Ok, car loses FP as soon as I turn the ignition off and if I clamp the return line, FP holds.
It has been 3 yrs since I put the new FP in, so does the return line go back into the FP?

I think so, but before I spend $100, I want to be sure.

 

IF IT IS THE RETURN LINE.......then your pump check valve is working. I would look at the fuel pressure regulator. Remove the vacuum hose to the regulator and look for fuel. I would guess that it is the FPR and that you need a new diaphragm.

If the line you are pinching off is actually the feed line, then I would guess the check valve in the pump is bad and replace the pump.

 

with what John said

 

The FPR does not hold FP in any way, its only function is to make sure there is not to much FP going to the injectors, excess is bled off into the return line.

So if the return line goes into the Fuel Pump and blocking off the return line makes the FP hold, then it stands to reason the check valve is bad in the fuel pump.

Or have I been working on carbed engines to much lately.

 

The return line comes off the FPR and returns to the tank. The return dumps the fuel back into the top of the tank. If the check valve was bad (this is in the fuel pump and goes directly to the feed line, through the filter and then to the fuel rail) it would allow the fuel to back flow through the feed line to the pump and back to the tank. Since you are pinching the return line closed and it is holding pressure, the fuel is NOT going back through the feed line....therefore check valve good.

To double check....are you pinching the line at the tank? If so, the feed line is at the top of the tank and the return line is below the filler tube. Both of these lines lead to the right as you face the rear of the car. The line that goes to the left is the fuel vapor hose.

 

Possibly.

 

I am going to double check, this is why i ask. Brain is not what it used to be.

Alright, I do not have a engine manual, so looking at the the filler neck, there are 2 line coming in from the right, top is fuel feed and bottom is return???

 

Looking at my FSM that looks correct to me Randy.

 

..... For whatever reason , the members of this forum expect the fuel pressure regulator to provide a positive seal and cause the fuel pressure to remain in the lines long after the fuel pump is shut off ... there is a metal disc on the fuel pressure regulator's diaphragm and a machined metal surface surrounding the regulators orifice ... spring pressure holds these two METAL pieces together forming a "seal " ..... I can't think of ANY other part on a car that depends on a metal to metal seal to be perfect ... ALL other machined metal surfaces get sealing assistance by way of an o-ring or a gasket or RTV ..... The fuel pressure regulator's job is to maintain a selected or specified pressure in the fuel rails while the engine is running ...........

................ Quite simply ... How does your car run ? ... If the running fuel pressure is within limits ... then look elsewhere for whatever problem you are attempting to diagnose ...........

 

If the stagnant fuel retained in the hot fuel rails and injectors do not retain pressure for awhile after the engine is shut off, the fuel can boil causing the next start to be a hard start condition. If I recall right, from a GM FSM for a C4 Vette, there should be some pressure for at least 20 minutes as the pressure gradually diminishes as the engine cools after engine shut down. The FP reg was engineered to act as a partial check valve gradually releasing this pressure. As previously described as a diagnostic proceedure, if rapidly losing fuel pressure at engine shut down, then clamping the fuel return line retains fuel pressure, you have a defective FPR.

 

First off, I am not expecting it to stay pressurized,but I have a hard start condition and sometimes the car sputters and barely runs and then will smooth out. I have had this car for 9 yrs and I know every sound it makes and I can tell when something is not right.
When the engine is shut off, you can here the fuel leaving the fuel rails.
also, car will not rev under load past 4k rpm's.
One thing I know about diagnosing, is that you do not rule out ANYTHING, even if you tested it once before.

 

Test or replace your ignition control module ... if the problem persists , then toss the Opti-spark ..........

 

If this were me, before I would start randomly replacing expensive parts, I would zero in on it being either a fuel or spark problem. Based on the failed "pinch the return line test", the FP regulator has been diagnosed as being defective and this would cause the conditions that you are having. I would not go replacing spark related components when I know I am having a fuel delivery issue.

Besides the fact that I know that I should be retaining pressure for several minutes after engine shut-off, just because I have proper fuel pressure while the engine is idling does not mean that I have proper fuel pressure under load at higher RPM. For example, if the FP reg was bypassing to much fuel back to the tank due to its valve stuck partially open, not only would it not hold pressure after engine shut-off but your fuel pressure could drop under engine loading causing a lean, missfire condition. In this case, the fuel pump may not be able to keep up with the fuel demand of both the engine and the fuel being bypassed thru the defective regulator causing low pressure to the injectors. Thus, I would double check my diagnostics and if I got the same results, replace the FP regulator, then repeat my diagnostics. If the diagnostics now pass and I still have the missing problem, at least now I know it is most likely not the regulator and I would start re-diagnosing from scratch.

 

The most effective way to diagnose fuel pressure issues is to install a temporary fuel pressure gauge and tape it to the windshield , drive the car to its problematic low-performance range and observe the actual pressure readings ... BEFORE you start randomly replacing parts ..... Just how common are ignition problems in LTx applications ?

 

The problem you describe sounds identical to mine. Same model year too. Did you decide what the problem was?