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Discussion Starter #1
I finally got around to datalogging the car in hopes to capture what it is that is going on lately. Basic run down of the car is built 2v motor, vortech, with Siemens Deka 60 lb injectors, twin GT pumps, dual fpdms, etc. Ever since doing long tubes it seems like the car just doesn't drive smooth while cruising. The car was retuned following long tubes and has continued to idle and run at WOT very well. While cruising it hesitates similar to an EGR issue where it feels like a very slight buck, BUT the EGR was deleted a while back and removed from the tune altogether.

Now moving onto the big misfire, took the car out today and did a WOT run up to about 6k rpm which was then followed by severe misfiring while trying to simply cruise at a constant speed. I managed to hold a constant rpm in 1st gear as the car misfired for a good 20 seconds. Taking a look at the datalog itself everything seems in order EXCEPT the Short Term Fuel Trim Bank 2, if you look at the pics below you can see while the car is misfiring its stuck at 1.25 and then when I press the gas pedal a bit it immediately returns to 0.991 and continues as normal.

Thus far I have done new plugs, COP's, fuel filter, o2 sensors, cleaned maf, and cleaned the air filter. No CEL has come up and I am absolutely stumped at this point. I really want to figure out the cause of the issue before throwing more money into a bottomless pit. If you guys can help me out a bit I'd greatly appreciate it.



 

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Did you datalog before and after you got a new o2 sensor? And have you tried swapping the sensor from bank 2 over to bank 1? Checked your plugs for any unusual signs?

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I just got on to post about the same problem. My car is pretty much identical mod wise. 460 whp with a V2. Idles fine, WOT is fine, but when cruising, it loses power for a few seconds and comes back in. Has SCT tuner and had it retuned with no luck. Hope someone can help out here.
 

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Discussion Starter #6
Ok well the misfire has returned, haven't driven the car in a while out of frustration haha. I got the cleaned injectors back and it misfired once again. Decided to take advantage of the black friday sale at PAS and got all new 60's. Problem seemed to be fixed until this past weekend when the misfire came back. I went ahead and did a compression test and everything is ok there (150-165 across the board). When I pulled the plugs I noticed that the cylinder #6 and #7 plugs smelled like gas and that they were noticeably more black than the other 6 cylinders. Cylinder #4 was another one that looked a bit different.

In the first picture I have the most recent plugs lined up on order of cylinder number. The top row is cylinder #1-4 and the bottom is #5-8



I decided to take out an old set of plugs from about a year back to see what they looked like (this was before I ever had an issue with the misfire). All 8 plugs looked pretty much identical to the one shown but look how different it is from the new plugs. With a flashlight I looked at the #6 and #7 piston and could see a noticeable amount of carbon build up on the pistons, something that was not there a year back (when I did the valve covers a year ago I checked all the pistons out of curiosity and they were all clean at the time)

 

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Your short fuel trims are perfect in both images not sure where you're getting your reference values. You are still describing a misfire which is very very rarely a fuel injector. The two plugs that are fuel soaked would be indications of a misfire causing fuel not to be ignited and burnt replace your plugs run car with data logger and misfire monitors when it misfires you should be able to observe which cylinder(s) misfire and then you can replace that coil or coils. Don't make it more difficult than it is. Good luck
 

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What are you gapping your plugs to? Try .028 if yours are gapped more. Is your bypass valve working properly?
 

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Can it be COP's? Are they OEM Ford's? different than the other 6? Boots in great condition (no cracks period?)
 

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Discussion Starter #12
Your short fuel trims are perfect in both images not sure where you're getting your reference values. You are still describing a misfire which is very very rarely a fuel injector. The two plugs that are fuel soaked would be indications of a misfire causing fuel not to be ignited and burnt replace your plugs run car with data logger and misfire monitors when it misfires you should be able to observe which cylinder(s) misfire and then you can replace that coil or coils. Don't make it more difficult than it is. Good luck
Not sure what images you are looking at but a fuel trim being stuck at 1.25 is NOT perfect in any way. My cruising stft's only fluctuate +/- 5% like they should but when it misfires heavily the stft sticks at +25%.

As I stated in my first post all COP's are brand new, maybe 150 miles on them. All of them are oem motorcraft with brand new boots properly installed with die-electric grease.

Plugs are BR7EF gapped at 0.028" so the gap isn't an issue. Bypass valve works just fine.
 

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Discussion Starter #14
With the original injectors the stuck fuel trim did in fact move with the injectors to the opposite bank. I figured it was an injector issue at that point so I had them cleaned which did nothing, bought new injectors for dirt cheap and the misfire was still there.
 

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You're wrong on short term fuel trims they should be anywhere from 0 to 7 percent 1.25 is not an issue whatsoever your looking In wrong places. When short term fuel trims send up a red flag is when you are in teens or up to 30 percent which is maxed out. And yes your short term fuel trim is going to spike to 25+ percent when a misfire happens PCMs instant reaction is to add more fuel..make sure your 02s are switching properly and that you didn't accidentally turn the egr tune off.
 

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Discussion Starter #16 (Edited)
The egr is deleted with it turned off in the tune. I'm not looking in the wrong places, I started with plugs and fuel filter then replaced upstream o2's since they were old anyway. COPs were due for a change and the injectors came back with not so great flow numbers even after cleaning. Everything is brand new at this point except the engine harness and ecu. The datalog for the o2's show normal voltage fluctuation, better with the new o2's. I'm no rookie when it comes to diagnosis, this issue definitely isn't some obvious fix.

I'm going to be data logging tomorrow with the new plugs. We'll see what happens
 

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Understood last but not least If your car is an automatic and you had a weak converter torque converter shudder could cause you to think you have a misfire or even confuse engine into thinking your running rough. Just an idea.
 

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Discussion Starter #18
T56 car so not an issue there, plus I know it's a heavy misfire, if I give it gas under heavy misfire it sounds like a two step.. When it gets into the misfire it's really bad. The general feel of the car reminds me of when I used to have the egr on the built motor and the egr wasnt adjusted in the tune, you could feel it slightly bucking all the damn time.
 

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Discussion Starter #19
Datalogged the misfire once again and it has returned to the passenger bank this time. Have the datalog available but noticed this forum doesn't support .csv type files for attachments. Tried to get it to misfire long enough to throw a code but had no luck with that.
 

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Discussion Starter #20
Here is a snapshot of the heavy misfire, graph showing bank 2 o2 voltages and bank 2 STFT. Managed to get the misfire to last a few minutes but it eventually went away the more I drove it through the city.

 
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