CPS Replaced, No Spark Still......

Ok got the CPS changed out on Saturday(after not getting the correct part from the stealership). Set it up, still cranking but no spark. Also no pressurization of the fuel rail. I'm starting to go bald with some of the hairs being pulled out. Cam sensor/pickup coil next, or coil?? I will be checking the dealership part to verify its good, but from reading on here the OEM parts seem to see less failure than the Chain Store parts do. Thoughts on where to proceed next? And yes I reclaimed my membership again, finally after about 3-4 years of non-existance.

Jeff

Ensure that the green wire is connected to your starter relay. Otherwise it could be the coil or dist. Or the cps you just put in. (Its been known to happen)

But an OEM CPS?? The threads that I have read doesn't indicate that the OEMs part fail nearly as commonly as the other "chain store" aftermarket parts do. I was thinking of the coil, and or the pickup/cam sensor.

Jeff

Time to hit the junkyard or a friends XJ to get some cheap parts for tasting with. As I recall a coil is around 50 bucks so throwing parts at it is expensive.
Just my 2 cents.
Ron

Would something else cause no spark besides the CPS? When the rain stops, and guests aren't at my domicile, I will get my readings and convey my findings, but I am almost sure that the CPS is not the problem. I was planning on upgrading my coil to the performance distributor's screamin demon coil, and upping the plug gap to .065". Goal is mpg's and a tad bit of performance at the same time, not looking to win any drag races. I am going to pull the coil and test it as well. Let me know if there is anything else I am missing, like its been said, I don't want to keep throwing parts at it, but I need it to be making some spark and then I will upgrade parts as needed.

Jeff

Does the fuel pump energize and run for at least a second when you turn the ignition key to the on position?

No it does not power up.

Ok.. we need to get that to happen first... if that doesn't work , your XJ will never start.
You need to check to see that the PCM is getting power from the battery when you turn the key to the on position and that it is properly grounded. You should check all the grounds under the hood and all the fuses. If the PCM is powered up and grounded properly it will output a ground signal on pin 51 of the PCM to momentarily activate the ASD relay and the fuel pump relay and you should hear the fuel pump energize and pressurize the fuel rail.
So, your going to need a Digital volt/ohm meter to test for continuity and voltage.
You will need to test for 12 volt power at the relay coils and the PCM. If the relay coil gets energized by the PCm grounding the other side of the relay coil, the contact will close and pass the 12 volt power thru to the fuel pump, etc.

Ok, so I need to figure out what the relay coils are. I can pull the harness on the PCM to determine pin 51. If the PCM is actually bad, then some of this won't happen, and I am wondering if the Jeep took a drive into the drink and got the PCM shorted or made it bad. I guess there is no real way to test for any of that now is there? All the fuses are good, at least all the ones under the hood, I haven't checked any of the ones in the jeep yet, but those are next. I will check the grounds, but the battery's ground wire is good, so now its the grounding of everything else. I appreciate the help here and I will post up my findings before I have to :explosion the Jeep. Since this was a purchase and the PO didn't really give me a whole lot of information on why it quit running, other than what his mechanic told him it "needed", some of which it doesn't/didn't, I feel that only $375, leaves me some room for fixing it up and getting some miles out of this one. The engine sounds strong, and until I get the NSS swapped out, I won't be able to get it to crank from the actual switch, but I have a starter switch on the solenoid to operate the starter, and I leave the key in the on position when I am activating the switch, so it should be working....I'll let you know in a day or so what I find out.

Jeff

Bypass the NSS or simply fix it. I might be logical to assume that if you have to Bubba-rig all sorts of stuff to get the engine to crank, the no fuel pump issue might be directly related to the same issue.

Until you fix the known problems, chasing a bunch of what-ifs (CPS, PCM) seems like a waste of time and money.

ihscoutlover said:

Ok, so I need to figure out what the relay coils are.
Jeff

Click to expand...

ok,.. here is some basic electrical info...

The relays have a coil inside of the relay. When you turn the key to the on position, battery voltage is typically applied to one end of the coil. When the other end of the coil is connected to ground (by the PCM), the circuit is completed and electrical current flows thru the coil, which causes the normally open relay contacts to close. When the relay contacts close, voltage is applied to a circuit to energize the circuit,... in this case we are trying to energize the fuel pump circuit.

So, you need to use a meter to see if the voltage is getting to the relay coil and the normally open contacts. If the PCM grounds the coil, it should close those contacts and pass the voltage thru to the Fuel pump. Naturally, all of this assumes your wiring is good, and relays are working. You need the meter to test the circuit for proper continuity and operation. You will need a schematic of your Jeeps wiring so you will know where to measure for voltage and where to check for point to point wiring continuity. If you are not familar with troubleshooting this kind of circuitry with a meter, you will need to find someone who can help you do it.

Tim_MN said:

Bypass the NSS or simply fix it. I might be logical to assume that if you have to Bubba-rig all sorts of stuff to get the engine to crank, the no fuel pump issue might be directly related to the same issue.

Until you fix the known problems, chasing a bunch of what-ifs (CPS, PCM) seems like a waste of time and money.

Click to expand...

Im not bubba-rigging the jeep just yet. I have dealt with bad starter wiring before, and this use of the starter switch is bypassing the NSS. If the NSS doesn't have anything to do with the actual actuation of relays and engine electronics, then I can leave that alone. But if the NSS does affect the engine electronics, then I have to fix that first. From what I have read in the FSM, I don't see that is an issue with what I am currently dealing with. No spark and no fuel. Since I have read here and in the FSM, that the CPS prevents a spark event from occuring. That would seem to be a logical part keeping the rest from working. Now that the CPS was replaced, I am still not getting spark. So I am back to square one, in that I still don't have spark. So now I need to verify that the relay circuits are being energized, along with making sure that all the grounds are clean and secured properly.

McQue, thanks for clarifying the relay coil thing. I have several meters and have done a bunch of emergency vehicle wiring, so tracking down some of these issues should be simple. I am trying to rule out some of the more simple things and then see where I go from there. I am planning some upgrades anyways, and so if some or any of these parts are going to need replacement, then so be it. This is going to be the winter time DD, and the summertime backup vehicle. Since I have an extensive knowledge with Scouts(beings they don't have computers or complex emission circuits), I am using that simple logic to base how I am going to troubleshoot it next. Sooner or later I will find the root cause of the problem and be able to report back my findings to help someone else out. Right now its the secondary backup, but will be the primary vehicle, which is why I am trying to narrow down what or where my issue(s) are so that I can get it back on the road again. Thanks so far for thoughts and suggestions, post up any other ideas for troubleshooting and then I will post findings after I have done some of the checks outlined here.

Jeff

Just to clarify, the neutral safety switch (or the corresponding clutch interlock switch on later 5 speeds) controls only the starter relay. If the NSS is bad, the engine will not crank at all. If it cranks, it's not that.

May just be a bad ignition switch and or wiring to that switch that is not getting power to the PCM.

To clarify, I am bypassing the NSS, by hooking a remote starter switch directly to the starter to crank the engine under the hood. I guess I am needing to find out if when the ignition switch is turned to the on position that things are getting juice correctly, or as indicated that the relay(s) are getting the continuity so that they can close, so that I can rule some things out. Also pin 51 on the PCM is supposed to be a ground signal, so when the ignition is turned on, then that wire in theory should give me continuity to vehicular ground.

And in so far as the underhood relays, well I have trouble shot the ones that were in it, and those appear to be working/closing correctly, per the FSM. I need to check the fuse box inside the Jeep to determine if I have a fuse blown, and if so, can it be related to the current issue. I did pull the annoying chime box out, so I can take it to the range for practice...jk.

Once the wife gets home, I can get out there and check a few of the fuses and such to see if I am missing something there, and then start into the relays and their associated parts to see if I am getting the correct signals.

Jeff

Can a bad temp sensor cause a no start?

I know it doesnt get read until the loop closes, but can there be a problem with it that would cause a no start, no spark situation?

stockli said:

Can a bad temp sensor cause a no start?

I know it doesnt get read until the loop closes, but can there be a problem with it that would cause a no start, no spark situation?

Click to expand...

Yes it can. I had that very problem with my 87. The intake manifold air temp sensor (IAT or MAT sensor) was giving out bad data. I forget which it was, but it was either hot cold, it would not start, and visa versa. New sensor fixed it.

Update:

I checked the ASD relay with the ignition switch on and off. Relay positions 85 and 87 show continuity when the ignition was on, and none when off. I have also pulled the coil and am running it through some testing. All under dash fuses were good, and I need someone with an owners' manual to either PM me with what fuses go where, as there are some slots missing fuses, one which is for power windows and locks, which this one doesn't have.

Ok, so where do I need to proceed from here? Thanks and keep the suggestions/help coming.

Jeff

A bad sensor can short out the supply voltage of the pcm, which in turn shorts the ASD circuit, preventing spark and fuel. I'd disconnect all TB sensors and cam sensor at dizzy and attempt to start it with just the CKP connected(it won't idle). I've had a shorted o2 sensor and bad coil be the cause of this.