Just wondering if when you test fuel pressure when the car is off (after priming it), is it normal for the pressure to drop just a little bit? Or should it always stay constant??

 

Well if the pump is not activly running then fuel will flow back into the tank, when you check the fuel pressure it will releave some pressure to put pressure on the guage if that makes sense.

If the pump is running it should be constant as the pump will always be trying to pump fuel pressure, if it gets to hgih the FPR will put it bank in the tank.

Make any sense or am I just rambling again?

 

I thought there was a check valve that prevented this?

 

True, I think there may be now that you mention it, but if it gets the the regulator it may just throw it all back in the tank if your regulator is leaking.

 

The regulator shouldn't let the fuel thru if the car's off and there's no vac signal to the regulator. Yes the gauge should show holding pressure when you turn the key to off, it may drop a few PSI, that's OK.

If it completely drops to zero then you either have a bad regulator or bad check valve. To test the regulator you'd crimp the return hose shut (use soft pliers so you don't damage the hose)- if the fuel pressure doesn't drop then, it's the regulator. If pressure still swings to zero, it's the in-pump check valve.

But it sounds like you're just losing a few PSI, so nothing to worry about.

 

Actually, I was just kind of trying to get a sense of what is normal. I am actually losing a lot of pressure. After just 15 minutes it went from 43 to 30 and then after 30 minutes in was down to 20. I stopped checking at 18.

I will definitely try your suggestion with the return line and see what happens. If the regulator is bad, I thought I remember reading somewhere that it can't be replaced separate, only as a unit with the rail........any idea if that is true?

You mentioned about the regulator and check valve. I was just curious about the fuel injectors. Is that a possibility too? While they are out I figure I might as well try the leak test just to see what happens (rag under the rail and watch for drips).

 

Hey bro! You think you have a problem? My fuel pressure (with ignition on) jumps to 40psi then in less than a minute drops to 20psi then it takes about a 1 1/2 to 2 minutes to drop to 0. With the engine running it stays on 40psi but as soon the I shut it off it drops just like with the ignition on. I've been searching for info for almost a week regarding an odd idle. When I step on the gas it struggles and eventually dies off. Could this be the culprit. Anybody? But in your case I have read that about the leaky injectors and there are a couple of good articles out there on how to do it. Hey tom I had not heard about the regulator test. But i wan't to try it just one question do I pinch the return hose while car running before turning engine off or just after turning it off. Oh and while I'm here. I wanted to test the fuel pump by way of the aldl but pin G does not have a wire in it. I searched and found something that made me believe the wire should be orange. but I'm not sure. What color should it be. What you may also want to do is remove the injectors and send them to cruzin performance, I believe. From what I hear they are great. Well guys i'll keep searching but If I can't find anything i'll have to post. So be ready.

 

I've sent injectors out to Cruzin Perf before, and yep, Rich does a great job.

The regulator test: You do that with the car off and the engine cool (so you don't start a fire). Crimp the return line shut; use those special hose-crimp pliers so you don't cut the hose. Then turn the key from off to "on" (not starting the motor) so the pump primes. The pump should prime up to dead head (max) pressure, 60 psi, and NOT drop.

I think - but the 90-92 3.1 guys will have to jump in - that the 90-92 3.1's had a special fuel pump test terminal in the engine bay. i think it was just us 85-89 2.8 guys that can use ALDL #G.

 

Ok, I tested things thoroughly tonight and here are the results:

- pinched return line closed (still dropped just as fast....down to 28 after 15 min, and keeps going)
- pinched the feed line closed (still dropped just as fast)
- pinched both closed (Still dropped just as fast
- no lines leaking
- usually there was pretty much no drops from the injectors...a couple times some dripped to the rag, but very little. Usually you only got fuel if you touched the rag to the tip of the injector (mostly 3 injectors)

So I guess it has to be the injectors, right? With only this small amount leaking, would a cleaning revive them or is a leaky injector pretty much screwed?

And would it be enough to cause the delayed chuggy start when hot (sitting only for a couple hours) that I have been experiencing?? It starts perfectly fine when cold.

 

check see if your manifold/tb smells like gas when it leaksdown. fpr might be screwed & have fuel leaking/shooting thru it (vacuum tube).