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Old 05-12-2009, 01:21 PM   #1
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Turns But Won't Start... Not an easy answer

Ok, I'll be detailed...

On a long trip home I found that my 98 Jeep TJ (4.0) was not starting well. I could get it to turn over but not start. I'd wait a few minutes and pump the gas and it would eventually start and I continued on my way. This happened three separate times and then twenty min. down the road after the third odd start I got a stutter and loss of rpm so I immediately pulled off the highway and it will not start in any way... Its been towed home and I've done some checks so here are the facts:

When adding starter fluid to the intake the engine will start for a second or so... thus, this is a fuel issue. (correct?)

I stupidly replaced the fuel pump and filters automatically first without checking that it worked I can confirm that the new one has power and is pushing gas all the way through the line.

The lines are clean and maintaining pressure.

The cps sensor does have power and appears to be fine.

I assume all of the fuel injectors are not clogged as some miraculous simultaneous full blockage of all of them is insane to consider. (right?)

The only thing I can think of is the computer, and when I say computer I'm not completely sure what I would need to replace or how to check it. (I'm not electrical savvy)

How should I proceed, what can I do to check for the computer or any other problems you can think of that fit the facts? I just need a bit of help before I toss out more money guess and checking....

Thanks in advance!

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Old 05-12-2009, 01:53 PM   #2
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That it runs with starter fluid and the fuel pump is known to be good means something is not allowing the ECM (engine computer) to turn the fuel pump on. I'd first suspect your CPS (crankshaft position sensor) has gone bad, or perhaps (but less likely) the "other" CPS which is the camshaft position sensor.

The crankshaft position sensor is mounted up high on the driver's side where the transmission bolts to the engine. It generates the engine's master timing signal off the flywheel and when it doesn't work, the engine won't run. If you have a low-voltage AC meter, unplug the sensor and see if it generates a voltage while the engine is being cranked. I think it's only 3 or 4 volts AC if I recall correctly. If no voltage is being generated, it's bad.

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Old 05-12-2009, 05:54 PM   #3
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Ok perhaps I have checked the wrong sensor because the one on the high drivers side of the trans is the one I checked. As far as the fuel pump it's getting power. It has refilled the fuel line after I released the pressure several times and it hums at key turn. I'm not able to get fuel from the end of the lime into the engine, there is the problem...

So does that change or help the suggestions?
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Old 05-12-2009, 06:07 PM   #4
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Quote:
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Ok perhaps I have checked the wrong sensor because the one on the high drivers side of the trans is the one I checked. As far as the fuel pump it's getting power. It has refilled the fuel line after I released the pressure several times and it hums at key turn. I'm not able to get fuel from the end of the lime into the engine, there is the problem...

So does that change or help the suggestions?
The sensor you described is the crankshaft position sensor. If the ECM (engine computer module) is not happy with all its inputs like from the crankshaft or camshaft position sensors, it will not give power to the ASD (auto shutdown) relay which is required for the ignition to provide spark and for the fuel pump to run after it has initially filled the fuel lines.

Also, you may be measuring power at the crankshaft position sensor but that's only a floating voltage from the ECM. When working properly, the CPS actually generates a low voltage AC timing signal that "rides along" on top of that DC voltage you measured when the engine is turning over or running.
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Old 05-13-2009, 06:33 PM   #5
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ok well there went a new crankshaft position sensor and a new camshaft sensor or a pickup coil as they call it at the store. No new luck. I was told it may be the computer... major suckage... but im still open for suggestions, like a relay or some other thing that I may have overlooked. thanks
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Old 05-14-2009, 06:24 PM   #6
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Problem solved, as it turns out in my annoyed haste I switched the asd and fuel pump relay after installing the fuel pump and failing to get the jeep to start. This actually presented the same problem as I had before but it turns out the darn relay was dead. after replacing the sensors and fuel pump I got angered and replaced all the fuses and relays and bam the thing works fine. So long story short I learned a ton and got the parts returned minus the fuel pump (chalk that one up to maintenance) and the thing is done.

if you ever have the problem and read this thread, spend the 20 bucks and replace the relays first and then bs around lol
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Old 06-24-2009, 02:47 PM   #7
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Anyone know the part number for the ASD relay? I wont get out of work and back to my jeep before the shop closes and don't have my service manual on this computer to lookit up.
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Old 06-24-2009, 02:59 PM   #8
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For the next person who has this issue, don't swap the ASD and fuel pump relays between each other since either relay (if one is bad) will prevent it from starting. In other words, it won't change the symptom if indeed one of them is bad. Instead, swap the ASD and fuel pump relays one at a time with something like the horn relay which also means you can easily test the relay with the horn button.
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Old 06-24-2009, 03:00 PM   #9
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I'm not 100% sure but I thought that a couple of those relays in the fuse box have the same number listed on them. If so you should be able to match up at the autostore.

Hmmm... now that I think abot it maybe it was only the Starter, Fog & Horn that share the same. Take a look to see if its that easy.

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Old 06-24-2009, 03:03 PM   #10
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If I recall correctly Chris, it's only the starter relay that is different (it is physically bigger) and most if not all of the other relays are the same.
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Old 06-24-2009, 03:13 PM   #11
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Quote:
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If I recall correctly Chris, it's only the starter relay that is different (it is physically bigger) and most if not all of the other relays are the same.
jerry, does that include the interrior of the jeep? I'm pretty sure I still have a brand new turn signal relay that i never returned, could that work?
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Old 06-24-2009, 03:48 PM   #12
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I was only referring to the relays inside the PDC (power distribution center). I don't believe the turn signal relay is the same physical size or pin layout as the ASD, fuel pump, or horn relays are.
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Old 06-24-2009, 05:19 PM   #13
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no i just checked. they definitely aren't.
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Old 06-24-2009, 05:30 PM   #14
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A little differnt now...

So i was starting to believe that I was in this same boat, but it started up fine and now is just wicked boggy on the acceleration.. if it was electrical, say relays or sensors, wouldnt the check engine light come on? Also if its the fuel line where should i begin? would the fuel filter/pressure regulator switch the check engine light on too?
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Old 06-24-2009, 06:16 PM   #15
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I am not 100% sure but I think the last time I was going to replace a fuel filter on a wrangler the filter was only obtainable with the purchase of sending unit and pump assembly May be not but it does sit on top of the sending unit and you can only get to it by dropping the tank.
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Old 06-24-2009, 06:30 PM   #16
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I'd give a snowball's chance in hell that this kind of problem could be even possibly the result of a clogged fuel filter. The TJ's fuel filter is positively huge, surface area-wise, and is considered by the factory as a lifetime filter that will never need replacing.

To reinforce that view, as explained by slf41002, Jeep engineering placed it inside the fuel pressure regulator that sits atop the fuel pump. It cannot be replaced without dropping the gas tank and replacing the fuel pressure regulator. It's nothing like the old fuel filters located in the engine compartment that we either replaced regularly or flushed backwards with gasoline.
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Old 06-24-2009, 07:29 PM   #17
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well i dunno what the heck is going on here, but shes working absolutely fine right now,..... checked all the plugs and they're in normal condition, could be replaced, so plan on throwin in champions tomorrow. i'm starting to think that it might have just been moisture build up in the tank, so when i put in dry gas on monday(with a full tank) just took a little time to get through the fuel line and into the chamber.
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Old 06-25-2009, 06:33 AM   #18
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You might want to check your O2 sensor for a bare wire, a buddy of mine had the same problem and was burnin relays left and right, was a bare wire on the O2 sensor grounding out........ just a thought.......
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Old 06-25-2009, 07:12 AM   #19
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http://www.wranglerforum.com/f5/97-2...des-32483.html check engine light finally came on and got a whole bunch of codes i thought i should just start a new thread for this issue.

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