97 Jimmy intermittent cranks but won't start

[MT-2500]

Originally Posted by mallenfam

Status (time for a final diagnosis?):

1) Jumping 12V to the prime wire does not get the pump running.

2) Measuring votage at the prime wire is ~0.300 V before turning the key to ON, then the voltage jumps around (momentarily ~1.0V and maybe 10V for a millisecond, but nothing steady or substantial) before the 2-second relay kicks off. The relay(s) located in the glovebox relay center do click before and after the 2-second period (I could not identify a relay box in the engine compartment, just a big flat ECM by the right fender?).

3) Does the relay clicking confirm that power is successfully flowing from the ignition switch through the fuse panel before reaching the relay?

4) The pump never showed signs of dying when the vehicle was running. Only now and one day a couple of weeks ago when going to start it and the pump simply doesn't prime for starting. Running the engine for a few seconds while spraying in starting fluid did not get the pump running again.

5) Checking power at the pump connections means I have to drop the tank right? I am going to be so bummed if I pay $300+ for a pump and that's not the cause (OK, I'll quit whining).

6) Do these symptoms confirm a dead pump?

Thanks for your shared experience and guidance!

Sorry about telling you it was in the under hood box.
Yes the wiring diagram does show the fuel pump relay in IP panel box but the one on left side.
But relay locater says it is behind glove box.
Feel the relay and check for a click on on the 1-2 second key on prime up.
I also like to check for good spark to spark plugs to when no start.

Look at fuel pump relay diagram.
You will see the prime connector wire is not a direct hook up to the fuel pump gray power feed wire,
Find the gray wire to fuel pump and jumper it for a good pump test.
There should be a plug in connector usually 4 wire behind or in front of fuel tank that is a good place to check for power to fuel pump and for ground.
If you have 12 volts on the gray wire there and ground on the black wire and fuel pump does not run then it is time to drop tank and go for a fuel pump.
MT

[mallenfam]

I am confident that the relay is working since it clicks on and off and I can both hear and feel it. I even swapped relays and got the same result. I also confirmed 12V always hot on both sides of fuse #9, so that is good.

I can't find/access the fuel pump connector to confirm wiring integrity, so I placed an order for a new pump from www.getgmparts.com for only $257 + $25 2nd day air shipping. The $115 ebay deal claimed to be a genuine GM pump packaged into their own plastic assembly - no thanks!

12V jumper to prime wire does not activate pump. In viewing the wiring diagram, I don't see how you could ever just measure 12V at the prime wire unless the oil pressure switch was closed, which means the engine would already have to be running. During the 2-second prime period, a good relay will have switched to the grey wire to the pump, so the red prime wire will be open-circuited in the relay during that period. But I'll check again after the pump is replaced - I could be wrong!

I'll let you know how it turns out - thanks for all the help!

[mallenfam]

FIXED!

Put in a new Delphi fuel pump. So apparently a when a pump goes bad, sometimes it just won't even try to prime when the key is turned.

Now on to the other lingering Jimmy problems...

[DINO55]

Glad to hear your 97 Jimmy is back in business, MT2500 called it right....