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  #1  
Old 10-12-2014, 12:44 PM
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Starting "Issue"

For the past 4-5 days my Jeep has intermittently had rough starting. Some times the Jeep will start up just like normal, the RPM jumps to about 1100rpm and quickly settles to about 800rpm. Then some times I will crank it, it will start almost like it's bogged around 500rpm, and then settle to 800rpm. Then today for the first time it failed to start on the first try and I had to try a second time before it started.

I've read that sometimes hard starts can be caused by a failing o-ring in the fuel pump. Possibly the issue here? I find it odd that it will hang at 500rpm on starting before jumping to the normal idle rpm. I'm almost wondering if it's a fuel issue or a sensor issue.

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  #2  
Old 10-12-2014, 01:36 PM
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Re: Starting "Issue"

I think that the failing O-ring in the fuel pump connection would cause more wide problems then only at start. You could check the fuel pressure at the fuel rail after some time engine off. Normal pressure is around 45 PSI and the fuel pressure regulator should keep the pressure (or at least the fuel) in the lines. A bad pressure regulator could drain the fuel back to the tank, with extended crank times as a result.
Other then this, are the IAC plunjer and air canal clean?
If you have a scanner which shows live data, you could check the TPS, which should be around 12% at idle.
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  #3  
Old 10-12-2014, 04:39 PM
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Re: Starting "Issue"

Quote:
Originally Posted by Frango100 View Post
Other then this, are the IAC plunjer and air canal clean?
If you have a scanner which shows live data, you could check the TPS, which should be around 12% at idle.
I doubt the IAC plunger and air canal are super clean. I've never cleaned them and the Jeep has 160k miles. But I wouldn't think it's the IAC because it idles perfect. When you normally start the engine there's a 1/2 second where the idle is at about 1200rpm and then quickly comes down to the 800rpm idle. This is like that except it bogs at 500rpm for 1/2 second and then comes to the 800rpm idle and idles fine. I'll see if I can get a video of it sometime (I tried now but it's starting just fine at the moment).

I do have the Torque app and adapter. The idle measures 10.6%-11% throttle.

I was reading the TSB below and it appears that if the fuel system doesn't hold pressure it would be the fuel pump. I'll rent a pressure tester and see if it measures ~45psi when I turn the key on and if it holds it above 30psi for 5 minutes.
http://www.wjjeeps.com/tsb/tsb_wj_1400201.pdf
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Old 10-12-2014, 06:02 PM
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Re: Starting "Issue"

I rented a fuel pressure tester. I'm not sure if this is a fuel issue or not. Of course, it was starting just fine when I did this. So I'm going to wait for a couple days with the tester in the Jeep and wait for it to happen and test at that point.

Running (60 PSI):


Engine Off, Key On (48 PSI)


After waiting 5 minutes with key off (45 PSI)
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Old 10-12-2014, 06:45 PM
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Re: Starting "Issue"

If the O-ring is the problem, you would have a low fuel pressure all the time. The fuel filter/pressure regulator will keep the pressure on the fuel rail when the engine (ignition) is off.
I would for sure check/clean the IAC plunjer, because that one will regulate the idle speed. For sure it will be DIRTY after so long used and never been cleaned.
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Old 10-12-2014, 07:10 PM
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Re: Starting "Issue"

Quote:
Originally Posted by Frango100 View Post
If the O-ring is the problem, you would have a low fuel pressure all the time. The fuel filter/pressure regulator will keep the pressure on the fuel rail when the engine (ignition) is off.
Ok, that's good information to know and I'll put that in memory. Since it did hold pressure, I'm going to rule both of those out.

Quote:
Originally Posted by Frango100 View Post
I would for sure check/clean the IAC plunjer, because that one will regulate the idle speed. For sure it will be DIRTY after so long used and never been cleaned.
I'll take it apart and clean it tomorrow.
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Old 10-14-2014, 03:48 PM
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Re: Starting "Issue"

I cleaned the IAC and TB and it doesn't appear to have done anything. I did happen to catch the issue on video and one of normal starting. Any ideas?

Normal:
http://vid184.photobucket.com/albums...psrbxjcbfd.mp4

Issue:
http://vid184.photobucket.com/albums...ps8mhr54am.mp4
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Old 10-15-2014, 04:42 AM
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Re: Starting "Issue"

You did mention the idle TPS % between 10.6 and 11. It should be a steady indication (when you don´t touch the accelerator ofcourse). I would monitor the TPS during starts and see if it changes, the times when it starts with the low rpm.
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Old 10-15-2014, 07:48 AM
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Re: Starting "Issue"

Quote:
Originally Posted by Frango100 View Post
You did mention the idle TPS % between 10.6 and 11. It should be a steady indication (when you don´t touch the accelerator ofcourse). I would monitor the TPS during starts and see if it changes, the times when it starts with the low rpm.
I think fluctuate might have been a poor choice of words on my part. It appears the resolution of the measurement is in 0.4% increments. So 95% of the time it will measure 11% and for a second it will change to 10.6% and then back to 11%. This tells me it's holding steady right at the change in resolution value. I'll try to take a video of the normal reading.

I'm still trying to get a reading with a bad start. I will report back then.
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Old 10-16-2014, 09:04 AM
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Re: Starting "Issue"

I do not recall that the TPS changes with 0.4% increments, but it can be that I did not pay attention to it.
However it could also be your problem. I never saw any change in the TPS % when at idle.
I'm not 100% sure about this, but I presume that the PCM takes the powerup TPS % as an idle reference. If then the % goes down during starting, it could shorten the injector pulse and inject less fuel, with a lower rpm as a result.
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Old 10-16-2014, 05:43 PM
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Re: Starting "Issue"

Quote:
Originally Posted by Frango100 View Post
I do not recall that the TPS changes with 0.4% increments, but it can be that I did not pay attention to it.
However it could also be your problem. I never saw any change in the TPS % when at idle.
I'm not 100% sure about this, but I presume that the PCM takes the powerup TPS % as an idle reference. If then the % goes down during starting, it could shorten the injector pulse and inject less fuel, with a lower rpm as a result.
I managed to data log the event and a normal start up. Normally, when idling the torque app shows 11% throttle on a digital readout and will briefly drop to 10.6% before going back to 11%. I data logged it taking a reading every 1/4 second. Normally it runs at 10.9804. About once ever 20 seconds for a single reading it goes to 10.5882. So for a 1/4 second it drops from 10.9804 to 10.5882. When the key is simply in the on position and the engine off, it reads 10.5882.

When I logged the issue, the throttle stays at 10.5882 until it gets up to normal idle speed and then goes to 10.9804.

I still don't know what to do here.
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Old 10-16-2014, 07:42 PM
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Re: Starting "Issue"

As long as the starting is not getting worse, i would not bother too much. Still would expect the TPS to be the troublemaker here.
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