2003 Jeep TJ will not start on first try

What happens the first two times? Does the starter just make one kind of loud clunk but it does not spin the engine?

Caradiodoc

The place to start is by having any stored diagnostic fault codes read. Many auto parts stores can do this for free. Hopefully the Engine Computer detected a sensor problem when it didn't start. The computer will turn on the Check Engine light if the problem could adversely affect tail pipe emissions, but there are many other codes that do not trigger the light.

Caradiodoc

Thanks for the suggestion Mr. G. I hadn't thought of that.

What you can try, chloew, is when it doesn't start right away, keep cranking for at least five seconds. If it eventually starts to run and pick up speed, suspect a leaking injector. My van would start on the second or third try if I didn't crank long enough. I have an injector that leaks the pressure down after about ten minutes and results in an unusually long crank time. After the engine cools down for a few hours, it starts up instantly after the raw fuel has condensed in the intake manifold. It also has to do with coolant temperature. Once the engine cools down, the injectors give a priming pulse for starting. That doesn't happen with the engine warmed up.

At the risk of flooding the engine, try holding the gas pedal down about 1/8" during cranking. If that consistently makes the engine start, then think about RunnerG's suggestion about the Automatic Idle Speed (AIS) motor. There are two things you can look for. The easiest is it is supposed to cause the "idle flare-up" at startup. The idle speed should go to around 1500 rpm, then come back down in a few seconds. If that occurs, the motor is working and the air passage is clear.

No idle flare-up will occur if the battery was recently disconnected or run dead. The Engine Computer must relearn "minimum throttle" before it knows when it must be in control of idle speed.

Another trick is to disconnect one fuel injector while the engine is running, and even a second one. If you have a tach, and the idle speed stays up, the AIS motor is working and the Engine Computer has control over it. I watched a Chrysler trainer do this with a V-8 Jeep. Eventually he had six injectors unplugged. Obviously it ran for **ap, but it still maintained the proper idle speed. He did that to show how much control the computer has over idle speed.

The other way to tell if it's related to an AIS problem is to connect a scanner to the vehicle and read the "AIS steps". The computer can position the motor to any of 256 settings, or steps. The higher the step number, the more the valve is retracting and opening the air passage around the throttle blade. Step 32 is typical for a properly running engine. If you find it is much higher than that, the computer is trying to raise engine speed without success. Remove the AIS motor and check for carbon buildup in the passage. This isn't too common anymore with the newer, cleaner fuels.

Most scanners will also be able to test the AIS function by commanding an increase in engine speed. The Chrysler scanners will go up to 2000 rpm. If no change occurs, you have to determine if the motor is not turning or if the air passage is plugged.

If none of these suggestions shed light on the problem, we will have to go back to looking for spark and fuel pressure when the no-start occurs. It's important to check for both if you find one of them missing. There are three systems; the spark, the fuel supply, and the trigger circuit that affects both of them. The trigger circuit is the most common one to cause a no-start.

Caradiodoc