Cranks, no start after full engine rebuild. - JeepForum.com
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post #1 of 10 Old 06-01-2020, 08:50 PM Thread Starter
max.
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Cranks, no start after full engine rebuild.

Hey everyone, I finally am trying to start my 2002 Jeep Wrangler sport with the 4.0 after a full rebuild. I already read through Chris's post on no starts and had no luck.
Here's my problem: jeep starts cranking, sounds good but after 3-5 seconds I'm getting low voltage so it starts doing that slow crank where it isn't really turning the engine anymore.

All grounds seem to be good, I wore brushed the battery connections, battery is new (bought it like 2 months ago but hadn't used it yet). It's an Acdelco size 34. Maybe it's just a sh*tty battery? I hooked up the ol jumper/booster box which gave it some powerful cranks for several seconds.

Testing for spark: I pulled the coil pack off and used a spark plug in the first 3 slots on the coil pack with the spark plug grounded to the battery. Got spark at 3 (I really could have done all 6 but i didn't wanna keep cranking it).

Fuel: I got a fuel pressure tester, hooked it up to the shrader valve, I get around 30-40 psi which somewhat quickly falls off to 20 and several minutes later 10. Similar to what my grand Cherokee does. Slightly lower than the 49psi I've been seeing but it can't be that bad right? I tested the fuel injectors resistance, all around 12 ohms.

Crankshaft position sensor: I replaced my broken off one with the spectrum premium s10074 from rockauto. Confirmed I had it hooked up, the connector is near the passenger side of the engine. Might just be my wiring.

I can barely turn the engine over by hand with a 1/2" ratchet (I'm not that strong, skinny college student). It is a fresh rebuild and I tried cranking it over a good amount so I'm assuming it's that? My '02 grand Cherokee for comparison was pretty easy to turn but has 190k on it and I didn't try starting it a bunch.

Any ideas on where I should look next? Is my battery not strong enough to power the starter for long enough? I still have the old battery which I could try and use next.

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post #2 of 10 Old 06-02-2020, 07:01 AM
BM3
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Fuel pressure should be 49 5 psi, you can try starting it with starter fluid. If it starts off that it would lead to a fuel delivery problem. I'm sure someone with more experience will chime in with some better info.
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post #3 of 10 Old 06-02-2020, 01:48 PM Thread Starter
max.
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Sprayed 3 seconds worth of starting fluid into the throttle bottle, still no start. Only cranks hard for about 2-3 seconds after full battery charging. All fuel injectors work, tested using a 9v battery. Doesn't mean it's getting enough fuel though for sure. Maybe my spark is off?
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post #4 of 10 Old 06-02-2020, 02:04 PM
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If you can get your plug to spark numerous times while testing the coil rail, that should indicate your crank sensor is working. BM3 gave good advice about using some starter fluid to see if the engine will at least briefly fire up; it does sound like your fuel pump is underperforming as well, though 40psi should be enough to get it to fire and idle. If the starter fluid gets things going briefly, I would advise you recheck your cam sensor install position and verify the injectors are working with a noid light before pressing on with further pump troubleshooting.

Your concern over the battery seems valid -- although it's new that doesn't necessarily mean it's fully charged or has a good cranking amp capacity.

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post #5 of 10 Old 06-02-2020, 02:08 PM Thread Starter
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Quote:
Originally Posted by mukluk View Post
If you can get your plug to spark numerous times while testing the coil rail, that should indicate your crank sensor is working. BM3 gave good advice about using some starter fluid to see if the engine will at least briefly fire up; it does sound like your fuel pump is underperforming as well, though 40psi should be enough to get it to fire and idle. If the starter fluid gets things going briefly, I would advise you recheck your cam sensor install position and verify the injectors are working with a noid light before pressing on with further pump troubleshooting.

Your concern over the battery seems valid -- although it's new that doesn't necessarily mean it's fully charged or has a good cranking amp capacity.
Hey, thanks for the tips, I don't have a noid light but I can look into getting one. How would I check cam sensor install other than it's plugged in? I am not sure what the name of the metal thing that sits in the hole that has the cam sensor attached but I used a drill to spin the oil pump before starting the first time. Does the exact orientation of the little slot matter? I just plopped the metal thing with the camshaft position sensor back on and tightened it down.
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post #6 of 10 Old 06-02-2020, 02:09 PM Thread Starter
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Also, any other ways to check for spark?
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post #7 of 10 Old 06-02-2020, 02:13 PM
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The cam sensor position is critical in that its signal correlation with the crank sensor signal is used by the PCM to determine the crankshaft's rotational position, thus both the ignition and injector timing. See the attachments below for the proper install procedure.
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post #8 of 10 Old 06-02-2020, 02:17 PM Thread Starter
max.
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Quote:
Originally Posted by mukluk View Post
The cam sensor position is critical in that its signal correlation with the crank sensor signal is used by the PCM to determine the crankshaft's rotational position, thus both the ignition and injector timing. See the attachments below for the proper install procedure.
Awww man this looks like work and thinking... It's 90 here today. I'll update here with progress or questions 🙂 thank you, I was not aware of this though.
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post #9 of 10 Old 06-02-2020, 05:10 PM Thread Starter
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Update: it's finally running!!! Thanks for your guys help! It was the camshaft position sensor/ oil pump driver! So happy
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post #10 of 10 Old 06-02-2020, 05:12 PM
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Glad you got it sorted.

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