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Mystery starting issue

penn4581penn4581 michiganPosts: 2
edited September 2015 in Buick
So i got this truck from my in-laws on the condition that i could get it fixed because they were tired of paying for it. Here is the problem...we took the truck out in the afternoon and it seemed to have a little trouble with hard accelerations but otherwise ran OK, 1 hour later we went out to leave and it would not start at all. acts like it is not getting any gas.
here is where it becomes the mystery, fuel pump tested (OK), fuel filter tested, (OK), fuses checked (OK), and checked the connection under car ( c305 i think (OK)), Injectors Replaced, new computer programmed by the dealer, MANY sensors replaced, relays replaced.
The only indication of something strange is one mechanic said there was a slight voltage drop at the injector when trying to start it. there has been a total of 4 or 5 differant mechanics that have all told me the same thing " It should be running"
I am willing to try almost anything now.

Comments

  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 22,972
    Crankshaft position sensor? That would give no spark until cooled some and then acts normal.

    Bad fuel pump? That might tie in with odd feel on hard acceleration due to not delivering enough pressure or volume. When it won't start, try hitting the underside of the fuel tank briskly with rubber hammer to vibrate pump while someone has the key at crank.

    Check wiring to pump and check the ground for the pump circuit--I don't know if it grounds near the tank or back up front. Check circuit diagram bbbind.com Fuel pumps can test okay and be giving problems due to overheating of a connection and the damage causing reduced power to the pump--don't know if that happens with pumps in Rendezvous or not.

    You really need diagnosis as to what's happening when it won't start:

    Does it have spark? If not then you know to check that circuit. Pull a spark plug wire off and place it with a tester or a spare plug lying on engine metal while cranking to see if a good spark occurs.
    Does it have the injectors clicking and squirting fuel and is that fuel at a good pressure.

    A longtime radio car repair guru in Cincinnati talked about duct taping a set of fuel pressure gauges to the outside of the windshield and monitoring the pressure while driving on cars that would act up fairly consistently. He would find the pump heated up or the wire heated and pump lost pressure on some.





    2015 Cruze 2LT, 2014 Malibu 2LT, 2008 Cobalt 2LT

  • penn4581penn4581 michiganPosts: 2
    Crankshaft position sensor has been changed, it it getting spark and 60lbs of pressure to the injectors but i dont think the injectors are firing.
  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 22,972
    penn4581 said:

    Crankshaft position sensor has been changed, it it getting spark and 60lbs of pressure to the injectors but i dont think the injectors are firing.

    Is the car starting and shutting down at times? Or is it completely dead?

    If dead, use one of the 194 light bulbs that has wire for connectors and put
    that into the electrical connector for an injector and crank. If it blinks, then
    injector(s) are getting pulse. If not, you've isolated it. Now to the circuit
    diagram for injectors. Fuse? As I understand the injectors are fired by grounding
    each circuit in the computer. You say you've replaced the computer, so
    check power to the injector on one side.

    bbbind.com for circuit diagrams. They ask for email address, but
    I never get anything from them; it just seems to be a part of signing in.

    2015 Cruze 2LT, 2014 Malibu 2LT, 2008 Cobalt 2LT

  • thecardoc3thecardoc3 Posts: 4,900
    Many get caught in the trap of doing random testing when the problem isn't occurring. All of the testing has to be done while the symptom is occurring to make any legitimate progress. Its one thing to ask do you have spark, fuel, or is one or both of those missing. The next thing that must be done is, once you prove what is missing you need to know what the computer needs in order to command that output and start testing for the presence or absence of those signals. Do you want to know what is worse than just random testing? Tossing random parts, which has the capability of adding an additional problem(s) on top of the original one.

    To test for spark, a spark plug sitting on a valve cover isn't sufficient. It only takes about 800v to jump a plug like that. You need top prove that the ignition system, can provide over 25,000 volts and that means you need a spark checker like the ST-125. To test for injector pulse, one good trick is to use a stethoscope and listen to the injectors that you can access while someone else cranks the engine. You could also try a little alternative fuel to see if the engine will fire after you confirmed spark to it.

    These kinds of problems are usually easily solved when approached with a solid game plan. That means you need to be ready to attack it whenever, wherever it occurs. Prove what you can and then set your plan in place for the next step in the process.
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