1994 Jeep won't start--Help!!!!

thumper · #1 (**permalink**) 07-20-2003, 08:00 PM

My daughter's jeep will crank fine but will not start. What are the most likely causes and how do I go about diagnosing it??? [addsig]

Jeepr89 · #2 (**permalink**) 07-20-2003, 08:00 PM

have you checked to see if it's getting spark? Also check to see if it's getting fuel. Those would be the places to start[addsig]

ad5at · #3 (**permalink**) 07-20-2003, 08:00 PM

Depending on the mileage, the pick up on the flywheel that senses crankshaft

position for the electronic ignition may be bad. I had to replace on of these

on my YJ after about 100,000. It is relatively easy to replace, but may be something

else. Check fuel pressure and make sure you are getting plenty of fire

through ignition system.

Only some suggestions, good luck! [img]modules/phpBB_14/images/smiles/icon_smile.gif[/img] [addsig]

YellowYJ · #4 (**permalink**) 07-20-2003, 08:00 PM

just a thought, maybe the electric fuel pump went out or is not working properly.[addsig]

btjeep · #5 (**permalink**) 07-20-2003, 08:00 PM

Curious what you found out about your not starting problem? I have a 95 that will not start unless the key is turned to the on position for a while 3-20 mins then it will start and run fine. It turns over but unless I wait a while with the key in the on position it will not start. After the waiting period it makes a clicking sound coming from the power distribution box then the fuel rail charges the clicking stops and it will fire right up.[addsig]

jprtroy · #6 (**permalink**) 07-20-2003, 08:00 PM

As mentioned eariler, Fuel, Spark, and air are the essitential's Missing one of the 3, motor won't start. With that knowledge, heres a question to ask yourself" What does it need to work?" list all the things it needs to run. Gas, spark, key, (to turn it on) spark plugs & wires, timing wheel sensor cap & rotor, MAP sensor, (fuel injected models) there's more involved but this will do for now.

Once you have a list, you can go about checking each item. It may seem like a lot of work, but most can be checked rather quickly with a quick glance. Like Gas. Is the carb. getting fuel? When you (or someone) steps on the peddle, can you see or smell fuel? If not, make a note, this will have to be fixed. If fuel injected, does the fuel pump turn on breifly? on at all? make a note.

Let's say it's getting fuel. The fuel won't burn without a spark. What generates the spark, ask that question again " what does it need to work?" For a spark, it's gonna need the battery, the coil, the ECM (electronic control module) or computer whichever.

It's going to need spark plugs,(are they gapped properly, clean, clogged?) wires, (are they good?) the cap & rotor. (are they good, cracked,? the rotor, does it still have a blade?)

To check for spark, you can remove the coil wire from the cap, and hold it close to any metal surface under the hood (with something insulated) that it'll reach, (carefull, don't have your hand close to the end, you may get ZAPPED) have someone turn the motor over. While it's "cranking" and the coil wire is close to metal, you should see a spark.

If not, well, that's why the motor won't start. Heres that question again "what does it need to work?" think, what causes the spark? well, there's the battery that supplies the "juice" or 12vdc. Theres the ECM (it sends battery voltage the coil) to create a spark) there's the coil, that amplifies the signal from the ECM to voltages that'll knock ya on yer butt, there's the coil wire, the cap and rotor.

Each of these will need to be looked at. We know there's no spark, so, either the coil or the ECM has gone south. Coils are lot cheaper than the control modules and usually go out more so than the control modules. You can test the ECM by measuring voltage on the coil's input. If , when the motor is cranking, you can find battery voltage on the input wires, chances are the ECM is fine. What's left? the coil.

Let's say there was a spark, it's getting fuel, still won't run. Hum? Timing? (the question again) well, the timing wheel pick up (sends signal to ECM, know's when to send sig to coil then) If it's bad, the ECM won't know when to send the "fire signal" there's more to it, but I think you can get the jist.

These were examples of how I determin what may be wrong. It may seem like a lot, but it really isn't. This form of troubleshooting can be used for practally anything that's broke. 2 simple question; Is it working? What does it need to work?

[addsig]