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Discussion Starter · #1 ·
In the many months I have been enjoying this website, I have tried to help as many people as I could. I've had two questions on here for a few days now that I really need help with, but noone seems to have any answers. I know some of you all know about these engines. And I also know that some of you have modded yours including nitrous, superchagers etc. And I'm sure that fuel delivery on these motors were an issue. So you mean to tell me that none of you have ever hooked a hand vacuum pump up to your fuel regulator and applied a small amount of vacuum to see if the diaphram was good or not? That is the correct way to check it and you are supposed to watch the fuel pressure guage to see if the pressure drops 3-10 lbs, which mine does. But it is not clear in the manual whether it is supposed to hold the vacuum that you apply. Vacuum is just dropping off real quick. Which to me would inducate a bad diaphram, but I'm not sure. Come on guys, I really need some help here.
 

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The pressure regulator diaphragm is just a simple spring calibrated diaphragm. Low vacuum, increase is pressure, high vacuum... decrease. There should be no bleeding off when vacuum is hand applied. A ruptured diaphragm can also lead to fuel leaking back through the vacuum supply line and causing a rich condition.. I've had this happen.
 

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Discussion Starter · #3 ·
The pressure regulator diaphragm is just a simple spring calibrated diaphragm. Low vacuum, increase is pressure, high vacuum... decrease. There should be no bleeding off when vacuum is hand applied. A ruptured diaphragm can also lead to fuel leaking back through the vacuum supply line and causing a rich condition.. I've had this happen.
I smelled the vacuum line, and it did have a fuel smell, but no visuable sign of fuel. I do have an adjustable regulator on it, and I have to turn it pretty far to get the pressure to rise at all, but it finally does. If I back it all the way off, it does go to stock pressure. That is what was confusing me. But when I apply vacuum with a hand pump, the vacuum just drops right off, which to me acts like a bad diaphram. The main problem I'm having, is the pressure building up after shut-off. If I adjust the pressure to 40 psi at idle(my engine is modded)when I shut the engine off, the pressure jumps up to 48. When I try to restart the car a few minutes later, the car has a little problem starting, and when it does, it stumbles for a minutes and blows out black smoke like a severe rich condition. Very embarrassing at shows. I've checked the IAC adjustment and it is ok.
 

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Hmmm.. Even with a higher pressure when shut off, the fuel shouldn't be by-passing the injectors. Properly functioning injectors will shut off completely and allow no fuel to enter the plenum. Sooo, being you have a little black smoke and a hard starting issue, fuel has to be getting into the combustion chamber somehow. You either have a leaky injector (usually this will cause a fuel pressure drop off after shut off) or it is sucking fuel in through a vacuum source, line, etc. I'd really suspect the regulator diaphragm. The one I had go bad was on a Chrysler van (principle is the same) and it caused a very hard start and a rich driveability problem. (I'm not real familiar with adjustable regulators mind you, but I know how they work.) When you are using the hand vacuum pump does it have a clear plastic line (so you can visually see if it is sucking raw fuel?)
 

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Discussion Starter · #5 ·
Hmmm.. Even with a higher pressure when shut off, the fuel shouldn't be by-passing the injectors. Properly functioning injectors will shut off completely and allow no fuel to enter the plenum. Sooo, being you have a little black smoke and a hard starting issue, fuel has to be getting into the combustion chamber somehow. You either have a leaky injector (usually this will cause a fuel pressure drop off after shut off) or it is sucking fuel in through a vacuum source, line, etc. I'd really suspect the regulator diaphragm. The one I had go bad was on a Chrysler van (principle is the same) and it caused a very hard start and a rich driveability problem. (I'm not real familiar with adjustable regulators mind you, but I know how they work.) When you are using the hand vacuum pump does it have a clear plastic line (so you can visually see if it is sucking raw fuel?)
My injectors are new(1500 miles or so on them), and I checked them for leaks when I installed them. They are ACCEL 30# injectors. So I'm sure they are ok. I'm not using a clear hose, just a vacuum line. I do have a brake bleed kit for the vacuum pump that I might be able to put inline to see if it is drawing in fuel. Should the pressure rise when the car is shut off? It holds the pressure pretty good. It will bleed off over night, because I've left it attached to see if it would hold that long. But it takes a very long time, and it is probably bleeding slowly through the vented cap. Plus, it starts great first thing in the morning. When I first turn the key on in the morning, the pressure goes to about 40 lbs, and the car starts right up. It is only after it has been run and shut-off that the pressure shoots up to 48 and it then acts like it is flooded when you try to start it.
 

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A little rise in pressure when shut off is normal (fuel is warm and no longer moving etc.) Slowly bleeding off over night is also normal. I'd take a look at that regulator.
 
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