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Unread 03-16-2015, 02:27 PM   #1
CamoX413
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1996 ZJ 
 
Join Date: Feb 2015
Location: denver, colorado
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misfiring help

everybody I'm having a problem out of my jeep today. I started up and ran fine i ran the air conditioner for a little while because it's 80 degrees here today I went into the store and came back out started up the Jeep and it started misfiring Idled pretty low but never died. it stopped after a few minutes but it keeps doing it intermittently.

I've got new plugs, plug wires, recent oil change. Also no CEL

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Unread 03-16-2015, 02:33 PM   #2
CamoX413
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Also new TPS sensor
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Unread 03-16-2015, 02:42 PM   #3
MrRoundel
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Do you have a fuel-pressure gauge to check the fuel-pump? It sounds like it could be fuel, especially since you've replaced the ignition wires, etc. Are the cap and rotor new as well? Regardless, you might want to pull it and look at the contacts, etc., to see if anything stands out. Good luck.
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Unread 03-16-2015, 02:45 PM   #4
CamoX413
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No fuel pressure gauge. Not sure even how to check fuel pressure lol. The cap and rotor are not new. I've been looking around for ones with brass contacts but haven't found any.
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Unread 03-16-2015, 03:14 PM   #5
MrRoundel
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You might try checking your battery and charging system. I've had some funky idling after jumping my bad battery. It would get very closet to stalling until it got a good charge on the battery. If you've got a digital multimeter, you can check the voltage across the battery terminals with car off and car running, and get some idea of the condition. I believe that you should have around 12.5 volts, with the car off, and over 13 with it running. As far as checking fuel pressure, IF one has a gauge, and had the injector fuel-rail that incorporates a schraeder-type valve, you can just thread the gauge fitting onto it, and get a read. Without one, I haven't the foggiest idea. Maybe if you have a dealer DRB scan tool. So I guess you check the things you have the tools for, and then either borrow some others, or take it to a reputable shop that knows Jeeps. Good luck.
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Unread 03-16-2015, 03:29 PM   #6
CamoX413
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okay I'll look into those suggestions and getting a fuel pressure gauge. My fuel rail does have what looks like a Schrader valve
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Unread 03-16-2015, 07:53 PM   #7
Uniblurb
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If you're running the OE fuel pump on your 96 there was a TSB (technical service bulletin issued for the 96 fuel pumps in particular. They are known to overheat and fail.

You may be able to borrow a loaner fuel pressure test kit at one of the area parts stores. Before connecting the gauge to the Schoeder valve let the pressure off by sticking a small object on the pin in the valve with a rag over it. You can also duct tape the gauge face to the windshield so you can see if the pressure stays stable as you drive around.

Fuel pressure spec should be 49psi +/- 5psi and the pressure shouldn't drop below 24 psi 10-20 min after shutdown or your check valve in the pump module could also be bad.

It should be noted if the fuel pump is bad it involves dropping down the fuel tank on the ground since the fuel pump module is in the tank.

Hard to beat the price of this brand new Bosch 67646 fuel pump module with free shipping and tank seal for $120. Bosch is now OE and Mopar just repackages them while selling them for over twice that price.

http://www.ebay.com/itm/New-Bosch-Fu...2512b8&vxp=mtr

Not saying this is exactly your problem and there's some real good info in the dirty dozen thread in my signature along with a couple crank sensor tests. Good luck!
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96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 93 4.0 XJ (spare), 96 4.0 XJ (son's)

-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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Unread 03-16-2015, 10:33 PM   #8
MrRoundel
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I told myself that the next time I attempted to insert the word that describes that tire-valve-like-thing into a sentence, I'd look up the proper spelling. I've spelled it at least 2-3 different ways, but haven't put the effort into finding out. Today was no different. So, CamoX413, you win. "S-c-h-r-a-d-e-r" does appear to be the correct spelling. Uni and I get the booby-prize. That said, I'm pretty sure that Uni usually spells it correctly. Were you messin' with me, Uni? Either way, I was about to spell it Schroeder, but that might upset a certain cartoon pianist and his lovestruck, antagonist girl-friend.

Interesting that in my travels I ran across another Schroeder, Stassi Schroeder. Whatever you do, don't check it out.

Good luck with tracking down the root of your ZJ issue.
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Unread 03-16-2015, 11:06 PM   #9
Uniblurb
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You've been watching waay to many Ricky Schroder movies MrR!

I have spell check and every time I type in schrader, or schroeder, valve it underlines it in red. But if I type in Schroeder it doesn't underline it as misspelled. Just who are they referring to where it has to be a capitalized and must be your cartoonist friend?? I'm not going to cap it, I did leave the "r" out of it last post, while Camo is correct!
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96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 93 4.0 XJ (spare), 96 4.0 XJ (son's)

-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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Unread 03-17-2015, 04:56 AM   #10
ZeeJay1997
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s.h.r.a.d... uh
s.c.h.r.o... uh
S.c.r.o.t... uh

call it a valve stem and you're good to go.http://en.wikipedia.org/wiki/Schrader_valve
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Unread 03-17-2015, 09:23 AM   #11
CamoX413
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I don't think I would have been able to spell it right either. I used the talk to text on my smartphone lol
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Unread 03-17-2015, 09:24 AM   #12
CamoX413
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I haven't had time to rent a fuel pressure gauge yet but will try this afternoon. I drove the Jeep for about 20 minutes this morning and there were no issues at all. I wonder if the 40 degree drop in temperature has anything to do with that
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Unread 03-17-2015, 10:23 AM   #13
Uniblurb
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Many parts can be temperature sensitive like the PCM, fuel pump, sensors, etc.. My bad fuel pump in my 96 4.0 would act up more when hot out. Also my faulty crank sensors malfunctioned more when cold or hot.

While it may not be your problem if you've only replaced the plugs/wires you've not done a complete tune-up. Below is a post of tune-up parts I used which included a brass contact cap and rotor.

http://www.jeepforum.com/forum/f13/s.../#post15809984

Those fuel pressure test kits aren't very pricey as can be seen below. May even find one cheaper at a parts store. But if you find a good parts store with a loaner one typically they charge full price, can keep for 30 days, while returning for a full refund.

http://www.amazon.com/Actron-CP7818-...ressure+tester

If you haven't changed your fuel filter in a while that's another maintenance item you can do while a good fuel injector cleaner/additive which can break down water helps.

As mentioned before there's some real good info in the dirty dozen thread in my signature. Look for the section on grounds and it's real important to have them good/clean. This is particularly important on the engine grounds where one of the grounds on the coil stud grounds the PCM which in turn grounds all the engine compartment sensors. Good luck.

PS. schrader or valve stem it is!
__________________
96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 93 4.0 XJ (spare), 96 4.0 XJ (son's)

-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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Unread 03-17-2015, 08:22 PM   #14
RedRiverT
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Join Date: Nov 2014
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The guys at the local parts stores have let me use the fuel pressure gauge out in the parking lot. I had a gas can with me to drain the hose into. They just hold my driver's license or credit card while I use it. It's easier than going through the whole "buy it then return it with a million keyboard clicks" process.
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Unread 03-17-2015, 08:42 PM   #15
RedRiverT
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Camo, you need to search on here, or simply go through the pages for the last couple on months. There are a lot of us on here who have had misfiring, dying, bucking, jerking, etc., episodes and there have been numerous things that are reported to have been the culprit. Like Uniblurb said, do the easy things on the 12 Things list first, like the grounds. They're all pretty easy. I haven't removed the alternator and cleaned its mounting surfaces yet, but mine is running fine now (knock on wood). My symptoms were significantly reduced after I cleaned the wiring connections of the back of the alternator and on the fuse box behind the battery (the Power Distribution Center). Yours sounds pretty mild right now, but it can go off the deep end quickly.
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