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AutoMD ... 1/14/2014
2000 GMC Yukon Denali 8Cyl5.7L - Engine
Hello i have 2000 gmc denali 5.7 cranks over and over but wont start or act like it wants to .I checked and it has 59 to
Hello i have 2000 gmc denali 5.7 cranks over and over but wont start or act like it wants to .I checked and it has 59 to 62 psi fuel pump and it has spark at number one cylinder
20 Answers
  • HouseCallAuto
    HouseCallAuto 1/14/2014
    1. Check spark at several spark plug wires with an adjustable spark tester set to 30 KV, it should fire bright blue.

    2. If not, check spark from the coil wire with the testers set to 40 KV, if it fires replace the cap, rotor and wires as necessary.

    3. If it did not fire 40 KV, verify there is good power to the coil cranking, replace coil.
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  • AutoMD Member
    AutoMD Member 1/18/2014
    I did change the Distributor cap and rotor and wires also new plugs and crank sensor still wont start any help
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  • HouseCallAuto
    HouseCallAuto 1/18/2014
    Plug in a code reader and see what fault codes are stored. This cannot be skipped. Confirm that the code reader can establish communication with the vehicle computer. If it can communiucate an d there areno codes stored, update this post with that info.
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  • AutoMD Member
    AutoMD Member 1/18/2014
    I just did it again po 108 was the code
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  • HouseCallAuto
    HouseCallAuto 1/18/2014
    Confirm that the map sensor is plugged in. Clear thiscode and see if it returns during further attempts to start it. It might be a bad map sensor. Without a live data screen to see while c ranking it is hard to say. The P0108 is a fault with the map sensor or circuit wiring. Did you unplug the map sensor for any reason with the key in the on position, because that would have set a code as well.
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  • AutoMD Member
    AutoMD Member 1/18/2014
    ok I cleared code tried to start for about ten min and read again and no code but it did sound like it wanted to start and it backfired
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    AutoMD Member
    HouseCallAuto 1/18/2014
    Check for codes after each several attempts to start it. I am not really expecting it to start. is there any chance at all that you have the firing order wrong from when you replaced the wires?
  • AutoMD Member
    AutoMD Member 1/18/2014
    Just checked firing order it is right . Last friday i was driving the truck no problems came home turned it off the next morning I tried start and battery was to weak to start then sunday night I put a new optima battery and it hasnt started since
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  • HouseCallAuto
    HouseCallAuto 1/18/2014
    I believe there is a problem with the distributor itself. Get the engine cylinder #1 to TDC on compression stroke and confirm that the rotor is pointing to the #1 cylinder wire on the dist cap. I am assuming you had no reason to remove the distributor or loosen it since you only replaced the cap and rotor. I will assume that you did not somehow install the rotor 180 degrees out - even though there are keyways I have seen this mistake made. result is no start and backfires.
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  • AutoMD Member
    AutoMD Member 1/18/2014
    wont that give a code if the distributor is off
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    AutoMD Member
    HouseCallAuto 1/18/2014
    This business is not an exact science. Yes a code can set but not always. You have to do testing sometimes. Cannot rely on codes only.
  • AutoMD Member
    AutoMD Member 1/18/2014
    I put carb and choke cleaner in the throttle body and nothing
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  • John's Auto Repair
    John's Auto Repair 1/19/2014
    Just make sure you have'nt fouled the plugs with all that fuel and carb. cleaner.
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  • AutoMD Member
    AutoMD Member 1/19/2014
    The truck started out of the blue today but ran like crap it gave me p0300 p0141 p0155 p0135 all o2 sensor codes I looked under the truck and the pipe before or after the cat was red hot .does this mean the cats are bad if yes can I cut off the pipe before the cat to get it to run and drive it the the muffler shop?



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  • HouseCallAuto
    HouseCallAuto 1/19/2014
    OK, so you have set 3 different O2 sensor heater codes. Erase these codes and see if they return, but also I kind of would like yto know why these set. Your Yukon has four different oxygen sensors. The codes listed P0135, P0141, P0155 represent a fault with three out of the four O2 sensor heater circuits. The O2 sensors all have 4 wires. The Black and Pink wires (Pink might be Tan) are power and ground for each sensor. The only sensor NOT represented by a fault code is the Bank 2 sensor 2 (located after the catalytic converter on the pass side).. However, confusing as it is, it does not seem logical or plausible for you to have a failure of 3 O2 sensor heaters so I want you to check for battery voltage at the Pink wire at each sensor, best way is to unplug each sensor one at a time and use a test light initially probing the Pink wire and the Black wire into the pin of the connector on the harness side. With the ignition key to the "on" position there should be battery voltage. If the test light does not show ANY power there determine whether the battery voltage on the Pink is missing or if the ground (black wire) is what is missing. If Pink has no voltage at all even when using chassis ground go to the ENG 1 fuse (20 amp) in the underhood fuse panel and confirm that the fuse is good. You can even do this first before you check for power at the O2 sensors. There should be battery voltage at both sides of the fuse with the key on. Also, I do not know why a 4th code did not show (P0161) which is for the Bank 2 sensor 2 heater. Because if the other 3 O2 sensors are not getting power then it makes sense that the this last one is also not getting power. Update me. The P0300 is not an issue right now. Do not cut off the cats. The pipes are glowing because you have no fuel control and you are dumping fuel that is burning in the converter and overheating them.
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  • AutoMD Member
    AutoMD Member 1/20/2014
    I cleared the codes and the only that came back was p0300 it was on twice it started up but still ran like crap .also check all the fuse under the hood and inside the the truck none were blown
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  • HouseCallAuto
    HouseCallAuto 1/20/2014
    If the cats are still glowing red hot then you are dumping in too much fuel which brings you back to checking components that control fuel flow and fuel injector pulse. Try unplugging the electrical connector from the mass air flow sensor and tell me what difference it makes when you start and run the engine with it unpligged
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  • HouseCallAuto
    HouseCallAuto 1/20/2014
    If the cats are still glowing red hot then you may be dumping in too much fuel which brings you back to checking components that control fuel flow and fuel injector pulse. Try unplugging the electrical connector from the mass air flow sensor and tell me what difference it makes when you start and run the engine with it unplugged.

    Now at this point lets focus on the P0300. If this were in a shop a shop would hook up a scan tool that the live misfire data can be seen in real time on each of the 8 cylinders. P0300 means there is misfires happening but the computer cannot identify which cylinders. On the live misfire screen a mechanic can see the misfire counts being logged for each cylinder. Knowing which cylinders are misfiring gives a direction to continue diagnosis. You are now being stopped by technology so we are winging it with trial and error stuff. You could have a bad injector dumping fuel or a bad valve spring or even there is an adjustment called cam retard offset that can only be set with a shop level scan tool like an OTC Genisys or snapon type scanner. I use a genisys. You can buy a Genisys used on ebay for under $500 that would be the Holy Grail for diagnostic info on your truck. These type situations were not meant to be diagnosed without a full function scan tool. By the way, when catalytic converters clog on Chevy trucks the result is similar to what you have going on so to rule out a clogged cat, remove the upstream O2 sensors and run the truck. removing the sensors completely allows the suspected exhaust restriction to be temporarily relieved without destroying anything. if it still runs the same (yes it will be loud) then that rules out the cats being clogged.
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  • AutoMD Member
    AutoMD Member 1/20/2014
    ok i pulled all plugs and found two that were fouled .put two new plugs in and i drove in for about 20 min then when i pulled to my house and stop it started running a little rough so i ran scanner and p0172 and p0175 came up
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  • HouseCallAuto
    HouseCallAuto 1/20/2014
    Remove the vacuum hose from the fuel pressure regulator and if you see even one droplet of fuel in the hose replace the fuel pressure regulator. P0172 and P0175 indicate a very rich mixture, dumping fuel.
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    HouseCallAuto
    HouseCallAuto 1/20/2014
    A fuel pressure regulator affects both banks. Your codes indivate a problem with both banks.
  • AutoMD Member
    AutoMD Member 1/20/2014
    I know that the fuel regulator is on next to the spider .can i check the vacuum hose to the fuel regulator without take off the upper manifold off ? thank you for all your help
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  • HouseCallAuto
    HouseCallAuto 1/20/2014
    Sometimes I forget. Yes of course its under the manifold attached to the spider. There is no vacuum hose that goes to it as it operates in a vacuum. That being said, if you are going to go through taking off the upper manifold you may want to consider replacing the injector ass'y which comes as a complete unit including the fuel pressure regulator. Question: When you check fuel pressure and you read 59 to 62 psi, does it maintain pressure on the gauge needle or does it drop off all the way down after the key is turned off? If the regulator is leaking the fuel is going to end up under the upper manifold . Does the oil seem to be contaminated with a heavy smell of raw fuel? That would set a P0172 and P0175 also.
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    HouseCallAuto
    HouseCallAuto 1/20/2014
    removing the upper manifold is not a bad job to do
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