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1998 Jeep Grand Cherokee Question: My jeep cranks but will not turn over HELP!!

 

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saynut, 5.2L V8, Loveland, CO, January 16, 2012, 18:55
 Rookie

I have checked the fuel pump, replaced the crankshaft position sensor and the distributor cap ( new alternator, map sensor and battery within past 6mo)....I smell gas and am getting a spark to the plugs but it still wont start...I need Help to figure this out....I am low on funds, a single mom with no family and trying to do all the work on my own...so any suggestions will be helpful

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  • Answer #1

    patrick mannion from Greg Solow's Engine Room, January 16, 2012, 20:42
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     Master

    I hate replacing parts without testing them and knowing the components are bad. When the car is failed it is important to check fuel pressure and delivery (using a fuel pressure gauge), next see that the injectors are being "triggered" by the computer ("listen" to the fuel injector. Using a mechanic's stethoscope (or use a long screw driver placing the handle end up to your ear place the metal tip end of the screwdriver against the body of the fuel injector), get a friend to crank over the engine while you "listen" to the fuel injector listen to each injector at the same point of the injector body. You should hear "click, click, click" as the injector is electrically opened and closed by the computer. If the injector is not being triggered you will not have fuel getting into the engine's cylinders. Disconnect the electrical connector at the fuel injector with the ignition key in the "on" position, (next position after the accessory position) you should have 12 volts at one of the two wires at the injector. This true for most vehicles but you need to consult a workshop manual for your vehicle to see that this is true for your vehicle. When the engine is running the second wire at the injector gets (triggered) grounded by the computer in your vehicle many times a second controlling exactly when and how much fuel gets injected into the engine. You say you have spark perhaps it's not strong enough. Check for ignition spark. Use caution when checking ignition spark firstly it provides very high voltage (about 15,000 to 40,000 volts) but it is low amperage, it can give an unexpected shock but is unlikely to kill anyone, secondly the spark produced can ignite any flammable gas or liquid (for example gasoline or the gaseous vapors of a lead acid battery). Remove the spark plug wire (or ignition coil if the ignition system on your car is coil over plug type), place an old spark plug with the gap between the electrode and shell of the spark plug "widened" to about .060" or .070" of an inch. Firmly ground the spark plug shell to a good engine ground. Hold the spark plug wire or coil with an insulated pliers and get a friend to crank over the engine while you watch for a pulsing bright spark jumping across the spark plug gap. Look on Youtube for a video on "Check for spark" or Check for ignition spark" I am sure someone has posted a good video clip. I have seen the computers go bad perhaps when the engine fails hit the computer with your hand as a friend is cranking over the engine if it starts the computer may have bad connections in it. I have used a company (http://www.siaelec.com/) they can test the computer in your car if it is bad they repair your computer. There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online
    Good luck I hope some of this helps.

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    saynut, January 16, 2012, 20:45
     Rookie

    I appreciate the impute and am truly grateful for your time...however I have already attempted all of these things and more and am at a loss for what else to try at this point

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  • Answer #2

    Loveland Tire and Service (18 Answers) , Loveland, CO - (970) 737-4336
    LTS January 25, 2012, 10:19
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     Technician

    Keep it simple. Forget the computer controls, fuel pumps, injectors for the moment and start with the basics. All an engine needs is fuel, fire(spark) and compression to run. They also need to come together at the right time. You need to verify you are getting fuel to the spark plug (emphasizing TO THE PLUG (is the plug wet or have you tried spraying something like carburetor cleaner into the throttle body while cranking the engine?)). You need to verify that the spark plug is firing(emphasizing THE ACTUAL SPARK PLUG needs to fire in the cylinder). You need to verify that you have enough compression to ignite the fuel (a compression test). You need to verify that the spark plug is trying to ignite the fuel at the right time during the compression stroke (a timing test, a tad more difficult but needs to be done). If all the above is occuring correctly the engine will start. One of the above is not occuring correctly and that gives you a path to troubleshoot.

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