Is it possible to lose fuel pressure as the motor warms up? The pressure is at 8 psi when the motor is cold. After about 15 minutes the gauge drops to 3 psi. It has dropped as low as 1 psi. I thought the gauge was defective so I replaced it. The new gauge is is showing the same thing. The pump is rated at 120 gph at 7.5 to 8 psi. Do I have two bad gauges? The motor is running a little rough at lower rpms. Once into high rpms it's hard to tell if it has smoothed out.
camaro man
Pull the gas cap off with the car running and see if the psi climbs back up. If the tank is sealed the pump will pull a vacuum in the tank which will cause the pressure to drop as the vacuum increases (or is it decrease since vacuum is neg pressure, you get the point though). If this is the problem then you need to buy a vented cap or findout why the tank vent is plugged.
I adjusted the 4 corner idle mixture screws and got the motor running smoother, but the gauge problem is still there. The replacement gauge is the same as the original. I'm wondering if there is a production lot of these made that are defective. I bought these from Jeg's and these were Jeg's own brand. I just can't see the motor running with almost no fuel pressure.
Same here with those Jegs guages, I replaced it with a differant guage but not liquid filled,,, I dont expect it to last too long due to vibration but it will tell me if the guage is bad... Something I noticed on this jegs guage,, it has a small set screw on inside pipe thread,,, I think this is a pressure dampner,, not sure. did not get chance to adjust it before it went bad. Anyone else see this screw?
I noticed the set screw, but I don't know what it's for. I bought the carbon fiber look 1-1/2" 0-15 psi liquid filled gauge for $24.99 from Jeg's. I was under the idea that the liquid filled gauges are the best if you have a lot of vibration. When the first one started to act up I bought a second one(same one). They are both did the same thing. When the engine is cold it reads 8 psi. As the engine gets hot the pressure drops off, eventually to 0. If I shut the engine off for a while and then start it the pressure comes up a bit. After about 10 to 15 minutes the pressure will be around 3.5 psi. If I let the engine cool of for a few hours the pressure is back to 8 psi. I thinking the this line or batch of gauges is defective. When engine was hot and the gauge read 0 pressure I unscrewed a fitting and gas was spraying out pretty good.
Understand what you are asking about the fuel line ,, but mine are wrapped with insulation.... The small screw in the back of the threaded fitting,, is I presume a dampening screw,,, ,, I have another in its place and its not acting the same way, but have messed jegs up as I tried to pressure and see if it is correct with other guages same pressure.... So I will try another one thats not made in china or tiawan.
My fuel line is routed a min. of 4 inches away from the headers and exhaust. I'm running ceramic coated headers so there isn't a lot of heat. I am running a 45 micron prefilter before the mech. pump and a 10 micron filter after the pump. The pressure gauge is located just before the fuel log and after the 10 micron filter. I also am interested in knowing how the Autometer gauge worked. I'm kinda thinking that buying a good gauge will fix my problem.
Sneaky pete, I never found the problem, but I think it was the mechanical pump. I spent a wad of money and changed my fuel delivery system. I went with a -10 AN line from the sump to an inline filter mounted in front of the tank, then directly to a Mallory 140 electric pump. From there I went with a -8 AN line to a Mallory 3 port regulator with a bypass mounted by the front of the engine. I installed a -8 AN line back to the tank. I mounted a fuel pressure gauge (the same one that wouldn't work before) after the regulator and the -8 AN ine to the carb. Now there's plenty of pressure and the fuel delivery system works fine. I hope with a few carb adjustments the motor will be running fine again. It still seems to be running a little rough with the Holley 850, but not bad. Last year I ran a Quick Fuel 950 with no problems till I had fuel problem this year. I put my Quick Fuel 950 back on and it runs smooth with the exception of a slight dead spot at 1800 rpm. Cant get rid of the dead spot by adjusting the air/fuel mixture screws. I really don't know much about carbs. A local speed shop did some work on my carb and I don't know what all they did, but I do know they took out the 30 cc power valves and put in 50 cc ones. I don't like dealing with this shop anymore. I don't get any results from them and It always costs me money.
Glad to hear your making out a little bit better. I think my problem must be in the guage (it's a liquid filled one). I have a pressure switch as well and even though the guage drops pressure after running for a couple minutes the pressure switch never did drop out, so I asume I really do have the pressure still. So I guess I'll try and bleed the guage (some how) and see if that fixes the problem. How much pressure are you shooting to the Holley? I believe they say any thing much higher then 7 psi will blow by the seats and cause a little flooding, but I'm sure you are aware of that. Later dude!
I'm running 7 psi to my Holley. Since my pressure stays steady now it probably wouldn't hurt to drop down to 6 or 6.5. By the way, my fuel pressure gauge is liquid filled too. I bought it from Jeg's for around $24.99.
I see your wanting to run some spray sometime.
I'm planning on getting the NOS super powershot with a 20 lb. tank late this summer or early fall. I want to get down to a 10 flat. I'm also switching my rear gears to 4.11's and I have some Moroso DS-2 front tires to try. I will settle for 10.7 to 10.9 without spraying. Good luck
I see your wanting to run some spray sometime.
I'm planning on getting the NOS super powershot with a 20 lb. tank late this summer or early fall. I want to get down to a 10 flat. I'm also switching my rear gears to 4.11's and I have some Moroso DS-2 front tires to try. I will settle for 10.7 to 10.9 without spraying. Good luckGo figure! Just had to keep prying the little rubber cap on the side of the guage about a dozen times and pressure stays constant now. Boy do I feel like a dumb a_ _ !
I'm in the process of hooking up the Edelbrock 100 - 250 system, put in the 100 jetting untill I get er all figured out and working properly.
I also picked up the MSD CD Digital 6 Plus, quite impressed with it so far. Hooked the secondary rev limit up to the line lock circut and set it at 3500 to test it out. Works good, smooth limit control just sputters and sits at that rpm and dosn't cut out like the old type (my neighbour thought I put in a trans brake and was waiting for me to brake something, LOL). Of course I am assuming the RPM is correct as I now need a adapter to get my tac (Sun Super II) to work.
Anyways things are looking up and hope to get to Yorktons annual 1/8's this weekend. Later!!
I'm in the process of hooking up the Edelbrock 100 - 250 system, put in the 100 jetting untill I get er all figured out and working properly.
I also picked up the MSD CD Digital 6 Plus, quite impressed with it so far. Hooked the secondary rev limit up to the line lock circut and set it at 3500 to test it out. Works good, smooth limit control just sputters and sits at that rpm and dosn't cut out like the old type (my neighbour thought I put in a trans brake and was waiting for me to brake something, LOL). Of course I am assuming the RPM is correct as I now need a adapter to get my tac (Sun Super II) to work.
Anyways things are looking up and hope to get to Yorktons annual 1/8's this weekend. Later!!
I am the guy that RickD is referring to as having this problem recently. It definitely was vapor lock. I have not completely fixed the problem, but I have gotten it under control for now. Ultimately, my fix to this problem will be to change over to an electric pump and utilize a regulator with a return line to the tank to keep the fuel moving and cool. My situation was exactly what you are describing and I too thought that it was a faulty guage, which it was not. I finally figured it out by running a piece of clear tubing from the tank to the inlet on the pump. After coming up to temperature, air bubbles started coming out of the inlet on the pump, yes, out of the inlet!, the bubbles would travel back into the clear tubing and create an air pocket that would grow and grow until it was about a foot long. The car would not shut down, and would not even really show any signs of starvation, but the fuel pressure would go down to 2 or 3 lbs, and my air/fuel ratio guage would go way lean. I have gotten it under control by wrapping the fuel line and also extending the inlet-side fuel line so that it runs away from the motor as much as possible. I also switched from a barry grant mechanical to a holley mechanical. The Barry Grant pump seemed to run hotter than the Holley does, adding to the problem. As soon as I can afford it I will be changing over to the system listed above.
Mike
Mike
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