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Delayed Spark! Help!

K

Keefer

NAXJA Forum User
Location
Parker, AZ
So i have a 4.0 1990 jeep cherokee and i am kinda obsessed with getting it to start within the first two cranks of the engine. everything besides the spark is good. the issue is, when i crank it it wont spark until about the 4th turn of the engine? any suggestions? just replaced crank position sensor to no avail. once in a blue moon it will start first crank.
 
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Separate the coil from the module, make sure the contacts are clean (free of corrosion) and they are clamping tight. Check the ground for the ignition module. The contacts between the coil and the ignition module get hot or old and relax, they get soft, be careful.

The coil to cap spark plug wire seems to be important, I don't now exactly why. But a resistance as close to stock as possible seems to work best. I've tried a dozen different kinds of cable for this wire, everything from solid core to various low resistance high performance wires and stock (resistance) carbon core works best.

The spark plug wires themselves seem to be less critical, but coil type solid core works best for me.

Shorten your CPS wires, there is a kit for this. I cut the wires maybe three inches from the firewall, routed the CPS wires so they positively wouldn't contact the exhaust manifold and cut off the excess then soldered them to the wires sticking out of the firewall (eliminating the connector). I had the kit in my 87 and did my own in my 88, both would start, before I could release the key from the start position.

Renix are kind of notorious for loosing the fuel prime (pressure) and having long crank times. Make sure your issue is spark and not fuel. Turn the key to run, then off, then to run again and then start, to make sure you have a good prime.

Make sure you don't have a slow starter, which is usually a cable or ground issue, though sometimes worn brushes. The starter has to crank well (some say reach 300 RPM) before you will get spark.

Took me awhile and some effort, but my Renix pops right over. Regular old Champion plugs, nothing exotic. The coil wound solid core plug wires did help the spark some and worked better than carbon or graphite core, but you always run the risk of radio or stereo interference (spark noise) using these wires. The carbon core wires work better for the coil to cap wire.

My quest was for a really a good idle, quick starts were an unforeseen but welcome outcome.

Almost forgot, the larger yellow wire going to the ignition module, in theory, should be the same as battery voltage, it never is. Seems to be a lot ( 1-2 volts) of line loss. I often thought of running a fused wire directly from the red wire stud on the starter relay to a relay and having that yellow wire activate the relay, so I could get max (available) voltage to the ignition module/coil. I never did that, never needed to, the lower voltage to the ignition module worked well enough for me. If that voltage gets too low from maybe a failing ignition switch, corroded connector or whatever a relay may help.
 
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8Mud said:
Separate the coil from the module, make sure the contacts are clean (free of corrosion) and they are clamping tight. Check the ground for the ignition module. The contacts between the coil and the ignition module get hot or old and relax, they get soft, be careful.

The coil to cap spark plug wire seems to be important, I don't now exactly why. But a resistance as close to stock as possible seems to work best. I've tried a dozen different kinds of cable for this wire, everything from solid core to various low resistance high performance wires and stock (resistance) carbon core works best.

The spark plug wires themselves seem to be less critical, but coil type solid core works best for me.

Shorten your CPS wires, there is a kit for this. I cut the wires maybe three inches from the firewall, routed the CPS wires so they positively wouldn't contact the exhaust manifold and cut off the excess then soldered them to the wires sticking out of the firewall (eliminating the connector). I had the kit in my 87 and did my own in my 88, both would start, before I could release the key from the start position.

Renix are kind of notorious for loosing the fuel prime (pressure) and having long crank times. Make sure your issue is spark and not fuel. Turn the key to run, then off, then to run again and then start, to make sure you have a good prime.

Make sure you don't have a slow starter, which is usually a cable or ground issue, though sometimes worn brushes. The starter has to crank well (some say reach 300 RPM) before you will get spark.

Took me awhile and some effort, but my Renix pops right over. Regular old Champion plugs, nothing exotic. The coil wound solid core plug wires did help the spark some and worked better than carbon or graphite core, but you always run the risk of radio or stereo interference (spark noise) using these wires. The carbon core wires work better for the coil to cap wire.

My quest was for a really a good idle, quick starts were an unforeseen but welcome outcome.
Click to expand...

New Fuel pump, New starter, Uprgraded ground cables all round.tested fuel pressure with a gauge, thats fine. i know the issue is the spark, when i pull off the coil to cap wire and crank it, it doesnt spark until about the 4th crank.
Where is this kit of which you speak to shorten the cps wires? sounds promising
 
I doubt the kit is still available, dealer only as far as I know. I never bothered to copy down the part number after I saw what it did. I just made my own the next time.

The kit was kind of overkill anyway, it replaced the wiring all the way to the ECU. Which IMO was kind of unnecessary. The problem is the connectors in the engine bay and the wiring being way longer than necessary (line loss).

http://www.naxja.org/forum/archive/index.php/t-1073761.html
 
update: i eliminated the connector for the cps without a change. i took my coil off and cleaned the connections, when i started it and first crank it fired up! i got so excited but when i turned it off and tried again, it did the same thing it used to, taking a while to fire up.
so where does the cps wires go to? maybe should run new wires? so confused:bawl:
 
Use an old plug, gap to 60 thousandths, hold it on a good ground and look at the spark. Fat and yellow, that sometimes splashes on the electrode isn't good. Small and yellow is way bad. Blue/white which you can actually hear go "crack" is good.

Try my recommendation of first turning the key to run, then off, then start and see what happens.

There have been threads about drilling one hole in the CPS a little larger and pressing the CPS down while you tighten it, to get the CPS a little closer to the tone ring. I've never done it.

The distributor cap really doesn't last long in a Renix, I typically use two caps to one set of plugs. Gently push the rotor to the side and see how much lateral play you have in the shaft. Up and down play usually doesn't mean much.

Try a different coil to distributor cap wire. I have an oscilloscope and have noticed the Renix can be finicky about that coil to cap wire. For some reason a higher resistance in the coil to cap wire works better, you seem to get a better more reliable spark. I've tried a solid core wire and low resistance wires from the coil to cap and picked up a noticeable miss at idle and the oscilloscope shows a lot more wasted spark (static).

Check your ignition module ground and check the voltage at the larger yellow wire at the ignition module while you are cranking the motor. The starter sucks the most voltage/amperage at the beginning of rotation (most all electric motors are like this). You may be getting way low voltage to the module for the first few rotations of the starter.

What voltage does your battery show at rest and what voltage does it show while the motor is cranking over.
 
What cruiser said..... the RENIX requires at least one full revolution of the crankshaft to synchronize and find #1 TDC
 
cruiser54 said:
It's never gonna happen. The ECU must see a certain RPM before it sends signals to start.

The stuff you're doing is great and all, and it will start "better", but never like you want.

Click on the link below and review posts 1,3,5, and 7. 13 while you're at it.

Sweet I'll see about doing some of those things. I'm not necessarily trying to get it to start instantly. I just want it to start sooner, when I take the coil to cap wire off and hold it near a ground I don't even get a spark until the 5th- 6th revolution.
When I turn my engine off and start it right back up it will fire right up.
I get down to 11.5 volts at the battery when cranking and 12.6 at a standstill. 14.9 when the engine is on.
I'll have to check the voltage at icm later on today.
Thanks for all the info guys!

http://www.cherokeeforum.com/f51/cruiser54s-mostly-renix-tips-153657/
Click to expand...
 
sounds like the sync sensor in the distributor may have failed.

The RENIX start up looks for crankshaft and camshaft synchronization. After it finds both signals, it will then allow spark and fuel, and start in sequential mode. Sequential mode is where each injector fires individually during it's cylinder's intake stroke.

If the camshaft sensor has failed, it will crank until 5 or 6 crank revolutions (IIRC) and then allow spark and fuel and start in non-sequential mode. Non-sequential mode is where all injectors fire a small amount of fuel onto the back of the intake valve at the same time, six times over.

Non-sequential mode will run noticeably rougher at idle, and have a lack of power as compared to sequential firing.
 
Digger87xj said:
sounds like the sync sensor in the distributor may have failed.

The RENIX start up looks for crankshaft and camshaft synchronization. After it finds both signals, it will then allow spark and fuel, and start in sequential mode. Sequential mode is where each injector fires individually during it's cylinder's intake stroke.

If the camshaft sensor has failed, it will crank until 5 or 6 crank revolutions (IIRC) and then allow spark and fuel and start in non-sequential mode. Non-sequential mode is where all injectors fire a small amount of fuel onto the back of the intake valve at the same time, six times over.

Non-sequential mode will run noticeably rougher at idle, and have a lack of power as compared to sequential firing.
Click to expand...

So if what your saying is true, my cam sensor has failed and If I unplug it I won't notice a change?
On another note I I get 11.7 volts at the icu when cranking.
I drilled the mounting holes for my crank position sensor out and pushed it closer the flywheel. Now I get solid .5 volts at the sensor.
I think I'll try replacing cam sensor soon
 
Keefer said:
So if what your saying is true, my cam sensor has failed and If I unplug it I won't notice a change?
On another note I I get 11.7 volts at the icu when cranking.
I drilled the mounting holes for my crank position sensor out and pushed it closer the flywheel. Now I get solid .5 volts at the sensor.
I think I'll try replacing cam sensor soon
Click to expand...

No. It is NOT a cam sensor, but a sync generator that ONLY affects the sequential firing of the injectors. I'm thinking you wouldn't notice a difference if it was GOOD and you unplugged it and drove it. I never saw one cause a driveability problem in all my years at the dealership. Only way we found out they were bad was when scanning the vehicle for something else.
 
cruiser54 said:
No. It is NOT a cam sensor, but a sync generator that ONLY affects the sequential firing of the injectors. I'm thinking you wouldn't notice a difference if it was GOOD and you unplugged it and drove it. I never saw one cause a driveability problem in all my years at the dealership. Only way we found out they were bad was when scanning the vehicle for something else.
Click to expand...

So if not the sync generator then do you have any suggestions as to why I still get a late spark when I turn the key?
 
Keefer said:
So if not the sync generator then do you have any suggestions as to why I still get a late spark when I turn the key?
Click to expand...

Because it's frickin' normal!!!

I've been around Renix Jeeps since they came out. People didn't like the way they acted when they were new. Just the way they are.

I was Service Manager and Shop Foreman at a Jeep dealer from 1980 through 1992. I currently have 3 Renix Jeeps. I've had 13 Comanches as demos.
 
cruiser54 said:
Because it's frickin' normal!!!

I've been around Renix Jeeps since they came out. People didn't like the way they acted when they were new. Just the way they are.

I was Service Manager and Shop Foreman at a Jeep dealer from 1980 through 1992. I currently have 3 Renix Jeeps. I've had 13 Comanches as demos.
Click to expand...

And you've never seen a single renix start up like a normal vehicle?
 
Keefer said:
So if what your saying is true, my cam sensor has failed and If I unplug it I won't notice a change?
On another note I I get 11.7 volts at the icu when cranking.
I drilled the mounting holes for my crank position sensor out and pushed it closer the flywheel. Now I get solid .5 volts at the sensor.
I think I'll try replacing cam sensor soon
Click to expand...

Yes. however, you may well see a change, too. In my experience, when a sync sensor has failed, you will have to crank it long enough to the point you think it's really isn't going to start after all, and just then, it fires up and runs 'normal'.

crusier seems a bit cranky tonight.:dunno: I too have credentials to stand on that I won't tout here, but I have been a master tech for too many years.
My first XJ was an 87 and was a basket case when I got it. If there was a tech bulletin out, it had the problem that was outlined.

RENIX do crank longer than the late models, but there are long crank times and then there are loooong crank times.
 
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