Well I'll just get into the symptoms of whats going on lately with my car.

Off Idle:

If I manually open the Throttle Body relatively fast (simulating hard acceleration) in the engine compartment the engine kinda dies for a second then compensates and revs up to where it should. Doing this repeatedly seems to cause a backfire that sounds like its coming out the TB/Intake Area.

Accelerating harder from a stop off idle causes the engine to bog/die for a second, seeming as though it shut off, when suddenly a second later it surges to life and takes off into the midrange.

Midrange:

Midrange seems strong like it used to, although will occasionally have surging power.

Top end:

The top end seems to die off around 4000 rpm's and up. This is the same at highway speeds as it is from a stop. More noticable at highway speeds. While driving if I take the engine to WOT, it rev's up through the midrange quickly or downshifts until it gets to the 4000 rpm range. Then it seems to die off, taking forever to make it to 5000 or even 6000rpm. It loses lots of power and will occasionally sputter a bit while up there. Every other time it will toss a code up there, and I'm going to pull it in a few minutes.

Other information:

I thought it might have been the tranny but after further diagnosis its something air/fuel/sensor related. I swapped out plugs and wires since a few wires looked cracked, that helped the midrange to smooth out, but the low and top end is the same.

Here is where it gets weird. I drove the car today. It ran same as usual to school. Then I started it 30 minutes later and it acted like it was out of gas. It died and started it again and it sat at 200-500rpms and was dying each time after I tried to start it. So I shut it off and let it sit. I then start it an hour later, starts right up, and runs perfectly with no symptoms of above until I restart the car after stopping at a friends. Then everything went back to hell.

So thats the low down on whats been up with my car. I dont want to do the "throw parts at it til it works" strategy so any help or past experience would be great. I bought a fuel pressure gauge to see if that maybe the problem, although I cant figure out why I am getting 0psi? It doesnt seem to be depressing the nipple in the shrader valve.

Thanks.

-Dustin-

 

Update on the fuel pressure. 15psi idle and 17-18psi WOT. I am going to look around but I am pretty sure that they should run in the 30's at idle and 40's WOT.

I am waiting on the laptop to charge to pull the code, but this seems more related to the problem to me.

Thoughts?

-Dustin-

 

Yep, fuel pressure should be 43.5 psi with the vacuum line removed. Start with the easy stuff though like replacing the fuel filter.

 

I just did the fuel filter a few days ago, thinking it might have been that. So that leaves what, the fuel pump and pressure regulator right? Anyway to test either?

-Dustin-

 

More than likely your fuel pump is dying a slow death, which isn't uncommon.

There is a chance it could be the regulator. The regulator should only allow gas to return to the fuel tank once full system pressure has been attained. If gas is leaving the regulator at 15 psi, it's not working correctly. You can also pretend you're a regulator by pinching down on the soft return line and monitoring fuel pressure... if you can make the pressure rise over 40 psi than the regulator is busted. Otherwise, you're pump just doesn't have the cajones anymore.

 

How can I tell if its returning fuel to the gas tank? I'll check the hose-pinch method later. Thanks alot.

Although since I am going with a rather larger H/C setup and possibly some juice it might be a wise move to get an aftermarket FPR with a Racetronix 255lhp pump, right?

-Dustin-

 

You could remove the return line from the rail and attach a hose draining to a bucket. If there's an abundance of fuel coming out at 15 psi than the regulator isn't maintaining pressure. The easiest is to restrict the return line. Be careful not to damage it though. A pliers with plenty of tape over the jaws and careful application of pressure should work fine on the rubber section.

As for the aftermarket equipment. If the regulator is fine I don't see a reason to replace it with something else unless you're talking LOTS of fuel but then you'd be looking at new lines, pump, filter, etc. You will more than likely need to replace the fuel pump so definitely go for the Racetronix 255 lph unit if that's the case. An upgraded fuel pump with the stock components (with the exception of the injectors) can support a lot of power, especially if you aren't jacking the fuel pressure way up.