Good Afternoon,

I have a C4 1985 I am trying to get started but have fuel issues I believe. We have spark and air so....

I am assuming that the line under the car that runs through the fuel filter is the feed line and the line that runs next to it that DOES NOT run through the filter is the return line.

I have isolated that there is resistance to flow in the fuel line between the filter and engine. I know this because using a syringe and pushing fuel through the line into the engine from the end that plugs into the filter is harder than it should be, there is back pressure and it squirts back out after the syringe is pulled off the line.

The segment between the fuel pump and the filter is good. There is no back pressure or resistance.

Thanks everyone.

In the picture there are two lines. One of them is unhooked - the one on the bottom or what would be on the passenger side. I am pretty sure that this one goes to the fuel pressure regulator. I can follow the other line to the rail.

The end of the lines into the rail and FPR

Not as good a shot but the same. Sorry about the thumb.


Is this correct?
Then, is the other line the return?

Does it make sense to bypass the fuel line between the filter and the engine externally for proof of concept that the original line in which there is resistance and back pressure in order to see if that is the problem keeping the car from starting.

 

Unhook the fuel feed line at the engine side and turn the key on to prime the pump. That will tell you pretty quickly if you're getting fuel up there.

The syringe method of resistance isn't a great one. The gravity of the fuel trying to climb vertically would force it back out of a low spot.

 

Good point.

 

Today's gasoline is Oxygenated and has ~10% Ethanol in it. Left sitting it will absorb water just like brake fluid is able to. If you are going to let the car sit for any time be sure to put some ethanol treatment in the gasoline and let it circulate around. You want treated fuel in the fuel lines when it sits for any period of time. I am not familiar with the system getting plugged between the fuel filter and the injectors.

I had similar questions with fuel flow and I measured the amount of gasoline that flowed in 15 seconds with the fuel Supply Line and then the same test with an open 3/8" hose connected to the fuel pump outlet. The long and short of it was that I had a blockage in my Fuel Supply Line. The fuel flow was not sufficient for the car to drive. I simply started to compare where the fuel line connects to the Fuel Pump Assembly as it seemed a good place to start. My blockage was behind the right rear of the Passengers seat where the fuel lines had the low spot.

New Fuel Lines are available from Classic Tube in Upstate NY and they are not the easiest to replace in their original paths. It turned out that my Fuel Supply Lines was indeed rusted shut INTERNALLY at the lowest spot on the fuel line. I had to run a new line so I tested it first with a good supply of fuel flowing through the Rubber hose first and then took the time to install a new Fuel Supply Line.

When you are ready to test the original line versus the hose be sure to have a fire extinguisher handy. I had the fuel flow into a marked container over time and it became very obvious that I had a blockage. Since water likes to collect at the lowest spot be sure to look for anyplace that might qualify as a low spot between the filter and the engine. The lines that the fuel filter supply gasoline to are hard metal (Steel) lines on my 1988 C4.

Have you tried a replacement hose between the Fuel Filter outlet and the FPR? I would try a piece of hose just for a test and plumb around the suspected blockage directly to the engine.

 

Thanks for the reply. Yes, that is on my list if the fuel pressure is known low as I now have a fuel pressure gauge. Im working down the line. I know the FP is good, the filter is good, the line between the filter and the FP is clear. I have new tubing for the line between the Filter and the rail also. If the pressure gauge reads low I know the problem is between the filter and the injectors including the rail, the injectors or the fuel pressure regulator. This is what I am thinking at this point in time.

C