okay first off i have a 1994 yj with the 4.0,..i had a problem where when i turn the key on the fuel pump would take a min or 2 to cut on and it proceeded to get worse,. this mourning i get in it to go home and the fuel pump never cut on,:(...soo i figured it finally wore out,...so go to the parts house to get the 100$ fawk in the ass,...get back drop the tank hook it up,...still nothing,..then i get the test light a see that there are three wires going in to the pump,...ground,.. a orange wire and a yellow,..the yellow is dim on the tester,...the red nothing,...then i take a battery and hook it into the red,...works fine>>>> Hmmmmm????....soo there i go through the cluster fuck of wires,...and get back to the relay/fuse box,... everything is fine sooo i got frustrated :mad3: and decided to hard wire the fuel pump in to the a/c relay hole(do not have a/c),...fuel pump works and cuts on and off with the ignition,...from then on i try to crank the enginge and it wants to crank up but doesnt,,...try try try,...nothing,....THEN i check for spark,.,..not getting anything from the distibutor,..or the coil,...and power is not even going into the coil,:(...finally my question,....could this be a bad ecu???:confused::confused: i go to college and need my square back,... need some ideas or answers asap,..thank you

It sounds like a worn out ignition switch, specifically in the on/run position. Happens on older yj's...

That would explain the hesitation then failure of the fuel pump to prime and the lack of power to your coil, and is the only thing those two have in common.

The main power wire to your coil is switched from the ignition, the negative or trigger wire comes by way of the CPS thru your CPU.

I would replace the switch and if that doesnt work I will tell you the other quickie tests for those systems, just pm me.

P.S. After replacing I would undo your wiring changes for the fuel pump since they will be un-necessary.

couldnt the CPS gone bad,...and doesnt it send a signal to the coil and the fuel pump? i was thinking about replacing the CPS and see what that does,.. idk?

I wouldn't suspect the Crank Position Sensor (CPS) its only function is to send a trigger signal to the CPU which in turn takes that white wire that goes to the coil and grounds it... causing the coil to discharge. If your CPS is working right you will notice the tac bounce while cranking.

The fuel pump power comes from the ignition switch.

The fact that you weren't getting power to the red wire on the coil speaks volumes.

I would go to the dealer.. change out your ignition switch... it sits on top of the steering column.

I had a similar thing happen to me and the wires were worn and broken just above the rear drivers side shock and it was tough to find with the factory plastic wrap that was around it.
Test your wiring from the fuse block to the back and see if you get different readings along the way.

does your check engine light come on for a second or two when you put the key in the run position?

I had a similar thing happen to me and the wires were worn and broken just above the rear drivers side shock and it was tough to find with the factory plastic wrap that was around it.
Test your wiring from the fuse block to the back and see if you get different readings along the way.

If it wasnt for his coil acting up as well... I have just seen this happen more than once.. Yj ignition switches wear out over time and they are also affected by moisture and humidity.

Mine does the same exact thing on mornings with a lot of dew on the ground if its been parked outside.

Since he has already metered to the fuse block...

Just let me know after you replace the switch lol...

don't forget about the asd relay which works in conjunction with the fuel pump and ignition. I've seen the ecu's go bad in which they don't 'wake up' after sitting all night. I pulled my hair out as you did trying a fuel pump, new hoses,all that stuff and it ended up being the ecu after all.

Its an easy test to see if it is the ecu or cps or ignition switch.

Once the fuel pump is primed (since you bypassed)

Take a length of 14 gauge wire and run it from the positive battery terminal to the hot wire (red) on the ignition coil.

Start it up.

If it runs, its the ignition switch, if it doesn't look to your ecu, or cps.

You can also keep the jumper wire there.. .adn tap ground the white wire...put a screw driver in the distributer end of the coil wire... place it about 1/4" away from a ground.
As you tap ground the white wire you will get a spark. (just dont touch the metal of the screw driver)

okay guys new update,..... replaced CPS and ignition switch still nothing!!!:mad3:,.... im going to check the input to the coil tomorrow,...the is a plug with a green orange stripe wire and a gray wire,..going into the coil,...which one should i test,..and i know i should test it while im cranking,... but i took my ecu out to see if it was fried,..but cant tell cause of that gel crap,... soo is there anyway i could test the ecu? i cant find the hook up for the scan tool either,..so any information would be helpful:D

Ok...lets start from scratch.

Your problem in very simple terms.

You had no gas, but now you have gas? You say that now you can hear the fuel pump priming after re-wiring it.

Are you absolutely 100% certain that you are getting good fuel pressure and good flow to the fuel rail? Have you pushed the lil button on the test port to make sure gas squirts all over the place? (USE A FACE SHIELD WHEN DOING THIS AND BE CAREFUL)

You said you have no + power to the ignition coil. Now your not shure which wire to test? Sigh, be more careful with your clues, or youll spend a ton of cash on problems that dont exiist. I will have to check my jeep when I get home to tell you which one primes the coil with the ig switch in the run position, but I am fairly shure it is green w/orange stripe.

As for testing the coil/ignition system. DO NOT PLAY WITH THE COIL WHILE CRANKING THE JEEP UNLESS YOU WANT TO GET ELECTRICUTED.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=4424 Best tool ever, you connect it between your main coil output wire and distributor, have a friend crank while you watch.. the light bulb flashes every time a spark throws.

If the bulb doesnt light. You need to.

A. check the positive input wire into the coil. It should read 12v with your key in the run position, if it does not. Jump a wire from the + terminal of your battery to the + input wire into your coil, and try cranking again. If it runs its an ignition issue, If that doesn't work..

B. Get a multi meter and test the resistance load across the coil. Please refer to your Haynes or other automotive manual for instructions values and warnings to do this, since I do not remember them all offhand.

If all of that checks out and its sparking fine to the distributor, then you need to take the inline checker and put it between the distributor cap and any cylinder and watch for the bulb to light up. If it doesn't its a distributor issue.

______________________________

The ECU test port sits in the wiring harness just above and to the drivers side the ECU on the firewall, is capped, square"ish" and about half the size of a box of tic/tacs, this will allow you to test proper ecu functionality.

Kinda hard to diagnose via forum, but I am trying.

okay guys new update,..... replaced CPS and ignition switch still nothing!!!:mad3:,.... im going to check the input to the coil tomorrow,...the is a plug with a green orange stripe wire and a gray wire,..going into the coil,...which one should i test,..and i know i should test it while im cranking,... but i took my ecu out to see if it was fried,..but cant tell cause of that gel crap,... soo is there anyway i could test the ecu? i cant find the hook up for the scan tool either,..so any information would be helpful:D

After thought

Did you replace the ignition switch, or the lock cylinder that the key goes into, they are VERY different items.

After you replaced the switch did you test the column wiring harness to make sure you are getting 12v in, and 12v out to all the appropriate wires?

Did you make sure you plugged the harnesses back in, and properly, and use some di-electric grease?

Did you make sure to put all the grounds back in place?

i replaced the ignition switch,. and the CPS i am about 75% sure it is the ecu cause while testing the coil i acidently testedthe wrong wire and it,...bluw the ignition fuse and the ignition or nothing worked for about 10 secs. and then just came back on,...im going to try and find an old ecu,... and yes i did check my fuel pressure and it is fine,... but if the ecu doesnt work,..then im going to bring it to my college and hook a scann tool to it,... the phenx: thank you for all your ideas,..if it wasnt for ppl like you on these forums then no body would ever get anything fixed :D

Lol thanks...just bored at work...and I know yj's really well... let me know if the ecu replacement fixes it.

My '91 YJ did the same thing. I would die on the trial.... crank, crank, crank, nothing. Then for no apparent reason, it would start some 1/2 hour later.

Direct jumped the fuel pump from the battery. It would hum like crazy. Plug it back into the wiring harness...nothing. Happened for years, on and off.

Finally replaced the ECU,, woalla, fixed it. I found mine at a junkyard.

Good luck, let us know if that's what did it.

Matt

Misspost