Quote:
Originally Posted by rodeo02
Sure, but it is a quick redneck 'troubleshoot' point!  |
You don't need to tell me about redneck testing... I've done 'em all, check out the truck in my sig and avatar (before lift and wheelbase mod), tell me that don't say redneck all over it
I'd be lying if I said I'd never done the spray test
, but I'm always worried about potential liability (as screwed up as the "justice" system is) from telling someone that and have them do it 3 ft. from a space heater while his buddy lights a cigarette and throws the match under the car... and have them end up owning my house and cars.
Quote:
Originally Posted by 56pontiac
UPDATE - I took the fuel pump that was on the car to the yard where I bought the used one. They bench tested it and it is good. So that would mean the problem is elsewhere in the electrical / computer system.  |
Just to clarify the electrical measurements, current is amps and is measured with a meter either a clamp-on inductive meter or an inline meter. This must be done with the circuit intact because you are measuring the amperage that the pump is using. Voltage is electrical "pressure" and can be checked with the pump unplugged, it sounds like that's probably what you were checking when you said you had current to the pump?
Check and see if the fuel system has a regulator on the fuel rail or not. I have an '04 Cavalier which does have a regulator and return line, but I
think all Cobalts regardless of year have a returnless system that uses the pulse-width modulation that Rodeo02 mentioned. These must be pretty good cars, I havn't seen one except for a battery problem, so I'm not familiar at all with them. If it is returnless, try unplugging the fuel pressure sensor (what tells the PCM what duty cycle to command). I would assume that would make the pump run at some "should work most of the time" duty cycle. If that makes the pump run, chances are the sensor is reading a pressure over what should be there, so the PCM is not commanding the pump on. Not all returnless systems are pulse-width modulated, some have the regulator in the fuel pump module.
You'll be miles ahead if you buy a new DVOM, especially one that has a frequency/duty cycle measurement on it. Also, if you didn't check for a good ground to the pump, do that before you do anything else.
EDIT: I got to thinking about it, and if you replaced the fuel pump relay, then most likely it is not pulse-width modulated. A relay is just a magnetically operated switch, which is incapable of switching as fast as necessary to control a motor's speed (and would weld the contacts together in no time). It's not impossible that the relay is just a safety measure to be sure that power can be cut when needed, but the output to the pump would have to come from a transistor inside the PCM.