Not starting

[irishboy02]

So, as youv read i was having an issue with my truck boggin down on me, similar to the feeling of not letting the clutch out on a m/t for about 5 days now. It also caused me to completely stall twice. I cleaned my charred throttle body and made it nice and shiney, problem seemed to get a little better, however was still there. Friday night, my truck decided to stall on me again when i got out of work at 11p. It was cranking and turning over but seemed as though it wasnt getting any fuel. I put my ear outside the truck as i turned the key and i could not hear my fuel pump getting power. Great, a blown fuel pump at 11p. Got a ride home and had my truck towed to my buddys garage the next morning. We start goin through everything and pulled the coil packs -no spark either. So now theres no fuel pump, no spark and no fuel pressure...hmm... Turns out, someway somehow im blowing the fuse under the hood #28 PCMI. Im shit out of ideas, i have 2 check engine lights. p0410 (secondary air pump- i disconnected this about 9 months ago if not more) and p0526 (fan clutch circuit - loose bolt from the fan shroud wiggled the wires a little too close to the blade and it sheered the wires. The wires are pulled now so theres nothing controlin the fan accept its pulley.

From the factory its a 15a. I was blowing 15a like crazy so i bumped it to a 20a just to be able to get it home. Iv gotten it to run down at the shop and was able to drive it home (about 20miles) and was driving it around in the city no problem, including multiple starts again. Now that its cold itl start and run for about 3 sec and then the 20a will pop and the motor die again. Iv been through about 25 20a fuses and i give up. Everything inside still works no problem. Im shit out of ideas and have no vehicle now - PLEASE HELP

[Trail X]

http://forums.trailvoy.com/showthread.php?t=56801

Not sure if this helps... sounds like a grounding problem.

I'll try to look through the factory manual when I get home to see what that fuse is connected to.

Found this too:

This fuse operates all ignition coils, all fuel injectors and supplies power to the PCM. I suggest starting out by disconnecting each of the coils and the fuel injector harness. Install a new fuse and see if it blows. If the fuse does not blow, reconnect each of these components one at a time with the key on and monitor the fuse. When the fuse blows, you will know which component is shorted.

[Stoked]

Wow, crazy. I dont have the answer but I can say a few things. Try not to up the allowed amp in the fuses. If it asks for 15, keep it at 15. Dont risk frying your circuits, the real problem is elsewhere. Why its blowing the fuse, seems there may be a short somewhere thats been getting progressively worse and now its blowing the fuse, check components that work with the PCM (obviously). Hopefully you can find out the issue and update us. Good luck!

[The Roadie]

I agree. Either a component on that circuit has an internal short, or the wiring from the fuse to each of them could have a short.

Bumping up the fuse is NEVER a valid troubleshooting tactic, since the wiring is sized to match the fuse. Upping the fuse amperage will only turn the WIRING into the fuse, and will help you locate the fault by smoking and then you find it by nose.

In my experience, a loose or intermittent ground will cause functions to not work, but they almost never turn into a phantom short through a sneak path that blows fuses.

A very careful visual inspection of the wiring, plus the traditional pull-all-the-components-on-the-circuit trick, should work. Yes, it's not easy or quick. But a methodical and non-panic process is the way. With a meter, you should be able to see the short if it's present all the time, but it may only happen when the PCM is powered up and trying to activate that circuit. That takes more electrical experience to troubleshoot. What I do in those cases is replace the fuse with a 100 milliohm resistor that will naturally limit the current to under 10A, then measure across the resistor differentially to check the voltage drop, which is proportional to current. Remove loads one at a time until the current drops significantly, then inspect the wiring to that load.

[irishboy02]

Unfortunately i dont have access to meters and all that fun stuff. Through visual inspection and wiggling inspection, at quick glance all grounds seem to be properly tightened. Im currrently looking for wireing diagrams to see what is run from that 15a.

The reason why i bumped to a 20 was just to be able to get home. There was a point where i was running off of a 15a but to make it home i bumped to a 20a. I am well aware that this is far from the safest/smartest ideas- esp since i dont carry a fire extinguisher with me. Any and all info you guys find for me please let me know.

[fishsticks]

A digital multimeter can be had for around $20 and will help you actually find the problem rather than guessing. Don't be a Benny or whatever it is you were talking about in the other thread.

[irishboy02]

So on the update :

I spoke with a guy who is a retired GM tech, a current GM tech and a former GM tech and they all spoke with the same level of confidence and new the issue as soon as i started explaining my symptoms.

Fuel pump

Apparently its set for some odd reason as the pump is on the oust, it will cut the spark at the same time the pump cuts out. As they both cut out, the computer goes into protect mode and this surge is what causes the fuse to blow. Theres some long complicated technical information that they started talking about but they were all able to sum it up the same way. A guy i work with has a suburban with 6" on 35s with the 5.3. He said he had this same issue at around 70k with his truck. It turned out to be his fuel pump too. I have the pump in hand but its way to cold out right now for me to crawl under there. Tomorrow im goin out when it warms up to 34 to work on it.

Ill keep you all updated.

[The Roadie]

Fascinating. I never would have guessed that even reading the shop manual cover to cover. Real-world experience wins out. Assuming they're right.

[Mooseknuckle]

Nice Brendan. Your right the high today is gonna be 37. If you need anything text me.

[irishboy02]

As per GM. "Well, we were under your truck for just under 5hrs trying to diagnose the issue. We decided were only going to charge you for 2hrs because we actually feel bad for you. Your whole truck is a short and we cant figure out where its coming from. We have never seen a case or incident like this. Our in house tech couldnt figure it out, we had a GM electrical tech come in and a GM elec engineer and neither of them could figure it out. This is actually causing your PCM to short out, hense why your blowing that fuse. We really dont know what to do from here. If we get anything further will give you a call back"


Needless to say this is my final straw with this truck. Once i get it back, i will be parting it out and selling it.

[The Roadie]

Damn, you'd think it had been in Katrina or somethin'.

[irishboy02]

The swap was completed about 6months ago by now. Theres been no issue or even a sign of an issue untill last week then boom that was it. Not saying the swap might have nothing to do with it, but its been quite a while and quite a few miles since then.

[Trail X]

This fuse operates all ignition coils, all fuel injectors and supplies power to the PCM. I suggest starting out by disconnecting each of the coils and the fuel injector harness. Install a new fuse and see if it blows. If the fuse does not blow, reconnect each of these components one at a time with the key on and monitor the fuse. When the fuse blows, you will know which component is shorted.

Have you tried this yet? You know which circuit it's on, it's time to test each component until one gives you the proper indication that it's the cause. It's a lot of work, but it's certainly worth the time to save the vehicle. You just need to purchase a multi-meter... it's worth it to learn how to use them. They come in very handy.

If you're really lazy and don't feel like trying the meter, there are certainly better shops than a GM dealer to try out - and most of them won't be as expensive.

Never heard of a shop charging you even though they didn't fix anything.

[irishboy02]

That is what GM does they charge for diagnosis fee.

With the fuse operational i cant even start my truck, the starter isn't receive power but the relay is ok. No coils are receiving spark and the fuel pump isnt receiving power either. The PCM has been shorted out too.

[Trail X]

When does the fuse blow exactly? It doesn't blow when the key is turned to on?

[irishboy02]

Apparently as our fuel pump goes, apparently a common issue, itl short the harness. Hense why i was blowing the fuse. However, the bigger issue is that when the fuel pump shorts out it fuses the wires together on its harness. So, the positive and negative are touching which causes the short. But to make matters even worse, this makes the harness surge, which blows connections at other points within the wiring, blind to the eye and apparently GM too allegedly.

On a lighter note. Theres a wiring guy near where i work that is amazing and highly recommended by many automotive guys up here. I also personally know 3 people who have had work done by him, as far back as 15 years. If he works on my truck (which he will) itl be his 4th TB hes worked on, all with this same issue; thats how i found out the root of the problem. Hopefully this will be able to keep this simple and quick and get me back on the road soon.

[MrSmithsTB]

You must be happy to learn that. Let this be a lesson to everyone to change the pump as soon as there is any sign that it is failing.

Hope you've found your fix.