Misfire.... where to start looking?

[Dave_C]

I took my car out for a drive yesterday. 08 with the 2.9 Whipple kit from Ford. Ford tune. 21.5k miles. Whipple since under 5 k.
Drove about 12 miles. Didn't push car hard. Once to 6k early in the drive 1st gear only then 5500 in 2nd. No issue. Felt fine.

Went to a store and parked it for 15-20 mins. Left store and drove about 1/4 mile ~30 mph and it started missing really bad. Felt like totally dead on 1or 2 cyl. Car was shaking at idle at a stoplight. It did not turn on the check engine light. No smoke and all gauges were normal. Turned around and headed home. Drove about 1.5 miles and it cleared up on its on. Like nothing had happened. Took it easy the rest of the way home.

Got home and used my cheap code scanner. No codes set. Couple of hours later I borrowed a very nice scanner on the chance my scanner couldn't see all the codes. Been there, done that, on my truck. No codes with the new scanner and all "live" data looked good. Took it for a drive with the scanner running. Pushed it semi hard. Ran great with no issues, codes or alerts.

Where do I go from here? I'm thinking coil on plug but don't want to just start throwing parts at it.

 

[hRnYg0aTw33d]

I'm by far not a professional tuner or engine builder, but I did have a misfire issue last year with my car. I changed out all my plugs first, then contemplated doing the coils before I found one of my 02 sensors was grounding out on the underside of the car. I replaced the plug and everything was fine. My advice would be to pull the plugs and check them all. Condition and gapping. They're cheap to replace and it's good piece of mind. If you have to, coils can be done next/as well. Also cheap insurance.


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[Catmonkey]

I would wait until a code presents itself. Not sure what happened, but throwing parts at it is not a good idea. If it is a misfire, it will eventually store a code to tell you what cylinder is misfiring.

 

[NightRide]

I would do all new plugs since they're cheap anyways and do mine yearly. Compression test isn't a bad idea every few years either. When i dyno tune my car they ask me when the last time i did plugs and fuel filter so i would start with the easy stuff first. If it's an issue it will come back just don't beat on the car.

 

[ponyboy96]

Hard to really tell, but I had a car do something similar back in the day. Turned out to be a bad MAF.

 

[99cobraUgotbit]

I agree with the OP about it being the 02's.

I did new plugs and still had misfires. I Also had the 2195 code so it has to be the 02's.

 

[RedVenom48]

What brand of furl do you run?

Its possible you have a coil going bad. Best bet would be to carry your scanner in the car. If it comes up again, DO NOT turn off the car untill you check codes. And check as soon as you can.

My misfire issue was that my front crank pulley bolt was missing the washer behind it. It was allowing the crank reluctor to vibrate. Engine interpreted that as a misfire.

Also, check plugs for any abnormal fouling or cracked porcelain.

 

[JB_2010GT500]

Check the ignition coils.


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[tktlwyr]

Hard to really tell, but I had a car do something similar back in the day. Turned out to be a bad MAF.

Curious as to if this ever set a code?

I've been chasing a gremlin for the last year. It's intermittent, doesn't set a code and depending on who's tune is run, the symptoms can be worse. Out of the blue, the AC will stop blowing cold (compressor shuts off) and the car begins to stumble/miss anywhere from a blip to a few minutes of running rough. The symptoms are less with a tune that uses the actual MAF transfer curve as opposed to the tune that adjusts the transfer curve. The car clears up if I go WOT, but this isn't practical let alone in a 730 rwhp car. LOL

No one can find the cause. The car has close to 100,000 miles. I've changed O2s, coil packs, plugs, battery harness, checked for vacuum leaks, fuel pumps, boost-a-pump, etc.

I've been thinking MAF next because of the way the car exhibits the symptoms with the different tunes.

Any thoughts people have are appreciated.

 

[RedVenom48]

If WOT operattion clears it up, that means in Open Loop operation it runs fine. Closed loop operation where its looking at all its sensor inputs is running abnornally. Also tells me MAF data to ECU is ok. Id start checking connectors for corrosion, especially at the ECU. Ohming each wire from sensor back to ECU terminal is a PITA, but at this point Id be suspect about harness resistance throwing off data and causing your car to run like poo.

If you havent already, data logging a non WOT drive pattern on a dyno or data log on the street may reveal the culprit as well.

 

[Catmonkey]

No one can find the cause. The car has close to 100,000 miles. I've changed O2s, coil packs, plugs, battery harness, checked for vacuum leaks, fuel pumps, boost-a-pump, etc.

I've been thinking MAF next because of the way the car exhibits the symptoms with the different tunes.

Any thoughts people have are appreciated.

You probably ought to start a new thread and run through your mods and what all you've done to sort through these issues in more detail. Sounds to me like the car is going into default and without throwing any codes in the process, is probably tune related. Have you data logged the car and has anyone reviewed the logs when this is happening?