After washing my car today, I started it up, let it idle (rather roughly) for a few seconds, and placed the transmission in reverse to back up. The engine immediately stalled out and I was unable to start it again. As is my luck, the starter decided to die at the same time, leaving me with a basically useless vehicle. After building a new starter from spare parts (doesn't that sound good, haha), I tried starting the engine again but it still wouldn't fire... but it does crank over now.

There is no pressure at the Shrader valve located on the fuel rail. I managed to get a few wimpy "psshs," but no gas whatsoever. The fuel pump runs when I turn the key, all fuses are working, and everything electrical is functioning properly. I disconnected the main fuel feed line and jumped the fuel pump relay. The pump whined and whined, but no gas came out of the line.

My car is completely out of tune (new engine), but it has been idling very poorly. It stalled numerous times this afternoon just sitting in my driveway. The pump also doesn't sound as loud as it used to... the whine is barely audible now.

According to the archives, these are typical symptoms of a bad fuel pump -- but I'm still confused since the pump primes without a hitch. The only other thing I can think of is a fuel line blockage, but the odds of that happening seem rather slim.

 

I've had pumps that still make the "whirring" noise but won't make any real pressure. Had a TBI pump a while back that sounded just fine but only made 2 PSI of measured pressure at the throttle body. If that can happen in a low pressure TBI type system, I'm sure it can happen in a high pressure TPI system.

Also, it's possible the FP regulator itself died and is passing ALL the fuel back to the tank, not allowing rail pressure to build, so you might want to temporarily block off the return line and see if you're getting any pressure at the rails again. If pressure suddenly shoots the moon, you know it's the regulator. If it still stays very low then it's probably the pump.

 

I managed to get the rail pressured, and the car to start, by hardwiring the pump ON and letting it run for a minute or two. After a brief "gurgle," my fuel pressure gauge shot up to 60+ psi and settled around 43 psi once I turned the pump off. Slowly, fuel pressure started to decline until it reached zero after about two minutes. Repeating this procedure a few times, the pump now works, but the fuel rail is pressurized only when the pump is on. I'm not sure why it hit 60 psi initially.

I blocked the return line and powered the pump, which caused the rail to be pressurized to 60+ psi (makes sense; no fuel return). Powering off the pump, while the return line was still blocked, caused all fuel pressure to be lost within less than one second. This should effectively rule out the regulator.

Blocking the supply line AND the return line, while the system is pressurized (pump powered on), the rail remains under pressure when the pump is turned off. This should prove that the injectors aren't leaking. Unblocking only the return line, the system still holds pressure. Finally, when the supply line is unblocked, all pressure is lost. Does this mean that the pump, specifically it's check valve, is not functioning properly? I also noticed that while the pump is on, wiggling the rubber supply line hose causes the fuel pressure to fluctuate. There are no leaks.

When I ran the car at idle with my gauge attached and the vacuum line unplugged from the regulator, fuel pressure fluctuated +/- 3-4 psi. Shouldn't this remain more stable, or are there larger tolerances? The initial "burst" of pressure when I first powered the pump is still a little confusing, because the regulator should be doing its job as long as it's working. I haven't seen anything higher than 43 psi since then, so it appears as if things have stabilized somewhat.

 

Sounds like the pump check valve symptoms I observed.

 

It sounds like something pump-related to me, too.

The fuel pressure should be a solid 43 PSI with the vacuum line unplugged under all conditions when the pump is running. I've seen some systems give a little "spike" in fuel pressure for an instant when the pump first fires up. I guess the regulator doesn't react absolutely instantly, but I am talking for only a very brief period of time.

Now the big question..... does it RUN??

If so, drive it around for a while and take some fuel pressure readings. I have found it very enlightening to drive around with the gague duck-taped to the windshield (temporarily!) so you can read it while you drive- especially under heavy load/high RPM conditions (WOT) where the pump is under the greatest load.

Most gagues don't have a line long enough to reach from the schrader valve up to the windshield so I cut into the gague line and patched in another 2 ft. of hose (just brass barbed hose unions and hose clamps- not tough to do).

 

I wonder if the 60 psi I experienced at first was due to a stuck regulator. If so, it's "unstuck" itself, but I wonder why it would do that (this was not really a spike; it stayed at 60 psi while the pump was on). The regulator has been doing its job since then.

Well, I decided to buy a new pump. I picked up the high-pressure Walbro 255 lph in-tank pump from Auto Performance Engineering. I'll be installing it over the weekend... should be an insanely fun time .

Damon, to answer your question, it does run -- just not very well. Whenever I get on the gas, sometimes it'll take off without a problem. Other times, the RPMs will kick up but I won't go anywhere... the motor feels a little "mushy," so to speak. Whenever I let off at anywhere more than 1/3 throttle, it almost stalls before it catches itself, RPMs fluctuating all the while. These are exactly the same symptoms that I observed when the rubber fuel supply hose broke one time, causing a loss of fuel pressure.

Through my datalogger, the BLMs are reading 150+ at idle and around 145 in driving, signifying a lean condition -- an indicator of lack of fuel (i.e. fuel pressure).

 

Yeah, you really should hook up that fuel pressure gague taped to the windshield like I described in the previous post. I almost GUARANTEE and "ah HA!" kinda discovery when you drive it around. Either that or it'll hold perfect pressure and you'll know that the problem is elsewhere. Please do this before you drop big bucks on a pump you may not need.

 

"Based upon conclusive evidence in this context, it can be determined through experimentation and analysis that fuel pressure and throttle are related in an inversely-proportional manner."



Seriously though, the more I pressed down the accelerator the farther my fuel pressure dropped... so much to the point that the car actually stalled the first time I tried it.

Installing the new pump was straightforward, though I'm pretty convinced that GM built these cars around the gas tank -- I had to bend the filler neck to get it out and bend the filler next to get it back in. Via a simple test, I found that the check valve on the old pump seemed to be in working order, leading me to believe that the pulsator may have been leaking, causing fuel pressure to drop at certain times. I removed it. That, and I'm sure that the factory pump is a little tired after eightteen years. The fuel rail holds pressure much better than before, but it still tends to bleed off -- it doesn't hold pressure for days like some people say. I think my fuel pressure regulator may be seeing the end of its lifespan, too... that could explain the surge to (and maintaining of) 60+ psi a few days ago. Maybe a valve is sticking?

My car seems to drive and idle a little better, but I'm fairly positive that its behavior is linked to an out-of-tune system. BLMs are still reading very lean, but I haven't turned up the fuel pressure to compensate yet. Through scanning I determined that my Bosch (yuck) oxygen sensor is just about dead, so I'm going to replace that before I start messing with fuel pressure. By the end of this, at least I'll know that everything is new...