I've been tracing a hard start issue, and I believe it's leaky injector(s). However, I want to make sure before I tear into the intake again.

I did the procedure where you pressurize the system and then block the return line, then see if the pressure drops. Well it did, ~20psi in 30 minutes or so. However, if I had a bad check valve in my fuel pump, wouldn't this give the same result?

Is there a way to hold pressure in both the feed and return lines so that I can rule out the pump?

Thanks in advance.

Build up the pressure and block both feed and return. see if the pressure leaks down. If it does not most likely its not an injector problem. there is a chart in the service manual to test your fpr, pump and injectors for leak down in pressure. I will try to scan it and upload it tomorrow.

after i drove mine for a while you could actually hear it leaking . what i did was drive it for a few min , shut the car off and remove the snorkel . then open the throttle and put my ear up to the throttle body and you could hear it hiss .. i was having hard start when warm issues along with idle surge , i also failed emissions because it was running rich . new injectors fixed it all .

Well, it wasn't the injectors. I took the fuel rail assy off the lower intake and suspended it, placed some blue shop towels under it, and pressurized the system. I was quite surprised to see that the injectors were holding 50+ psi with no drips whatsoever. And yet, the FP still dropped 20-30 psi in about the same # of minutes.

I've got the Helms book, but the check valve is not actually a "cause" on the diagnosis chart for anything, although it does mention elsewhere that a bad one can allow fuel to flow back. Is that the only other explanation or could it be something else? I'm pretty sure I don't have any leaks so it seems like that's the only thing it could be (but I've not dealt with the fuel system that much)

It has been suggested to block both lines after pressurization.
Have you done this, or is this what you did when you "pressurized the system."
I can see the difficulty in locating a small dry gas leak, but not a liquid gas leak.

Where do you block the feed line? On the braided section? The return line has a rubber section that's easy to block but not the feed.

Got back from work today and still no fluid from the fuel rail assembly whatsoever (rails, AFPR, injectors) - yet the pressure went down to 15psi.

I guess I'll try to block the braided line, too, but I've never done that - doesn't seem like a good thing to do.

Most likely it's your fuel pressure regulator. Helm's states that in their testing procedure.

it could be the fpr or there is something on the sending unit by the fuel pump which I think is called the pulsator. It mentions that in the service manual about fuel pressure drop.

I think you're right; althought I'm not quite sure yet. I'm at the point on the chart where if you pinch the return line and it holds, the regulator is bad. It's not exactly holding, but I think I'm waiting on the return line to fill up between the regulator and the pinch before the pressure will hold.

I've kept the pinch on the return line, and am cycling the fuel pump to try and fill the lines. I also pinch off the feed line after pressurizing, just in case I've also got a bad check valve in the pump. I think my theory is proving out because it seems to lose less pressure each time I do this.

Does that logic sound right?

nm

Ok I'm about at my wits end. I pressurize the heck out of the fuel rail assembly and clamp off both fuel lines, yet I still can't get it to hold pressure. There are no signs of leakage anywhere on the assembly, and I've pinched the fuel lines to the point that I think I should replace them when I'm done.

Is it possible that there is a leak and that the fuel is evaporating so fast that there are no visible signs? It still loses about 1psi/min.

I'm thinking of putting in-line shutoff valves on both lines, with pressure gauges on both sides of each valve, and use this to pinpoint the leak.

Any ideas?

If you pinched both lines and it holds then there is not a problem with your injectors. No your fuel is not evaporating super fast. You will have to look at your fuel pump assembly in the tank. Either bad pump or that pulsator in the tank.

Where is my fuel pressure going then? I've got both lines pinched in the engine bay and the pressure test valve is on the fuel rail assembly.

Ok I re read your post and I missed that the fuel pressure still droped with both lines clamped. At this point I would replace the fpr and see what happens.

I replaced the diaphragm and am getting the same result. I even tried a different gauge to make sure it wasn't that. I am now double-vise-gripping each line, but I'm not confident it'll change anything.

Where exactly could all my pressure be going when there's no visible sign of leak??

I think you're chasing a ghost. You started out looking for a hard start issue, but you've effectively ruled out a leaking fuel system as the cause. All systems bleed down over time (back through the pump and regulator). Vice grips on the lines will not completely block them at that pressure. Time to look elsewhere IMO.

You're probably right. I do want to make certain that there's nothing leaking before I put it back together, though.

I went to the hardware store to get some fittings so that I could place valves on the pressure & return lines just up/down stream from the fuel rail assembly - but I could not find a fitting to match the return line! I'm pretty sure the feed line is 3/8" NPT.

Does anybody know for certain what size these fittings are?

The return line is 5/16", but you have to have a compression fitting. Not the common double flare fitting. You know the hard lines that go underneath the alternator, look at the end of them. That is a compression fitting. If you don't get that fitting, you will be getting some serious pressure drop i.e. fuel leaking.

Just did a little research; looks like they are 3/8" & 5/16" "Saginaw" fittings with 16mm and 14mm threads, respectively.

Anybody know where I can get fittings for these "around town" or are they special order only?

Thought I 've seen repair parts at the parts store. Adapters at a Performance shop.