97 Jimmy intermittent cranks but won't start

1997 Jimmy W 4.3 auto 4dr 4wd 150k miles (currently also having the combination problem where the transmission defaults to third gear all the time and the ignition key won't come out, but I'll deal with that later unless it's related)

Had this problem for the first time a couple of weeks ago where the engine cranked over fine, but wouldn't start (located miles from home).

After sitting for a day, it started fine. I got it home and replaced the fuel filter just in case. Immediately after replacing the filter, I turned the key and didn't hear the pump prime. I thought that possibly trapped vapor in the line might be a factor, so I relieved the pressure at the shrader valve in the engine compartment. I turned the key, the pump primed, and it has started fine ever since...

Now it has happened again (also far from home) - the pump does not prime when the key is turned on. I am concerned that just replacing the pump won't cure the problem if something else is causing the pump not to prime when the key is turned on. I've seen posts about jumping 12V to a prime wire to check the pump. Does this work for a '97 and does this mean a wire from the pos battary terminal? If the pump is not dead, then will the 12V jump cause the pump to prime and then the vehicle will then start?

I also saw a discussion about a VCM and relays in the glove box.

Before I pay to tow, are there some diagnostics I can do to find the cause and hopefully get it restarted? And could this be related to the "ignition switch harness failure"?

Many thanks!

At sounds like your fuel pump is not running. You could put a voltmeter on the wire to the pump. When you turn the ignition switch on it should have voltage for a few seconds. Then go off. If it has voltage, replace the pump. If not, check fuse and pump relay for voltage but remember you will only get voltage for a few seconds when you turn the key on.

Thanks for the pointers, especially the 2-second window. I'll check these out first and reply later on how it went.

But please keep the ideas coming in case these don't work, and also for others who may need this thread later.

Yes 12 volt from positive jumper to fuel pump prime wire wire but use a fused jumper.
The fuel pump should run when jumped.
The prime wire/connector is also a good place to test for pump getting 12 volts.

If the pump has 12 volts and does not run the wiring to it or the pump is bad.
With it jumped and pump does not run take a rubber hammer or 2X4 and whack the bottom of the fuel tank.
Sometimes you can wake up a dead pump and make it home.

Also on a no start check for good spark to spark plugs.
And on a 97 always check ign switch for power to everything.

Thanks for the additional input that I will follow when I get back to the truck this afternoon.

Here are the current issues:

Prime wire identification. I looked on the driver side fender back near the hood hinge. The only wire that I found with an open end was red (no grey cover) and ended with a female spade connector. Is this really the correct wire? If not please give me a kick in the right direction.

Dead battary. Although the vehicle broke down yesterday, it wasn't until I got there that I found out from my daughter that the lights were stuck on even though the switch was turned off. The old jumper cables I had with me conducted so poorly that part of the length got pretty warm when jumping, so I don't know if full voltage was available to the Jimmy engine compartment.

I measured voltage at the wire that I described above when turning the key on. The reading jumped from millivolts up momentarily to 1 V then maybe 10 V, then back down again. I jumped 12 V (except maybe less if the jumper cables from my car to the Jimmy were underperforming) over to the mysterious red wire w/ female spade and heard no pump prime sound when the key was off or on.

I forgot to look for the pump relay. Is it somewhere in the glovebox?

You will need to get your battery up to full charge.
Check you PM for wiring diagram.
The relay is in the under hood fuse box and relay center.
The prime wire will be a single wire with a plastic end on it for a male spade hookup.

MT-2500: I can't thank you enough for all the advice now and in the past! (unfortunately next I'll be fixing the transmission fault to third gear protect mode and stuck key in ignition problem)

For now, it looks like I found the correct wire for fuel pump prime. With the battary fully charged, the voltage at the wire sits a fraction of a volt before turning the key to ON, then it jumps around a bit and just momentarily jumps to 1 and maybe 10 V (for milliseconds maybe, too quick to tell) near the end of the 2-second prime period.

Providing a 12 V jumper does not activate the pump, with or without the key ON. Clunking on the side of the gas tank didn't help at any point either (nor did the ride home on the back of the flatbed towtruck).

Since there appears to be no voltage at the prime wire (and looking at the wiring diagram you sent),does that possibly indicate a bad relay?

I did not yet get to check the relay in the under hood fuse box and relay center. There are three relays mounted on the upper center of the firewall. Are they related?

By spraying starting fluid into the intake, the motor would fire and essentailly run on the fluid, but not run on its own. The ignition switch seems to work correct other than not letting the key come out. I plugged in the code reader to clear the codes, which sometimes then frees the key, but this time there were none since the battary had died and the key remains stuck even though I did the clear code process anyway.

If I need a new pump, then fine, I'll search for a Delco unit. But I don't want to do a $500 repair and then find out it wasn't the pump, but something else. Your continued guidance is appreciated!

1997 Was the year for the "Bad Ignition Wiring Harness" The no pump whining is the first symptom of it. Next time it does not start, turn the key to the on position. Look for the airbag light, brake light, SES light, Security light... If these lights are not lit up with the key turned to the on position and you did not hear the fuel pump prime for 2 seconds, then you have a Bad Ignition Wiring Harness on your truck. Good luck and keep us posted on your progress...

Thanks DINO55. The normal gage lights do come on, even though the pump doesn't prime.

So now the question is, since the prime wire tests result in no voltage and no pump response, does that indicate that the pump may not be the problem?

Fuel pump relay is in the under hood relay box
If you jumper 12 volts to the prime wire or the gray wire that feeds the fuel pump from the fuel pump relay the fuel pump should run.
Check for 12 volts to the fuel pump at the fuel pump plug in and good ground there to. Also the check plug in at the fuel pump.

Get the fuel pump running and with good pressure.
And go from there.

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!

If you have followed what MT-2500 suggested in post #10 and the pump is not whining, then you have a bad pump. Double Check everything first before you run out and purchase a new one. Don't skimp on the new pump, AC DELCO...................

Thanks DINO55. I did not drop the tank to check at the pump, but all tests at the prime wire are dead and the pump relay seems functional (I even swapped the relays around).

The cheapest pump (model #AC Delco MU112, GM 25178731, Delphi FG0071) I could find was $328 at GM Parts Direct, except for an ebay vendor that claims to be a new genuine Delco MU112 for $115!

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=160145457600

If this is real, I am going for it!

*** Bear in mind that I am having the combination problem where the tranny defaults to third gear only (second gear if the shift lever is put into first or second) and the key won't rotate all the way in the ignition for removal *** But this problem has been happening more frequently that the no-prime problem that just cropped up.

Also $257 at http://store.getgmparts.com/fuel-pumps.html

I would be all over the one on Ebay.

Good luck with the pump swap and let us know how it goes, remember to take your time and do a "SEARCH" for some more information on swapping the fuel pump...

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

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 (http://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!

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...

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