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Help! no power to fuel pump or coil!!!

9K views 27 replies 7 participants last post by  beefers92 
#1 ·
Hey guys i'm in need of some electrical expertise. I have a 93 yj 2.5l. While driving the other day it just shut off as if the key was turned off. all fuses and relays check out to be fine. when I turn the key to the ON position my check engine light, seat belt light, and shift light all come on. I can not hear the fuel pump kick on and from what I have tested there is no power going into the coil. Any help on this would be most helpful.

Thanks in advance!
 
#6 ·
Yea, it does have all those symptoms of the CPU failure. Odd about the lights coming on though, but I don't think the crank sensor would kill the fuel pump. The good thing is that it's a very cheap and easy job to replace them. And lets face it, sooner or later they are going to act up!

I know I have posted this a hundred times, but it is very worth the download!
http://pdfcast.org/pdf/1995-jeep-wranger-fsm-complete-electrical-system
 
#7 ·
Check for the ground wire attached near the drivers door/ hinge strap holder. If you broke it with your one of your big clodhoppers :) it shuts the engine down and it will not start back up. It is the fuel pump ground wire IIRC.

If that don't work then pull the VSS plug on the VSS sensor on the transfer case and hit the key again does it start? Bad VSS switch. If the VSS dies your crank and cam sensor got no voltage. You will get no fuel or no spark.
 
#14 ·
Wow, If I read the right it looks like the fuel pump problem could also be causing the coil to lose power. Thats kinda strange. When my CPS went I still had power to the fuel pump. So here is what I am thinking. He needs to use 2 jumper wires and should jump the ASD relay and the fuel pump relay and then check for power to both the fuel pump and coil. Its early so my thinking may be wrong. While doing this he should just dissconnect the VSS. Once its running he can reconnect it. That way its taken out of the equation. He should also check all the above mention fuses. Also this may have been asked already but maybe he should do it again just to be safe. Are there any stored CEL codes. DOes the check engine light come on at key on and go off after 30ish seconds. This sounds like it may be the Brain surgery issue(2 bad capaciters in the ECM). If it is not the cap issue even if the sensors are bad it sounds like the fuel pump should still prime at key on but stay off after that. Also with the key on shouldnt there be 5 volts at the 02 sensor. It looks like if bad sensors the 02 should still get power but if it is a bad wire the 02 would not get power. Hopefully I am not making this more complicated than it needs to be. All this to find a $5 part thats causing the problem most likely.
 
#15 ·
The fuses are the first thing to check no matter what and I mean pull them and test them not just eyeball therm. Next the horn relay can get pulled and be used to test the ASD relay.
The crank, cam & VSS are on the same 8 volt circuit. If a dead short occurs in this circuit there will be no fuse popping, but none of these sensor can send a signal back to the ECM. The VSS is the usual culprit. It could be bad wiring anywhere in that circuit also or the other two sensor are junk, who knows.....:confused:

Some time back I was helping a fellow JF member locally (Rat). Oue89YJ was helping also (Thank the JF Gods) suggested unplugging the VSS sensor after we had swapped out or tested everything under RAT's hood. The damn thing fired right up! The only issue was Rat had no speedometer because his '95 YJ speedo was driven by the VSS sensor.
Bottom line is until the OP makes has a game plan to eliminate possibilities he will chase his tail until he flies up his own butt and disappears!

CEL check first, then fuses, then relays, then sensors and wiring.
And they have redundancy built into these systems. Or in plain English if Chrysler to keep the ECM small they melded up a bunch of similar sensors doing the same job! At Chrysler they must hire ex- Gov't bureaucrats as electrical engineers whose thinking is; The straightest distance between two point is a straight line...going the other way!:eek:
 
#17 ·
First off thanks for all of the suggestions! I have tested all fuses via continuity tester. Tested the relays via horn relay slot. If I leave the key on nothing changes. There are no stored codes. I replaced the crank sensor with no luck. I am replacing ecu Sunday.... When I jump the fuel pump relay and the asd relay pump comes on and sounds like it has low power. Still no start. I will test voltage at the relays on Sunday as well. Again I appreciate all the help thus far, you guys are awesome. There will be an update Sunday night!
 
#19 ·
So did some more testing this morning and it looks like I have low voltage on the 8 voltage circuit. I'm getting 2.5 volts at the vss white/orange wire. Do the relays need a certain voltage to switch on? If this is an issue where do I go from here?

Y'all have been a great help so far keep it up!
 
#21 ·
Ok so I fixed it. Turns out I am freaking stupid! Pulled all the mega fuses to test again and found the 30 amp fuse in the f1 slot was blown. Replaced fuse pump primed and it fired right up. Thanks again for all the input I'm sure it will help in the future.
 
#22 ·
:rofl: All of that back and forth diagnosis and the end result was a blown fuse. Somebody owes Siva and Laybackman some cool refreshing adult beverages. Nice job anyway guys! :thumbsup:
 
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