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Unread 12-02-2011, 03:32 PM   #76
The Rat
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I'm not gonna say the new crankshaft sensor didn't do anything...but I can't say that it did either. I think I need to pinpoint another issue because this didn't resolve it.

Managed to get it started and running without stalling earlier, then just now I got it running and it stalled completely dead as if nothing had happened. Haven't taken it for a drive, but let it run for about 15 minutes after disconnecting the battery.

Still open to suggestions. Should I break open the PCM and replace the capacitors anyway? Any other sensors that would cause an instantaneous loss of power?

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Unread 12-02-2011, 06:09 PM   #77
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Quote:
Originally Posted by The Rat View Post
I'm not gonna say the new crankshaft sensor didn't do anything...but I can't say that it did either. I think I need to pinpoint another issue because this didn't resolve it.

Managed to get it started and running without stalling earlier, then just now I got it running and it stalled completely dead as if nothing had happened. Haven't taken it for a drive, but let it run for about 15 minutes after disconnecting the battery.

Still open to suggestions. Should I break open the PCM and replace the capacitors anyway? Any other sensors that would cause an instantaneous loss of power?
If the CEL is lighting up as it should I do not think it is the problem. I would look for good vacuum to the MAP sensor and also check for any bad wiring in the harness under the hood. Problems that come and go are often wiring related.

Another thought... Do you have fuel pump wiring that is bad??
I would be moving all different parts of any wiring I could find while this rig is running just to see if you have a bad connection. An example is fuel injectors they share a common circuit. So do many of the sensors.
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Unread 12-02-2011, 06:34 PM   #78
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Yeah, been messing with all the wiring and vac lines and everything is good. I'm 90% sure that pumping the gas pedal has been helping it start...but I cannot for the life of me say why.

Is there any sort of relay or circuit that would cause a complete loss of power (or spark, considering it doesn't shudder but instead just die immediately) but only within like a minute of startup?
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Unread 12-02-2011, 06:40 PM   #79
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Got me thinking that also maybe I should get my battery load tested? Is it possible that a bad battery could hold a charge and crank the engine to no end but not be able to reliably start it and maintain the start?
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Unread 12-02-2011, 06:47 PM   #80
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i know my motor has to have a real good hot battery to start it, or it will just keep turning over and not run.
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Unread 12-02-2011, 08:14 PM   #81
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Quote:
Originally Posted by The Rat View Post
Yeah, been messing with all the wiring and vac lines and everything is good. I'm 90% sure that pumping the gas pedal has been helping it start...but I cannot for the life of me say why.

Is there any sort of relay or circuit that would cause a complete loss of power (or spark, considering it doesn't shudder but instead just die immediately) but only within like a minute of startup?
Quote:
Originally Posted by The Rat View Post
Got me thinking that also maybe I should get my battery load tested? Is it possible that a bad battery could hold a charge and crank the engine to no end but not be able to reliably start it and maintain the start?
The battery is part of the starter circuit. If it was NG it would go dead...often. If the alternator was NG you would eventually end up with a dead battery. Another tell tale sign you have a bad alternator is your headlight brightness would dramatically change with the RPM level of your engine.

OK, If pumping the pedal gets it going either it is not getting fuel OR the TPS is messed up. Is the throttle shaft in your TB loose/worn? That could cause your issues.

How about your coil? It produces high voltage. They can 'wink-in, wink-out' with no logic. Lose that = no spark and it shuts down. Fire this bad boy up and bang on the coil some! Hey, it doeesn't cost anything to bang on that devil.

Did you ever do the 'key thing' to see if there are any stored codes? Ignore 12 33 55.
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Unread 12-02-2011, 09:11 PM   #82
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I agree with above, when I'm at a loss I always like getting the engine running and tapping on all the components with the butt of a screwdriver or a tiny hammer, also, wiggle all the wires and lines and see if there's any change. Just watch for the moving parts........
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Unread 12-02-2011, 09:51 PM   #83
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Maybe you have a bad MAP sensor??

Try this; Unplug the electrical connection on the MAP sensor. Then attempt to fire her up. If it starts and runs well then I think the MAP sensor is NG.

If it doesn't start up or runs really crappy just plug the plug back into the MAP sensor. What does it do? If it runs well then maybe the MAP sesnor is OK.

Now while running pull the vacuum source to the MAP sensor. What happens? If it falters or stalls then the vacuum source or the vacuum line itself might be the problem.

The MAP is a variable resistor type of sensor. It takes engine vacuum and tells the PCM, in voltage, what the engine vac is. That is a back up signal to substantiate what other inputs are sent to the PCM.
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Unread 12-04-2011, 10:35 PM   #84
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Gonna get back to work and check all those things out tomorrow. Coil, MAP sensor, vac lines (which I'm sure are good), and basically tap on everything real good.

The battery definitely charges, so no bad alternator, but I would assume it would be under quite the load within the first minute or so of start-up, which is why I had the thought that maybe that was the problem. Might get it checked anyway if I get ambitious. Running out of time here, lost the weekend to schoolwork and babysitting my dog who I haven't seen in almost a year (picture related).
image-3255676156.jpg  
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Unread 12-05-2011, 12:11 PM   #85
The Rat
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MAP sensor is definitely good. Started it up with it plugged in and then unplugged it and it ran like garbage. Broke the vac line to the back of the valve cover by accident but fixed it, if I block it at all it starts to stall out.

Still the same issue though, idles perfectly fine and holds around 500rpm but requires some gas pedal finesse to start it. I can't even explain a definitive technique, but what I usually do is time my depressing the gas pedal with turning the key and it eventually starts up and will either run for about 45 seconds and stall or keep running and run just fine.
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Unread 12-05-2011, 12:24 PM   #86
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Just sat in it and let it run about 15 minutes. Eventually stalled out once I let it idle the entire time. No reason, no CEL on shut down. Put the pedal to the floor and cranked for a second to clear it out, then cranked it while pressing the pedal down and it sprung back to life. Signs of a bad TPS?
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Unread 12-05-2011, 02:06 PM   #87
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You said you were going to swap the tps in an earlier post; did you get a chance? Instead of shotgunning it by throwing parts, do you have a meter to check things out with?

Your issue sounds like the IAC.
http://www.jeepforum.com/forum/f12/q...-body-1262267/
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Unread 12-05-2011, 03:04 PM   #88
The Rat
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Quote:
Originally Posted by Que89YJ View Post
You said you were going to swap the tps in an earlier post; did you get a chance? Instead of shotgunning it by throwing parts, do you have a meter to check things out with?

Your issue sounds like the IAC.
http://www.jeepforum.com/forum/f12/q...-body-1262267/
Didn't have a chance, the TPS I grabbed for my buddy was a different style. It isn't showing a code or anything, so I can't really justify why I think it would be the TPS other than the fact that starting it while pumping the pedal seems to work. I looked up how to test it, and I don't get how I would test voltage across connectors while they are connected.

Already cleaned the IAC when I pulled the TB.
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Unread 12-05-2011, 03:20 PM   #89
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Quote:
Originally Posted by The Rat View Post
Didn't have a chance, the TPS I grabbed for my buddy was a different style. It isn't showing a code or anything, so I can't really justify why I think it would be the TPS other than the fact that starting it while pumping the pedal seems to work. I looked up how to test it, and I don't get how I would test voltage across connectors while they are connected.

Already cleaned the IAC when I pulled the TB.
You have to 'back probe' them. Go to Michaels and get some stout straight pins, or use a 4pd finish nail. With the plug installed on the sensor you can stick them through the wire insulation or the back side of the plug then use your multimeter to measure the values you are looking for.

Older YJ.....If you have any bad wiring in the harness you can get intermittent lost continuity for either a signal or a ground. EXAMPLE: if the ASD relay or VSS or any other sensor you have does not send or get a signal it expects to get or send, the engine dies.

Before I threw any more money at this engine I would strip the engine harness of every strip of covering it has and look for a bad connection.
Your pumping the pedal to get it going would make one think that the TPS is the problem. Unplug it and attempt to fire it up.
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Unread 12-05-2011, 03:30 PM   #90
The Rat
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Wouldn't unplugging the TPS cause it to not start anyway?
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