89 motor swap into 90. Now no spark ?

I cracked the block near my RMS on my original motor. Just bought a new one instead of fix the old.
Finally got it all together. Now to have no spark. I have fuel for sure. All I haven't put back on is the air box and some vacuums. That shouldn't effect me though.

I made sure my ground was tight and clean. Any idea what could stop my spark? This is my first time playing with 4.0s at all. So I wouldn't be surprised if I missed something stupid. Feel free to insult me.

check crank sensor-- it's easy to break it if you didn't remove it before pulling the engine. It is also possible to pinch the wires upon installation and create a short to ground.

I checked the sensor. Reads 268ohms. I believe that's in operating range. Not sure what else to look for

Check to make sure your CPS is plugged into the correct harness connector - mine had not one, but three identical female plugs that fit the CPS (all in the same general proximity). I got the wrong one and panicked awhile back after replacing my head gasket. It predictably causes an endless-cranking nospark situation.

The 87-90 Renix XJs had the CPS poorly wired thru the notorious C101 connector on the firewall. From what I've gathered from the old-timers here, it became enough of an issue that there was a TSB issued that re-routed the CPS; bypassing the C101/main harness. Apparently my XJ had that done - the tech back in the day never clipped off the old connector. As to what the third one is the jury is still out

hillcameron415 said:

I checked the sensor. Reads 268ohms. I believe that's in operating range. Not sure what else to look for

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Checking the resistance does not insure the sensor is good. Don't ask me about how I came upon this tip, but, are you sure you have a rotor in the distributor:jester:

LMAO, or that the rotor is installed all the way on the shaft LOL, don't ask,

Test across the two CPS wires while cranking. There must be at least 0.50 volts AC reading on a multimeter. Post up what you find.

Found .3v there. So I replaces the crank sensor.
No dice.
Still is without spark.
What else is could do it? Coil? ICM?

old_man said:

Checking the resistance does not insure the sensor is good. Don't ask me about how I came upon this tip, but, are you sure you have a rotor in the distributor:jester:

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And yes I have a rotor in. New cap new rotor. As well trying others.

If I take the center plug wire, going to the coil. And I put a spark plug into the end, I have no spark when cranking.

hillcameron415 said:

And yes I have a rotor in. New cap new rotor. As well trying others.

If I take the center plug wire, going to the coil. And I put a spark plug into the end, I have no spark when cranking.

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Not trying to disparage your efforts or knowledge, but when you did this, did you have the threads of the sparkplug touching the block?

hillcameron415 said:

Found .3v there. So I replaces the crank sensor.
No dice.
Still is without spark.
What else is could do it? Coil? ICM?

Click to expand...

Like I said before!
"There must be at least 0.50 volts AC reading on a multimeter"

The aftermarket CPSs are crap. and the OEMs were not much better.

The Fix is to pull the CPS, measure the hole size with a numbered drill bits/set and open up the mounting holes using one drill size larger. I just used what I had in my set (I may have gone a little larger). I forget the size. Several old threads here on this mod going back 15 years.... But a larger drill bit, with in reason, is OK as there is plenty of space to get way closer to the flex plate with out hitting it.

Then you push the CPS down from the top side towards the flex plate teeth and hold it as close to the flex plate teeth as possible and tighten the 2 mounting bolts. That should get you at least 0.50 volts AC while cranking.

Also the Battery must be fully charged, enough that the cranking voltage is no lower than 10.0 volts while cranking (check that before you pull the CPS), and the starter must be getting that 10.0 volts or more at the starter and be a good starter for the engine RPMs to be high enough to get the 0.50 Volts AC out of the CPS. Other wise the ECU can not read the CPS signal, and thus no spark as the ECU sends no signal to the ICM.

Oh, and I said to post up you findings, I did not say to run get a CPS and replace it , but I guess I should have been more clear. Think I was in a rush at the time

According to Cruiser54, ex Jeep dealer service manager, they learned decades ago to drill out and move the CPS closer to the flex plate as part of the fix, the other fix was bypassing the C-101 bulkhead connector and I think soldering wires, but moving the CPS just .05 inches (my estimate from memory, may have been a weebit more) nearly doubles the CPS output voltage and results in 100% starts for over 12 years now on my 2 Renix jeeps, 87 and 89. My thanks to Cruiser54 for teaching me that trick!!!!

Ecomike said:

Oh, and I said to post up you findings, I did not say to run get a CPS and replace it , but I guess I should have been more clear. Think I was in a rush at the time

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Yeah I jumped on that. I have about 6 posts on jeep pages in Facebook and they all said CPs too, so I tried it.


So here's my update

I borrowed a friends coil/ICM and distributor. And I got it to fire up. Yay me right? No. After I started putting things together I started it and revved it a bit. And after a sec it started to poop out. And now I have no spark again.

My fuel pump relay is ticking like a mofo, does any of that have anything to do with ign? I still have fuel on start.
Now my CP's is reading .4v not .5 anymore. You think it went bad that fast? Or do I have short somewhere?

Also if anyone has info on what wires need to have what voltage and when, that would help me pin stuff down. I know yellow wire feeds stuff, and so does some orange wires. I have a Chilton's manual handy. I just don't know what I should look for in those wires

Mine would start one day and not the next, start and run for one trip and die-non start for the rest of the day, at .30 volts.

Lots of possible issues, but if you did the mod (Did you do the mod or did the new CPS have 0.50 Volts AC output when you tested it?) did the MOD get you up 0.50 volts and did it not start even then, or ?????? We need an exact step by step sequence of what you did and what the results were, forensic report style, not emotional style.

What happened first, when did you first read 0.50 volts on the CPS and after what? When did you swap the ICM, coil and dizzy in relation to other events? Do you have the dizzy indexed properly? plug wires criss crossed, Are you getting spark now, but no start?

Renix fuel power runs through 3 different circuits, it gets power before cranking on a timer circuit, then a second circuit for cranking then a third circuit for running, so pressure in the run spot, engine off does not pressure or flow while running or cranking.

I would continue to focus on the sometimes no start that is only partly fixed. Renix loves to start when it wants too and can be caused by many electrical issues, the first of which is a CPS with less than .50 volts...The fuel pump is also electrical.

Go back to basics on the non start, does it still have fuel in the rail under pressure and does it spark when cranking. No spark is usually the CPS. Check the bolts, did the CPS move, loose bolts? Next up is a loose contact under the ICM coil to the ICM guts, open it up and clean the spring metal contacts and tighten them) or dirty ground on the ICM bottom?

The dizzy may be off by one gear on the indexing, but that would cause poor running, not a total non start as I recall.

@ecomike I emailed you.

And how would I go about checking why a relay is ticking like crazy? Because my fuel pump relay is clicking, and it never did that before, when the motor ran. Maybe it's just a coincidence, or maybe it might have something to do with my other electrical/spark problems

hillcameron415 said:

@ecomike I emailed you.

And how would I go about checking why a relay is ticking like crazy? Because my fuel pump relay is clicking, and it never did that before, when the motor ran. Maybe it's just a coincidence, or maybe it might have something to do with my other electrical/spark problems

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Next thing to do ( due also to the clicking fuel pump relay while it was it running) is pull and clean the connectors and the block ground at the oil dip stick which is where all the sensors and ECU are grounded. They are notorious for creating problems like yours. Also pull and clean the contacts on the relays under the hood one at a time. Q-tips and sudsy ammonia works great!! Rinse with solvent and dry.