Won't start

[93gmcjimmy]

Ok I got a '93 GMC Jimmy 4x4 with the "W" code 4.3l. I had it crap out on me last night and leave me stranded. It just shut off while driving down the highway. I finally determined it to be the pickup coil. I replaced the pickup coil and now it won't start again. I made sure I got the timing right and decided to do a fuel pressure test. I get 12 psi on the nipple on the back of the motor next to the plenum. I don't get any leakdown it just holds 12 psi. I just changed the fuel filter about two weeks ago. It just seems odd that both went at the same time. is there any other way to test fuel pressure closer to the pump or is this as accurate as it gets? I really don't want to drop this tank.

[93gmcjimmy]

Ok I dropped the tank and put in a new fuel pump. Still 10 to 12 psi. I checked and am getting 12 volts to the pump. I pulled the fuel filter and it's clear. I can't figure this out. Why am I only getting 12 psi at the nipple??? Any suggestions?

[old_master]

The grey wire at the fuel pump electrical connector should show battery voltage for approx 2 seconds when the key is turned to the RUN position. After the 2 second "pump prime" voltage should drop to zero. The black wire should show less than 5 ohms resistance to ground all the time. If both of those tests pass, the pump is faulty. What brand fuel pumps are you installing?

[93gmcjimmy]

I installed a Delphi fuel pump from O'Reilly's.

[old_master]

Check voltage, resistance, and voltage drop at the fuel pump module connector. If all that checks ok, check fuel pump maximum output at the fuel filter.

[93gmcjimmy]

I will check the resistance tomorrow. I know I am getting twelve volts but didn't see for how long, I will check that as well and report back.

[93gmcjimmy]

Ok this may seems like a dumb question but how do I check the ohm resistance on the pump? I have a volt meter that does ohms. Do I put one wire into the plug from the vehicle and the other into the connector on the pump?

[Scrapper]

where did you buy the fuel pump? because sounds like he said might got a reject. also did you replace screen and sock also?

[old_master]

Disconnect the electrical connector from the pump. The resistance test is done at the electrical harness connector, (not the pump). Set the meter to ohms, touch one probe to the black wire termianl and the other test probe to a good, clean chassis ground. There are 2 black wires in the harness connector, check both of them. Resistance must be less than 5 ohms on both wires.

To test for voltage at the pump, set the meter to volts. Touch one probe to the grey wire and the other probe to a good, clean chassis ground. Must show battery voltage for 2 seconds when you turn the key on. After 2 seconds, voltage should drop to zero volts.

[93gmcjimmy]

Ok I checked the wiring to the pump. The gray wire turns on and off like it suppose to. The other wire is actually purple on my truck and it show 1.29 ohms to ground so I assume that is fine. The only other idea I have is a clogged line. Which seems extremely unlikely but not impossible. Any ideas where to go from here?

[old_master]

Voltage and resistance are ok. If you can hear the pump run during the 2 second pump prime and it still shows 12psi, you need to check fuel pump maximum output at the fuel filter. If pressure still shows low, the pump is faulty.

If maximum pump output pressure shows 80psi to 100psi, the pump is fine and there might be problem with the fuel pressure regulator not sealing correctly. You mentioned the pressure holds when the pump shuts off, so it can't be a leaking injector, external leak from the regulator, leaking check valve in the pump, or the pressure line from the pump all the way to the injector. The possibility does exist that the pressure line is restricted somewhere between the pump and the test port by the distributor.

[danielsatur]

1) Disconnect engine side of fuel filter and put a 2' of fuel line on the filter, and into a spare gas can.
2) Turn the key to the on pos only for only a few seconds to check the fuel flow going into the gas can.

I have seen alot of bad gas filters, fuel pumps, and dirty gas tanks!
I even heard of a ping pong ball in a gas tank causing problems.

[old_master]

Originally Posted by danielsatur

1) Disconnect engine side of fuel filter and put a 2' of fuel line on the filter, and into a spare gas can.
2) Turn the key to the on pos only for only a few seconds to check the fuel flow going into the gas can.

That's not a bad idea to check for flow however, the PCM will only allow the pump to run for 2 seconds and then shut off. If you bypass the fuel pump relay and allow the pump to run continuously with the line connected to the filter, the pump will only pump about a pint and then just dribble fuel out of the line, (the fuel pick up for the pump relies on fuel being returned from the regulator). If you've ever tried to drain a tank on one of these using the pump, you know what I'm talking about. Not really a conclussive test.

[93gmcjimmy]

Old Master, if I pull the plenum off the top would I be able to see leak from the spider? Or do you think it's leaking internally? I replaced the spider and the return line about 3 years ago but the truck has been sitting for about 2 years. Is the hub of the spider also the regulator?

[old_master]

It's very likely you wouldn't see anything leaking because it's holding pressure. A broken or weak spring in the regulator could cause pressure to regulate too low and still seal at a lower pressure. IF something is leaking, it's leaking past the internal seal in the regulator, which is possible, but not probable. If the spider lines were leaking, it would show up on the leakdown test. Pressure would not hold when the pump shuts off. Checking fuel pump max output is what you need to test first as it is the most likely cause.