Hey there, I' m fresh owner of 93 Jeep XJ with 2.5L engine. Car is cool but it has one drawback, it doesn't start. From what I have already deduced the engine is cranking, fuel pump is working but there is no spark. Coil, distributor, plugs and cables are new.

I already checked some diagrams and tried to check transition between pins etc. and it seems fine. For example: 1 pin from coil transits to 19 pin in ecu and 2 pin transits to 57 pin in ecu (and few more, ill be checking it more closely tomorrow).

As I checked on forums (don't know if its true but it appeared several times), ignition coil have 2 pins, 1 should get 12V from ASD relay and 2 should get signal from ECU (don't know if it should be ground or voltage signal). What is weird, on 1 and 2 pin appears ground, not still but its pulsating quickly. One ground is much weaker than other. Those grounds are with ignition on and off without any change.

I also checked crankshaft position sensor and it seems fine. I also checked pins going to that sensor and on 1 pin there is ground, 2 have 5V and 3 have 4V (shouldn't it be signal cable and have 5V only when sensor sees data?). I checked it with unplugged sensor.

So, my question is, what should I check first? I don't know if its the ecu problem but its weird since fuel pump is working. I think tomorrow I'll start with checking if ecu is getting ignition signal and check pinout to ASD relay.

Would be glad for any help or hints. Sorry for poor terminology but I'm new here. Thanks!

P.S. Sharing diagrams, I'm working with

 

Check your grounds, especially the one near the dipstick. A bad ground can cause all the weird voltage readings you're describing.

Since you have no spark, the usual suspect is the Crankshaft Position Sensor. Even if it tests okay, it can still be bad. Make sure it's fully seated and the gap to the flywheel is correct. A faulty one will prevent the ASD relay from sending power to the coil.

Your ASD relay is likely not engaging. Listen for a click from the power distribution center when you turn the key to "run." If no click, the ECU isn't getting a signal from the crank sensor to activate it.

Double-check that the new coil is the correct part. An incorrect coil can cause these issues.

 

Thanks for reply, I checked grounds and even added some extra just to make sure they're fine. Unfortunately I checked if ECU gets ignition signal and I think it seems fine. From what I already checked:

ECU pins:
3 - gets 12V all the time
9 - gets 12V when ignition is on but it turns to ground when ignition is off
5, 11, 12 - are grounds
29 - also ground but don't know if it should be ground

And the most important part, I don't know what happened since yesterday but fuel pump stopped working. When you turn ignition on there is no clicking from relays, nothing really happens. Also I think when you turn ignition, "Check Engine" light should appear but it's not.

I think I'm losing this battle, for me it seems like ECU problem or really messed up bundle. Any ideas how can I check if ECU is good or what should check next?

 

If you have an OBD2 reader (if not get one),, plug it in and go to live data,, check the "RPM" data as you crank,, It should show something, if it is showing Zero,, change out the CPS to start with

 

Does this thing even have OBD port? I thought the only way to read codes in this car is by counting the check engile light. Where can I find it?

Also, I checked that O2 sensor is not connected at all, could it be a reason of no spark, fuel and check engine light?

 

I don't think a 93 will have OBD2 and live data? The fuel pump should run for a few seconds when you first key-on. Then it turns off until it sees cranking. So if you don't hear the pump kick on again while cranking that would point to the crankshaft position sensor being faulty. The ASD provide power to the coil and the injectors, and the engine computer controls the ground side. Can you tell if you have injectors firing?

 

Ok, so i tried to cheat on ASD relay a little, and I gave ground to 85* pin that should trigger it and spark appeared! Fuel pump also started working.

Unfortunately Jeep still don't want to start, tomorrow I'll probably start with checking if injectors are working as You said. But Check Engine on ignition still don't want to light. Also I'm not sure if spark cables are connected correctly, has anyone have some diagram how to connect it?

 

Ok, so I checked and injectors are not working at all.
There is no ground and no 12V on them.

I guess it's more ECU problem and something is still holding it up but I'll check wires just to be sure.

Update:
I checked it wrong, the wires are okay, going where they should.
On every injector I have 12V all the time (after cheating the ASD relay, without it there is only ground)

But, I guess ECU triggers injectors by ground and from what i checked:
1 - weak ground pulsating (it pulsating always, when ignition is on and when cranking engine)
2 - strong ground pulsating (same here)
3 - nothing
4 - nothing

It's strange that 3 and 4 injector have no sygnal from ECU at all, and 1, 2 pulse all the time, maybe its because of the ASD relay cheating and the ECU goes crazy?
Any ideas?

 

I'm slowly running out of ideas so I went back to the basics a bit. I took back what I did with ASD relay and started by checking CPS and CMS once again, they show infinite resistance on B and C pins so i guess they're okay. Then I started checking wires to these sensors and they seem fine.

But again, I unplugged both sensors and started checking what multimeter would show:

2 pin on sensor - this is the only thing that works fine here I guess, it goes to 4 pin in ECU and provides ground after switching ignition on

3 pin on sensor - this one should provide 5V to the sensor after switching ignition on. It somehow gives 9,8V.

1 pin on sensor - as I checked some forums this one should be signal wire and give feed to ECU with 5V when sensor sees rotation. As I checked, on this wire is 5V still after turning ignition on. Maybe I'm wrong but shouldn't there be no voltage at all?

For me it seems like ECU is giving voltage where it shouldn't. Since I have no better idea what I should do I will give ECU for checking. When I took it apart, I noticed that it had already been repaired once. I hope that's not it because there is no way to find ECU like that here.

 

The drk gr/orange should be hot (12v) whenever the asd is energized...definitely crank key position, possibly on key position with engine not running. The grey wire is the pulsing ground needed to make a transformer (coil) function with dc power. The pulsing ground comes from the ecu based on crank position sensor inputs from rotating flexplate. Offhand I don't know if the pulsing ground is a steady ground and the ecu interrupts, or if steady open and the ecu adds the ground...it must pulse to operate. If you also lost fuel pump, check the fuse 15. -30A and fuse 2. -15A just to left of ASD on your schematic

 

Dark green/orange only have ground, only when I activate ASD relay manually it turns to 12V.

I think ECU might be broken since it gives 5V hot to signal cable for CPS, CMS and Speed sensor. Or maybe it should put voltage here?