jackc Posted March 6, 2007 Report Share Posted March 6, 2007 I'm reassembling my 93 4.6 Eldo after removing the intake, cleaning the EGR passages, and replacing the injectors and FPR. With everything back in place and connected, the fuel pressure hits 40 PSI when the key turned on (not running). Then it holds there for a little while, then begins dropping. On a 93, its very hard to see if something is leaking, because everything is inside the intake plenum box. Does anyone know how long the fuel pressure should hold at 40 before it starts to drop? The FSM doesn't say, but there seems to be a built-in assumption that it will drop since the system re-pressurizes itself each time the key is turned on. Link to comment Share on other sites More sharing options...
JimD Posted March 6, 2007 Report Share Posted March 6, 2007 I do not have the answer you are looking for. I think it will vary depending on the condition of the check valve in the pump. If you do not smell raw fuel with the system pressurized, you should be good to go. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
zonie77 Posted March 6, 2007 Report Share Posted March 6, 2007 It should hold a fairly long time if the system is in good shape, probably for hours. The check ball that holds the pressure has been a problem on GM cars. Sometimes it can leak back and not cause a problem, sometimes it sticks wide open and the car won't start. I've had that last scenario, you get pressure but it instantly drops to 0 when the key is off. Yours will probably run a long time with a slight leakback. But NO guarantees! Link to comment Share on other sites More sharing options...
jackc Posted March 6, 2007 Author Report Share Posted March 6, 2007 If you do not smell raw fuel with the system pressurized, you should be good to go. Thanks guys. As of last night, I'd managed to get raw fuel everywhere, including a pretty good size puddle in the floor of the intake (With the lid off of the intake, things tend to shoot apart when you hit it with pressure - I finally bolted down the top gasket to hold everything, but still be able to see inside the manifold) Hopefully, it will evaporate today and I can tell better what I've got. I did see the reference to the pump check valve in the FSM, so yes - that is a consideration too. My pump is noisy, so its on my list too - but I'm not there yet. I guess I'll watch it awhile longer and see what I can conclude. Link to comment Share on other sites More sharing options...
JimD Posted March 6, 2007 Report Share Posted March 6, 2007 Curiosity got the better of me so I grabbed the guage, a stopwatch and the keys to the '04. Cold engine, 20 hours sitting = 0 psi. Key on and off several times for full prime = 38 psi. 15 seconds elapsed = 36 psi. 60 seconds elapsed = 36 psi. 2 min's elapsed = 35 psi. 5 min's elapsed = 34 psi. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
jackc Posted March 6, 2007 Author Report Share Posted March 6, 2007 Great info, Jim. Thanks Link to comment Share on other sites More sharing options...
brmurph Posted March 7, 2007 Report Share Posted March 7, 2007 My manual says it should not drop more then 5 psi in 10 minutes. If it does then to check the fuel pump check valve, fuel pump flex pipe, the valve or valve seat withing the fuel pressure regulator or the fuel injectors. Link to comment Share on other sites More sharing options...
Ranger Posted March 9, 2007 Report Share Posted March 9, 2007 As of last night, I'd managed to get raw fuel everywhere, including a pretty good size puddle in the floor of the intake With the top of the intake off, turn the key on, but DO NOT crank the engine. Look for fuel leaking out of the nipple on the FPR. Replace it if any fuel leak from it. Link to comment Share on other sites More sharing options...
clarkz71 Posted March 9, 2007 Report Share Posted March 9, 2007 I hope his FPR isn't leaking, he said he just replaced it. Link to comment Share on other sites More sharing options...
Ranger Posted March 10, 2007 Report Share Posted March 10, 2007 Right you are Clark. I missed that. Link to comment Share on other sites More sharing options...
rmac-etc Posted March 29, 2007 Report Share Posted March 29, 2007 Spoke with a knowledgeable Porche mechanic this weekend (at my daughters wedding), and the topic of fuel pump pressure came up, cause i recently replaced mine. He said that he has found that bad or marginal fuel pumps may deliver adequate pressure, but not adequate volume. I think he mentioned this in conjunction with not just racing porches but his gm truck (memory addled by champagne at this point .... Just wanted to communicate this point that the pressure may be ok, but the volume may not. How to measure/test that, I don't know. Link to comment Share on other sites More sharing options...
Logan Posted March 29, 2007 Report Share Posted March 29, 2007 The GM service manual suggests that the fuel pressure should hold in a over night condition. They never do. At least none of the GM ones I have tested during diagnostics. Most maybe 5-10 minutes....very few up to an hour. Logan Diagnostic LLC www.airbagcrash.com www.logandieselusa.com www.ledfix.com www.ledfix.com/yukontaillightrepair.html www.ledfix.com/ledreplacements.html www.ledfix.com/j42385toolrental.html Link to comment Share on other sites More sharing options...
jackc Posted March 29, 2007 Author Report Share Posted March 29, 2007 After checking and fiddling, checking and fiddling, I finally got my numbers back in the range of JimD's. No more problems. Some lessons learned: 1. A northstar can run just fine on the set of mismatched fuel injectors that it came with. 2. A set of reman fuel injectors will not necessarily be good. But Rockauto will make things right. 3. A new GM FPR will not necessarily be good. 4. I should replace things one-at-a-time so I know what's causing what. Link to comment Share on other sites More sharing options...
JimD Posted March 29, 2007 Report Share Posted March 29, 2007 .... 4. I should replace things one-at-a-time so I know what's causing what. This should be #1. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
jackc Posted March 29, 2007 Author Report Share Posted March 29, 2007 .... 4. I should replace things one-at-a-time so I know what's causing what. This should be #1. Absolutely. I stand corrected!! Link to comment Share on other sites More sharing options...
JimD Posted March 29, 2007 Report Share Posted March 29, 2007 Glad you are back on the road. So a new out of the box FPR was bad? That is not something everyone would check; but they should. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
jackc Posted March 29, 2007 Author Report Share Posted March 29, 2007 So a new out of the box FPR was bad? Yes - Fuel pressure would not hold with the new FPR. It took me awhile to convince myself that was the problem - but it held with the old one, leaked down with the new one. The guys at my local dealer made it right for me. I'm blessed to have great parts guys there. Link to comment Share on other sites More sharing options...
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