scenario:

one morning i start my bird (warmup) and car just dies. tried starting again and no luck, crank wont catch at all.

troubleshooting facts so far:

**2 problems**
1) tested wires underneath rear seats and only getting .025 volts when ignition on. looked at schematics and supposed to be getting 12v drive from ECM (the ECM?!?!?,awww man. dont tell me that...)

2) bypassed 4 wire relay and and jumped outer wires to complete circuit (what the relay is basically supposed to do when ingition on) and gettin 12v now, but pump no turn on (damn, pumps gone.)

so basically step #2 i was able to determine that the pump is out of commission. but step #1 is where i am stuck. could it be the ECM? is this a known issue? maybe something else?

any suggestions are appreciated...

thanks in advance! -john

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'86WS7
Ram Air...
*EiyseWhite*

 

I'm not an electrical tech so don't get your hopes up lol

Unless I'm mistaken (and I have been b 4) there should just be a tan & a black wire to the FP. the tan is the +12 which should only have +12 if the car is actually running. The black is ground. A 3rd wire will be present at the connector as well which is just the fuel sender, I don't know about voltage but, it will change resistance depending on how full the gas tank is (it's a ground as well).

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[This message has been edited by deadbird (edited September 21, 2001).]

 

The hot wire to the fuel pump, which should be tan color (as stated above) from a connector by th ECM to the fuel pump, will only be hot for about 10 seconds after the ignition switch is turned on. The ignition must be turned off for about 30 seconds before the relay will cycle again for another 10 seconds. It will be constantly hot with the engine running, either from the ECM or oil pressure switch.

 

here's and idea. on my 87 V-6 one day, i drove it to school, came home and was getting ready to leave again and all it would do is crank. i went through all the wiring diagrams with a multimeter and checked all the mechanical stuff. i spent a few hundred dollars on parts i suspected, but it turns out that the power wire to the ecm-fuel pump was corroding!! pretty ****ty, but all it took was a splice and i was back in shape. good luck

thadd

 

cool, i hope its that easy for me.

quick question...where was the corroded part of the wire located? maybe its a common issue.

thanks for all the help guys.

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'86WS7
Ram Air...
*EiyseWhite*

 

If you're wondering how the system works, it's like this:

You turn the key to Run. Fuel pump comes on for a couple of seconds, to pressurize the system.

Then you turn the key to Start and get the engine going. At this point, the fuel pump stays on all the time.

So, if you're testing the wire for 12 volts with a meter, you'll need two people. One to lay under the car to read the meter, and the other to sit inside and turn the key to Run. Or, put really long wires on the meter and bring it inside the car with you.

I HIGHLY doubt that both the wiring AND the fuel pump failed at the same time. Make sure you do some more troubleshooting before you go through all the fuss of replacing the pump.

I'm pretty sure the GM cars have a fuel pump fuse. Do be sure to check that.

Let's see. I know you said that you bypassed the underhood relay. But there's a chance (no insult intended) that you simply did it wrong. Or, that you did it right, but the break in the wire is AFTER the relay.

So, what you want to do in either case is meter it right near the fuel pump, not up front under the hood. Ground one side of your meter, use the other lead to probe the fuel pump wire, but do it near the rear end of the car.

From there....if you have power, the pump is probably bad. If you have no power, either 1. the relay is bad 2. you bypassed the relay wrong 3. there's a break in the wire somewhere from the relay to the back of the car.

 

Chris,

you are absolutely right. well i didnt actually fix the problem yet, but all the while troubleshooting, i left out one part.

the system will only pressurize for a couple of seconds. at that time will the fuel pump only be recieving 12v. afterwards the voltage'll drop, because the system is pressurized.

the test is to have someone testing the wires closest to the fuel pump when turning the ignition on. during those few seconds, i should have a reading of 12v, which afterwards should drop as the fuel pump turns off. (sounds about right?)

jeez, i almost made a desicion to pick up another ECM to test with, not to mention replacing the relay & pump.

if this works, i owe you one BIG TIME!!!

p.s. stick around Chris, i may need your help, but i'm crossing my fingers...thanks BTW!

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'86WS7
Ram Air...
*EiyseWhite*