fuel pump ? 91 corsica

[richrd]

I'm back. started a 5 page arguement with my last question, let's see if we can beat that.

(history) work car was cutting out at times.

Now, the fuel pump does not turn on. No pressure at the rail. Checked the plug at the tank.

I have 8.6 volts at A/B and nothing at A/C

What controls the pump voltage. Am I correct that the pump only runs as flow / pressure is called for, or does it run continuously when key is on.
the "C" wire is the fuel guage sender, right?
Thanks
Rich

[dougbfresh]

On my wife's 91 Grand Prix (3.1 liter engine) when we had it, it had a diagnostic pigtail by the battery that would allow you to send +12 DIRECTLY to the pump, a good, quick diagnostic for checking the pump. The pump will only run for a few seconds if there is no oil pressure. This allows the car to start but keeps the pump from running in an accident or a low oil pressure scenario. The pump will shut off in several seconds with only the key on and the engine not running. Put the pressure gauge on it, Touch +12 to the pigtail and you "should" have mid 30 psi at the fuel rail.

[FieroSpeeder]

You should be getting battery voltage at that plug. Hopefully your battery voltage is 8 volts. Otherwise it should be 12volts. So you may need to trace that wire to the relay. The relay may be bad and causing to much resistance.

I have to check alldata for the wiring diagram, if i dont forget.


The pump turns on when the key is first turned on for 2 seconds, when the oil light turns off or when the vehicle is running. So if you can get someone to turn the key on and test it right away. Or crank the motor over but dont burn the starter.

[FieroSpeeder]

if i remember it still. C is the power going to the pump, and A is the ground.

[richrd]

using my old m/c logic, I decide to find the releay and check voltage there. put the volt meter in the fuel pump plug and started unhooking relays. Had 8.6 volts at the plug and still had 8.6 after unhooking all 5 relays I could find.

So, tell me if I have this right. fuel pump is unplugged. I turn on the key. it should be twelve volts. would the voltage stay at 12 or would the computor (?) shut it down after the fisrt start up, the two second run you hear when turning the key on?

Where is the relay, any idea? I checked the 5 mounted on firewall. maybe I should sell it for scrap and buy another basket case.

thanks

[dougbfresh]

you will only have +12 for 2-5 seconds. Did you find that diagnostic pigtail by the battery? That's why they put it there, to quickly test the pump.

[richrd]

no, haven't found it yet, but haven't dug too deep either.

What I know. the pump is disconnected, so there is no pressure build up.
When the key is turned on I have 8.6 volts at the plug. It drops a few tenths when cranking the starter. I have the same 8.6 when ever the key is on. Over 12 at the battery.

what happened to the other 4 volts. where is the relay. I guess I have to start at the pump and trace the wires back up to look for a break.

Did I mention that I hate working on four wheeled machines

Thanks again

[richrd]

I'm back, took a break from the car. should throw it away, but can't admit defeat.

Thanks for the help so far, I've made some mistakes and learned a few things with your help.

I've found the diagnostic pigtail.

had some qustions about hte pump so replaced it to eliminate one problem. Now have pressure at the fuel rail, car will not start.

Guess I need to learn about injectors, but wonder if it could be electrical.

back to it.

rich

[dougbfresh]

Now you have to see if the injectors are firing. There is only 1 or 2 injectors you can see with the infamous PLENUM on. You can remove the one injector connector you can get to and put a "NOID" light on it to see if it's firing when you crank. Also see if your getting spark by grounding a plug with one of the spark plug wires and see if your getting spark. You need to have the correct load on (i.e. a spark plug) or you can fry the ignition module.

[FieroSpeeder]

Originally Posted by dougbfresh

Now you have to see if the injectors are firing. There is only 1 or 2 injectors you can see with the infamous PLENUM on. You can remove the one injector connector you can get to and put a "NOID" light on it to see if it's firing when you crank. Also see if your getting spark by grounding a plug with one of the spark plug wires and see if your getting spark. You need to have the correct load on (i.e. a spark plug) or you can fry the ignition module.

spark plugs dont have a load And that isn't how ign modules can "fry"

[dougbfresh]

Originally Posted by FieroSpeeder

spark plugs dont have a load And that isn't how ign modules can "fry"

Resistance is a load in an electrical circuit, "most" plugs have some resistance. The old screwdriver in the plug wire to ground test is not recommended for testing spark for 2 reasons, 1-the Higher Energy of modern ignition systems can be tough on humans if they get zapped by it and 2-Too high of an air gap to jump puts strain on the ignition system, possible destroying components. A real or test plug keeps the gap correct. I either use a real plug, a test plug or an inline test light to see if I have spark.

A snipet from http: //www.nology.com/silverdetail.html :

"When reading spark plug advertisements, one can get the impression that small diameter center electrodes, uniquely shaped electrodes or built-in resistors are the best. Think again. A RESISTOR is exactly what the word implies. When the spark crosses the point of resistance much of the spark energy is lost. A resistor is like an electronic obstacle and could be the cause for a weak spark. Due to manufacturing tolerances and lack of quality control, even non-resistor spark plugs often have a resistance of 10, 100 or even 1000 Ohms. Always check spark plugs for resistance before use."
There is more spark plug info on this site but the point is, plugs do present an electrical load to the ignition system. A large air gap is an open circuit with large (infinite resistance). With enough energy, electricity can jump these large resistances and heat from the spark can make the resistance of the air lower, like in Jacobs Ladders you saw in old horror movies, the spark would start low, heat the air above lowering the resistance of the air above and the spark would travel up the wires terminating on the top of the Y shaped wires.

[FieroSpeeder]

wow, copying stuff from a website makes you "know" stuff.

Even read what you copy and pasted. Plugs are not even suppose to have resistance, but if your getting your plugs from China, they are going to be a POS.

So why do you need a "load" on the ignition system now? Copy and paste something that says, Ignition systems need a load. What you copied even states resistance is bad. And why would a screwdriver not work. It barely has any resistance. Even sam memmolo knows that.

And how does an ignition module work? Because how would it get fried? I'm asking you this because i already know this stuff. Be like dorian and surf the web then come back pretending your a professional.

[FieroSpeeder]

Originally Posted by dougbfresh

Resistance is a load in an electrical circuit, "most" plugs have some resistance.

I wonder how cars that have plugs with no resistance run. ROFL

[dougbfresh]

Repairing Old Fiero's for a Living?

[FieroSpeeder]

Originally Posted by dougbfresh

Repairing Old Fiero's for a Living?

If a customer brings one to the shop, why refuse business? I charge the same no matter what vehicle. I make more then your two fake degrees.

Originally Posted by dougbfresh

And as a matter of fact I do have 2 degrees in electrical engineering from U of I. The MS is in Electrical Engineering and Computer Science.

I dont know how you consider computer programming as an electrical engineering degree. And anyone who cant even grasp a simple electrical system on the car wouldnt even be an electrical engineer. If that was even close to being true, you wouldn't need to copy and paste from a website. And even with copy and pasting, your information on the most basic car circuits is so off.

inline test light to see if I have spark

just one of many examples.