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'04 Classic intermittent cranking no-start

Old 04-01-2019, 09:25 PM
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Default '04 Classic intermittent cranking no-start

Hey folks, I've been scratching my head on this issue for a couple of weeks now, every so often I won't be able to start my car on warm afternoons. Cranks wonderfully, but it won't start. At first I suspected an ignition problem, but starting fluid and a good inspection/tune-up eliminated that possibility. I bought a fuel pressure gauge and confirmed that I wasn't getting any fuel pressure until about a minute of leaving the key on had gone by, no fuel pressure for a while, then suddenly a full 53 psi. On checking the fuse panel, I discovered that the fuel pump relay was making a buzzing sound, but eventually would click over and the pump would prime. So, naturally I swapped the relay, seemed good for a couple of days, then it came back again, okay... maybe it'* the fuel pump, the car has 250K miles on it, probably due for a new fuel pump anyway, I changed the pump and filter, felt pretty proud of myself. Wasn't particularly difficult. The problem went away for another week. Now it'* back again. If it would stick around for a little longer maybe I could diagnose it. By accident I discovered I could make the turn signal switch buzz in exactly the same fashion as the fuel pump relay by parking the car the previous night with a turn signal on. So I know I'm dealing with an electrical fault somewhere, I'm just not sure where power flows in this car that'* half '03 malibu and half '04 malibu, They're very different cars.

Does anyone out there have any helpful information? I can use a voltmeter, but I'm not exactly an electrical genius here.
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Old 04-02-2019, 10:02 AM
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So you replaced the fuel filter and the whole fuel pump module?

Then it does sound like an electrical problem.......next time it won't start, have someone crank it over and with the palm of your hand hit the UBEC......... the underhood fuse block that contains the fuel pump relay......if it starts, this may be where your connection problem is.....there are usually three blocks of circuits here, with two screw/bolts holding them tight in the fuse block......some are torx, some are hex head......but with the fuse block cover off, you should see 6 of them......make sure they are tight and have not come loose.....if that does not solve your problem, you may have to take it apart(disconnect bat first), and look for corroded or burnt terminals.....
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Old 04-07-2019, 03:51 AM
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Update: On inspecting a bad tail light, I discovered that the right rear tail light assembly was very full of water, the two lower brake light lamps were cracked and submerged in water. Although fixing this doesn't seem to have solved the issue, it seems like the problem is both less frequent and less severe. Note to all the 97-05 malibu/classic owners out there, drill a drain for your tail lights, it'll probably save you some headaches.
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Old 04-14-2019, 04:08 PM
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Originally Posted by Tech II View Post
So you replaced the fuel filter and the whole fuel pump module?

Then it does sound like an electrical problem.......next time it won't start, have someone crank it over and with the palm of your hand hit the UBEC......... the underhood fuse block that contains the fuel pump relay......if it starts, this may be where your connection problem is.....there are usually three blocks of circuits here, with two screw/bolts holding them tight in the fuse block......some are torx, some are hex head......but with the fuse block cover off, you should see 6 of them......make sure they are tight and have not come loose.....if that does not solve your problem, you may have to take it apart(disconnect bat first), and look for corroded or burnt terminals.....
Just tried hitting the fuse panel with the fuel pressure gauge hooked up, didn't see any fuel pressure change, still zero. I'm tempted to take the panel apart just to check for corroded connections, are there any other places in the car besides the battery and fuse block that would cause low voltage to be reaching the fuel pump relay, turn signal switch, and gauge cluster? because these systems seem to be the most affected by the problem.
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Old 04-14-2019, 09:10 PM
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I am confused....I found a wiring diagram that shows the f/p relay is in the rear fuse block?

Do you feel the relay click when the key is turned to on?

Need to check G301 and G302, and also if you get power at A9 for 2 seconds when the key is turned on....



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Old 04-15-2019, 03:31 AM
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I'm going to try to post video of the problem in action and maybe you guys can get a better idea of what'* going on.

-Here'* the first video I took, when I began to suspect the fuel system.

-Here'* the second video I took, a few hours before I figured out the left tail light was full of water, it still does this, despite my draining the water and replacing the tail light circuit board.

I've had the fuel pressure gauge hooked up to the system, and in both cases I receive no fuel pressure when this is going on. I can usually mess with the blinkers a bit and the problem will go away, but that'* definitely not a long term fix. Maybe it could be a bad ground somewhere?

-Thanks again
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Old 04-15-2019, 01:15 PM
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Did you find out if your f/p relay was in the front relay center or the rear?
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Old 04-15-2019, 02:49 PM
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Best I can tell it should be in engine compartment fuse block, 18 is FP relay & 48 fuse is for the injectors.
The videos did not work for me, hope this helps.
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Old 04-15-2019, 09:46 PM
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Well, if 18 is the f/p relay, then feel that relay as you turn the ignition on...it'* only going to be energized for two seconds.....

If it doesn't click, turn key to off....wait 10 seconds......take the palm of you hand, and repeatedly hit the UBEC, and continue to hit it as you turn the key to on to see if that relay clicks and you have fuel pressure....If it still doesn't work, pull the f/p relay....

Below is the schematic for '04 Classic, my previous one was for an '04 Malibu......

Turn key to on......then probe the 4 legs for power with a grounded test light......one leg should light up...make a note of it....that is your 15a fuse....

Turn key off....Probe one of the other 3 legs.....turn key on....only one of the legs should light up for 2 seconds.....If it doesn't turn key off for 10 seconds....the try another leg, turn key on and see if it lights......if it doesn't go to the last leg.....turn key off for 10 seconds, and then turn on.....one of those three legs should light for 3 seconds....if none do, we are not getting power from the PCM.......

If one leg lights for two seconds and goes out, make a note of that leg.....

Now we have two legs with power, the other two legs, one goes to ground the other goes to the f/p..... most test lights have a probe on one end, and an alligator clip on the other...un-ground the test, and attach an open paper clip to it, to use as a probe.....

With key on, insert test light probe in the leg that had the constant power from 15a fuse......the other end with the paper clip, touch a good ground to show brightness of the test light.....now, one at a time insert the paper clip end into the two legs that had no power....the ground circuit should make the test light bright(as when you grounded it).......the other one should be dim, attached to the f/p circuit....

If one circuit was not bright, then you have a splice pack problem, SP103.....

So now you are going to use a jumper wire, and you will go from the leg with the constant power from the 15a fuse, to the to the leg that was dim, which goes to the fuel pump......you are now powering the f/p with the 15a fuse and should now have pressure on your gage...if you don't, you have an open/bad connection between the relay contact and the f/p, or a splice pack problem, SP302.....





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Old 04-24-2019, 03:25 PM
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okay, I found out which pins are the 15a supply, and the 2 second signal from the pcm. however, when I probe the other two pins, both light up equally bright... bad ground connection, right?
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