2005 Pontiac Montana problem starting

Discussion in 'Bad Dog Cafe' started by chrisgblues, Nov 20, 2014.

  1. chrisgblues

    chrisgblues Tele-Afflicted

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    I know there are some great car guys on this forum...hope you can give a fellow guitar player some advice.

    I have a 2005 Pontiac Montana Extended Base, V6 and I think it's a 3.4L engine. Anyway, I have an INTERMITTENT problem at startup. Most of the time it starts normally...but other times the engine turns over many times, like 15-20 times before it starts...but it DOES eventually start. I drive it daily and this happens maybe 4 times a week. When I say it turns over, I mean very violently...the whole van shakes a lot. Seems like there's LOTS of power even though the battery is at least 5 years old. I think it only ever completely failed to start twice, but I'm concerned it will get worse (the turning-over seems to be getting more frequent).

    Here is what I tried to do for troubleshooting, I tried turning the key to the ON position for a second, then turning off, then turning ON again to give the fuel pump a chance to power up before I started the engine. This seemed to help for a week or so, until one day it didn't help. Then I was back to the same old problem. Also I tried to see if it happened only on cold starts, or warm starts, but it happens with both...so that's not the issue.

    My experience with intermittent problems and my local service center, is that they just start replacing parts at random because there's usually no outward signs of failure...that could get expensive for an old van. Any advice on how to troubleshoot? I'm not a mechanic obviously...

    Thanks!
     
  2. Hell on a Six

    Hell on a Six Tele-Meister

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    I'll try and give some suggestions you may be able to do yourself.

    My first inclination is that you are looking at a fuel pressure loss. You're probably considering the same as you already know to turn the key and let the fuel pump build pressure to see if that helps.

    If you have a fuel pressure gauge, that's where you start. If it holds pressure for more than one minute after key up, your problem is elsewhere. If it leaks down pressure, start at the regulator.

    You have a fuel pressure regulator on the injector rail that has the job of maintaining system pressure. First easy check is to inspect that for signs of external fuel leakage. Inspect the attaching vacuum hose. Next, disconnect the hose and inspect for internal leakage. Have someone key up the vehicle while you watch it and see if any fuel comes out the vacuum port. With any luck, you find the issue right there.

    Beyond that, you could remove the fuel rail from the engine with the injectors connected and do the same key up while inspecting individual injectors for leaking. Your concern, being intermittent may well be an injector sticking open or leaking down. This may also support your concern of the violent cranking, with raw fuel leaking into and flooding a cylinder with the engine off.

    Beyond that, it may not be such a bad idea to go ahead and take it to the service center. They'll have the equipment to monitor the fuel pressure and scan the powertrain module. Any stored history codes may provide hints, and live sensor data can be seen on the scan tool that will also be helpful in diagnosis. Yep, intermittents can be hella tricky to deal with. They'll likely want an hours diagnostic fee up front to check it out, but a good mechanic/facility with the right experience with your vehicle is most often going to be the fastest and most accurate diagnosis. I know Pontiac is gone, but most of the mechanics that worked on those vehicles are still at GM dealerships, rolled into Buick/Cadillac/GMC shops.

    Hope that serves as some amount of help atleast. Good luck, hope it's a simple fix for ya.
     
  3. stealyerface

    stealyerface Tele-Afflicted

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    Something to try.

    In that particular year, the GM vans had a terrible design, by which there was an entire wiring harness that ran under the carpet, and went from the inside of the truck to the outside, by way of a pass-through the floor.

    If you are seating in the driver's side 2nd row, the harness would be under your feet.

    Oh wait, that means that if a child sits in that seat with muddy, wet, snowy, salty boots, all of the aforementioned stuff sinks into the carpet, and gets into the harness that includes the electrical connections for the fuel pump, injectors, sending unit etc??

    Yes.

    Have your mechanic carefully take up the carpet, find the pass through, and grease and lube that connection/harness, where the contacts might be compromised.

    That may take care of it.

    ~syf
     
  4. Toto'sDad

    Toto'sDad Tele Axpert Ad Free Member

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    I don't know how many miles you have on the vehicle, but I've owned several GM vehicles I put a lot of miles on as a salesman. The most I ever got out of a fuel pump was 150,000 miles, one failed at only about 70,000 miles. They intermittently failed/slow started for a short while before failing altogether.
     
  5. Slow Reflexes

    Slow Reflexes Poster Extraordinaire

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    I also used to drive a GM van for a living - the owner informed me that I should never let it get below half a tank, because the fuel pump relied on being immersed in gasoline for cooling and that it would die if not coddled.

    That sounded like the dumbest thing I ever heard, so of course I ignored it. I just went ahead and did my fuel stops when I had to have fuel, like I'd always done in my cars. Naturally, the fuel pump died. The second time, it dawned on me that maybe the owner wasn't full of crap on that one.

    Don't know that it has anything to do with your situation, but if it does turn out that your fuel pump is bad you might give that some consideration.
     
  6. Obsessed

    Obsessed Telefied Silver Supporter

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    This was my first reaction to your issue ^^^^^^^^.

    Yep, those fuel pumps that are inside the fuel tank can go out on you, so best to get it in to check ASAP. They will have to check a few things before they go there, but I think the odds will be there.
     
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