Elephantismo

First post, w00t!
I figure this belongs in this forum because the TPI cars have higher pressure fuel pumps.
Ok i've got a 91 z28, 305 tpi car. First problem i had was a wierd one. If i made a full throttle run to third(manual) the jarring or heat or something would vaporize fuel in the line or something causing low fuel volume and the car would run rough and die if i stopped it. If i floored it after this happened it would run way strong, stronger than normal(lean im guessing). I could kill the motor, purge the fuel rail at the pressure test bung and it would start back up and run fine.
Finally, (and with dumbluck) i decided to replace the fuel pump. Pulled the tank down expecting to find trash and there was none. No rust, no trash. i completely emptied the tank and replaced the pump. The problem was then fixed. I did not think to check the fuel pressure though. The car ran great... for about a month.
Now the car starts and idles but its pretty rough. This problem started while parked. It makes no power and only the first 1/16 of throttle has any response at all. It has a low roar comming from the fuel tank area. There is no fuel pressure on the line after priming the system a couple times even. My guess is that its another dead fuel pump. But i would really like to know why they are going so fast.
The guy i bought the car from replaced the sending unit and pump a few thousand miles before i bought it. The car showed no symptoms when i purchased it. The sending unit and fuel pump were replaced with dealer parts in Jul 01 with an odometer reading of 105k miles. At the same time the motor was rebuilt. The car now has 132k miles. The sending unit has set for a bit but it looked really clean. I checked the resistance across the sending unit wires and they were all zero. Im thinkin my next step is to drop the tank yet again, but i dont want to miss any hidden problems. Any ideas?

ZZ28ZZ

Crawl under car and inspect the fuel lines for being partially crushed or kinked. That will kill a pump pretty quick. I knew someone that sabotaged someone elses car by crushing the metal part of the fuel line with vise grips (long story). A large stone could do the same thing.

Verify fuel filter is clear.

Verify fuel pump is getting good power.

If all that's good, then drop the tank. Pump may have fallen off its bracket. Pulseator (sp?) may be bad if still installed.

Elephantismo

Fuel lines have no kinks or leaks
Fuel filter is new, fuel lines carry atleast 100 psi of air pressure with no bleed down.

Ok, the first problem is back. The low roar coming from the tank was because the small section of line going from the pump to the sending unit inside the tank burst. The section supplied with the new pump was heavy wall, non- braided emmision hose. I'm guessing that is why it burst. Now the pump seems to have picked up its old habits agian.
The section of hose was replaced and the fuel pump was replaced again as well. Now this pump has began to cause problems similar but more frequent than before.
Revving the car in nuetral, or while driving can cause the fuel pressure to drop off radically even after idle rpm has returned. There is no change in the voltage going to the fuel pump when this happens. I measure across the red wire and the grey wire to the black ground going into the fuel pump.
The red wire vs. black showed 3.8-4.0 volts, the grey wire vs. black showed 12.7-12.9 volts.
I measured the resistance across the grey wire (im thinkin thats the fuel pump power wire), and my tester just reads OL when the key is on. The resistance across the pump is 1.1 ohms when the key is off. (is this right?)
The fuel pressure at idle when its running well is 47 psi, solid. revving results in a brief 2psi drop and then it comes up to 50 psi, suggesting the FP regualtor is working right.(i believe the vacuum lines are meant to increase fuel pressure when vacuum drops, anyone knwo if thats correct?)
The fuel pressure drop seems to be more recurring when the car is cold but under long distance conditions it gets frequent at random times.
When the pressure drops, killing the motor and purging the fuel line is always enough to cure the problem.
In addition to the pressure drop, the pump picks up a pretty distinct whir.
I have repeatedly checked the tank for trash and i have never found anything significant, or anything at all anymore.

I am pretty much out of ideas. I'm going to replace the FPreg. anyways. I'm also going to try running a hot wire from my amp straight the the fuel pump with a switch for diagnostic purposes. It occured to me that the oil pressure sensor could be going out and a flickering signal might not show up on my tester.

What would a mechanic do? Anyone know of any problems like this before?
Please help

ZZ28ZZ

I would tape a fuel press gauge (connected to fuel rail) to the windshield and go for a drive. I'd also run a temporary test wire to the fuel pump + so you can monitor the voltage with a voltmeter while driving.

You can also do a crude flow test by disconnecting the (supply) fuel line where it goes from rubber back to metal. Place disconnected rubber fuel line into a sutiable container, jumper the fuel pump and see how much flow you're getting.

Elephantismo

sounds like a plan. I was listening to the fuel pump last night and it sounds like i have fuel flowing into the tank after the problem starts. That seems consistent with some kind of regulator trouble. I'm pretty sure i ddint burst the hose again because i used regular 3/8 emmision hose this time with metal hose clamps.
I was kinda thinkin that mayb the regulator is stuck shut and it ruining the oneway diaphragm in the pump? I'm not sure if the one way valve is in these fuel pumps, but i dont know where else it would be.

So for now im gona take it for a drive with a fuel pressure guage on the window and get an EE friend of mine to use his laptop to monitor my fuel pump power on ms intervals.
Additionally im gonna run the regualtors return line into a container for a few minutes after the problem starts.
And im gonna pull the FPR vaccum line and see if it leaks or has leaked.

Elephantismo

Woot. nothing more than a bad fuel pressure regulator. Fixed

Plus the car hauls ballz; faster than ever b4.