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Hopefully the last no spark issue ever

O

oldie eye

NAXJA Forum User
Location
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What besides the CPS is needed to provide spark in an '87 4.0? I have primary coil voltage, and the most maddening intermittent spark. After some major work, I had no spark. I wiggled stuff for about an hour, then wiggled the 4 block grounds for the umpteenth time and got momentary spark. I rewired them, and now have good grounds, but no spark. 2 hours of checking and wiggling and no spark, I wiggled them again and got spark. Now steady ground at the wires (before ringlets) but no spark. 1 hour of wiggling later I got a little spark when I wiggled the head temp sensor wire, now no spark. I have primary voltage, and a new CPS (never even driven on it). I need CPS, ECU grounds, & anything else to trigger the secondary ignition?
 
I should mention that I just changed the wiring harness from relays to ECU, the ECU, CPS, & that's about it. I tried swapping the 2 middle (of 4) relays, no difference. The relays are from the donor harness. The CPS shows 230 ohms at the ECU connector.I think the ECU is good because it did run for a second or two on two seperate occasions. The harness, relays & ECU came from a junkyard. I have no FSM, but wish I did. Also the TPS is untested from a junkyard. If the TPS ESTA NO BUENO would that screw things up?
 
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It sounds to me as if you have a loose or broken wire somewhere in the harness .If you are wiggleing them and you start to get spark thats is a good indication of that. The wire may be broken inside the insulation where it cant be seen. Another thing to check is the igniton control modual under the coil . I recently had a similar problem and found that to be the source.good luck.
 
I know I'm asking for an easy answer to a gremlin question, but can anyone think of anything else? I have good ground to the b11 & b12 terms. at the ECU, the TPS gets & gives correct voltage, & the CPS is A-OK. What on earth else do I need for a spark trigger?
 
A really quick check shows no cont. to ground for the LATCH RELAY GROUND at the ECU (A9) & no voltage present for the LATCH BATT +. This is with the key on. This doesn't sound right, although I have no reference.
 
Sorry to fill my thread w/ my own posts, but I am TRULY desperate & have finally found some consistency in the spark. I am an old man in the dark, & trying to test for spark w/ a wire connected to the starter solenoid, key on, & touching my home-made lead to the pos. batt term to get a crank. If I momentarily crank it 3-5 times, on the last shot I get a steady spark until I take the wire off the term. Then nothing. DOes this have something to do w/ starting voltage for ign. versus run voltage for ignition? Starter or latch relay maybe?
 
oldie eye said:
Sorry to fill my thread w/ my own posts, but I am TRULY desperate & have finally found some consistency in the spark. I am an old man in the dark, & trying to test for spark w/ a wire connected to the starter solenoid, key on, & touching my home-made lead to the pos. batt term to get a crank. If I momentarily crank it 3-5 times, on the last shot I get a steady spark until I take the wire off the term. Then nothing. DOes this have something to do w/ starting voltage for ign. versus run voltage for ignition? Starter or latch relay maybe?
Click to expand...

'Sounds like some type of starter/ignition bypass if I understand correctly? Dunno it by memory but if you read wiring diagrams, here's a couple that might help you qualify your spark issue.

Wiring

Ignition

Good luck
 
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XJXJ, the text mentioned a bypass briefly but didn't say anything about it in particular, but that is also what I'm thinking too. It doesn't matter if I crank w/ the key or w/ the remote wire, same thing. It will spark after several momentary contacts w/ the battery, it will crank & even run (poorly) but then no spark until I repeat the the sequence of several momentaty cranks. Also, & this is very wierd, at several points the starter pinion wouldn't re-engage the ring gear & just made the grinding noise(obviously, because of the momentary contact requirement to get spark, the flywheel was still spinning, the pinion can't engage) & the spark was so rapid it seemed like the CPS signal picked up on the starter pinion instead of the ring gear. If the spark increases speed that drastically w/o the ring gear slipping on the flexplate (brand new flywheel, never driven on) what on earth could that mean? COuld the CPS pick up on the scraping vibration of the pinion?
 
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oldie eye said:
XJXJ, the text mentioned a bypass briefly but didn't say anything about it in particular, but that is also what I'm thinking too. It doesn't matter if I crank w/ the key or w/ the remote wire, same thing. It will spark after several momentary contacts w/ the battery, it will crank & even run (poorly) but then no spark until I repeat the the sequence of several momentaty cranks. Also, & this is very wierd, at several points the starter pinion wouldn't re-engage the ring gear & just made the grinding noise(obviously, because of the momentary contact requirement to get spark, the flywheel was still spinning, the pinion can't engage) & the spark was so rapid it seemed like the CPS signal picked up on the starter pinion instead of the ring gear. If the spark increases speed that drastically w/o the ring gear slipping on the flexplate (brand new flywheel, never driven on) what on earth could that mean? COuld the CPS pick up on the scraping vibration of the pinion?
Click to expand...

Well bud, I studied the wiring diagram and didn't see any type of ballast resistor for the ignition only the fuel pump. But, the ECU does look at the green starter solenoid wire for start signal information. Dunno what Renix does with that information inside the ECU?

The rest of your post I'm not understanding? Did you change flywheels ro something? The CPS isn't close enough to the starter for the starter gear to have any effect on the signal. Perhaps you have some weird grounding going on?

Check all of those grounds and follow the wiring diagram to verify B+ on the right components.

'Sorry I can't help you better than that. Hang in there, you find it.
 
This is a VERY interesting problem (to me, I'm sure you're angry about it) . Let me do a little thinking & research before I throw my two cents in. At 1st glance it looks like it could be a few obscure issues. Think about these:

1) some kind of crank vs. run voltage issue
2) If it will spark AFTER several momentary cranks, I would think relays may be involved, as 2 of them power down a few seconds after you crank; 1, then the other. The several second delay & staggered shut down of the relays may help indirectly guide you to the light at the end of the Jeep. I assume you crank for 1-2 secs w/o spark, stop cranking, then re-crank while the engine is still spinning? & THEN you get spark after a few of these cycles?
3) Latch?
4) I have heard many starters spin w/o catching the ring gear, but never triggering the CPS at that accelerated speed, something may be amiss w/ your starter, CPS, or ring gear.
5) The ECU does need a certain RPM from the CPS to run, I assume you've got that or you'd never have any spark.

Stay cool, I'm sure an ignition Guru will be along shortly, I'll do some studying :read: & make a few calls :callme: !!
 
Beav350, you are correct about how the spark can be consistently created. it seems that if I let the flywheel stop, it won't spark. I beleive now that something w/ the CPS is wrong, because a few times when I try to crank w/ the flywheel still going (it's soooo bad) & the pinion just grinds and spins FAST, I get the FAST spark (like 1000-2000-3000 rpm style), & sometimes nothing til the flywheel is almoststopped then 1 single spark (w/o the crank moving at all!) Since the CPS triggers the ECU, maybe something bizarre is up. XJXJ, I just replaced the flexplate w/ a new $31 unit from Axiom, & it certainly looked like the right one. It ran Ok before, then I changed the harness (but not the injector part of the harness, just the main bit), relays, ECU, CPS, Flexplate & TPS.
 
Thinking about, it seems that if the ign. key is in the run position, then cranking remotely eliminates many variables. The onlt thing I can think of is the flexplate (trigger). I'm leaning toward a flexplate/CPS issue, although I'm going to look into the starter solenoid/ECU relationship for you.
 
I was thinking about this & I had an idea: It seems that your starter is triggering your CPS, intermittently. Electric motors function by switching polarity, so if you have spark at the same rate as your disengaged but spinning starter, then you may have your wiring goofed up, and the starter is triggering the ECU. It sounds ridiculous, but the CPS works sorta the same way, only w/ a magnet., If you have a junkyard harness, the wires may be slightly different, do you have the old harness to compare to, wire by wire? The CPS may not even be doing anything, try pulling it out & if you still have this random spark, then you'll know for sure. I don't know, just an idea. I wish I could think of how the spinning starter (free of the flexplate) could trigger spark at the same super fast speed. This WILL keep me up tonight...
 
I disconnected the CPS, no spark at all. the replacement harness is from an '88, my jeep is an '87. Original and replacement harness are for an auto. I took the ECU from the same Jeep I got the harness from, & every wire seemed to hook up the same as my old harness. The only difference is: My original harness had the CPS connector up top by the intake manifold, the plug came out of the upper harness for the injectors. The replacement harness had 2 wires for the cps that came from the ECU directly. I spliced the CPS into the ECU through the firewall. SInce I only replaced the part that runs from the Relays to the bulkhead conn. & down to the ECU, & not the upper injector bit, I don't know if that matters. There has to be some issue w/ the CPS, as it fires sometimes at starter speed, & it triggers the spark. The flywheel is the same type as I had before, & I removed the CPS to make sure it was clean & mounted properly. No difference. I'm at a loss.
 
oldie eye said:
I disconnected the CPS, no spark at all. the replacement harness is from an '88, my jeep is an '87. Original and replacement harness are for an auto. I took the ECU from the same Jeep I got the harness from, & every wire seemed to hook up the same as my old harness. The only difference is: My original harness had the CPS connector up top by the intake manifold, the plug came out of the upper harness for the injectors. The replacement harness had 2 wires for the cps that came from the ECU directly. I spliced the CPS into the ECU through the firewall. SInce I only replaced the part that runs from the Relays to the bulkhead conn. & down to the ECU, & not the upper injector bit, I don't know if that matters. There has to be some issue w/ the CPS, as it fires sometimes at starter speed, & it triggers the spark. The flywheel is the same type as I had before, & I removed the CPS to make sure it was clean & mounted properly. No difference. I'm at a loss.
Click to expand...

From "a" schematic - C-1 & D-1 on the ECU connector are the CPS wires for sig/gnd, put your ohm meter across those with power off and connector removed from ECU. You should see 200-300 ohms or the same as from the CPS itself.

'Sounds like you've changed a lot of stuff and I'm not sure I wanna know why? (((LOL ))) Anyway, print that diagram and follow the basic things that influence ignition. It's really not that many items but you need to follow the diagram, keep track of what you check and how.
 
Yeah, I have changed a lot, but it all needed changing. The first thing I did was check CPS resistance, its like 200 ohms or so. The weird thing is the fact that she will spark, intermittently, at the spinning starter (not spinning flywheel) speed which is many times faster than it should be, plus the flywheel IS NOT TURNING?!
 
oldie eye said:
The first thing I did was check CPS resistance, its like 200 ohms or so.
Click to expand...

My question was if you checked CPS resistance at the ECU input/connector to qualify the wiring harness that has been changed?

Yes, something seems funky about the starter circuit but instead of getting too hung-up there, my suggestion is to trace ignition/starter on the diagram and make 100% certain all inputs/outputs for ECU, ICM, sensors & relays are wired correctly.
 
Follow XJXJ's advice, & also clean the bulkhead connector at the d-side firewall. Make sure all the wires check out at the right places w/ continuity & no shorts to ground. Then at least you'll eliminate the wiring and can focus on the components. I've asked a lot of people today about the rapid spark following the starter speed when not engaged in the flywheel, & it's stumped everyone, especially considering that they (the starter & CPS) are on opposite sides of the bellhousing & apparently should not be electrically connected. Maybe one of my friends will hit on the answer & offer some advice, I'll let you know if that happens.
 
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