Problems with XJ starting!! Need your suggestions!

After searching and trying different things all day, I am having no luck!

I have a 1990 with 4.0 and AW4

I was driving doun the highway, and my engine was cutting in and out. I pulled off the main road and it died and didn't start.
I popped the hood to check the infamous CPS connection. Unplugged and re-connected it with no luck.
I then unplugged and re-connected my MAP sensor and it started. As soon as I put it in gear and gave a little gas it started cutting in and out again. As soon as I stopped it died again. Tried starting...nada. Reset the MAP again and it started. Did the same thing again, except this time it won't even try to fire. I towed it to my work and have been messing with it for two days!

I am getting no spark at the coil...plenty of fuel.
I have a friend that brought me his jeep that runs fine to try parts off of.

Here's what I've tried from his:
MAP sensor
Ignition module and coil
Cap and Rotor

I have also tried:
Used CPS
Brand new CPS
Used ECU (I tested this a while ago and it's fine)

I checked my TPS with an ohm meter, and it's not shorted and gives varible resistance while slowly pressing the throttle. I would have swapped his in, but I had a small fire about a year ago that melted the connector, so I hardwired the sensor. (before I rewired it I had the occasional high idle we all love, but bypassing the connector fixed mine)

Now for the fun part...I re-installed the parts I borrowed in my buddies XJ, and now it won't start either!!! (At least he doesn't need it anytime soon, and isn't mad either..lol)

I checked the MAP connector for shorts and found none. I Checked the wired at the Ignition Module and am getting ~12v on the larger yellow, Good ground at the black. I also did an ohm test from the smaller yellow wire to the connector on the ECU.

Any more ideas??? Now I get to fix 2 Jeeps...yay

Start relay any good? That's my first thought - since A) you don't mention replacing it, and B) I remember going through about four of them one summer in my 88.

Got tired of that and wired in a Bosch - I really should see how I did it, so I can write it up for everyone else here.

Your start relay is the gold box in front of the four relays, behind the battery. I'd have to look to see how, but you can jump the relay as a bypass to see if that's the issue. With the key off, you'll be able to crank, but not start. (With the key on, you'll be able to start it from under the hood - I tend to wire in a "bump" switch underhood for when I'm working on things...)

Just a thought. That would relate to your "won't try to fire" - you don't say if it's a no-crank, or a crank-no-start condition, so I'm wondering (there are various levels of no-start to troubleshoot, it's useful to know which one.)

I'd also get a "noid" light (about six bucks) and plug it into a fuel injector connector - watch for flashing when you crank. That will help confirm operation of the ECU, CPS, and maybe SYNC in the distributor.

Get a "spark tester" (it's got a plug terminal on one end, and a crococile clip on the other, with an adjustable gap in the middle.) This will verify operation of the ECU, ICM, and maybe SYNC (I keep saying "maybe" because if the SYNC sensor isn't working, the ECU will "guess" until it finds something it likes.)

If you don't have the RENIX FI manual, you can download a (mostly) complete copy from the strokers egroup (groups.yahoo.com/group/strokers,) files section. I say "mostly" - as I recall, it's got two page 58's and no page 59. I'm looking for a page 59 that I can plug in, or a compleat copy to begin with.

Post resuts, and we'll see what else we can come up with.

5-90

Sorry, It's cranking fine, I just dont have any spark.
I tested for spark with a tester both before and after the distributer, nothing.
It's getting gas, I used the old fashoned pull a plug and smell routine. I may double check this with the "noid" light you suggested if I can find one.
Since whatever the problem is took out my friends components too, I am going to have the alternator bench tested tomorrow to make sure it's not the voltage regulator. I will also test for shorts again.

my jeep did the same thing accept i came home and it wouldnt crank the next day...i replaced distributor, cap, rotor, and it ended up being the crank sensor in the back of the engine on top of the tranny bellhousing... maybe that will help, i had same problem no spark

suthernoutlaw said:

my jeep did the same thing accept i came home and it wouldnt crank the next day...i replaced distributor, cap, rotor, and it ended up being the crank sensor in the back of the engine on top of the tranny bellhousing... maybe that will help, i had same problem no spark

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This was my first thought, I am not so lucky, I have tried two sensors (1 used 1 new)

Since whatever it is caused my friends Ignition mod or MAP sensor to go bad, I would think It must be shorted or over powered?
I am going to fix his first so I can narrow down what component mine is frying. (crossing fingers it's the MAP since it's 1/3 the price, but I won't be that lucky)
I will go later today and test the alternator voltage regulator.
I have misplaced my service manual, so If anyone has schematics of the ignition system, it would be very helpful in my testing for shorts. (I signed up for the strokers group, just waiting for the email so I can join.)

TRAILREADYXJ said:

This was my first thought, I am not so lucky, I have tried two sensors (1 used 1 new)

Since whatever it is caused my friends Ignition mod or MAP sensor to go bad, I would think It must be shorted or over powered?
I am going to fix his first so I can narrow down what component mine is frying. (crossing fingers it's the MAP since it's 1/3 the price, but I won't be that lucky)
I will go later today and test the alternator voltage regulator.
I have misplaced my service manual, so If anyone has schematics of the ignition system, it would be very helpful in my testing for shorts. (I signed up for the strokers group, just waiting for the email so I can join.)

Click to expand...

Thanks Langer1,
I had the alternator and ignition module tested. The Alt is fine but the module failed. I am still concerned there may be other problems, unless the other module went bad while swapping it around. (seen this before, I install 12v stuff for a living.)
I read it may not be safe to test the signal from the ECU to the Ignition Module. I have a really good DMM, has anyone had problems testing this?
Can I test the signal with the module out of the jeep?
The only thing I tested on this wire is the impedance and to make sure it wasn't shorted to ground. I did these tests with the ECU and Battery Disconnected.
The power, and ground test fine, and the tach wire is not shorted.
I would just hate to fry another Ignition Module.
I am going to swing by the junkyard on the way to work tomorrow and get 2 used Modules, hopefully I can get one of the Jeeps running.

TRAILREADYXJ said:

I read it may not be safe to test the signal from the ECU to the Ignition Module. I have a really good DMM, has anyone had problems testing this?
Can I test the signal with the module out of the jeep?

Click to expand...

Anyone test the signal from the ECU to the Ign Module? I assume it is a DC pulse, but don't want to damage the ecu by improper testing.
I would like to test this before sticking in a new part if possible.

TRAILREADYXJ said:

Anyone test the signal from the ECU to the Ign Module? I assume it is a DC pulse, but don't want to damage the ecu by improper testing.
I would like to test this before sticking in a new part if possible.

Click to expand...

Test it connected on DC volts, it is a pulse so you need a DMM with the bar scale or a analog meter to see it.

I have acutally fried 3 ignition modules due to what ended up being a bad ground. I guess the spike/arking really fried them. These were aftermaket (wells) icms but never had any problem with the OE Siemens (formally renix) i would prope your wiring and check your gorunds then go for the ignition module. The ignition circuit as langer's diagram shows is very simple

Well I put in a good module (tested first), It' still doesn't start. I pulled the new module out to have it tested and it was fine, so at least I'm not frying modules. I also put a good module in my friends Jeep with the same results.
Is there a fuse somewhere I'm missing??? I still get 12v at the ICM, and the ground is good, reads no resistance at all. (well maybe .001 ohms)
I tried to test the pulse wire but It either isn't getting signal or my meter just isn't quick enough to show the results.
I also tested the coil(s) and they are within spec.
I also tried another MAP sensor.


I'm starting to loose hair over this!!!

something is telling me that something is telling the ECM not to fire the coil.. the main bad guy on this is our friend the CPS... considring the CPS is new... now i have had TWO bad aftermarket CPSes ... so that coudl be... i would check your wiring to the CPS.... chrysler issued a TSB about rewiring that to eliminate two of the bulkhead connections. I had this same problem 5 yrs ago.. over and over and over again... I must have looked at thait wiring diagram 1000 times It was the following:


#1 defective autozoo CPS was number 1
#2 bad ground from block to firewall
#3 bad distriub indexing from thinking it was the Cam Sensor on the distrib.

TRAILREADYXJ said:

I'm starting to loose hair over this!!!

Click to expand...

Do some basic sensor tests, before all of it falls out. I've found many problems in my '89 XJ (and eliminated many needless parts swaps) armed with an DMM, analog voltmeter and the manual.

First of all, start here: http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

The critical sensors that are required to start the Renix 4.0 are: 1) CPS (Make sure you check it's operation with an analog vm, not just a resistance test), MAP, TPS and CTS.

serge said:

Do some basic sensor tests, before all of it falls out.

Click to expand...

There's actually plenty left..lol...I have been around Jeeps long enough to expect trouble..lol

serge said:

The critical sensors that are required to start the Renix 4.0 are: 1) CPS (Make sure you check it's operation with an analog vm, not just a resistance test), MAP, TPS and CTS.

Click to expand...

I will try testing these again, I have tried 2 CPS sensors and a MAP sensor. not saying they were not bad, especially with my luck!

The thing I don't understand is my friends Jeep doesn't start, and it ran fine before I swapped out the ICM and MAP. I put in a good ICM (tested @ autozone first) since his tested bad. I know his CPS etc... shouldn't be bad.

I will do some more tests today...It just sucks because I have to drive an 8 MPG F-150 for now!

Okay, I tested all the sensors and found that the CTS is reading open!
Would this acutally keep it from starting? I hope so since it is the only thing that tested bad.
I will get a new part anyway, but to know this could cause the problem would be great!
I won't get a chance to try till tomorrow, assuming that the part is in stock.

TRAILREADYXJ said:

Okay, I tested all the sensors and found that the CTS is reading open!
Would this acutally keep it from starting? I hope so since it is the only thing that tested bad.
I will get a new part anyway, but to know this could cause the problem would be great!
I won't get a chance to try till tomorrow, assuming that the part is in stock.

Click to expand...

Try unpluging your buddies CTS and see, I doubt it though.

Had 92 did the same thing check the coil wire , sounds stupid buts that what mine was .

Well the sensor was a no go. It was getting late yesterday when I tested it and my meter was on the wrong setting...doh

Here's a rundown on everything I have done so far:
Remember I am getting no spark at the coil.

I have tested the following going by the FSM and they are all well within spec.
1) CPS
2) ICM
3) Coil
4) Sync Sensor (pickup coil)
5) MAP sensor
6) TPS
7) Plug and Coil wires
8) CTS
9) ATS
10) I also tried a different ECU, but am not ruling this out since it had a bad ICM when I tried it. The old ICM may have fried both???

I used an analog meter to test the pulse signal at module and there is none.
I guess I will go through the joy of testing these sensors at the ECU harness to rule out any wiring problems.

Its going to take a bit but the next step is to go from the sensor to the ECM with every wire to check for grounding out and for continuity... i would start with your CPS wiring.. If you have a C-101 bulkhead connector thats probley a good start

Listen to this:
I had exactly the same symptoms and it seemed that when just jiggle the wires at the sparkplugs it gets better...I changed all the stuff you did and reflashed the computer at one shop and they never figured out what it is and then the stealership told me its contaminated fuel...
It was the connector to the fuel pump check that, the one that's waaay on the back you'll see it hanging. That harness is exposed to the elements and when it gets old does tricks that look like a spark issue.
Let us know...
Boris