99 XJ Hard Starting - JeepForum.com
 
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post #1 of 8 Old 11-16-2013, 10:19 AM Thread Starter
99XJPilot
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99 XJ Hard Starting

Just bought a XJ about a month ago and having some problems starting when cold. I've read alot of the threads on many forum's but I want some opinions. It starts fine when I've drive it for awhile. But when it sits for alittle bit then it will crank and crank. I have to press the gas pedal all the way to the floor just to get it started. When it does start it runs like crap for a min or so, then it runs perfectly fine. Ok things that I've already replaced. I've replaced the TPS, Fuel check valve (fuel pressure reg), IAC valve, IAT (intake air temp), spark plugs, spark plug wires, & cap and rotor. I've cleaned the throttle body. I've also checked the fuel pressure, which is fine. I'm starting to think it's a Crankshaft position sensor or a bad ground somewhere. The battery and alternator is good. There is a check engine light. I scaned it with a Snap-On Solus and it comes up with a cylinder 5 misfire, which I think is cause by the rough ilde when it does decide to start. Any suggestions on what I should check or replace?

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post #2 of 8 Old 11-16-2013, 10:50 AM
tjwalker
It's the crank sensor!
 
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A good (and simple) first step in helping you troubleshoot this problem is called “the poor mans prime”

1. Turn key to ON position (do not crank the engine!)
2. The fuel pump will energize and run for about 2 seconds. Be sure to wait until it stops running.
3. Turn key to OFF position
4. Repeat above steps 1-3 two more times
5. NOW crank the engine over

If the engine starts quickly and cleanly after performing this procedure, you may have a check valve issue. Know that there are two check valves. The primary one is on the regulator and the secondary one is on the fuel pump itself. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the fuel pressure leaking down and the subsequent stumble upon startup is the engine clearing the excess fuel that has leaked into the cylinder because of the faulty injector. Possibly cylinder #5 in your case.

99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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post #3 of 8 Old 11-16-2013, 11:04 AM Thread Starter
99XJPilot
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I've done the "poor man's prime" and that has little or no effect. I didn't know that there was two check valves. I just thought it was built in the fuel pressure reg. But if the injector or check valve was bad then I should see a pressure drop. Right? When I perform the fuel pressure test both running and before start up, they never fell below 45 psi.
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post #4 of 8 Old 11-16-2013, 11:19 AM
tjwalker
It's the crank sensor!
 
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As for engine management sensors, the one that comes to mind that could be related is the "coolant temp sensor", located on the thermostat housing.

If that sensor sends incorrect input data to the computer, it might think the engine was cold when it actually is hot and or vice versa. Which can mean tough starting for a hot engine. This sensor can be tested, but proper testing is a PITA. You can perform a simple test of checking resistance with a cold engine vs a hot engine and compare to the specs found in your repair manual. If any doubt, replace the sensor.

This does NOT sound like a crankshaft position sensor issue to me. Freshening grounds is never a bad idea. Wouldn't hurt to get some compression readings on this "new-to-you" vehicle, especially with a mystery misfire on cylinder #5. Swapping the #5 injector with a different cylinder also not a bad idea.

Where did you buy your throttle position sensor (what brand?). I have had very poor luck with many aftermarket TPS sensors; I buy mine exclusively from Jeep.

99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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post #5 of 8 Old 11-16-2013, 11:22 AM Thread Starter
99XJPilot
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Ok sounds good! Thanks for your help! I will look at it tonight. I will post later tomorrow or tonight, if that fixed my problem.
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post #6 of 8 Old 11-16-2013, 11:32 AM Thread Starter
99XJPilot
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I bought everything from autozone. Yea I'm not a big fan of aftermarket parts but I'm on a budget since I'm a college student. lol
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post #7 of 8 Old 11-16-2013, 11:46 AM Thread Starter
99XJPilot
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Also I've unplugged the CPS and then it starts fine. So that's why I was kinda leaning towards the CPS.
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post #8 of 8 Old 11-16-2013, 04:37 PM
tjwalker
It's the crank sensor!
 
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Quote:
Originally Posted by 99XJPilot View Post
Also I've unplugged the CPS and then it starts fine. So that's why I was kinda leaning towards the CPS.
ummmm, you must have unplugged something else.

If the crank sensor is unplugged, you will have NO spark and NO fuel going to the fuel injectors. Guaranteed!

99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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