My car has been running like crap lately and i have narrowed the problem down to either the adjustable fuel pressure regulator or my fuel pump. My car works fine when it isnt warmed up but after that it is usualy lean under acceleration. Either the pump isnt giving the car enough gas or the regulator is messing up the fuel pressure. How can I tell which is really happening.

 

If you have a fuel pressure gauge that will attach to the fitting on the fuel rail, it's pretty straight forward.

Attach the fuel pressure gauge and start the car. With the engine idling you should have a steady pressure, say for example 45 lbs. If you remove the manifold vacuum from the diaphragm of the fuel pressure regulator, the fuel pressure should jump up immediately by 5 lbs or so, in this case up to 50 lbs.

I have attached a vacuum hose to mine (non-third gen, but very similar) and applying vacuum / pressure decreases/ increases the fuel pressure respectively.

Perhaps the adjustment has loosened up and changed on you?

 

If your fuel psi reg. is bad, it usually tears at the bladder behind the housing and dumps fuel into the engine. If you are getting tons of fuel, i would suspect the regulator. If your not getting enought fuel, suspect the fuel system and target each component at time. Get a fuel psi gauge, chekc the psi in park, under load. Make sure you plug the vacume sourch at the reg when you check the psi.

 

I am gettin no fuel pretty much. I had set the afpr at 45 psi when I first put it on and checked it and it was fine and recently when it was running like crap, I tested it and it was at 22psi. I set it back up to 45 but I think the pump is weak thats why the fuel pressure decreased. Sound right to you guys? I am a novice when it comes to fuel systems so thanks for all the help.

 

Well, I understand your reasoning, but if 45 psi of fuel pressure was available from the pump, you shouldn't have had to adjust the regulator from 22 to 45 pounds. The regulator should have maintained 45 psi regardless of volume (within reason).

If you've got the stock Fuel Pressure Regulator on hand still, perhaps swap that back in and look into the adustable one to check for damage, grit etc. Assuming it's serviceable, of course.

 

Ice,

If you were able to readjust the pressure regulator to get 45 PSIG, the pump obviously can make the required pressure. Your FPR has some issues.

 

I had to turn the regulator 4 full turns to get it back to 45 and it doesnt even stay there. The fuel pressure is all over the place. I have the origional regulator and I might swap it back in but why would the fuel pressure just randomly drop unless the fuel pump was getting weak.

 

The fuel pump only moves a column of fuel along the fuel line. The regulator is connected to that flow of fuel and will divert any fuel volume back to the tank that is in excess of what is required to overcome the balance spring in the regulator. The fuel pump does not determine ultimate system pressure. The only time the fuel pump can control pressure is that if it cannot deliver at least the minimum quantity (volume) of fuel that is required by the engine. When the engine is not running, that is essentially zero.

It is possible that the pump is failing, but if readjusting the regulator can raise the system pressure, the pump is obviously capable of delivering the amount of fuel necessary at that pressure to satisfy the regulator balance spring. If the pump were failing, it isn't likely that you would be able to raise pressure by regulator adjustment without stopping the pump, allowing it to equalize pressure differential, then restarting the pump. If the pump is allowed to remain running and pressure can be raised, you likely have a regulator problem.

It is more likely that either of the two fuel filters is clogging ( the inlet filter in the tank or line filter), or there is debris in or damage to the disc valve or valve seat of the regulator. If either the disc or seat was damaged when the regulator was apart, stable fuel pressure control may be impossible. These two pieces are lapped together to a mirror polish, and any surface rust or debris can ruin the valve assembly.

 

Where are the fuel filters? I know that one is under the car just in front of the tank. Where is the other filter?

 

There ia an inlet filter on the bottom of the fuel pump. It's more of a strainer than a filter, but can get clogged with debris just as easily.

 

If the fuel pressure regulator was the problem, what would happen? Would it cause it to run rich or lean... mine is running lean. Also, my car backfires after you stomp on the car hard and let off the gas...idk what would cause that either.

 

how do you know it is running lean? or better yet, what makes you think it is running lean?

 

I have an air/fuel mixture gauge that shows me it is running lean while i am driving. It runs lean until about 3/4 throttle. Then it gets to normal. Its messed up.

 

IceBlue91z28, my gauge reads the same way with my fuel ratio and I have a real bad smell of gas all the time but no drips.the smell is coming from the engine and there is no leaks I can seemy FP gauge reads about 43psi at idle but the needle bounces up and down about 2 psi real fast. I say take you FPR aprt and inspect it. I have to do the same thing when the weather warms up. I think you can get a new seal from the dealer for a few bucks.

 

This sucks. I hate when my car runs like sh**. I get so mad. Im gona take the regulator off I guess and put the stock one back on see if it changes anything. What really doesnt make sense with this whole thing is the backfire after I let off the gas.

 

a backfire is caused by raw fuel being dumped into the hot exhaust and exploding. my car does this once in a while.

 

But heres why it is weird. The car runs lean...so ttheres not much gas getting into the engine in the first place so idk how it would dump fuel into the exhaust...but when I let off the gas, the air/fuel gauge does get rich real fast for no reason. None of this makes any sense lol. Why would my car run fine in neutral, run lean when driving, and backfired. I was thinking it was my pump but now im leaning towars my holly afpr.