  No where do I see request for pressure check at WOT.  The car won't even run at WOT.  So keep your condescending comments to your self.  I can do without it.  If you have some advise, then provide it.  

Before you go running your mouth, i had the initial reply on your 1st topic that said check fuel pressure, then again said it in that topic, and it has been mentioned since by others, yet you still havnt done it, and yourself just said that you "assume" its fine. So if you want to assume it instead of checking it, quit bitching at me.

Fuel pressure was checked.  It was checked at idle and at fast RPM.  It was not checked under load, as I do not have that capability yet and it was not recommended by anyone that I specifically check that way.

Regarding my use of the word "assume", not all assumptions are bad.  It's interesting, though, how some love to jump on the opportunity to chastise anyone for using that word as if it automatically meant being an idiot.  If you took the time to understand the context of my sentence and not just fixate on the use of that word, you'd realize that I am asking if I've actually made a good assumption or not.  I'm just a fellow car enthusiast trying to fix my car, man.  

I'm sure you're very knowledgeable about this stuff but if I have to put up with an arrogant tone I'd rather solve it on my own.  There are proper ways to communicate.  

[c00nhunterjoe]

Funny how you chastise me on your use of the word assumption when it was another member that called you out on it. If you checked the fuel lressure at idle, then you have no excuse to check it under load. Ziptie the gauge to a wiper arm.

I am not arrogant, quite the oppositte actually, but when you start posting multiple topics on the same problem, and ignore requests for the most basic of basic tests, then my frustration with you is justified. To date you have swapped carbs multiple times. You have pulled the distributor apart, you have made lots of fancy data log charts, you have done compression tests, you have vacuum checked your system... but you still havnt checked your fuel pressure under load.... which your graphs actually pointed towards that 2 topics ago and its still not done.
      So no, im not being arrogant. Im not an ass. I am sitting here beating my head against the wall in frustration because i am trying to help you and you wont listen.

[firefighter3931]

It's possible that the in-tank foam sock on your pickup has clogged. How old is the fuel system in this car ? Have you measured fuel pressure with the engine under load ?


Ron

Sock was missing on the sending unit.  Fuel lines are original.  Hose between sending unit and metal lines just replaced.  Fuel pressure during cranking is 4-5 psi.  Not checked under load but I am assuming it would not drop below that, correct?

If the fuel pump is old it's certainly a possibility that it can't keep up under increased load. Heck....most of the newer pumps are not that good. The only pump i'll use is the Carter HP 120GPH street pump that Mancini sells.

As mentioned above ; just zip tie a guage to the wiper arm and take a drive. Stab the gas and pay close attention to what's happening with the pressure. 


Ron

[CRW-FK5]

Funny how you chastise me on your use of the word assumption when it was another member that called you out on it. If you checked the fuel lressure at idle, then you have no excuse to check it under load. Ziptie the gauge to a wiper arm.

I am not arrogant, quite the oppositte actually, but when you start posting multiple topics on the same problem, and ignore requests for the most basic of basic tests, then my frustration with you is justified. To date you have swapped carbs multiple times. You have pulled the distributor apart, you have made lots of fancy data log charts, you have done compression tests, you have vacuum checked your system... but you still havnt checked your fuel pressure under load.... which your graphs actually pointed towards that 2 topics ago and its still not done.
      So no, im not being arrogant. Im not an ass. I am sitting here beating my head against the wall in frustration because i am trying to help you and you wont listen.

If you're getting that worked up about it then I'd suggest you ignore my posts.  Don't beat yourself up about it.  It's not worth it.

[CRW-FK5]

It's possible that the in-tank foam sock on your pickup has clogged. How old is the fuel system in this car ? Have you measured fuel pressure with the engine under load ?


Ron

Sock was missing on the sending unit.  Fuel lines are original.  Hose between sending unit and metal lines just replaced.  Fuel pressure during cranking is 4-5 psi.  Not checked under load but I am assuming it would not drop below that, correct?

If the fuel pump is old it's certainly a possibility that it can't keep up under increased load. Heck....most of the newer pumps are not that good. The only pump i'll use is the Carter HP 120GPH street pump that Mancini sells.

As mentioned above ; just zip tie a guage to the wiper arm and take a drive. Stab the gas and pay close attention to what's happening with the pressure. 


Ron

Thanks, Ron.  Fuel pump is new but stock Autozone part.  I measured flow (cranking) at around 37 GPH.  Will try and extend the gauge up and see what happens under load.  When I took the carb apart last night I noticed fine black particulate in the bottom of each bowl.  It was strange because I just had it apart a few weeks ago and saw the same thing then (and cleaned it out).  I am suspicious that it might be particulate from one of the hoses (not assuming though), possibly indicating weakness such that under high suction it is actually partially collapsing.  That would appear (hope I'm okay using that word) to be consistent with the condition I'm experiencing.

[c00nhunterjoe]

Funny how you chastise me on your use of the word assumption when it was another member that called you out on it. If you checked the fuel lressure at idle, then you have no excuse to check it under load. Ziptie the gauge to a wiper arm.

I am not arrogant, quite the oppositte actually, but when you start posting multiple topics on the same problem, and ignore requests for the most basic of basic tests, then my frustration with you is justified. To date you have swapped carbs multiple times. You have pulled the distributor apart, you have made lots of fancy data log charts, you have done compression tests, you have vacuum checked your system... but you still havnt checked your fuel pressure under load.... which your graphs actually pointed towards that 2 topics ago and its still not done.
     So no, im not being arrogant. Im not an ass. I am sitting here beating my head against the wall in frustration because i am trying to help you and you wont listen.

If you're getting that worked up about it then I'd suggest you ignore my posts.  Don't beat yourself up about it.  It's not worth it.

Funny you say that. Have you noticed that the old timers that have the knowledge are not chiming in? Only other one left is ron. So since you wont listen to me, how about you listen to ron and ziptie the gauge to the wiper arm and give him the answer.
  And not that it matters, but a stock replacement carter from advance/autozone will not supply enough fuel for my mild 383. Pressure dropped to 2 psi by part way into 2nd gear. (4speed)

[cdr]

from  c00nhunterjoe
Funny you say that. Have you noticed that the old timers that have the knowledge are not chiming in? Only other one left is ron. So since you wont listen to me, how about you listen to ron and ziptie the gauge to the wiper arm and give him the answer.
 And not that it matters, but a stock replacement carter from advance/autozone will not supply enough fuel for my mild 383. Pressure dropped to 2 psi by part way into 2nd gear. (4speed)
[/quote]


                                                     

[CRW-FK5]

Funny how you chastise me on your use of the word assumption when it was another member that called you out on it. If you checked the fuel lressure at idle, then you have no excuse to check it under load. Ziptie the gauge to a wiper arm.

I am not arrogant, quite the oppositte actually, but when you start posting multiple topics on the same problem, and ignore requests for the most basic of basic tests, then my frustration with you is justified. To date you have swapped carbs multiple times. You have pulled the distributor apart, you have made lots of fancy data log charts, you have done compression tests, you have vacuum checked your system... but you still havnt checked your fuel pressure under load.... which your graphs actually pointed towards that 2 topics ago and its still not done.
     So no, im not being arrogant. Im not an ass. I am sitting here beating my head against the wall in frustration because i am trying to help you and you wont listen.

If you're getting that worked up about it then I'd suggest you ignore my posts.  Don't beat yourself up about it.  It's not worth it.

Funny you say that. Have you noticed that the old timers that have the knowledge are not chiming in? Only other one left is ron. So since you wont listen to me, how about you listen to ron and ziptie the gauge to the wiper arm and give him the answer.
 And not that it matters, but a stock replacement carter from advance/autozone will not supply enough fuel for my mild 383. Pressure dropped to 2 psi by part way into 2nd gear. (4speed)

I'm not sure of your point about old timers (of which I myself am becoming) but if they don't chime in then they don't.  Not a big deal.  I certainly hope they would, though, as that's a big part of what these forums are for.  I know I see it that way, but everyone has a choice.  

I am curious on your comment, however, about the stock pump not being able to supply even a mild 383.  What is different about these than what I was using back in the 70's on my big block Mopars when I had to replace a pump?  I had no issues with fuel delivery back then.  Feel free to reply, or not.  I will figure this out eventually.

[firefighter3931]

It's possible that the in-tank foam sock on your pickup has clogged. How old is the fuel system in this car ? Have you measured fuel pressure with the engine under load ?


Ron

Sock was missing on the sending unit.  Fuel lines are original.  Hose between sending unit and metal lines just replaced.  Fuel pressure during cranking is 4-5 psi.  Not checked under load but I am assuming it would not drop below that, correct?

If the fuel pump is old it's certainly a possibility that it can't keep up under increased load. Heck....most of the newer pumps are not that good. The only pump i'll use is the Carter HP 120GPH street pump that Mancini sells.

As mentioned above ; just zip tie a guage to the wiper arm and take a drive. Stab the gas and pay close attention to what's happening with the pressure. 


Ron

Thanks, Ron.  Fuel pump is new but stock Autozone part.  I measured flow (cranking) at around 37 GPH.  Will try and extend the gauge up and see what happens under load.  When I took the carb apart last night I noticed fine black particulate in the bottom of each bowl.  It was strange because I just had it apart a few weeks ago and saw the same thing then (and cleaned it out).  I am suspicious that it might be particulate from one of the hoses (not assuming though), possibly indicating weakness such that under high suction it is actually partially collapsing.  That would appear (hope I'm okay using that word) to be consistent with the condition I'm experiencing.

The black particulate certainly sounds like rubber hose breaking down. The etanol based fuels are really hard on fuel systems. I would replace all the rubber hose and try blowing compressed air into the fuel line to make sure it's clear and unrestricted. 

The std replacement pumps are hit or miss. The only pump to use if staying with a mechanical is the Carter HP pump. I've used several of these over the years with excellent results. My last 440 made 535hp/540tq and this pump was able to keep up under extreme conditions. Raced it for several years at the track and it never let me down 

http://www.manciniracing.com/cabheen5psis.html

With the pressure test you'll be able to see what's up. If the pressure drops below 4psi with a stab of the throttle you'll know the pump is suspect. If it maintains good pressure the problem will most likely be carb related. These things can be frustrating to hunt down so just eliminate things one at a time and you'll find the problem and correct it. 


Ron

[c00nhunterjoe]

To be able to say what exactly is wrong inside, i cannot. They cruise fine, just cant supply wide open. My 383 might be 400hp at the crank, no more.

[firefighter3931]

To be able to say what exactly is wrong inside, i cannot. They cruise fine, just cant supply wide open. My 383 might be 400hp at the crank, no more.

the issue I would suspect is the spring loading the diaphragm on the low-end pumps. It's probably adequate for cruising but once the pump is stressed the spring most likely just begins to float (at high rpm) and fuel pressure nosedives. 

Just a theory but probably more closer to the truth than not 



Ron

[crj1968]

I had similar issue once.  I just wired a cheapo electric pump to a gas can in my passenger floor board....car ran great and at least I knew where to begin.

Mine turned out to be some sort of weird gunk built up in the metal lines....starving the pump

wire up an electric pump to a gas can- just don't go flying around any corners