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Fuel pressure problem returns

69roadrunnerragtop

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Ok i hope you RR guys can help me figure this out. sometimes my fuel pressure drops to 1-2 psi. i been having this problem for 2 years now. it seems to be when my engine temp gets up to 195* or higher. this weekend i drove my car to Carlisle about 270 miles one way. i left at 4:30 am got there around 9:30-10 am. my RR ran 180* the whole way there fuel pressure sat at 9psi and only droped to 8psi for a second or two when i hit the gas this sounds normal to me. but later in the day when it hit 90+ the engine temp went up to 190* and thats when my problem came back. my pressure droped to 5 psi running at 2500 RPMs and in traffic it would go down to 2 psi. the next morning the fuel pressure was great again till the afternoon and it got hot again and the problem came back. i left carlisle early and about 1 pm hit traffic but it wasnt to hot out engine temp hit 185* fuel pressure held ok. today i drove it at about 3 pm and fuel pressure was down low again engine temp 190 outside temp 93. when i drove home at 9pm it was much cooler at night and pressure was great. this is what i did sofar. replaced fuel pump numurous times, all new fuel line 1 pice front to rear. new filter,new tank, new pickup, new tank vent tubes. here is a list of what is in my RR now BTW i have a 440.
what i have in my RR now starting at the front to rear.
1- Summit racing 750CFM, part number SUM-M08750MS mechanical secondary carb
2- Summit Racing SUM-230102 fuel filter
3- 6 -an fittings and braided hose connecting carb to filter to fuel pump
4- Carter street strip fuelpump 120GPH 9psi #GM4862
5- 1/2 inch aluminum fuel line routed as far away from the exhaust in stock location on outer lip of rocker panal and up INTO trunk and droped down right at the tank pickup
6- New 1/2inch pickup tube sender switch.
7- new tank with all new vent tubes. and new gas cap
can anyone explain to me why im having thease problems.
i never had thease problems when i had the old AFB carb, stock fuel pump, old rusty 5/16 fuel line, old broken sender pick up, and old rusty leaking tank, as far as i can remember.
 

dutchrunner

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If you have a oil filled fuelpressure gauge , I already know what's wrong.

I had same issue and changed/checked all.
Fuelfilter/pick-up in tank , changed pump , changed oilfilled gauge , checked flowrate , checked ground , made direct ground to battery.
All where always oke'.
Found out that these oilfilled gauges will drop to 0psi if the get realy hot under hood.

For me it was always the same : 7.5psi when starting.
Waiting for 10 minutes and 5.5psi.
Driving 1 hour and 0.5-1psi.
Waiting/cooldown for 3 hours and again 7.5psi.

Thrown mine away and engine is still running.
Checked in between with other gauge(autometer electric) and pressure always oke'.

If in doubt check with electronic pressuer gauge.
 

ACME A12

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Since it is temperature-related it seems like a classic case of vapor lock. You might try adding an electric pump located near the tank. One of the reasons that newer vehicles are not so susceptible to vapor lock is because the pumps are submerged in the tanks taking advantage of both cooler temps and positive system pressure. Insulating the fuel line (especially underhood) and adding a phenolic spacer under the carb are a couple of other tricks. I'm sure some of the other guys will have some ideas too. Good luck!
 

69roadrunnerragtop

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No its not an oil filled gauge, its an autometer sport-comp non oil filled gauge. i also assumed it was the gauge so i added one of those small 1 1/4" gauges right at the -AN fitting at the carb since there was a 1/8 npt plug there.


dutchrunner said:
If you have a oil filled fuelpressure gauge , I already know what's wrong.

I had same issue and changed/checked all.
Fuelfilter/pick-up in tank , changed pump , changed oilfilled gauge , checked flowrate , checked ground , made direct ground to battery.
All where always oke'.
Found out that these oilfilled gauges will drop to 0psi if the get realy hot under hood.

For me it was always the same : 7.5psi when starting.
Waiting for 10 minutes and 5.5psi.
Driving 1 hour and 0.5-1psi.
Waiting/cooldown for 3 hours and again 7.5psi.

Thrown mine away and engine is still running.
Checked in between with other gauge(autometer electric) and pressure always oke'.

If in doubt check with electronic pressuer gauge.
 

69hemibeep

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The only thing I would suggest would be to add a vapor separator and return line like the hemi and A12s used to reduce vapor lock
 

69roadrunnerragtop

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last summer when i had this problem i tried a Holly blue pump by the tank, and a regulator at the fire wall and still had the problem. then a friend lent me his holly red to try without a regulator and still had the problem.
I didn't think of a the carb insulator cause i have a 1/4" baseplate gasket that came with the carb.
i routed my 1/2" aluminum fuel line from the tank it goes up into the trunk where there was a rubber plug ,down under the back seat out another plug in the floor along the rocker panal lip, up in the front fender well over the shock mount down and into the engine bay at the square hole right at the fuel pump with 8 " of 6-AN braided hose connecting it to the fuel pump. i did this to keep it well away from the exhaust to prevent vapor lock.


ACME A12 said:
Since it is temperature-related it seems like a classic case of vapor lock. You might try adding an electric pump located near the tank. One of the reasons that newer vehicles are not so susceptible to vapor lock is because the pumps are submerged in the tanks taking advantage of both cooler temps and positive system pressure. Insulating the fuel line (especially underhood) and adding a phenolic spacer under the carb are a couple of other tricks. I'm sure some of the other guys will have some ideas too. Good luck!
 

69hemibeep

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69roadrunnerragtop said:
A vapor seperator and return line?

69hemibeep said:
The only thing I would suggest would be to add a vapor separator and return line like the hemi and A12s used to reduce vapor lock
I actually had a vapor lock problem on my jeep and used a similar cure. I ran a 1/4" line back to the tank into one of the vent holes and used a fuel filter at the carb that has a return port on it, I don't have the part # at this moment but its a certain size so you don't loose flow to the carb. This cleans the vapors out of the fuel and returns it to the tank, it works great. Ma mopar used a vapor separator just above the pump on A12 and hemis to do the same thing at a cost of $70 or more for the separator.
 

Roadcuda

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Ray, I was looking into a phenolic spacer for my cars but no one could find any for my Carter avs or afb carbs. Do you have a source for them?
 

SomeCarGuy

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IMO the aluminum line isn't helping. That will transfer heat to the fuel faster than steel line.

Seems like Carter pumps have become trouble prone in the last decade or so. The Edelbrock pump I got in 2008 was awesome. Spendy, but awesome.

The vapor return line may help if you have crappy gas up there.

I ran stock parts in the car in my sig. Had a 3/8 steel line. One steel filter up near the carb. Eddy pump, used AVS for a time and Holley for a time. Aluminum intake w/ crossover blocked. Also had 190 stat in it.

Car NEVER had an issue, even when I just ran a THIN paper gasket under the carb. That made it take 2 seconds to hot start. W/ the 1/4" stock style spacer it fired in about half a second. Never had a vapor lock issue even on 95-100 degree days.

We have decent gas here though.
 

69hemibeep

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SomeCarGuy said:
IMO the aluminum line isn't helping. That will transfer heat to the fuel faster than steel line.

Seems like Carter pumps have become trouble prone in the last decade or so. The Edelbrock pump I got in 2008 was awesome. Spendy, but awesome.

The vapor return line may help if you have crappy gas up there.

I ran stock parts in the car in my sig. Had a 3/8 steel line. One steel filter up near the carb. Eddy pump, used AVS for a time and Holley for a time. Aluminum intake w/ crossover blocked. Also had 190 stat in it.

Car NEVER had an issue, even when I just ran a THIN paper gasket under the carb. That made it take 2 seconds to hot start. W/ the 1/4" stock style spacer it fired in about half a second. Never had a vapor lock issue even on 95-100 degree days.

We have decent gas here though.
You have a point on the gas ours is crappy and we have higher temps
 

69roadrunnerragtop

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Ok found this on another site it says on 440HP motors and 426Hemi motors a fuel vapor seperator is used to prevent vapor lock like you said.
http://www.dodgecharger.com/forum/index ... ic=16569.0
its a scan of an old facotory serviace manual.
So i looked up on year one catalouge and found this
part # X868 is a Fuel vapor separator-1968-1971 440 and 426 Hemi cars used a special vapor separator which simultaneously filters the fuel using a screen and routes heat-vaporized fuel back to the fuel tank. Finished in black just like the original, this vapor separator is correct in size and shape and has the correct lettering.
so i went to my local autoparts store to see if i can get one and no way But he found something that sort of rplaces it.
http://shop.advanceautoparts.com/webapp ... _-10711125
it has 3/8" in and out and 1/4" return with the same size vapor orafice but the return comes out the side instead of the bottom. i bought it and some 1/4 fuel rubber line, and 1/4" steel line. i installed all this today. i drove around this after noon it was hot got the engine temp up to 195 by driving around in stop and go traffic and my pressure stayed steady at 6 to 6.5psi. just for kicks i pinched off the rubber vapor fuel return and within 10 minutes my problem came back. as soon as i removed the vice grip my problem went away immideatly. the only differance is instead of having 9.5 psi fuel pressure i have 6.5 with the return line hooked up, thats fine with me as long as its steady and my summit performance carb recommends 7 psi max anyway so to me it is perfect.
Hey 69Hemibeep thanks for the idea you were right on the nose with the problem.
if you were here i buy you a beer :cheers:
 

69hemibeep

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69roadrunnerragtop said:
Ok found this on another site it says on 440HP motors and 426Hemi motors a fuel vapor seperator is used to prevent vapor lock like you said.
http://www.dodgecharger.com/forum/index ... ic=16569.0
its a scan of an old facotory serviace manual.
So i looked up on year one catalouge and found this
part # X868 is a Fuel vapor separator-1968-1971 440 and 426 Hemi cars used a special vapor separator which simultaneously filters the fuel using a screen and routes heat-vaporized fuel back to the fuel tank. Finished in black just like the original, this vapor separator is correct in size and shape and has the correct lettering.
so i went to my local autoparts store to see if i can get one and no way But he found something that sort of rplaces it.
http://shop.advanceautoparts.com/webapp ... _-10711125
it has 3/8" in and out and 1/4" return with the same size vapor orafice but the return comes out the side instead of the bottom. i bought it and some 1/4 fuel rubber line, and 1/4" steel line. i installed all this today. i drove around this after noon it was hot got the engine temp up to 195 by driving around in stop and go traffic and my pressure stayed steady at 6 to 6.5psi. just for kicks i pinched off the rubber vapor fuel return and within 10 minutes my problem came back. as soon as i removed the vice grip my problem went away immideatly. the only differance is instead of having 9.5 psi fuel pressure i have 6.5 with the return line hooked up, thats fine with me as long as its steady and my summit performance carb recommends 7 psi max anyway so to me it is perfect.
Hey 69Hemibeep thanks for the idea you were right on the nose with the problem.
if you were here i buy you a beer :cheers:
I'll travel a long way for a :cheers: and bench talk, ask Ray :yesnod: I'm glad it worked out. :party:
 

ACME A12

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Good call on the return line, Bob. :thumbsup:
A return from the fuel bowl itself is another option in extreme cases. Not what you want when you're trying to keep the underhood area tidy however...
 

Roadcuda

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sam z

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I'm reading this thread with a lot of interest.

My only question is why only Hemi and A12 cars? This seems like a
good idea for any car.
 

droptop

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69hemibeep said:
69roadrunnerragtop said:
A vapor seperator and return line?

69hemibeep said:
The only thing I would suggest would be to add a vapor separator and return line like the hemi and A12s used to reduce vapor lock
I actually had a vapor lock problem on my jeep and used a similar cure. I ran a 1/4" line back to the tank into one of the vent holes and used a fuel filter at the carb that has a return port on it, I don't have the part # at this moment but its a certain size so you don't loose flow to the carb. This cleans the vapors out of the fuel and returns it to the tank, it works great. Ma mopar used a vapor separator just above the pump on A12 and hemis to do the same thing at a cost of $70 or more for the separator.

Filter looks like this. Just run a small line to the tank and tie into a vent line.
 
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