I'm having trouble with fuel pressure. As the car warms up, the pressure drops. From 7-8 psi down to 0. It is a 86 camaro. The 2.8 has been changed to a carb'd 350. I replaced the in tank pump by using a sender from a carb'd firebird. I replaced the fuel line. I replaced the mech pump. Any idea where to check?

 

I usually start with the last work done. I would suspect you have a restriction in the pick up/ fuel sock. Did you verify that the tank was clean when you had it down? I assume youre checking pressure in the line from the pump to the carb. Do you have an in line fuel filter? Could it be clogged? Pretty simple fuel supply sys. You have a restriction somewhere.

 

I'm sorry, let me clarify. All of the work performed is an attempt to fix the pressure loss. Ever since I put in the 350, I started losing pressure. The computer and all of the wiring is gone, so the electric pump was out of the question. Could it be possible I need a electric pump near the rear to help prevent vapor lock? Yes the filter is new. I put it past the pump, but before the pressure gauge. The original filter has been bypassed. The sending unit and strainer looked to be in very good condition. I agree it's a simple process. That's why I am going nuts. The car left me stranded twice.

 

Does your mech. fuel pump have a return line to the fuel tank??

Auggie

 

No it doesn't. Just the two.

 

What type of fuel gauge are you using? If its a liquid filled one on your fuel log then its probably the gauge. I just had the same problem. It drove me nuts. Sorry I didn't read far enough to see that you are actually getting stranded.

 

It is a liquid filled. It's a summit. I thought about it being the gauge, but when it loses pressure, the carb empties and the car dies. After 10 minutes or so, it will pick back up and run for a few minutes. Then stalls again. When I changed out the sending unit in the tank, I changed the fuel line. I moved it to the passenger side. I ran it as far away from the headers as I could, but as everyone knows, there isn't alot of places under there. It was recommended that I put the fuel line back where it belongs, and maybe wrap it.

 

Because your system dosen't have a fuel pump return line to keep the fuel pump cool the liquid fuel is turning into a vapor and the fuel pump doesn't pump vapor. Install a return line which will really help your problem and knowing how a mech. fuel pump works will also help.



Auggie

 

Thank you for your clarification. You still most likely have a supply issue. I hear what Auggie is saying about vapor lock. You say you have a two port fuel pump with no return line. A simple solution is to install a filter with a 3rd vapor port. This is available at any parts store. You can then connect the vapor port to the vehicles original return line. However, unless youre dealing with very high tempuratures, Im not sure that vapor lock is your problem. Does your fuel line run close to the exhaust system anywhere? That could cause a fuel heating issue. I still think you need to look at your fuel supply. Could you have a hose that is collapsing? Fuel hose can collapse internally and appear okay on the outside. Could you have a pinched hose? The vapor return is a good idea, plus it will increase fuel pump flow and point out a supply issue.

 

Thanks for the reply Doc. I replaced the fuel pump with a 3 line. I rerouted all the lines away from any exhaust. Still had the problem. I decided to try and run a short line straight from a gas can into the pump. Works fine. Turns out the strainer in the tank was twisted and blocking the tube. I cut off strainer and installed another filter just before the pump to help keep crap out of the pump. So far so good. I kept the return hooked up and still have 6-7 psi. Thanks to all who helped. Larry

 

Cool! I was just thinking too. One quick test for restriction in your supply to a mechanical pump would be to install a low pressure/vacuum gauge in the supply line. I would think that anymore than a minimal vacuum reading would point to a restriction. Ill experiment with this the next time I have an issue with a carb application.

 

I have a air operated vacuum pump that I use for testing the inlet fuel line on snowmobiles for air leaks but how would you appley that to the fuel pump supply line on a car? Would the tank have to be compleatly empety??

Auggie