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Unread 09-16-2011, 02:32 PM   #1
4x4_Medic
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Post-modification oops.

Ok, I had my killswitch thread in here, but since this is now something new, I think it needs a new thread. I tried wiring a killswitch in onto my fuel pump relay. It worked for a moment, then when I tested to make sure the car wouldn't start afterwards, it died and I havn't been able to bring it back to life since. I have removed the switch for now, and spliced the wires on the relay back together.

My engine cranks, the fuel pump is working, because I know I have fuel pressure, and it was working fine just before I put the switch in. Does anyone have the slightest idea of what it could be, so I don't have to drag this thing over to a shop?

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Unread 09-16-2011, 02:34 PM   #2
superj
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did you burn up a ground or something?
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Unread 09-16-2011, 04:10 PM   #3
4x4_Medic
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Honestly, I have no idea. I only know just enough about electrical systems to put the switch in. I have no idea what I should be looking for. One of the reasons I'm asking here. Which grounds might I have damaged, and where would I find them? Things like this are what's really throwing me off. I checked the fuses and they were all good. Checking my fuel lines, I know I'm still getting fuel flow, so the pump is working. I just can't figure out what's keeping this thing from kicking over, now.

Last edited by 4x4_Medic; 09-16-2011 at 04:28 PM..
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Unread 09-16-2011, 04:32 PM   #4
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how do you know you are getting fuel?
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Unread 09-16-2011, 04:37 PM   #5
4x4_Medic
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The fuel rod on my engine has a little test port on it. If I touch the port with a screwdriver, I get a little flood of fuel. I try cranking again, and tap the fuel test port again and I get the same little flood of fuel.
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Unread 09-16-2011, 05:03 PM   #6
shadowulf
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Check for a loose ground. I had something similar happen when I installed my tilt steering wheel. In short, no ground = no fuel injection. And when you find it, hook you switch inline with it. Its a killswitch dream, no fuse and hard to bypass unless you are looking for it.
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Unread 09-16-2011, 05:07 PM   #7
4x4_Medic
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Well, where would I find these grounds? Because the one thing I touched was the power distribution box under the hood, which I've done before when trying to find the right wire before I did this, and had nothing bad happen, and the white/yellow wire coming to the fuel pump relay, which is now re-connected. Other than those two areas, I have touched nothing.
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Unread 09-16-2011, 06:55 PM   #8
sbsg2005
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Have you checked to see if you have spark, you know you have fuel pressure but can you tell if the injectors are firing?
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Unread 09-16-2011, 07:25 PM   #9
4x4_Medic
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No, I can't tell if I have spark. I don't have a spark plug socket.
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Unread 09-16-2011, 08:41 PM   #10
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take a plug wire off... stick a screwdriver in the end of it... position the screw driver so that its close to something metal but not touching... then turn the engine over while watching for sparks to jump.
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Unread 09-16-2011, 09:29 PM   #11
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Ohhhhhh.....ok. Just got to wait until someone else is around, then.
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Unread 09-16-2011, 09:58 PM   #12
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When you push the little valve (schrater valve) in on the fuel rail it should shoot out with a bunch of pressure, not just sorta flow out. The pressure in the system when the pump is functioning properly is about 40PSI. There should be enough pressure in there so that when you push the schrater valve in it will probably spray into your eyes (happened to me the first time I did it without wearing safety glasses) and all over you in the process. If you arent getting a high pressure blast then your pump isnt functioning properly. It could have simply lost its prime, which should build back up with cycling the key a couple of times.
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Unread 09-16-2011, 10:26 PM   #13
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Quote:
Originally Posted by 4x4_Medic View Post
The fuel rod on my engine has a little test port on it. If I touch the port with a screwdriver, I get a little flood of fuel. I try cranking again, and tap the fuel test port again and I get the same little flood of fuel.
figured but thought id ask.

Quote:
Originally Posted by MoparFreak69 View Post
When you push the little valve (schrater valve) in on the fuel rail it should shoot out with a bunch of pressure, not just sorta flow out. The pressure in the system when the pump is functioning properly is about 40PSI. There should be enough pressure in there so that when you push the schrater valve in it will probably spray into your eyes (happened to me the first time I did it without wearing safety glasses) and all over you in the process. If you arent getting a high pressure blast then your pump isnt functioning properly. It could have simply lost its prime, which should build back up with cycling the key a couple of times.
mine never does this. it kinda dribbles out. has always run fine. weird.
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Unread 09-17-2011, 11:52 AM   #14
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Quote:
Originally Posted by fratis View Post
mine never does this. it kinda dribbles out. has always run fine. weird.
Your Jeep either has TBI or a carburetor (if you have the original engine in it), the pressures in the fuel line are lower than 92+ MPI engines. The carb functions between 3 and 8 PSI while the TBI system works at somewhere around 20 PSI. A dribble is normal for these earlier systems, not for later higher pressure systems.
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Unread 09-17-2011, 12:00 PM   #15
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no its a 91, mpi.
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