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Old 11-30-2009, 04:42 PM   #1
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Hard start. Where to start looking?

My 93 YJ with the 4.0 and 5 speed has been giving me some trouble starting. It starts just fine when it is hot, but has been getting worse at starting after it has been sitting for a while. It sputters a little a couple times before starting. Sometimes it fires up then dies after about 2 seconds of running (when the rpms normally drop).

The odd thing is that so far, it has not given me any problems from a true cold start (overnight) other than dieing immediately then firing right back up. The Jeep runs just fine when it does get going. I always hear the fuel pump when I turn the key, and I just recently replaced the fuel pump anyway.

I don't even know where to start looking on this. I never have another person around when this happens, so I have not been able to check for spark.

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Old 11-30-2009, 05:31 PM   #2
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I just took a look at the throttle body and it looks pretty gummed up. I think I will take that off tonight and clean it out. I checked fuel pressure at the rail and judging by the geyser that erupted from the check valve, that isn't my issue.

I am hopeful that cleaning the throttle body will do the trick because it does like to sputter and die before actually starting.

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Old 12-01-2009, 12:02 PM   #3
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Here is a little more info:

Tried to start it this morning with no success. It didn't even try this time, which is unusual. I checked fuel pressure at the rail and I didn't even get a dribble. I could hear the fuel pump start every time I turned the key to "on", but still wasn't getting any pressure at the rail. The pump and the filter are both brand new, so I don't know what the issue is.

Is there something in between the pump and the fuel rail that would not allow fuel to flow to the rail?
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Old 12-02-2009, 12:40 PM   #4
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Anybody?
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Old 12-02-2009, 01:27 PM   #5
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shouldent be anything from filter to fuel rail, Are you sure that new pump is actually pumping it could be obstructed i would disconedt at filter and see if it comes out, then try again, trace fuel line up the frame rail and make sure by some fluke it is not dammaged, past that im not sure!
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Old 12-02-2009, 03:38 PM   #6
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I have narrowed the problem down to a fuel delivery issue. The pump always comes on, but sometimes it doesn't pump. I changed the (already 1 month old) fuel filter, and it worked last night. Today, however, the problem is back.

What I did yesterday was disconnect the "out" line from the fuel filter and clicked key to "on". I could hear the pump come on, but my garage floor was still dry. I tried this several times without so much as a drip. I took the filter out entirely and it would spit out gas. I assumed that the filter was the problem, but apparently I am just very unlucky. With the filter out, I was able to make it spray gas every single time I turned the key (7 or 8 times over 3 or 4 hours). I changed the filter and it worked fine until today. Now with the new filter, it is doing the exact same thing as before. The pump comes on, but I have no fuel at the rail. After trying for a while, it usually fires up and runs perfect until I turn it off again.

To be clear, whats happening is I turn the key to "on" and the fuel pump comes on. Sometimes it starts, sometimes it doesnt. I think that I can hear the difference in the sound of the pump when it works and when it doesn't. It almost sounds blocked when it doesn't work. What could be stopping the pump from delivering fuel to the rail? It is a new pump, and I never had this problem with the old one. Could my pump be somehow defective?
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Old 12-02-2009, 03:59 PM   #7
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could be a defective pump, or could be somthing in tank is blocking pick up, try it again and if it doesent pump gas, try removing gas cap if there is a blockage that might release the pressure enough to make obstruction move. I had this problem with an old ford once. not sure if you are suffering same thing but could be worth a try!
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Old 12-02-2009, 04:04 PM   #8
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I was thinking that something could be blocking it, but I don't understand how that can be the case. It runs just fine everytime I park it, I don't get how something could then get in the way. If it ran poorly, I would be more inclined to blame blockage, but I just don't see how that is an issue here.

My next try is going to be wait until it won't start again, then immediately disconnect the fuel filter. That will really tell me if the pump is working fine or not.
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Old 12-02-2009, 04:51 PM   #9
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Well just confirmed, the fuel pump is not pumping gas.

I removed the filter, turned the key on, heard the pump kick on but did not see any gas come out. Does this mean the pump is defective?
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Old 12-02-2009, 05:03 PM   #10
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or blocked.
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Old 12-02-2009, 05:12 PM   #11
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After doing nothing but cycling the key, the pump eventually will squirt some fuel.

Someone please explain to me how it could be blocked if it never has a problem once started? I don't doubt entirely that could be the problem, it just doesn't seem to fit the symptoms. I have never had so much as a sputter on the road, and I never had a problem with my old pump until it completely died.
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Old 12-15-2009, 07:03 PM   #12
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Did you ever figure this out? I am starting to have trouble starting in the same manner you did, but I have not even started with changing the fuel filter yet. My first guess on mine is fuel line too.
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Old 12-15-2009, 07:42 PM   #13
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The pump is most likely bad.
It is a electrical device and could have a intermittent problem.
I would replace it.
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Old 12-20-2009, 01:03 PM   #14
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If you taken the fuel line off the filter and sometime it pumps and sometime it don't, But you hear the pump running you could have a bad pump. You will have to take the tank out check and see if the the pickup tube on the pump is loose or off. If you don't see anything wrong remove the pump and bench test it. You will have to improvise a little. Get a big jar big enough to set the pump in. Put a hose on the delivery side of the pump should be the bigger one of the two (3/8 ). Put the other end of hose in the jar so when the pump comes on its just recirculating,that way you don't have gas spraying everywhere. Fill the jar up until its above the pickup tube. If you have a battery charger with 10 to 20 amp circuit this will work or you can use a battery and some jumper cables. Your wiring harness should have 3 wires a ground which you took off when you removed the pump a pos that goes to the pump should be orange. The 3rd wire goes to the fuel gage. Look at the pump and see what color it is and trace it back to the connector to be sure.get a paper clip and put it in the end of connector for the pos to the pump. Now hook your neg(Black) from power source to metal chassis on the pump this will be your ground, and pos (Red) to the paper clip.Keep pulsating the pump to confirm if its working every time. Hope this helps>
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Old 12-20-2009, 01:09 PM   #15
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Ran out of room on last post, if pump is good, your fuel pump regulator on the front of fuel rail may be bad. Its at the front and its round and has a small vacuum line on it. if this sticks open you won't have fuel pressure.
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Old 12-20-2009, 03:01 PM   #16
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yes and no i have this problem with my camaro u wont have good fuel pressure but it should cause the pump to not pump. but it could be the check valve in the pump letting all the gas flow back into the tank. causing u to have to cycle the key to get gas up to the rail. or the pump is weak and not getting the right fuel pressure get a tester and check the pressure.

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