Hey folks, I have a 96 mustang Cobra that has a mis fire under acceleration. Doesn't seem to happen all the time but more often than not. I bought the car several years ago as a project. At the time I it had several issues many of those have been addressed. one that is still haunting me is this nagging misfire. I have replaced plugs, wires and coil packs. Fuel filter. I will add that for some reason the car will drain the battery if I keep it hooked up. Don't know why it does this or if that could be related to my misfire issue. As you guys know there isn't really anything that should draw power while the car is off. One thing I've read is the amps for the factory Mach 460 system have been known to quit "going to sleep" when the key is off. Can't seem to find a fuse dedicated for these amps to remove. But any way not even sure that is causing my misfire. One issue at a time . I would really like to fix the misfire first. The car is a blast to drive but would be even better without the misfire. If anyone can point me in a direction I would greatly appreciate it. I do my best to do as much of my own repairs myself. I'm an old school diy mechanic and I can do most anything to old school cars but sometimes I get stuck
Car miss firing under load
- Thread starter bobcat
- Start date
cobrajeff96
Well-Known Member
More than likely there is a bad coil pack or a bad plug or wire or some combination of them. You can easily test for them...
First, trip the fuel safety inertia switch in the trunk to disable the fuel pump in order to keep the engine from flooding. Pull one plug at a time, leaving it fully connected to the ignition system. Ground the plug's ground strap to some bare metal, maybe the top of the strut assembly while someone cranks the key. You should see a very strong spark. Just repeat it for all 8 cylinders.
First, trip the fuel safety inertia switch in the trunk to disable the fuel pump in order to keep the engine from flooding. Pull one plug at a time, leaving it fully connected to the ignition system. Ground the plug's ground strap to some bare metal, maybe the top of the strut assembly while someone cranks the key. You should see a very strong spark. Just repeat it for all 8 cylinders.
Thanks for the response. Like I mentioned in my post or maybe I wasn't clear in my description I inherited this issue from the previous owner. Since I purchased it and because I have no clue about the previous maintenance I one at a time replaced each set of items to no avail. I did the obvious stuff . I first replaced the plugs, then the wires and the coil packs (twice on the packs because I purchased a used set of OEM coils the first time). The car idles fine and runs down the road good. The problem mainly happens when I stand on it. With the car running I removed each wire one at a time and there was a noticable difference in the idle each time so I'm fairly confident that each plug is firing( at least at idle speed).
Give me a old school engine with a distributor and carb and I'm off the chain but this is a different beast. I've read how dependable these 4.6 4v engines are the way it revs after it gets past the misfire makes me believe it's something simple. I will add that it also has another issue that may or may not be related. The car will drain the battery if I leave the battery connected and it sits idle for a couple days. Nothing is on or running when the key is off. I've removed fuses in an attempt to locate a dead short but haven't found anything. After doing some research I found that some folks had a problem with the amps on their Mach 460 systems not "going to sleep" when the key is off. I can't find a fuse dedicated to the amps to remove.
Big possibility it might not be the sparkplugs or sparkplug wires, but could be the mass air flow sensor. Rule out any spark issue. Use the method @cobrajeff96 suggested.
Be sure all the wires are engaged on the coilpacks.
Shove a sparkplug into the wire plug boot end to see how deep the plug goes into the plug boot. Sometimes excessive boot material will cover over the nut portion of the plug and the boot will push itself off and away from the plug terminal.
Double make sure there is zero moisture within the wire plug boot and sparkplug hole. Modular engines are NOT happy about water. Dont use water ontop of these engines
You might grab a can of mass air flow cleaner from the part store, watch a how to youtube vid, and clean the maf sensor. The maf may have never been cleaned and will produce symptoms as you described. Be sure to disconnect the negative battery terminal before unplugging any sensors.
Be sure all the wires are engaged on the coilpacks.
Shove a sparkplug into the wire plug boot end to see how deep the plug goes into the plug boot. Sometimes excessive boot material will cover over the nut portion of the plug and the boot will push itself off and away from the plug terminal.
Double make sure there is zero moisture within the wire plug boot and sparkplug hole. Modular engines are NOT happy about water. Dont use water ontop of these engines
You might grab a can of mass air flow cleaner from the part store, watch a how to youtube vid, and clean the maf sensor. The maf may have never been cleaned and will produce symptoms as you described. Be sure to disconnect the negative battery terminal before unplugging any sensors.
Thanks for the advice. Will take a look at the mass air sensor. I already have some crc cleaner on hand
