Random misfire

BHernandez

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Is the A/C on or off for these testing sessions? Could also be your A/C WOT cut sticking.
 

RAU03MACH

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Lol I was going to say I just had bad luck with NGK TR6 and just switched to Autolite AR103's.
3 out 8 new in a box autolight plugs
Had a slight crack in them
And the engine would spudder and skip out
Motor craft is my preferred plug
Till that 2 peice shit came out
 

lwarrior1016

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Some more driving today. The Kam has unfucked itself and seem to drive normal for cruising.

I figured out I can get it to stutter just by stabbing the gas to even 50% throttle. I'm wondering if it's an o2 sensor issue but o2 sensors aren't used at wot. It's acting like it's sluggish to catch the fuel change or something of that makes sense
Out of curiosity, how long has this tune been in the car? Any changes to the car since tuning? Was the car tuned on e85?
 
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apsmith49921

apsmith49921

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Out of curiosity, how long has this tune been in the car? Any changes to the car since tuning? Was the car tuned on e85?
Tune has been on the car for several months. I've got a 93 tune and an e85 tune. I used that e85 tune all spring and summer without issue. 93 tune seems to be doing the same thing.

I ordered o2 sensors and camshaft and crank position sensors. So that's my next step it's only 80 bucks so might as well give them a try
 

lwarrior1016

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Don’t know what kind of oxygen sensors you ordered, but we’ve have problems out of bosch sensors. We use NTK sensors or motorcraft sensors, they give the most consistent results.
 

NXcoupe

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If you got E70, you would be running very rich on your E85 tune which would present itself more under wot than other places. Also, you need to tighten plug gap when on E85, which under wot can cause misfires from spark blowout. I run my E85 plug gaps around .045 and 93 at .052 to .056, this on 5.0 pushrod engines. The cobra engines are much more prone to spark blowout due to valve and plug orientation and combustion chamber design.
Jmho.
 
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apsmith49921

apsmith49921

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I checked the fuel and it seemed to be good. Issues still happen on 93 so I'm going after some sensors now to see if that changes anything
 

96blak54

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Pull each plug wire and shove a sparkplug into the end. Make sure make sure each plug boot isnt so long its difficult to engage the boot terminal onto the sparkplug. I find many times inconsistency with plug wire boots being to long, requiring the boot to be shoved over the hex to snap onto the plugs terminal. This is to long and needs to be trimmed back. If the wire is a slip fit into the boot, simply push the wire into the boot more.

Ive owned and worked on a bunch of different modulars over the years and this situation was always a problem. I also have a few sets of old wires including a set of Ford performance 8mm that i keep just because i have a hoarding problem, but they all have trimmed boots because the darn things wouldnt stay on the terminal. The extra boot length would push the terminal clip off the plugs terminal. Cause a bunch of headaches in the upper rpms

The last set of wires i purchased were from Vatozone and to my surprise the wires would slip thru the boot. I didnt have to do any trimming on the boot ends.

Just an idea. I hope you get it figured out. Spark issues suck.
 
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The first thing I would do is, check compression and do a leak-down test before chasing electronics. These tests can tell you a lot.
 
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apsmith49921

apsmith49921

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So no updates really apparently all my new things are on the way by horseback across the country. Should have new o2 and cam/crank sensors tomorrow though. I'll swap those out when I get time. I'm also waiting on my coil pack connectors to show up. I've got a known good set of coils to eliminate the spark plug wires
 
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apsmith49921

apsmith49921

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Next update. COP harness done waiting to get valve covers to test this out. While I waited I cleaned the injectors. Got this nifty device on Amazon that pulses them. I shot carb cleaner in all 8 I may have had some dirty ones but it's hard to tell because it's a semi inconsistent test. However all 8 spray good in identical patterns. If I get time and weather is OK next week may take it for a rip
 
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apsmith49921

apsmith49921

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Some one on another forum mentioned cleaning the maf. Originally it crossed my mind but looking at the data I did I tossed that thought aside. I was only focusing on the RPM dips (highlighted yellow).

Took a deeper look after he said that and I found something I didn't see before. Right before each rpm dip I'm seeing drop off on the MAF counts. I converted that to voltage and its about a .05v drop over that short time. Now we all know obd2 isn't the best and data does blip out sometimes. However it does this every single time before the rpm drop.

So I pulled the maf out and I noticed some what seems to be filter oil or something like that all over the plastic. This is a 20 year old lightning maf and instead of let's clean it and play that game this is enough data for me to spend the 140 bucks on a brand new granatelli maf and filter I got off ebay.

I looked at my previous logs and I would have occasional a drop that lasted a single cell but this is multiple data points in this log. I also have a log that reads the exact same rpm and maf voltage is average. 05v lower on the whole curve. What do you smart tuner folks think?
 

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BHernandez

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Ok so the car is a 97 cobra. Full mods in signature but fbo e85 NA.

Random misfire at wot. I replaced coil packs and it got slightly better. Data log shows 0 misfire occurrences, fuel pressure holds solid not a single blip. Any ideas? Plugs are about 20 miles old. Coil packs brand new.
Gap and heat range correct?
 

Venompower

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MAF_RPM.JPG

Here's the graph from my last data log, comparing MAF counts to RPM. I have a flat spot as well and may just swap in a new MAF for next season.
 
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apsmith49921

apsmith49921

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Yeah its a good theory. I like graphs but it's hard to see those small inconsistencies I could in my Excel file. My new maf showed up today. Too bad my car is sitting with out brakes lol
 

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