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Unread 07-25-2011, 07:42 AM   #1
bchap05
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1994 YJ Wrangler 
 
Join Date: Apr 2011
Location: Boise, ID
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Where to start intermittent cut out

Sorry this is kind of long but the problem has been intermittent so I feel I need some detail. Jeep is 94 4.0.

So last weekend we took the yj up to my parents cabin and it ran perfectly fine on the way up. While up there I did a little driving on dirt roads. On the way home there is a 7% grade that I got about 1/4 mile up and it started cutting out bad. I pulled over, turned around and went back down. Checked the engine didn't see anything apparent and headed back up. Made it to the top which is probably 4 miles or so, with it only cutting once at the very top. Make it back into the city and it starts cutting bad to the point where I didn't think I would make it home, but we finally sputter into the driveway.

My dad has a samari and he said he had knocked his plugs loose on that road before so I checked that first and it ran perfect all week going to and from work. I assumed it was fixed.

This weekend we went camping 150 miles from our house. On the way there it runs perfect including climbing the 7% grade again, and going up hill most of the way. While there we did a bunch of off roading and while climbing this steep trail it cuts again. Check the wires, drive down the trail, and about 10 minutes down the road its cutting again. So I turn it off then back on, drive 10 minutes and it cuts. We get back to camp stopping every 10 minutes to restart because it starts cutting out every 10.

We check the engine and find the hose going to the top of the engine (not the air box one) looks very loose. We plug it back in put some automotive silicon on it and let it sit over night. We get go on a 40 mile drive with off roading again and it runs fine. So I'm assuming now it was the hose.

Head home yesterday and get about 20 miles up the road and it cuts. We then pulled over every 10 minutes for the rest of the way home. Before the 7% grade we stopped for 20 minutes and let it sit. We barely made it up going about 25-30 mph the whole way and stopping 3 times for restarts. Made it back to the house with restarts every 5 minutes as it was getting worse.

Wake up drive to work this morning and its fine again. So it appears it has to be warmed up, under load, and it will reset and run fine for 5-10 minutes after restarting the engine. When it cuts it feels like its not getting gas or air. If I let off the gas it runs fine if I touch the gas it sputters when it does this. Air filter is new, so I'm thinking either hose, fuel pump, fuel filter. Any ideas on where to start?

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Unread 07-25-2011, 10:33 AM   #2
kloppk
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1992 YJ Wrangler 
 
Join Date: Oct 2006
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Check the pressure at the fuel rail.
Could be that your fuel pump is starting to die or the filter(s) may be clogged.
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Unread 07-25-2011, 11:20 AM   #3
bchap05
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1994 YJ Wrangler 
 
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Yeah I'm leaning towards fuel pump dying since turning the vehicle on and off seems to reset it for a bit. If it was clogged I would think it would remain clogged regardless of if I restart the vehicle or not. I'll check the pressure and see what I find.
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Unread 07-25-2011, 11:46 AM   #4
notmyj
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1992 YJ Wrangler 
 
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Checking fuel pressure may not show you a problem unless your driving it, under load while reading fuel pressure. It is possible to have good pressure but not enough flow. I would start with a fuel filter. Check all connections at the TPS, CPS, Fuel pump, etc. Look for any corrosion, and go over the engine harness very closely. Look for any wires rubbed through, etc.
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Unread 07-25-2011, 01:11 PM   #5
bchap05
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1994 YJ Wrangler 
 
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Thanks, I'll change the fuel filter tonight when I get off work. Problem is I won't be able to test it without going on a 40 minute or longer drive to get it to start doing it. I just got back from lunch and it was fine there and back so its not going to do it in city driving unless it gets worse or I drive for a long time.
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Unread 07-25-2011, 02:02 PM   #6
clush
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Mine does the same thing and has been for a long time. Same year and same engine as yours. I first noticed it while pulling a small boat up a big hill on the interstate. As time progressed it got to where it did it while going up hills, etc with no boat. And now it will run for like 15 miles regardless of whether or not its an incline or whatever and start missing. It seems to idle fine, it only misses if you are under load and giving it gas. Feels like it is starving for gas. This was all before I retired the jeep after buying a new truck. Once I bought the truck I decided to let the jeep sit until I came up with the $ and time to do a semi-restoration.

I had some other issues that am in the process of fixing right now - I fixed some rust, put a new lift on, etc etc etc and haven't gotten aroudn to fixing that yet. But I did try the usual stuff at first, new fuel filter, distributor cap, plugs, wires, O2 sensor as well. Once I get my other stuff done I am testing fuel pressure - so far I am leaning towards it being the fuel pump.
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Unread 07-25-2011, 02:51 PM   #7
bchap05
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1994 YJ Wrangler 
 
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I'm hoping to solve mine soon as its my daily driver so I'll let you know if I figure out what it is. I'm also leaning fuel pump since I really don't think turning the engine off and on would solve the problem for 10 minutes or so if its the filter. Does your slightly miss or get to the point where you can't go? While I could normally easily go 65 on the highway once it starts to slightly sputter it maxes at about 50 then it slows to 30 and I have to start down shifting to even keep going.
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Unread 07-25-2011, 02:58 PM   #8
clush
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It sounds exactly like yours. If I let it sit for a week or two and the drive it will go like 15 miles, get hot and start missing. On the interstate you will have to get down to like 30 MPH. Eventually you can pull over and turn it off - and after like ten mins it will start and run OK for just a couple mins and start acting up again. I think the electric fuel pump is weak and gets hot & breaks down. But that is just speculation at this point. I wish I had an answer for you please let me know when you get it fixed. Here is a pic of mine after some rust repair and interior herculiner this from this weekend. I am on schedule to hopefully get it back on the road by Thanksgiving.
photo0293.jpg  
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Unread 07-25-2011, 03:35 PM   #9
bchap05
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Looks good I've thought about lining mine but haven't really gotten to working on the interior yet. Sounds like the same problem with one difference. On mine I don't have to wait 10 minutes for restart. I finally got tired of pulling over so once I would hit a straight away I would put it in neutral, turn it off, then back on while coasting and be fine for another about 10 minutes.
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Unread 07-25-2011, 08:15 PM   #10
bchap05
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Changed the fuel filter tonight and took it for a 20 minute drive down the freeway. It started cutting out after about 10 minutes like before. It didn't cut out as bad and was able to maintain speed but I also probably didn't drive far enough to make it as bad as before. Fuel pump replacement is next.
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Unread 07-26-2011, 07:28 AM   #11
Que89YJ
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Try and diagnose it. Rent the fuel guage from the parts store and connect it up to the schrader valve on the fuel rail. pressure should never drop below 31PSI. 10 minutes is interesting. Read the fault codes by cycling the key. 10 minutes is about how long it takes to go into closed loop and start to read the sensors after the temp sensor does its thing. That would leave me to believe that you have either a bad O2 sensor or a cracked manifold giving it a bad o2 input. Read the resistance on the O2 sensor cold and hot and see what you get and check the exhaust manifold for cracks and loose bolts.
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Unread 07-26-2011, 08:33 AM   #12
danlee
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I had some of the same symptons, but it ended up being a bad wire. It would only show up when it was hot, resistance value went up, if you haven't changed your wires in a while, it is fairly inexpensive, may or may not solve your issue.

Let us know what you find
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Unread 07-26-2011, 09:22 AM   #13
clush
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Hey Bchap mine was like that at first - turn it off and coast for a few seconds and then start it back up without stopping and it would run OK for a few mins. It will still do that sometimes. But eventually mine kept getting worse. I have noticed that the longer u sit the longer it will run without messing up again. If you let it sit for a few hours it runs the 10-15 miles again. If you turn it off and coast for a few seconds and then start it back up it runs Ok for only 30 secs or so, sometimes not even that long. Check your fuel pressure and see what it says, no doubt. Maybe check it after it starts missing again too.
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Unread 07-26-2011, 11:21 AM   #14
bchap05
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Lots of good ideas, I'm going to go grab a gauge on my lunch break. I'm hoping it something other than the pump. Especially after reading about lowering the tank or cutting the floor to get to it.
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Unread 07-26-2011, 05:26 PM   #15
bchap05
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1994 YJ Wrangler 
 
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Well O'Reily's was worthless they don't rent fuel pressure gauges and its never had the check engine light on so it didn't pull any codes. Anyone know if Autozone or Napa rent them?
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