94 Coupe w/150k on it, recent tune-up including optispark and fuel filter. Car won't start, was no fuel pressure. I was advised to disconnect the vacuum line to the regulator to eliminate that as a possible problem early on and it made no difference. Checked the fuel pump relay, removed fuel pump and applied 12 volts to it and it ran. Interestingly the pump would not run on a battery I hooked up to it that was putting out 10 volts but did at 12 volts. Put it back in, still won't start but there appears to be more pressure than before because a lot more fuel comes out of the Schrader valve. For some reason I can't get my pressure gauge to thread onto the valve though so I can't measure it. It worked in the past and I can't figure out why it won't thread on now.
Any ideas?

 

It only takes 5 psi to spray out of that schrader valve...thats not a good gauge.
The pump circuit is simple. IF there is power to and from the FP relay, the pump is bad if its not charging the system to 40+ psi with ONLY key ON, no crank.

Your engine will not fire with less than 25 psi...it might gurgle and try, but it can't run without at least 25-30 psi constant.

10v is not that much less than 12v and should have made the pump at least try. A burnt up motor takes more amperage to run,. and fuel pumps are abused horribly with every corner the car takes, every time there is only 1/4 tank of fuel, and everytime the engine is revved. Gas cools and lubes the pumps and unless you have yours in a "well" so thats its always submerged in fuel no matter what, its probably just worn out.

Get a new pump, new tank gasket and fix it..

If you need proof, get a volt meter on the pump wire harness plug at the pump/sender assy under the boot and turn the key ON...you should see power in the plug for 2 seconds which is the way its designed. Pump gets power 2 seconds then goes off until the engine is running. Weak pumps do not charge the rails with enough fuel to start so the pump cannot run again until the engine starts...THATS catch-22.

On your gauge...hold the stem UP and out of the collar as you try to turn it and start the threads. They sometimes loose the 1st thread and if the stem inside is touching the needle tip it cannot grab anything....so hold the stem/hose up , out of the collar as you turn it. Turn it backwards and see if you can "feel" if there IS an end thread...then go back the other way. If you have an EFI O-ring kit, the schrader valve comes out but you must replace the o-ring with rings made for gas and injection pressures.

 

Thanks leesvet. That was quick. I guess I'll just go ahead and get a fuel pump then. Now that I think about it, I had been running it kinda low on fuel lately and it was low the night it quit. It was fine until it was shut off and then wouldn't start again.

I'll have to check the Schrader valve threads again. That makes sense as well, which is good because I couldn't believe I was having such a hard time repeating a procedure I had successfully done before.

Thanks again
Rod

 

My fuel pump put me on the side of the road at 186k.
If you replace it you'll be good for another 15yrs.
Pump output is directly related to voltage.
Racetronix has some info on their page on pump output vs voltage.
They have a wiring upgrade kit.

JS

 

ALWAYS, run a minimum of 1/4 tank, if you want your pump to live. The fuel cools them as the run. If you get below 1/4 tank it can expose the pump and they heat up. Heat=loss of life expectancy.

Make sure you got a good 12v back at the pump and a good ground for it. I made a test LAMP out of a old sealed beam just for this. If the fuel pump circuit will light the lamp it will definitely run a fuel pump. The lamp draws over 5A unlike a test lights puny .3A or so.

Electrical 101, just because you got voltage does NOT mean you have amperage. Good luck, let us know what happens.

Half a tank, and it will probably run forever.

 

Not much to really add to this thread, all the good stuff has bee said.

The only thing I can add is my fuel pressure gauge is also a real hard to get the thing threaded. That is because there is not enough room behind the valve and it is hard to line up the fitting because the hose hits the firewall wires and things. Just got to work with it and can be frustrating.

 

Okay, with the new fuel pump installed, and the gauge finally attached (seems I wasn't getting it lined up quite right), the car still won't start even with 45 pounds of pressure at the gauge. I know I have spark because it tries to run with starting fluid in the intake. Frustrating....any ideas?

 

Take a quick check for 12 volts on the injectors. Turn key ON, check one injector per side, either wire will do. Check for 12 volts in reguard to ground. If no voltage, check the injector fuses.

If voltage is good, then you need to check the injector drive (pulses) using a noid light. Connect it to one of the injectors and see what the results are.

If you have injector drive, I would still check for correct spark. You need a 1/2 inch healthy spark from the plug wires. Check at coil and plug wires. Make sure there is no arking on the hot coil wire where it goes thru the water pump.

I would think its got to be a fuel delivery or spark problem. Even if there was a problem with a engine sensor, broken wire, IAC or something else, I think that would show up as a runability problem and not a starting problem.

 

I don't seem to have spark. Not sure where to go at this point. Seems like a healthy spark should be pretty easy to see.

 

Two of the most common things to go bad that would cause no spark is the ICM or the opti. If you check for drive on the injectors and have it, that would indicate the opti is probably working because you need the clocking pulses out of the opti to drive the PCM which makes the drive for the injectors.

If you have injector pulses it might me a good bet the ICM is no good which drives the coil. It's easy to replace, $100 or less, and buy a GM-Delco part not a junk substitute.

Further troubleshooting can be done to confirm the ICM might be bad. Remove the connector of the ICM, and check for 1.0 - 4.0 volts AC on pin B, the white wire. Ground the negative lead to metal on the engine. Have a friend crank the engine to see if you have this voltage while you watch the meter. You need to crank it to get the voltage.

If you have the AC voltage, then the opti and PCM are working. That then would confirm the ICM may be defective, a common part to go bad. Of course the coil could be bad but the odds are usually low.

 

No voltage on the white wire. Bought a spark tester and there is no spark. Coil checks out ok. Apparently there is no injector drive either because I get nothing from the noid light. Sounding more and more like the Opti again. It just seems strange that it happened at the exact same time as the fuel pump.

 

If you did everything right and your testing is valid, on the surface it does sound like the opti is not driving the PCM.

I would first check the pin connections and plugs for the opti and PCM. Also just for the heck of it check the PCM fuse #33 and fuse 22 & 23.

There is also a MAXIFUSE #1 (20A) that feeds the PCM and fuel pump. Unlikely it's bad (under hood).