Hey Jeep land, my 4.0 ZJ won't start! Did plugs, wires, cap and rotor, made sure 5 times that the wires were in the right place. It just cranks... Has spark at the coil, none coming out of the cap? Thoughts?
Maybe a pic of the rotor and cap? If you've got spark going into the cap there's not many places it can go wrong. What color is the spark at the coil? Nice and blue or weak and pink?
Well those look right. I've had people get caps missing the center electrode or rotors missing the tip. Is the spark at the coil firing 6 times per rotation? Or as best you can estimate. How are you checking spark?
Take another look at the rotor. Why is the spark contact mark for the coil off center? Why is the contactor arm on the rotor silver and black? Why isn't anyone suggesting brass contacts at all seven points in the cap, and all across the rotor?
I think it just looks off center because of the angle. Doesn't really matter, you can see the wear mark where the carbon button is touching so it's making good contact. All the rotors have a silver contact there because you need spring steel to keep the rotor in contact with the cap and have decent wear. The center point of the distributor is always carbon, even when the wire terminals are brass, for the same reason. The rotor tip is brass painted black. I've had several rotors in my 93 and they were all like that. If Jamann want's he can scrape a bit of paint of to verify. Wouldn't matter at this point anyway if it was aluminum or steel. Brass contacts wear better but, when new, aluminum (and steel in the rotor) are electrically just fine. That wouldn't stop a good spark.
I was going to suggest filing the paint off of the rotor contact tip. While I'd think the power of an ignition spark would blow that paint to hell on first firing, it would be worth a shot, IMHO. It's more likely that your new coil wire is bad/open. I know that you said it wouldn't fire with the old stuff in place. That's baffling. Good luck.
Just for fun, go buy a quality cap and rotor and swap it for the one you have. I always try to look at the last thing that has been changed when I have a problem. Might be a cheap fix since if that fixes it you can try to get a refund on the first cap and rotor.
New cap and rotor just to be double sure, problem persists. I want to lean toward the crank sensor given the no spark condition, or maybe the dizzy, but I didn't really mess with either of these in the process of the tune-up, so it would be a pretty odd timed failure as it was running fine before I did so. I will keep y'all updated... thanks for the continued insight.
Bummer another new cap/rotor didn't solve your strange problem. Hate to even ask but you do have the small black cap on the distributor cap between the 2-4 plug wires as in the photo Nick-B posted? In other words the inner square tab on the cap, along with round tab, line up with the square/round tabs on the distributor lip the screws go into? Wouldn't even ask but the rotor button doesn't look like it's hitting in the middle of the rotor spring prong and have seen people get their caps turned 180 degrees off. Sorry for asking and you do seem to know what you're doing.
While I mentioned some testing of the cam sensor that would be for fuel while you're correct in the crank sensor controls spark. Typically if you have spark the crank sensor would be good but have seen a couple others on here even with spark the crank sensor was bad or worked intermittently.
There's a couple crank sensor tests in my signature but believe the below one is even better in checking for crank sensor signal (p.2). You're turning the engine over by hand while back-probing the crank sensor connector with a meter while an analog meter works best. Make sure the coil wire is completely pulled and instead of messing with injectors pull the fuel pump relay in the PDC.
You're looking for 8v of power on the signal wire intermittently as it passes the signal points on the flexplate/flywheel. Believe the 95 has the same wire color coding as the 93 and checked the 2nd below diagram where these are correct in the testing link.
I wouldn't install an aftermarket crank sensor since just too many problems with them. But the Mopar ones are darn pricey but worth it if the crank sensor tests bad. Good luck.
Bummer another new cap/rotor didn't solve your strange problem. Hate to even ask but you do have the small black cap on the distributor cap between the 2-4 plug wires as in the photo Nick-B posted? In other words the inner square tab on the cap, along with round tab, line up with the square/round tabs on the distributor lip the screws go into? Wouldn't even ask but the rotor button doesn't look like it's hitting in the middle of the rotor spring prong and have seen people get their caps turned 180 degrees off. Sorry for asking and you do seem to know what you're doing.
While I mentioned some testing of the cam sensor that would be for fuel while you're correct in the crank sensor controls spark. Typically if you have spark the crank sensor would be good but have seen a couple others on here even with spark the crank sensor was bad or worked intermittently.
There's a couple crank sensor tests in my signature but believe the below one is even better in checking for crank sensor signal (p.2). You're turning the engine over by hand while back-probing the crank sensor connector with a meter while an analog meter works best. Make sure the coil wire is completely pulled and instead of messing with injectors pull the fuel pump relay in the PDC.
You're looking for 8v of power on the signal wire intermittently as it passes the signal points on the flexplate/flywheel. Believe the 95 has the same wire color coding as the 93 and checked the 2nd below diagram where these are correct in the testing link.
I wouldn't install an aftermarket crank sensor since just too many problems with them. But the Mopar ones are darn pricey but worth it if the crank sensor tests bad. Good luck.
Thanks for the response. The cap is indeed installed correctly. Checked again just to be sure. Tested the crank sensor today, just over 7v in, about 5v on the signal wire.
The output from the crank and cam sensor should be a square wave with the amplitude of the input voltage so it will not read the same as the input voltage on a digital meter while using the starter to spin the engine. That's why Uni mentioned it's best to use an analog meter. Honestly I wouldn't condemn the crank sensor based on the 5vdc reading from a digital meter unless you are turning the engine by hand. If the voltage is actually low, it should pop a code.
Cam sensor is checked the same way as the crank sensor, did you see if it has an output?
As always Zee nice to have you come around and clarify info!
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
Jeep Enthusiast Forums
18.5M posts
726.7K members
Since 2000
A forum community dedicated to all jeep owners and enthusiasts. Come join the discussion about performance, engine swaps, modifications, classifieds, troubleshooting, maintenance, and more!