fuel pressure issues
06-28-2012, 10:01 PM
#1
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fuel pressure issues ive got some questions. my edelbrock quietflo 160gph pump seems to be having trouble keeping up to my pressure needs even at idle. it starts off fine at 7.5 psi, but then after a few minutes of idling it slowly falls to like 4 lbs and ive even seen it read 0 on more than one occasion. its a all new fuel system from the ground up even the carb and fuel cell. the floats are set perfect on the carb when its at 7.5 psi and they dont really seem to change when the pressure gets low or even at 0 so im confused. is 8an fuel line too big for a pump like this to keep pressure? i couldnt see that being a problem but i have to ask. ive purchased everything but the tank carb and lines 2 times now and ive got way more money dumped into this problem than i should have. its frustrating spendin 200 bucks on a pump only to find out that wasnt the problem. tell me im stupid and the gauge should be bad or some **** please. thats the only thing in the system that isnt brand new i will be buying a new gauge before the weekend tho. if thats the case im gunna be pissed at myself for not trying the cheapest simplest route first... i can get pics or even vids of the pressure/system if needed, i just need this sorted out. thanks for lookin and any help will be awesome.
06-28-2012, 10:34 PM
#2
7.5psi is too much at the carb, turn it down to 5- 5.5psi.
Is this a deadhead, or return style system?
if the pressure is falling, you either have a pickup problem preventing the pump from moving fuel, or the pump itself is not moving the fuel for what ever reason - wiring/voltage issue maybe?
Is this a deadhead, or return style system?
if the pressure is falling, you either have a pickup problem preventing the pump from moving fuel, or the pump itself is not moving the fuel for what ever reason - wiring/voltage issue maybe?
06-28-2012, 10:57 PM
#3
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i guess i was just going by what pro systems said for the fuel pressure. its a returnless style/deadhead setup too. im going to buy a new gauge tomorow or this weekend and double check that too. if that doesnt work i will try to turn down the pressure and double check my wires and current draw... i also pulled the line from before and after the regulator and filled a couple 5 gallon cans pretty quickly. it had a nice flow with both the old and new pump when i tested it too...
06-28-2012, 11:12 PM
#4
good call on the gauge, if it is moving good volume of fuel, then thats where I'd look.
The reason I suggest 5-5.5 psi of pressure, is that at about 8-9 psi the needle an seat in the carb starts to loose its ability to close against the pressure. Some guys run more, some less, I like 5.5psi.
The reason I suggest 5-5.5 psi of pressure, is that at about 8-9 psi the needle an seat in the carb starts to loose its ability to close against the pressure. Some guys run more, some less, I like 5.5psi.
06-29-2012, 02:22 AM
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I have seen wiring cause a problem like this the pump was loosing ground as it vibrated and pressure would jump around as the wire rattled at the ground. I would just check your wiring quick make sure its all good ?
06-29-2012, 05:52 AM
#7
Liquid filled gauges can be pretty unreliable when they get hot. You can try a different gauge in a place where it won't get hot.
Larger line can only help the pump, not hurt it. Excessive flow can cause a low pressure, but if nothing is moving the line should fill up and hold pressure.
If you have any type of air leak in the line before the pump, a loose fitting or something, then that can cause erratic pressure.
If the problem is a loose power wire or ground then I would think you could hear it in the sound of the pump.
Is the tank properly vented? If you draw a vac in there the pump can stop pumping.
Another obvious problem is the regulator could be bad. If you got a second pressure gauge and put one before and after the regulator you could quickly eliminate the regulator as the problem.
Last thing is maybe you need to go to a return style regulator. That is a pretty big pump to be running into a dead head. At idle the pump is just sitting there spinning against the same slug of fuel in the rotor. Maybe it is heating up and boiling basically. If you have ever heard a pump that is cavitating it is a pretty distinct sound.
Is the pump near the bottom of the tank or is it mounted higher than the tank? Keeping a positive pressure at the inlet to the pump helps.
Do you have a prefilter and is it clogged?
Last I think Speedtigger had that same edlebrock pump and swapped it out for the same reason, it didn't keep a steady pressure. You might search on some of his posts to see if that was really the case.
Larger line can only help the pump, not hurt it. Excessive flow can cause a low pressure, but if nothing is moving the line should fill up and hold pressure.
If you have any type of air leak in the line before the pump, a loose fitting or something, then that can cause erratic pressure.
If the problem is a loose power wire or ground then I would think you could hear it in the sound of the pump.
Is the tank properly vented? If you draw a vac in there the pump can stop pumping.
Another obvious problem is the regulator could be bad. If you got a second pressure gauge and put one before and after the regulator you could quickly eliminate the regulator as the problem.
Last thing is maybe you need to go to a return style regulator. That is a pretty big pump to be running into a dead head. At idle the pump is just sitting there spinning against the same slug of fuel in the rotor. Maybe it is heating up and boiling basically. If you have ever heard a pump that is cavitating it is a pretty distinct sound.
Is the pump near the bottom of the tank or is it mounted higher than the tank? Keeping a positive pressure at the inlet to the pump helps.
Do you have a prefilter and is it clogged?
Last I think Speedtigger had that same edlebrock pump and swapped it out for the same reason, it didn't keep a steady pressure. You might search on some of his posts to see if that was really the case.
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06-29-2012, 07:03 PM
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Liquid filled gauges can be pretty unreliable when they get hot. You can try a different gauge in a place where it won't get hot.
Larger line can only help the pump, not hurt it. Excessive flow can cause a low pressure, but if nothing is moving the line should fill up and hold pressure.
If you have any type of air leak in the line before the pump, a loose fitting or something, then that can cause erratic pressure.
If the problem is a loose power wire or ground then I would think you could hear it in the sound of the pump.
Is the tank properly vented? If you draw a vac in there the pump can stop pumping.
Another obvious problem is the regulator could be bad. If you got a second pressure gauge and put one before and after the regulator you could quickly eliminate the regulator as the problem.
Last thing is maybe you need to go to a return style regulator. That is a pretty big pump to be running into a dead head. At idle the pump is just sitting there spinning against the same slug of fuel in the rotor. Maybe it is heating up and boiling basically. If you have ever heard a pump that is cavitating it is a pretty distinct sound.
Is the pump near the bottom of the tank or is it mounted higher than the tank? Keeping a positive pressure at the inlet to the pump helps.
Do you have a prefilter and is it clogged?
Last I think Speedtigger had that same edlebrock pump and swapped it out for the same reason, it didn't keep a steady pressure. You might search on some of his posts to see if that was really the case.
Larger line can only help the pump, not hurt it. Excessive flow can cause a low pressure, but if nothing is moving the line should fill up and hold pressure.
If you have any type of air leak in the line before the pump, a loose fitting or something, then that can cause erratic pressure.
If the problem is a loose power wire or ground then I would think you could hear it in the sound of the pump.
Is the tank properly vented? If you draw a vac in there the pump can stop pumping.
Another obvious problem is the regulator could be bad. If you got a second pressure gauge and put one before and after the regulator you could quickly eliminate the regulator as the problem.
Last thing is maybe you need to go to a return style regulator. That is a pretty big pump to be running into a dead head. At idle the pump is just sitting there spinning against the same slug of fuel in the rotor. Maybe it is heating up and boiling basically. If you have ever heard a pump that is cavitating it is a pretty distinct sound.
Is the pump near the bottom of the tank or is it mounted higher than the tank? Keeping a positive pressure at the inlet to the pump helps.
Do you have a prefilter and is it clogged?
Last I think Speedtigger had that same edlebrock pump and swapped it out for the same reason, it didn't keep a steady pressure. You might search on some of his posts to see if that was really the case.
this seemed to be the problem. stupid me thought i was goin with the cheapest part first and forgot the gauge could have went to ****.
i was confused about it hurting since it goes thru such small jets in the carb compaired to the fuel line size
tripple double checked this thanks tho
tank has one 8an line as the vent with a breather filter on the end of it to keep dust from going in
this was my initial thought, so i bought a new one and it didnt change the issue....
i will look into this if the problem comes back
i was worried about the wiring going to the pump seeming small but its bigger than the wires on the pump from factory so i kinda tossed that out the window. and the truck is too loud to hear changes in the pump even at idle with the exhaust on
pump is at about the bottom of the tank maybe a few inches higher than the end of the pickup
brand new pump, but i did check the old pumps pre-filter screen tho. it was clean
i will look into this too, kinda sucks since i just spent another 200 on a pump and another 90 on 2 new quick fuel regulators. on the plus side i did find out that it was all just a bad gauge or the fluid filled gauge was heating up too much and causing pressure reading problems. stupid summit junk haha
Last edited by 89gmcs15; 06-29-2012 at 07:10 PM. Reason: im confused at how to reply to multiple questions in one quote
06-29-2012, 08:46 PM
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Seems that with a new gauge the fuel pressure holds steady. Im bummed that this is what the whole problem was and it cost me over 290 and time to fix a 10 dollar part but oh well live and learn. now I have a issue at wot at higher rpms... falls on its face at about 5500/5800 rpm. Gotta check my floats again since the fuel pressure has changed it seems like the fuel level is a touch low. I cant quite see the level in the sight glasses now... Maybe thats my high rpm stumble/issue I guess thanks for all the help so far.
06-29-2012, 09:01 PM
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06-29-2012, 09:43 PM
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Ill have to look at it again. Unless it lost its memory somehow it should be still at 6800. It almost acts like its a fuel issue somehow. maybe I need to check my plugs for fouling since my pressure was so far o uh t of whack.... When I put the new gauge on my pressure was way up at like 12 and I had to turn it down a ways before it reacted on the gauge. Could fouling be causing a high rpm issue?
06-29-2012, 10:37 PM
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Ill prolly just buy a good gauge, ive got a oilfield supply store 30# dry with a collar reducer bushing and a nipple to test it out. Ive akso got the fuel set to 7.5 psi just like before. Im going to doublecheck the float levels tomorow and get them right cuz I know theyre alittle low. Ill report back tomorow with what I find and prolly pull plugs and check them. Anyvidea of what I should run for plugs and gap? Carbed lq9/ls3 with good sized cam th400 with a decent stall rated at 3600 RPMs and conservative timing set at 29 degrees all in by 3k. Sorry for typos and missed letters im on my phone
06-30-2012, 11:05 AM
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ill have to look into those plugs cuz im totally not sure whats in it since i got them a year ago ha. my setup is at like 10.38 cr. it runs pretty good for what it is i just gotta get these little issues worked out so i can really mash on it
06-30-2012, 07:26 PM
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I have read quite a few posts about spark plugs here where the common gap for these engines seems to be .050" because the coil packs are more powerful than an old HEI or points set up.
