misfire cylinder 4

So, a few months back, I started getting a misfire. Eventually it got to the point where it showed misfire on cylinder 4. I went through and replaced the plugs and wires (all platinum plugs at $8 a piece) and also went ahead and replaced the coil pack for cylinder 4. It fixed the problem to an extent, but I still had a small misfire under load. I continued to drive the car. Right after starting the car up, it would run fine. After it warmed up, it would start to misfire under decent acceleration or when trying to accelerate when running really low rpms until it downshifted. The other day it got really bad again and was misfiring under really small load. I checked the obd scanner and it showed a misfire on cylnder 4 again.

My scanner is also showing a code for a maf sensor problem, and a heating issue with one of my O2 sensors. I've had both of those codes since I bought the car 5 or 6 years ago.

Any help I could get would be great. I think I have the car in my signature but just in case I don't it's a 97 with the supercharger. I just surpassed 215k miles. The first misfire started a little before 200k miles. It has a fairly new fuel pump (little over a year old), fairly new fuel filter (probably 40k miles old), the airbox is gutted and the two fuel lines running to the fuel rail have been replaced with the dorman kits.

If you need any more info just ask.

Hey check your compression, very low compression will cause misfires, which I really hope that's not your problem

What's the best way to check my compression? It's weird that the new plug wire and coil pack got rid of the misfire code but now it's back over 15k miles later.

yah that is weird, well they have compression testers at O Reilly's auto parts for like 20 bucks, it has instructions on how to use, its also nice to know the compression all your cylinders have to! but maybe its bad wires, were they cheap wires?

you can also get a filer, and file the spark connecters where the park plug wire connects, then wipe it clean all nice a silver again!

The wires were pretty cheap. I think they were like $20 or something. Spent more on the plugs than the wires. Was told to get higher end wires, but the last time I went to auto zone and advanced auto, they told me they didn't have any better wires. They just offered the one set. They acted a little dumbfounded when I mentioned that I was looking for higher quality wires. I'll stop in and pick up a compression tester after work and see what i've got.

thanks for the help

The $18 compression tester should do what i need right? I shouldn't need a $150 kit

sweet man! yah these cars you cant really go cheap on, my cars fuel pump is going out and I bought a cheap one from autozone, then bought a wheel bearing that was 50 bucks and now that's going out, so from now on im not going cheap, I guess our cars are stubborn, but I recommend going on zzp and getting 10.5 mm wires which are 40 bucks more then oem, or get 10.3mm wires that are the same price as oem, your choice, but next paycheck im getting 10.5mm wires because ive heard amazing reviews on them.

nah just that cheap one:)

will do. Was hoping to get this things back into tip top running condition so I could focus my money on my 240Z on jeep cj5 mud truck and my 3800sc fiero swap

That's so cool!!! Now the fiero would be an amazing car to drive, these motors are strong, mine is having slight problems to but they get fixed, AA had a chipped piston and had upgrades and mods he was doing, and his engine lasted a long time! I love these motors

Cheap wires will cause this. If you have to get them online, get them online. AC Delco, Packard or Bosch are generally acceptable.

I have a set of custom fit Taylor wires and they have lasted a very long time. When I start having issues I'll make another set of Taylors.

You may also have a problem with an injector, but I'd suspect the wires first.

yah the stock oem ones are pretty good to!

Did you clean your MAF? What did you do about your O2 sensor codes?

Haven't cleaned maf sensor. Checked compression. 121 on cylinder 4 and 121 on cylinder 1. That's a relief. Unplugged the maf sensor and the car ran the same. When I get home from work tomorrow I'll see how it drives with the maf unplugged. It should run worse unplugged right? I ordered the 10.5mm zzp wires. No biggy spending the money. The o2 code had been there since I bought the car years ago and my mileage has been the same. Right around 20-23 mph

MAFS can be weird. Especially when they're dirty. Use some electronics cleaner on the wires. Brake and carb cleaners can cause corrosion. It probably will run worse when it's unplugged. Speaking of unplugged, what does the spark-plug look like when you pull it?

A bad O2 sensor will ruin a catalytic converter over time. You may want to address that soon.

The plug had gas residue on it when I pulled it out. Didn't look fouled out. So it looks like it's a spark issue and not an injector problem. Unless the injector could be malfunctioning and spraying all the time. Not sure what all could go wrong with an injector. I just assume a failing one won't spray as well leading to a lean cylinder.

That was supposed to say 20-23mpg not mph. The zzp 10.5mm wires should be here within the next couple days.

Sorry, just tuning in. Feels like you have gone way out of bounds trying to diagnose a misfire.

Based on the observation of a fuel-soaked plug (pulling plugs is the very first thing you should do), this confirms no spark in cyl #4. Injector is functioning. That rules out fueling issues.

If plug looks good other than fuel-soaked, we can rule out the plug.

Pull wire #4 to confirm a dead miss. Hold the wire close to ground to observe any spark. If none, try swapping the coil with another, retest. Although since #2 is getting spark, it suggests the coil is good.

If you do see a spark, and if the dead miss make engine run rough at idle, replace wires with quality wires. This is means the miss is occurring under load (in boost). Leave the swapped coil to see if the misfire moves under load.

I really suspect the wires much more than coils, compression or a fuel injector. Since you replaced a coil, that could be the issue. With some of the cheaper parts out there, never assume replacing parts will solve the problem unless you know for sure the parts are good. Stock coils should last a long time with healthy plugs and wires.

The OBDII codes for O2 and MAF are definitely problems that need addressed, but imo they are not causing your misfire, since those would not single out cyl #4. 02/MAF issues would create problems with random cylinders, if any misfires at all. Most of the time issues related to these sensors will throw a rich/lean code. A MAF code can indicate the MAF sensor is faulted or unplugged.

My advice: diagnose and fix the #4 misfire issue, then move on to testing the O2 & MAF sensors.

I'm pretty sure it isn't the coils. I tried swapping the coils, reset the code and the misfire was still on cylinder 4. I assumed the plug was fine as it's pretty much brand new, the gap is right, and it doesn't look fouled. It's just confusing that I got cylinder 4 misfire, replaced plugs, wires, coil pack and the code was gone for a few months and now misfire cylinder 4 is back. What are the odds of that same wire or plug going bad right away unless something else is messing up

Coils swapped and no change. Good. We can rule out the coil.

Quote :

What are the odds of that same wire or plug going bad right away unless something else is messing up

Based on what I've read from other members' experiences over the years, odds are better than you'd think that $20 wires aren't going to last for very long in our engines. Since you replaced plugs and wires, and the problem went away for a while, I think it's looking more like one of those items is at fault.

You've checked the plug, so seems like a bad wire is suspect. Why #4 again? Coincidence, until you get another misfire 3rd time around. I would swap #4 spark plug into another cylinder when you replace the wires, just to be sure the plug isn't causing this.

duster_do_little wrote:

Haven't cleaned maf sensor. Checked compression. 121 on cylinder 4 and 121 on cylinder 1. That's a relief. Unplugged the maf sensor and the car ran the same. When I get home from work tomorrow I'll see how it drives with the maf unplugged. It should run worse unplugged right?  I ordered the 10.5mm zzp wires. No biggy spending the money. The o2 code had been there since I bought the car years ago and my mileage has been the same. Right around 20-23 mph

Hey let me know how you like those, im getting some within the next couple of weeks!

Maybe your ignition module, under the coils or your #4 coil is going bad. Did you see any white spots on the old spark plug wire? Another possibility could be a stuck or worn fuel injector. In any case it's probably something simple.

make sure your wire routing is safe, that nothing is crushing the #4 wire.

Odds are good that cheap wires will fail again.

Try swapping the #4 and #6 wires if they will reach and see if the problem gets better.

wires were supposed to be here today. 2 day shipping...left wyoming, MI the 3rd and got to grand rapids. Left grand rapids the 4th and said estimated delivery was the 5th, but still says in transit. Hopefully they show up tomorrow. Plan on running a bunch of seafoam through the car when I swap the wires too. If the injector is plugging up maybe that will help.

Kind of sad, my subwoofer was 5-7 day shipping from missouri and got here in 2 days, but the wires were 2 days from my state and aren't here lol.

The wire looked to be in good condition. no burn marks, no crush marks. Should I take those metal covers with the spring off the wires, or are those there to keep the end from getting to hot and drying out?

A lot of people just dont reinstall them, u should be fine, but I would put them on your new wires( my opinion)

They're heat shields for the plug boots. Mine were missing on the front, so added them for free (a yard gave them to me).

My OEM wires looked nearly new when they began to fail. I even polished them up with armorall. I could have easily sold them as used wires. They probably would have served many more thousands of miles on a NA 3800 engine.

As far as my misfire going away after new plus and writes the first time. The code went away and the misfire got really subtle and was still noticeable after the car warmed up while under really heavy load.

Also. No idea how the wires are because I was supposed to get them yesterday. The day before that they were in Grand Rapids which is just under two hours away and now they're in Detroit, which is over 2 hours away. So they managed to travel about 5 minutes day one. Then day two and three they went 20 minutes further away?!? I'll let ya know how they are If/when I get them