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Old 04-26-2013, 07:35 PM   #1
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Fuel problem or ecu

Hello All
i recently had to replace my fuel pump. Well i have the proper amount of fuel pressure now. Had a problem with the Jeep not starting and having to wait 10 minutes with the key on to get it to start. It would do this every time. Replaced the fuel pump and this seems to have fixed some of the problem. Now when it sits for a while I turn the key on and it will attempt to start but then it will run very rough and stall. Eventually it will smooth out and run just fine. Also the check engine light will go on and off while it's running very rough The fuel pump pressure is right where it should be while it's doing all of this any ideas please help!

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Old 04-28-2013, 06:01 AM   #2
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First off, so your "turn the key on for 10 years (jokes) to prime the pump before you start" problem is solved, right??

What year is that bad boy? Is it EFI or Carb'd? Have you checked your cylinders for compression? You said the "Check Engine Light" comes on?? Have you checked the computer for codes?

If you're getting proper pressure the whole time, and you KNOW that fuel is making it all the way to the engine - I wouldn't think that it's a fuel problem... Unless your carb jets or injectors are bad...

If it's carb'd, for the initial rough running condition, I would suggest that your choke on the carb could be either shot or going bad... I know that's what happened to my J-truck when the thermostatic choke finally bit the dust. She'd take a few more cranks than normal to start and then would stall and run rough for a little bit because the air/fuel mixture was off. It could still be a number of other things if it's carb'd - but that would be the first thing I would think of if this was happening to one of my vehicles. (Actually, I think the thermostatic choke IS going out on my YJ's carb as well, but I plan on getting a totally new carb - so I'm leaving it be) An easy fix is rigging up your own manual choke - like what's on old tractors. You can also install a new thermostatic choke - but that's just another part that one day will fail again. A properly set up manual choke will never fail. But I really REALLY don't think the "Check Engine Light" would come on with a bad choke on your carb...

With EFI, I'm not so confident - I know a bit about it, but I'm better with carbs... Have you checked your O2 sensor (though I don't think that's your problem)? MAP sensor? I know the TPS and CPS can cause some rough starting and stalling issues... With EFI, in my mind, it started getting a lot more complicated because a majority of the sensors and what-not are needed to be working properly for the computer to tell the injectors (and other systems) what they need to be doing in order for your engine to be running properly. Your ECU COULD be bad - though if it's ONLY during the initial starting/"warming up" thats running rough, I would doubt that it would be strictly the ECU that's at fault.

Give us some more info and we might be able to help diagnose a little better... What all has been replaced recently? What all have you checked other than the fuel pressure?

Sorry... That's all I got for now.

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Old 04-28-2013, 10:32 AM   #3
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Ok update to the problem, Tried starting it this morning same deal had to turn on key and wait ten minutes then it fired right up. Its a 95 wrangler fuel injected I have replaced the tps and the fuel pump. Fuel is at the proper pressure now fuel pump engages and i see the pressure gauge jump to 40 psi for a second so I know the fuel rail is pressurized. Its a 2.5 l 4 cyl. not sure where to start next.
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Old 04-28-2013, 11:23 AM   #4
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Just to add another idea i warmed up the ecu with a hair dryer not sure why just a hunch. turned the key on and it fired right up. Any one else ever heard of this?
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Old 04-28-2013, 12:20 PM   #5
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Just to add another idea i warmed up the ecu with a hair dryer not sure why just a hunch. turned the key on and it fired right up. Any one else ever heard of this?
Search ECU BRAIN SURGERY I think this may help you.
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Old 04-28-2013, 08:27 PM   #6
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Search ECU BRAIN SURGERY I think this may help you.
x2 on this!
I never even thought of that and then when I read Redrider94's post I was: Should've thought to mention it...
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Old 05-16-2013, 10:35 PM   #7
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Hello all

I am a very happy Jeeper today! Found the answer to the other half of my problem. On a very expensive hunch i bought a new ecm plugged it in and the beast roared to life with the first crank! dont want to jinx it so ill try several different times throughout the next couple of days and see how it acts. There was a definite fuel pressure problem which is fixed and the gas tank is mounted back up. Had to take it back down when i reversed the rubber fuel lines! But all good now!
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Old 05-16-2013, 11:23 PM   #8
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Hello all

I am a very happy Jeeper today! Found the answer to the other half of my problem. On a very expensive hunch i bought a new ecm plugged it in and the beast roared to life with the first crank! dont want to jinx it so ill try several different times throughout the next couple of days and see how it acts. There was a definite fuel pressure problem which is fixed and the gas tank is mounted back up. Had to take it back down when i reversed the rubber fuel lines! But all good now!
That's GREAT to hear!
Hopefully she keeps firing for you!
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Old 05-17-2013, 07:29 AM   #9
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yupper, those capicitors in there do that for sure. On really cold mornings I had to wait almost 20 minutes sometimes for mine to kick in. Def. the PCU/ECM. Been great since replacing it a few yrs back.
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Old 05-21-2013, 05:28 PM   #10
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Yeah hope this nailed it. Been trying at different times of the day and it keeps turning over and starting! Also the previous owner just told me she still has the bikini top and brand new plastic windows for the soft top that she will give me !
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Old 05-21-2013, 10:09 PM   #11
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Yeah hope this nailed it. Been trying at different times of the day and it keeps turning over and starting! Also the previous owner just told me she still has the bikini top and brand new plastic windows for the soft top that she will give me !
Nice man glad it's working out for you. She must be a really nice lady to give you that top.
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Old 05-22-2013, 07:33 AM   #12
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Fix the caps in your old ecu and sell it.
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Old 05-23-2013, 09:22 AM   #13
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Gonna turn in the old one for a core charge. On an unrelated topic.... does anyone know how to remove the original factory skins from the frame? The soft winows I mean. The replacement skins attach with velcro. The originals look like they are sewn on. do I need to Cut the sewn areas to remove it?

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