cal30_sniper

iTrader: (16)

Hey all,

The GTA left me stranded in Austin on Wednesday night. I was on my way home for Thanksgiving, pulled into a parking lot at a place to eat, and it just died. I got it restarted after a couple of cranks (five I think), and it ran for a few seconds and died again. I let it sit for a while and grabbed a bite to eat, came back out, and it still wouldn't run long enough to move under its own power. I could get it started, but it was running terrible, and would die any time that throttle was applied. At one point, it started and ran perfectly for a few minutes, but then suddenly died and failed to start again.

Long story short, I ended up using the Suburban to tow this thing back to my place, missed Thanksgiving altogether, and spent all day today trying to figure out what on earth is wrong with it. Here's what I've found so far:

1. Checked ECM by bridging ALDL ports. The SEL flashes Code 12 over and over again, but no other codes.

2. Plugged in ALDL cable and diagnosed on Datamaster 32. All readings look normal. TPS is functioning perfectly. I'm getting cranking voltage for the Fuel Pump Voltage reading (9ish while cranking, 11.7 for three seconds after letting off the switch, then down to 0). I'm getting an RPM signal while cranking, and a MAF reading of ~6grams per second while cranking. The only things I could really see that were weird was that with the key in run, but not cranking, the MAF reading was 23 g/s. I'm not certain if this is normal or not? I also was not getting an Injector Pulse Duty Cycle or Pulse Width reading, even while cranking (both values remained at 0). Finally, the Target RPM reading was ~3100 rpm? Are these values normal for just cranking, or is something screwy there?

3. Checked Rail Fuel Pressure. There is none. I can hear the Fuel Pressure Relay cycle on and off when I turn on the key, but the fuel pump isn't making any noise whatsoever. Likewise, I can hear the relay cycle off 3 seconds after I stop cranking. Still, no fuel pump noise.

4. Bridged the Fuel Pump Test port on the ALDL output to 12V battery power. Still no fuel pump turn on. However, using a voltage tester, I was getting 12V when I bridge the BAT source on the Fuse Block with the Fuel Pump Terminal on the ALDL connector. This tells me that the Fuel Pump circuit is completing, because it's grounding. The only ground I see in that circuit looking at the wiring diagrams is after the fuel pump, which implies that 12V is actually getting to the pump (or a nasty short somewhere in between).

5. Checked Fuses. All are good. This tells me there's probably not a short.

6. On the off chance that it might be screwy, I replaced the Fuel Pump Relay. No help. Pump is still not turning on. No rail pressure.

Any other ideas other than a bad fuel pump? I find it kind of hard to believe that it just died completely without warning. That sounds more like an electrical relay or ECM problem than a fuel pump. Every other pump I've had go out was a gradual affair, that sometimes worked and sometimes didn't, didn't supply enough pressure, or didn't supply enough pressure after it got hot.

I'll pull the tank to replace the pump if I have to, but I want to be completely certain that's the problem before I do. Is there any other way to check that power is actually getting to the pump without pulling the tank?

Thanks,

-cal30sniper

Damon

Cal, I think you've done a good job wrestling the problem to the ground already. It's the pump. It's just locked up or has shorted windings. Any case, it's time to change it out. Might want to upgrade to a Walbro 255 or other aftermarket pump while you're at it.

DO NOT buy some Autozone/Pep Boys cheapie. They have known quality control issues and sometimes die withing only months of being installed. Dropping the tank to change the pump isn't a fun job in these cars- don't do it more than once.

I assume you were just "passing through" Austin, right? Probably what caused the fuel pump to have a heart attack. A city that wants to cecede from TX, which itself wants to cecede from the US. More than a 30 year old fuel pump can handle, I suspect.

sailtexas186548

iTrader: (2)

as a final check, unplug your fuel pump back by the tank and supply 12v directly to it - if it doesn't come on then it's time to pull the tank

cal30_sniper

iTrader: (16)

Nah, I was just on my way through Austin headed back to visit the family out in West Texas. One of my best friends from the Academy was home on leave, so I dropped in to grab dinner with him. Little did I know I'd be spending the next two days there...

Thanks for the responses guys. I went ahead and ordered a Walbro 255 kit from Racetronix, hopefully I can get it put in next weekend.