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Old 04-01-2013, 09:48 AM   #1
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Misfire on startup?

1997 Jeep Wrangler 4.0, 140k miles. Need some help figuring out this problem. For the past few months I have been dealing with a check engine light on cylinder #1 misfire. The only time it does this is at cold start up. Turns over then 5 seconds later for maybe just a second or two it sputters from 1000 rpm to .750 then back up again. After that runs flawless.Now I have noticed that it takes longer to start up than it used to, maybe 3 or 4 seconds after cranking the key vs. The normal one or two seconds. I Can't stand check engine lights I need help! Have replaced all plugs, wires, distributor cap, rotor, injectors are good, timing good, I put a new distributor in not too long ago, I read somewhere about a crank position sensor could that be it? Also have reset the check engine a few times and it will cone back on after 10 start ups maybe more. Thanks in advance everyone.

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Old 04-01-2013, 10:29 AM   #2
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No one has had any issue like this that might be able to help me out?

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Old 04-01-2013, 10:49 AM   #3
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I've got a very similar problem just like yours but mine also occurs anytime I'm over 55mph. I've had little to no help or explanation of why this happens or how to fix. Maybe someone can lead you and I in the right direction.
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Old 04-01-2013, 10:54 AM   #4
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Any oil smoke (blue) blow out when it happens on start up? If you had a valve seal leaking it would drip oil into that cylinder overnight. But, when you start it there would be a puff of blue smoke as a tell tale sign.

Could be a lot of little things to cause that type of symptom. give the group some time and you should have some more answers.
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Old 04-01-2013, 11:48 AM   #5
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Am having similar problem. Buddy I bought jeep off of couldn't figure out, been doin it for a while. I know he changed crank sensor and didn't fix. I just joined forum, couple days ago, to try and get some help with this. I have thread in general discussion for this reason
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Old 04-01-2013, 01:10 PM   #6
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I had the problem about 8 years ago and it was the fuel filter on my fuel pump was clogged. I took the pump out, cleaned it and have not had an issue to this day. There was a bunch of brown goop on the mesh filter over the intake....
Missed the part where u said it runs flawlessly after start up. My jeep would bog down while trying to accelerate
Run an OBD when check engine light comes on
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Old 04-01-2013, 01:40 PM   #7
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The code was a P0301?
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Old 04-01-2013, 02:28 PM   #8
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The code was a P0301?
yes, throwing code p0301. Just started it up now getting ready to leave work and it didn't miss out at all, only seems to do it at first start up in the morning or when hasn't been ran for 12plus hours. Such an odd jeep! Lol
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Old 04-01-2013, 09:37 PM   #9
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Changed the Crank Position Sensor today, upon replacing startup was very quick compared to usual, and did not miss out. I have reset the PCM, Engine light is gone, will let you know how things go in the next few days, so far so good.
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Old 04-03-2013, 06:25 AM   #10
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Changed the Crank Position Sensor today, upon replacing startup was very quick compared to usual, and did not miss out. I have reset the PCM, Engine light is gone, will let you know how things go in the next few days, so far so good.
I have a 1391 code popping all the time. I have changed out the crank and cam sensors. No change. Unlike your issue, I am not noticing any negative starting or performance effect. When I changed the clutch, having a leaky rear seal, changing too, ensured the magnets were clean when I put back together. No change. So, now, I am checking wiring as I go. Due to warrantee, I also have changed out my headers three times over the course of the code throwing and also increasing my injectors from 19 to 23 lbs, as I believe part of the code also state misfire due to crank or cam sensor; but since changing those items didn't solve the issue, I am perplexed. No vacuum leaks, ignition components all up graded, new distributor, as the cost was similar for the cam sensor, si I replaced the whole thing to take distributor bearing play out. Good luck with your search...
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Old 05-21-2013, 08:55 PM   #11
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Update: Cylinder one misfire check engine light comes and goes still, here is the second problem now. When starting it will turn over for 5 or more seconds before start. So usually I crank it for a second, turn key off then crank again and starts right up in a split second. If I were to shut it off and start it up again within 30 seconds, no problems but a minute or more takes forever to fire again. Its almost like fuel isn't staying in the injectors or lines after a certain amount of time. Can anyone shed some light on this second problem Im having? I'm hoping that this is why the cylinder one misfire code is being thrown as well from this problem, so I can eliminate both my problems at the same time, appreciate any info, thanks!
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Old 10-08-2013, 09:01 PM   #12
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I'm at the point now to start up the engine I have to turn the key 2 or 3 times to prime the injectors prior to start, or else I will have to crank for 5 second or more. Also, by doing this it helps avoid the short misfire I get which causes the cylinder one misfire code. Here's a list of things I'm going to replace next week hopefully to resolve the issue. Coil Rail, Fuel Injectors, Fuel Filter/Pump. Anyone have any other suggestions? Thanks...
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Old 10-08-2013, 09:33 PM   #13
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I have the same problem. I've heard that it could be the fuel pressure regulator that stops the fuel in the lines from draining back into the tank, goes bad and then you have no fuel at the engine when you go to start. I'm not positive. But sounds logical. I'm sure someone can confirm this.
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Old 10-09-2013, 08:05 AM   #14
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I found this link and I believe that it is the fuel pressure regulator, I'm going to go ahead and replace that as well as the fuel pump... http://www.wranglerforum.com/f5/repl...tor-79784.html
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Old 10-09-2013, 11:59 AM   #15
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Let me know how it goes! If it works for you I'll prob end up doing mine.
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Old 10-09-2013, 04:35 PM   #16
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Let me know how it goes! If it works for you I'll prob end up doing mine.
Will do! Ordering parts now, hopefully start on it this Monday.
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Old 10-09-2013, 04:42 PM   #17
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I swapped out my entire fuel module last week and that solved the fuel drainback problem. Now it starts instantly.
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Old 10-09-2013, 04:48 PM   #18
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I swapped out my entire fuel module last week and that solved the fuel drainback problem. Now it starts instantly.
Awesome! Thanks buddy!
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Old 10-10-2013, 07:10 AM   #19
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I swapped out my entire fuel module last week and that solved the fuel drainback problem. Now it starts instantly.
How much does that cost? Just so I have an idea. I need to do this.
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Old 10-10-2013, 07:22 AM   #20
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How much does that cost? Just so I have an idea. I need to do this.
I just ordered a spectra premium whole fuel pump module off of amazon for 155 shipped to my house. I went with this brand because they are made here in Indiana where I'm from and have good reviews. I wasn't about to order a mopar unit for 300 + which is actually a Bosch unit. I'm not a fan of them.
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Old 10-10-2013, 07:23 AM   #21
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I replaced the entire module because there was also fuel gage issues but you can just replace parts also. The entire module cost me $153 plus shipping. Amazon and Rock Auto had decent pricing.
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Old 10-10-2013, 07:54 AM   #22
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Will do! Ordering parts now, hopefully start on it this Monday.
Hey how much was the regulator and how long did it take you to get it swapped out. I need to replace mine
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Old 10-10-2013, 08:04 AM   #23
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Hey how much was the regulator and how long did it take you to get it swapped out. I need to replace mine
The regulators I saw alone were 80+dollars so you might as well just replace whole fuel pump since you will already have the tank dropped to get to the regulator anyway. Especially if its the original on your jeep. The regulator just sits on the very top of the fuel pump module so if you order a new pump it will come with it already.
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Old 10-10-2013, 08:51 AM   #24
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Damn I was hoping to not have to drop the tank. But yea I might as well just replace the whole setup
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Old 10-10-2013, 09:07 AM   #25
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Damn I was hoping to not have to drop the tank. But yea I might as well just replace the whole setup
Dropping the tank really isn't that hard to do I have done it once before when I converted my 15 gal tank to a 19. Just make sure to try to have your tank on E and have a two jacks on each side to lower down the tank one you get all your bolts off.
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Old 10-11-2013, 08:10 AM   #26
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Misfire on startup

I wrote earlier on a constant P1391, and I believe P0463 codes popping. Though the codes are different, man this all seems related. As per my earlier post, and nothing has changed in performance, I have changed everything noted on this thread, even the cam sensor (actually the whole distributor, it was cheaper) except the stuff in the fuel tank, which, P0463, if that is the right code based on memory, as it is very sporadic where 1391 is daily, starts to put my issue in prospective. Regarding the starting issue, which now I am even more on board with the prospect of 1391 and 0463 are related, I too need to turn the key to ignition, hear the pump run and stop prior to engaging the starter. If I do not, about 4-7 turn overs happen compared to two.
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Old 10-12-2013, 01:07 PM   #27
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Let me know how it goes! If it works for you I'll prob end up doing mine.
Great news everyone! Replaced whole fuel pump module, and problem solved pretty damn happy today! Started at 8 am this morning got done at noon, also did oil and filter change while I was at it. My Jeep and I couldn't be happier!
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Old 10-13-2013, 06:34 PM   #28
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What kind of fuel pump did you install?
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Old 10-13-2013, 06:39 PM   #29
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What kind of fuel pump did you install?
Spectra Premium amazon $155
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Old 05-02-2014, 10:40 AM   #30
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Well my Jeep is at its old ways again...Just started the long cranking again randomly. Surely the fuel pressure regulator couldn't have gone out again? Hasn't even been on there for a year yet, so frustrating!

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