1999 chevy tahoe will crank and cut off sometime in the am, if left for an hour it will crank and run.
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NOTE: In order to perform a meaningful diagnosis, it is necessary to utilize either a code scanner or code reader. A test light, ohmmeter, digital voltmeter, vacuum gauge and jumper wires may also be required. However, you obviously do not need any of the aforementioned items to inspect vacuum hoses, wiring, or disconnected plugs,sensors or adapters.
Before undertaking any repair or diagnostic work, be sure to inspect wiring for proper connection, burned or worn/chafed spots, and cuts.
Be sure to check hoses that are hard to see beneath the air cleaner, compressor, alternator, etc.
WARNING! I'm sometimes accused of not giving short answers. However, my philosophy is that too much is better than too little.
Still with me?
This is how your problem is researched in my shop. Out of the box, I'd say that you have a problem with the fuel management system. However, there's a good chance that it's something simple and inexpensive like a clogged fuel filter or water in the fuel tank. However, as stated above, today's computerized vehicles can only be accurately diagnosed with the use of a code scanner or code reader. (AutoZone will loan you one -- FREE) You need a fuel pressure gauge so as to ascertain that fuel pressure at the manifold is at least 41 psi and holding steady. (AutoZone will loan you one -- FREE). The fuel pressure regulator may also be defective or clogged, Disassemble it and check if the screen is clogged. If so, use a small pick and remove the screen. You won't interfere with proper functioning of the regulator by removing the screen.
• My second area of concern would be the manifold pressure sensor which is located under the hood, center, rear engine area, above valve cover, mounted in bracket.
• My third area of concern would be the ignition control module.
• My fourth area of concern would be the heated oxygen sensor.
• My fifth and final area of concern pertains to you only if your vehicle is equipped with anti-theft electronics. A malfunction in this system will tell the computer to cut off the fuel supply immediately. If your code reading indicates this to be the problem, your cheapest remedy will be to install anti-theft override bypass unit. You can build one yourself or buy a commercial unit for under $30.
However, you must remember that these are nothing more than starting points and not guaranteed solutions at this preliminary stage. Only a code scanner or code reader will give you true analysis. (Remember that AutoZone will loan you one -- FREE)
First a little background for your edification. You may be aware of all this but we've never done business before and all assumptions are off the table.
For an engine - make that any engine and irrespective of manufacturer - to run, you need three things to happen inside the engine, compression, fuel and ignition, without any one of these components the engine will not run.
• Compression - Engine compression caused by crankshaft rotation and pistons moving up and down inside the engine block. If the timing belt or timing chain fails it will cause the camshaft to become out of correlation with the crankshaft or allow the camshaft to stop rotating. Either of these conditions will cause the engine to lose compression and sometimes cause internal engine damage.
• Fuel Delivery System - The fuel system includes: fuel pump, fuel injectors, pressure regulator, fuel filter and pressure lines. This system is used to supply fuel under pressure to the fuel injection system, the lack of fuel pressure or volume will cause the fuel delivery system to fail and the engine to stall or not start.
• Ignition Spark Delivery System - The ignition system components include: spark plugs, spark plug wires, distributor (if applicable), crankshaft angle sensor, camshaft angle sensor, ignition coil, ignition module, knock sensor and PCM (powertrain control module). The engine relies on the ignition spark to be delivered to the combustion camber at the correct time. If the ignition spark stops or is delivered at the wrong time the engine will not run or run poorly.
Whenever your engine cranks but does not start, runs rough, staggers, sags or cuts off, follow this Troubleshooting Guide. As stated above, some of these steps require a code scanner. They are costly but AutoZone will loan you one for FREE.
Most vehicles operate by the same principle; basic troubleshooting procedures apply to most cars.
• Step 1: Anytime you have a problem with electronically controlled components such as an engine, transmission, ABS brake, or SRS (supplemental restraint system, Air Bag) inspect all fuses using a test light and check the under hood power distribution center and under dash fuse panels. If all fuses test okay continue to the next step.
• Step 2: To check for problems with electronically controlled components such as an engine, transmission, ABS brake, or SRS (supplemental restraint system, Air Bag) and the fuses test okay a trouble code scan - borrowed from AutoZone - is needed to identify any system trouble. Use this easy-to-use simple scanner tool to retrieve trouble codes and see if they relate to the specific problem, like a crank angle sensor failure code. If the trouble code present does not pertain to the immediate problem like an EVAP code ignore it until a later time, after the car is running.
NOTE: Scan the system again after the vehicle is running. The reason is that non-related codes can be detected after the engine is running because sometimes false codes can be triggered by the engine not running. Once the engine is running again the code present might cycle and turn itself off. You might say "if the engine doesn't run shouldn't it have a trouble code?" Sometimes conditions occur that will not be detected by the computer, example: if the fuel pump fails the computer cannot detect the failure, so the engine doesn't start and the computer thinks everything is okay with no codes. If no trouble codes are present proceed to the next step.
If you have trouble using the code scanner or interpreting the codes click on the following link and use my access code (carrepair): Free Automotive Repair information for Users of a Code Scanner
All the best
Jul 03, 2011 |
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