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Old 01-12-2012, 08:47 AM
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Starting Irritation and Crank Position Sensor

I have a small irritation on my WJ and I took it to a workshop to have it sorted out.

Basically when I get to my Jeep it rarely starts on the first turn of the key. It cranks over strongly, but you have to crank it for a while before it starts, and then it will idle roughly before settling.

However, if you crank it only for a second or so on the first start attempt, it will usually start immediately on the second attempt and idling and so is usually fine very quickly.

The workshop measured my fuel pressure (as that seemed like a good place to start according to JeepsUnlimited and JeepGarage), but it all checked out fine, no injectors are leaking and the pressure is constant.

They then scanned all the error codes and the only weird one is for the CPS. Could the CPS cause this and is it worth replacing it as it is quite expensive ?
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Old 01-12-2012, 10:20 AM
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Re: Starting Irritation and Crank Position Sensor

This sounds more as that the fuel pressure goes down to 0 after a while. When you prime it first, it seems to be ok. There where some issues with an Oring of the fuelpump going bad. Im not sure, but i think that the pressure regulator in the filter/regulator assy, should keep the pressure with engine off. Before you start the engine, check if there is pressure in the fuel rail by pressing the schrader valve on the rail. When fuel comes out under pressure, then that is not your problem.
Regarding the CPS, i would clear the faults and check if it comes back again.
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Old 01-12-2012, 04:17 PM
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Re: Starting Irritation and Crank Position Sensor

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Originally Posted by Frango100 View Post
This sounds more as that the fuel pressure goes down to 0 after a while. When you prime it first, it seems to be ok. There where some issues with an Oring of the fuelpump going bad. Im not sure, but i think that the pressure regulator in the filter/regulator assy, should keep the pressure with engine off. Before you start the engine, check if there is pressure in the fuel rail by pressing the schrader valve on the rail. When fuel comes out under pressure, then that is not your problem.
Regarding the CPS, i would clear the faults and check if it comes back again.

This!

Pretty common for them to fail in this way, allowing residual pressure to drain back into the tank. This way when you go to start it it must re-pressurize the system before it gets enough fuel coming out of the injectors to run. With the fuel pressure gauge installed it must maintain most of its pressure (above 35psi) for at least 5 minutes or your likely going to need a pump assembly.
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Old 01-25-2012, 04:13 AM
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Re: Starting Irritation and Crank Position Sensor

Quick update:

I have replaced the Crank Position Sensor and the Throttle Position Sensor, but the problem still persists. I have not measured the fuel pressure myself, but checked for fuel at the schrader valve on the fuel rail. After an hour of the car standing there is still fuel spraying out the valve. However after the Jeep standing for a day there is no pressure at the valve anymore.

Seems to be fuel pump / o-ring right ?
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Old 01-25-2012, 04:23 AM
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Re: Starting Irritation and Crank Position Sensor

I would say so yes. I have the same problem, but it's very intermittent, about once or twice a year. It will play up for about a week, then for months it's fine.

I had to replace my CPS a while back. Symptoms were the engine feeling like it was stalling while drving, but it didn't actually cut out.

At the moment this problem has reared its ugly head again, so it's probably time for me to fix it once and for all.
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Old 01-25-2012, 10:15 AM
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Re: Starting Irritation and Crank Position Sensor

To be sure that the problem is not with the fuel pressure regulator, i would change the filter/pressure regulator first. (at least when its externally of the tank, as on my jeep)
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Old 01-25-2012, 02:31 PM
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Re: Starting Irritation and Crank Position Sensor

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Originally Posted by Frango100 View Post
To be sure that the problem is not with the fuel pressure regulator, i would change the filter/pressure regulator first. (at least when its externally of the tank, as on my jeep)
X2 on the regulator although our '99 has been that way for years. Just too lazy to change it and if its the fuel pump it probably wont get changed until it quits. It's nothing more than a minor inconvenience for us. I just cycle the key twice before starting the first time of the day. No problems once it's already been running though.
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Old 01-25-2012, 03:01 PM
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Re: Starting Irritation and Crank Position Sensor

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Originally Posted by cheapjeep View Post
X2 on the regulator although our '99 has been that way for years. Just too lazy to change it and if its the fuel pump it probably wont get changed until it quits. It's nothing more than a minor inconvenience for us. I just cycle the key twice before starting the first time of the day. No problems once it's already been running though.
You're almost as lazy as me Dave


Almost...
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Old 01-25-2012, 03:18 PM
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Re: Starting Irritation and Crank Position Sensor

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Originally Posted by StoneCold View Post
You're almost as lazy as me Dave


Almost...
^^^ You ever notice how much you enjoy working on things that don't need fixing like moddin our Jeeps,but it's like going to the dentist to work on something that actually NEEDS fixed?
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Old 01-25-2012, 03:22 PM
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Re: Starting Irritation and Crank Position Sensor

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Originally Posted by cheapjeep View Post
^^^ You ever notice how much you enjoy working on things that don't need fixing like moddin our Jeeps,but it's like going to the dentist to work on something that actually NEEDS fixed?
Ha ha ha ha! Yep!

I'm badly needing to fit my akebonos. I've had them for months, but I'm gonna do the dash cluster bulbs next.

Brakes who needs 'em lol.
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Old 01-26-2012, 01:09 PM
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Re: Starting Irritation and Crank Position Sensor

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Originally Posted by cheapjeep View Post
X2 on the regulator although our '99 has been that way for years.
I have now replaced the CKP, CMP and TPS sensors, but with little effect. I guess next up is the fuel filter/regulator.
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Old 01-27-2012, 11:25 AM
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Re: Starting Irritation and Crank Position Sensor

Quick update:

So I went out to continue my "daily diagnoses" of the problem when the Jeep would not start at all, no matter how long I primed and/or cranked the engine. I then checked for fuel at the schrader valve, again nothing, but this time permanently, I could not get fuel to the rail with priming/cranking.

I guess my fuel pump has left the building so to speak. Is there a chance though that it could be the fuel filter/pressure regulator somehow, or is this now definitive ?
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