90woodyxj said:
Hmm. Yeah the CPS is proven good because I used it in my Jeep back when it was running well and put in a new one to try to fix a problem I had a while back, which turned out to be a short underneath my radiator. Swapped out the CPS this time as a first theory. Wires aren't on manifold and seem to be okay. Been trying to get ahold of a decent tester recently again. Just seems funny that I would replace the ignition module and coil and it would run fine for two days then do it again. After having not run for so long.
Im just getting so sick of constant electrical problems. This jeep is a never ending nightmare.
Possible no spark,
CPS not giving a good signal, wiring or heat (or cold/temp.). Mine once refused to start and I dumped a bucket of water on the CPS. After it cooled back down it started just fine. Don't even ask how I came up with that idea, just a hunch.
Coil or module, most times it's power in, in the wiring or the ignition switch or maybe the trigger wire (small yellow wire at the module).
Coil to cap wire, shorting to ground (or another wire), which can be a sometimes thing.
Really weak spark, back to the wiring again.
You really need a digital volt and ohm meter, they really don't cost much. You can get a decent one for $20.
Fifty percent of the time, the problem is in the wiring or a connector.
The wifes old 87 would periodically crap out, turned out to be a wire at the firewall end of the injector harness. A known trouble spot that is often overlooked. The harness flexes every time the gas pedal is moved. I've found broken wires under the insulation in this area. But this is actually not a likely cause of your no spark though.
Three XJ's with a combined age of 50 years and I've never replaced a coil or ignition module in any of them. My 88 gets a motor mud pack at least once a week and a high pressure motor wash nearly that often, the coil is doing fine.
Ignition coil facts, 35,000 volts is 35,000 volts whether it is made by a stock coil or an after market coil. Much more voltage than that isn't going to ignite the fuel air mixture any better, but will likely just burn the electrode off the end of your plugs much quicker. Also excess high voltage isn't necessarily a good thing because the voltage may have a higher tendency to find alternate ground paths.
In summary, enough high voltage to reliably ignite the fuel air mixture is enough, more just burns up plugs and causes lightning storms in the distributor cap and the plug wires.
Adding more high voltage without increasing the diameter of the distributor cap isn't recommended. the spark has a tendency to jump to adjacent poles inside the cap or even to ground inside the cap.
More spark isn't necessarily better. Most of the performance coils are designed for very high compression ratios and/or very high RPM's or designed to work outside of the normal envelope. And are likely to cause problems at low to mid RPM's. And when hooked up to a stock module, may cause premature failure (they may be a poor ohm match).
