ffrh911

iTrader: (2)

I did ngk tr55 plugs and msd wires with my full exhaust about two months ago. Gapped plugs to I believe .050 which is what I was told by looking at past threads.
Decided to data log today. The log ended before I finished my drive on i95. I checked the 23 minutes of logging and found 1 count misfire on the four cylinders listed. That was near the end.
So I went to the graph and saw at 8 minutes I had...
9 counts in cylinder 9
2 counts in 7
2 counts in 3
3 counts in 1
it says I was at 0% absolute throttle so It was when I was at a stoplight but when I saw the single counts on the one side it was around 2,000 rpm with cruise control on at 70mph.

If anyone reads this I just would like an explonation. Would running too rich cause these misfires? Thanks for your help!

James Linder

You could be running too lean. Are you sure that the fuel injectors you installed are properly represented in the PCM tables. If you modified your intake then you could be running lean because your MAF transfer function needs to be calibrated (higher). Lean misfires are not uncommon and could go away when you get on it because you have your PE vs RPM enrichment set high enough to make the problem go away at high RPMs.

Would need to know more about what you have done to your engine to be more specific.

James Linder

I remember a friend put in a new starter and pinched one of the wires going to the crank position sensor and caused the car to misfire and run really bad. Sometimes it would run normal but when he got on it it would miss out and even back fire and sometimes simply die. You can only see this sensor if you remove the starter and then look up at the block directly above and beside where the starter resides. You will typically see your RPM guage drop to zero temporarily when this problem occurs. I presume that when these sensors start to die they can cause sporatic problems before they go completely dead.

MUSTANGBRKR02

iTrader: (91)

One whole side of the motor, then I would look at the coil harness on that side.

ffrh911

iTrader: (2)

Just did another log. I'll answer everyones ?s in a bit.
At 86 kph, 3 counts cylinder 6, 1 count cylinder 7, and 1 count cylinder 8.
There all very random. That was only a minute into the log. I'll post more info here shortly. Thanks fr all info btw!!

rpmauto

iTrader: (14)

I have been having alot of trucks come in the po300 and all one bank missing, low voltage oxygen sensor culprit. I would think since you are logging data that you would know what your o2 voltage and trims are. Just something to check if you havent.

joecar

Small counts like that are ok.

When the counters are constantly incrementing to large numbers then you have problems (and the misfire DTC's will set).

battousai

iTrader: (3)

You have 9 Cylinders??? NICE!!!!!!!!

ffrh911

iTrader: (2)

James- I never installed new fuel injectors, all mods in sig...
James again- yes I had to remove the stock one once, twice the car has actually dropped to about 500 rpm then it goes up and down for a second. It did it once after I went wide open a few times.
Mustang- it only did this once. The next time I looked at the log I couldn't find it again.
Rpm- yes I did see tht I believe around 44 volts or something?? But all four were working and only two are plugged in because of the exhaust I switched to.

ffrh911

iTrader: (2)

Haha your the only one that noticed... I'm not even going to edit.. And I meant 5 for the record.

One more big question, I know a guy who has a dyno jet, I told him if i wanted to get tuned that I also needed to turn my 02 sensors off, he said I had to pay 100$ for one Hp tuners credit to be able to turn the o2s off. Is that true??

ffrh911

iTrader: (2)

When I said this below I meant these three happened at the same time but all the other little misfires were random.........


At 86 kph, 3 counts cylinder 6, 1 count cylinder 7, and 1 count cylinder 8.
There all very random.[copy]

flame

iTrader: (13)

Check for an intake gasket leak. What are the fuel trims like?

James Linder

I guess I do not understand why you would want to turn these off unless you are talking about the rear ones which are not needed. However the front ones are essential for your car to operate in closed loop. Are you wanting to go to speed density (open loop) tuning all the time or for testing purposes? Please explain.

James Linder

What condition are these in? Are any of them arcing against the headers? Look for burnt area on wire and white area on header where the arcing would be occuring.

ffrh911

iTrader: (2)

Flame- what's a good number for ltft and stft?
James- yes just the back o2s I need turned off and the wires are two months old and look fine.
It runs great and j personnaly never noticed a misfire untill I hooked up the computer...

ffrh911

iTrader: (2)

Stft- anywhere from -4.69 to 6.25. Mostly in the negatives but two or there positive number.
ltft- anywhere from -3.91 to 10.09
what are they suppose to be at? And our they suppose to be relatively the same. My u7198x only shows half of what it's saying and doesn't scroll over. Idk why..

James Linder

if a car runs absolutely great but logging shows misfires does this mean there has to be a problem or could it be a misleading indicator. Seems like I have heard of this phenomenon before with certain set ups, but cannot remember for sure. Are you having any performance issues? I still wonder about the crank sensor possibly in the process of going bad although they usually just die unless they are shorted out when reinstalling a starter sometimes.

flame

iTrader: (13)

If fuel trims are +-5% its acceptable. Usually with a stock camshaft the misfire detection is still reliable. Anyway you look at it the engine should be tuned properly for the mods done. If the misfire is evident then it should be repaired before the tuning.

ffrh911

iTrader: (2)

No the car is not tuned for the exhaust it has besides turning COT off. The missfires only happen every two minutes or so. Majority of time it is single but occasionally there are multiple ones like stated.

If the fuel trim is going past +-5 what do I need to do that.

Also how do I calculate air fuel ratio?

ffrh911

iTrader: (2)

And James no I have great power. Non of the gears feel as quick as first and second but it still goes.