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Unread 09-06-2013, 11:34 AM   #1
JoeZedJ
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1996 ZJ 
 
Join Date: Aug 2012
Location: Shelton, Washington
Posts: 18
Fuel pump? Injectors? 4.0 ZJ running poorly, misfires, hesitates

Hi All,

Ok my diagnostic abilities are starting to run out on my '96 ZJ 4.0 and need some assistance. My Heep for quite a while has been, every now and then, seeming to misfire. It almost instantly jumps and runs "ok". I have never been satisfied that it has been running in normal condition. I have read through tons of threads trying to diagnose my issue. It seems like the RPM needle is always bouncing, never just solid on RPMs, at idle or any straight driving. I one time got a CEL code of "Random Misfire" and "Cylinder 1 Misfire" at the same time. I changed the plugs/wires etc. after that, never got the code again. Still seemed to run the same...

Recently things have been getting worse. One day she just shut down on me while driving, nothing, would turn over but no start. I rolled it home, ended up replacing my CPS, go figure. It started right back up ran great for about a week. Now its starting to "misfire", lack of response/hesitation when I hit the pedal. I am starting to think I have a fuel delivery problem. Fuel pump maybe? Possibly an injector problem? My question is how do I really test things out to see if its one or the other?

Here is what I have done to date to rule out (hopefully) any other ZJ related issues:

-New fuel filter (Wix about 5k ago)
-New CPS
-New TPS
-New MAP sensor
-All new plugs, wires, coil, cap and rotor (OEM specs)
-No fouled plugs or cap
-Going to clean the IAC today just for S&G
Like I mentioned I am leaning towards fuel delivery at this point, before I drop the few hundred bones on a new pump assembly I wanted to ensure a good way to just test the pump out, any help on that would be great!

Thanks guys...


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'96 ZJ 4.0 Laredo
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Unread 09-06-2013, 01:56 PM   #2
Oldfrog
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1997 ZJ 
 
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Did you install a Mopar crank sensor?

Clean your throttle body, clean and tighten your grounds, check your battery voltage and then read this thread:
http://www.jeepforum.com/forum/f13/1...talls-1407423/
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Unread 09-06-2013, 02:05 PM   #3
sebian
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Not just the crank, but the other sensors should be Mopar as well. The Jeeps are like PMS'ing women when it comes to sensors!
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Unread 09-06-2013, 03:01 PM   #4
JoeZedJ
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Join Date: Aug 2012
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Thanks Oldfrog and sebian, no I didn't use Mopar sensors, just the ones from O-Reilly's/Schmucks...

My grounds, battery etc. very clean, I'll post up some pics soon. I am also going to video a drive and hopefully catch the symptoms. I'll post that up as well. The thread you mentioned is interesting, I have read it and will work on the easy items first. I.e. swapping the fuel pump relay...

This is why owning a Jeep is so much fun right?

Cheers!
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Unread 09-06-2013, 05:11 PM   #5
JoeZedJ
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Location: Shelton, Washington
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Cleaned etc.

Ok so I cleaned the IAC, it was gunked up, not ridiculous though. Cleaned up the TB as well, had some decent carbon deposits around the plenum. Re installed everything, and then swapped my fuel pump relay with the horn. Took it for a quick spin around the 'hood, didn't really notice anything. No "misfires" but still seems to be hesitating slightly when I hit the gas. Idle might have improved a bit.

I will drive it later on again for a longer run and see how it does when I go pickup my fuel pressure tester from the store. There are some steep grades which will help.

Will be awesome if its just a relay issue...one can only hope.
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Unread 09-06-2013, 05:23 PM   #6
dusterdude
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Install a mopar cps,that should fix you
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Unread 09-06-2013, 10:22 PM   #7
power
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I would check fuel pressure at the fuel rail. My girlfriends 94 IL6 had similar symptoms and it was a fuel pump. There was not enough pressure at the fuel rail it would sort of come and go. I replaced the fuel regulator which didn't help. Her pump was going. If it is your pump, make sure you get the right one she got the wrong one and then we couldn't figure out why it wasn't delivery the correct pressure. Long story short and after much researching we got the right pump and ran fine. You can fab up a cheap pressure gauge to take the reading off of the valve on the fuel rail.
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Unread 11-02-2013, 10:42 AM   #8
JoeZedJ
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on and on...

So, coming back to this problem, I have replaced the CPS with a MOPAR CPS and still same issues.

To add I have also done this:
-Replaced stator
-Replaced coolant temp sensor

Still I am having issues with it "misfiring" or when climbing a hill it drops down a gear and kind of hesitates. It is difficult to diagnose, mostly because it is very random.

I am hedging back on fuel delivery issues. I am going to check the fuel pressure today. I am also considering picking up a PCM from the boneyard.

Anyone have anything else on this?
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Unread 11-02-2013, 12:55 PM   #9
Oldfrog
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1997 ZJ 
 
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Fuel pressure should be checked for sure.

Getting a pcm from a junkyard is a crapshoot. Getting one from one of those two outfits in Florida is a higher priced crapshoot. Get one from Kolak, a vendor here, or get an A1-Cardone brand...and even then, you can get bad ones. (I'm on my 5th PCM now).

If you have methodically worked your way through Zeejay's list of 12 things to do/check without results, you may well need a PCM. Next is trying to determine exactly why and there are only two reasons that I'm aware of. 1. The inherently poor workmanship of some of the factory PCMs. and 2.: Something in your vehicle's system is frying them..such as intermittent connections, poor or frayed wiring, bad O2 sensors, etc. In my case, I suspect that at one point it was the non-Mopar o2 sensors. I have since replaced them with NTK and yet another Cardone PCM. That was over 1000 miles ago.

Your 96 model could ( and most probably does) have bad capacitors and/or solder joints inside. There is a write up about it...and how to fix it yourself, if you're so inclined.
But before you change it, make certain that your o2 sensor is an NTK. ( I think the 96 only has one...instead of 2)
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Unread 11-02-2013, 09:15 PM   #10
xrunndonex
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I have a idear take a fuel gauge take that bad boy attach it to the scharder valve and run it so the face can be taped to the windshield and bam any random things happen you will know what it is... I'd double up on fuel system though
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Unread 11-02-2013, 10:59 PM   #11
Uniblurb
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Actually it very well could be your fuel pump the way you describe it hesitating/trying to downshift when you put it under a load going up hill. I just posted below where there was TSB 6088876 issued in 97 where there's a known problem with the 96 ZJ fuel pumps in particular since they overheat causing malfunctions. If your's lasted 17 years you're lucky and mine failed last year.

http://www.jeepforum.com/forum/f13/1...l#post17254186

If you don't want to buy a fuel pressure tester you can borrow a loaner fuel pressure kit from Advance and/or Autozone, keep for 90 days, and return for a full refund. But not a bad thing to have around. I may end up buying this Actron from Amazon for $42 w/free shipping. It's the same one you get as a loaner but probably doesn't have the case with it.

As posted in that thread/link, and below, you sure won't beat $90 w/free shipping for a whole new Bosch 67646 fuel pump module for your 96 4.0.

http://www.ebay.com/itm/NEW-BOSCH-67...83a539&vxp=mtr

As with anything else do testing before jumping-the-gun/throwing parts at it. It wouldn't be a bad idea to test the new Mopar crank sensor if fuel isn't your problem.

Believe it may have been the pre-OBDII (95 and earlier) 4.0's which may have only one o2 sensor. The 96 4.0 has 2 with the downstream being a NTK 23016 and the upstream is a NTK 23121.

Good luck!
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-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 11-03-2013, 07:11 AM   #12
ZeeJay1997
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moparcranksensorophobia claims another victim. the man has put two crank sensors in the vehicle with no joy. there are aftermarket crank sensors that work as well or the same as a Mopar. After all, SOMEONE has to make those things, Chrysler sure doesnt.




taping a fuel pressure gauge to the windshield is a great idea.
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Unread 11-03-2013, 07:54 AM   #13
JoeZedJ
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...

Uniblurb, after I dot done posting my reply yesterday I spent some more time cruising the forums and I came upon that exact thread. Thanks for sending it my way! I was actually getting ready to PM you. I also checked the eBay module for 90$ WTF! I almost thought too good to be true until the forums said the seller had a good rep. NAPA wants $325 for the same dang thing.

Gonna head out this morning before football consumes my afternoon and test the fuel pressure...

Thanks again everyone for the suggestions. I'll post up a video of my pressure readings and such for review. I might just pull the trigger and buy the pump now.

Joe
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Unread 11-03-2013, 08:02 AM   #14
JoeZedJ
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Location: Shelton, Washington
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ZeeJay, your 12 step program should have a code name like "Friends of Chrysler" or something maybe more creative. I printed off the thread for future fails. Yes, I did fall victim to sensor overkill. I guess that's what sometimes searching the forums does to you. I did start with the logical stuff, spark, ignition, fuel etc. Then before I dropped my fuel tank and mega bone$ on a new pump I read the forums. LOTS of posts on the CPS, dirty IAC, TPS, MAP etc....

Thanks again for what you do!
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Unread 11-03-2013, 09:54 AM   #15
Oldfrog
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There are lots of CPS and IAC posts, because they are common failures. Especially dirty IACs.
These are finicky animals when they get old. If they were women, I'd have kicked mine to the curb a long time ago. Women are much easier to find a suitable replacement for.... A good 4X4....not so easy.
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Words of wisdom, Posted by Zeejay:
"..it's not air, it is the opposite of air... suckage so to speak."

Stalling? Work through Zeejay's list
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