Well I just fired the new motor up yesterday however I am having huge fuel pressure issues. It was fine when first started, however about five minutes inot the break in the fuel pressure began to drop drastically it was floating just at 6.5psi. However, when we blipped the throttle right before breaking it in, it dropped dramatically. It would float around 3psi. No amount of adjustment on the regulator would bring the psi back up. We quickly shut it off for fear of melting something. The car is an original L69 car, and the previous owner had a carter electronic pump on it. I replaced it with a slightly higher flowing carter pump, and added a fuel pressure regulator. I am still running the stock 3/8 lines. It is feeding into a bone stock 4150 holley. I don't have the return line hooked up, however it ran fine with the previous setup not hooked up. The car is also equipped with a new in line filter. I seriously have no clue what do at the moment. The only thing I could think of was maybe vapor lock? Any thoughts or suggestions would be helpful.

 

Vapor lock is the inability of a pump to draw fuel due to a heated supply line. The combination of low pressure from the pump sucking and the elevated temperature changes the fuel from liquid to vapor, and the pump can't pump vapor. Hence, vapor lock.

If your electric pump is back by the tank, it isn't vapor locking. If it is up in the engine compartment, it might be vapor locking.

Is the mechanical fuel pump still in place, or was it taken out of the system? Where is the electric pump mounted?

 

There is no mechanical pump hooked up. Just a block off plate where it once was. The electric pump is mounted to the rear of the car. I am about to go outside and see what I can find out as it is my day off. I am just mistyfied as to what could be the problem as everything is new.

 

You may be losing voltage to the pump for some reason, if both pumps acted the same way. Try monitoring the voltage at the pump when it does this.

Or, your fuel filter clogged up.

 

The filter is fine, just bought it and I double checked that already. I did however find a leak this morning. Seems that I forgot to teflon tape one of the pressure ports on one of the AN fittings. That helped a little to stabalize pressure, but now when I blip the throttle the pressure just dumps, and it gets as low as 3psi. I am not sure what is causing that.

 

Just to chime in here for a sec. Isnt 6.5spi just a tad to high? Shouldnt you rather be around 5-6psi?

 

4-6 psi is the typical recommendation. The Carter mechanical on my 396 is putting out around 7 psi, the Holley doesn't seem to care. Some people run 8 or 9, that's starting to stretch it. As long as the needle and seat can handle it, it really isn't a problem.

 

Check to see if the filter is put on the right way most filters only flow one direction. Just a hint there. And also like someone else said I would check the voltage to the pump and see what it is and keep it hooked up and monitor it for a little bit when driving and see what your pump is getting at all times. Also that leak could have been one killer on fuel pressure. But 6.5 psi with a carb is ok I mean you dont really need a lot of pressure.

 

I haven't had too much more time to play with it this week. However I took off tuesday to figure this problem out because it is making me go crazy. I will let you know what I find out.

 

Well I thought I had it all figured out but maybe I don't. Oddly the fuel pressure seemed to be fine for a little while. Now today it took a dump again. I am thinking there might be some junk in the line. Keep in mind I don't have a filter before the pump, just before the motor. So maybe some junk for the tank got stuck in the pump itself or possibly the lines. However I have never needed a filter pre-pump on any setup I have ever used. Maybe I am just ignorant and I do need it but luck has shown through on the last few cars I have owned. Any input would be helpful. I guess there is a first for everything...

 

i hope you're using a real guage and not those cheapie 1.5" ones that read differently when they get warmer.

 

Yeah I do have a "real" line pressure instrument. I do also have that autometer 1.5" line guage as well. I have one of the see through filters though and it is obviously taking a dump when both guages read low I look at the filter and sure enough fuel is barely getting to it. Today it happened only after I warmed up the car for some time. I run edelbrock headers which run pretty close to the fuel line, but I swear vapor lock shouldn't be an issue. But then again with a new motor that is fairly beefy and headers maybe it is putting quite abit of heat on the lines. I am still not too sure...

 

mayb fuel pump

 

Well maybe I should be more specific on my setup. I am running a carter CRT-P4601HP electric external pump mounted next to the tank, fuel lines are stock. The car is emission deleted so it has no charcoal canister. The regulator is the typical holley two port deisgn and the return line is blocked off. The gas cap is the stocker non vented item. Car is an l69 and does not have the helper electric pump. It just had a lower output electric external carter when I got. The car ran ok, but when I swtiched everything over now it just loses presurre after warm up.

 

run a return style regulator if you don't think the pump is the problem, mallory #4309, move the fuel lines by bending them, wrap them in heat insulation for fuel lines, and then it should clear up.

 

I really didn't want to buy another regulator because I have a pretty trick mounting system right now, however it seems as this is my major problem and the pump is brand new so I have little else to do. I would much rather my car run properly then look blingy underhood. The three port design does it at least have two discharge ports?

 

Sure enough it is vapor lock. I barely have time to work on the car so I wasn't able to work on it during the day too heavily. Well after class today I wanted to recreate my problem and analyze the situation under daylight conditions when I can actually see things. Let the car run for about 15 minutes at part throttle and idle around to get everything nice and warmed up, sure enough the fuel pressure dropped sharply after the warm up. I looked at my fuel filter and I could see nothing but vapor filling the filter with very little fuel dribbling in:


So I shut the car down and acutally started to look through the mess that is my engine bay right now. Well I never noticed it before but since I put new motor mounts in the headers and the whole motor were raised some and sure enough they sit alot closer to the fuel lines then ever before. The pics below show how close they are. I am running a two port holley non-return style and the fuel was boiling in the lines because it was just sitting there waiting to be pushed into the fuel bowls of my 4150. I am going to have to run the three port return style regulator suggested above and get some fuel line wrap and that should be the end of my problem. Thanks for all the help guys!

 

i had a similar problem to yours.. the pressure was jumping around.. the worst was during a run.. i was one my way to a mid 12 run and i dialed in a 12.99.. i let off half way through 4th and the pressure jumped to 9+psi.. the guage i have only goes to 9psi.. flooded the motor like crazy.. then i readjusted the regulator, readjusted the floats and that fixed the problem till i got home.. after that i cleaned out the regulator really good, put the fuel pump on a manual switch from the battery and i never had pressure problems again..

 

that's too much rubber hose as well, replace it with brake line or something similar and smaller 2" sections of rubber hose, that's a fire hazard. Furthermore ditch those crappy see through filters and run a real one, even the fram ones in the filter aisle that have 2 hose barb ends would be better

 

This car is a daily driver and the hose is new and routed away from most any significant heat source. Keep in mind if I routed the lines directly over the valve cover the lines would kink and it would grow hotter due to sitting on my aluminum valve covers which are exposed to more heat then god....

 

i'm just offering advice, obviously you've never seen the threads on here where cars catch on fire because of rubber hose. Just trying to help out man, steel line is under $5.

 

Sorry if that came off harsh. I think I am just tired of sinking money into the car as for me I went to the local speed shop and got some braided line now. As for fuel filter that is up in the air still....