Car running poorly/missing- part 2

ghunt81

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So I posted that the car was running bad on 1/4 tank or less of gas.

Well, I have noticed that it actually running bad/missing at any fuel level, except it's totally random.

For example this morning I drove it to work, started out OK then started to feel like it was missing mostly at lower RPM's. It doesn't do it as much above 2500 RPM but I have noticed that it does sometimes.

Drove it to lunch, it was doing it part of the way out to lunch. Stopped at a store, got back in the car and it was running flawlessly. Stopped for lunch, afterward again running fine.

Then when I left work and went home it was missing randomly again.

Thoughts??? I'm confused. I'm getting no CEL. I just did Autolite plugs and OEM coil packs 2 years ago. Is this a sign of a failing fuel pump?
 

Dino Dino Bambino

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Have you scanned the ECU? You may have fault codes even without a CEL.
It'll be a lot easier to troubleshoot the problem if you can log live data using something like an ELM 327 Bluetooth OBD 2 dongle paired to a car scanning software app (e.g. Car Scanner, Forscan) downloaded onto your smartphone or laptop. It's a very useful device, and it could save you a lot of money by not randomly buying parts that don't fix the problem.
 

86GT351

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Don't fall for the NO Check Engine Light. Get it scanned with a quality scanner that can read Mode 6. Might give you some additional info.
 

Laga

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Get Forscan. I’ve put it off for a long time thinking it would be too complicated. I finally pulled the trigger last week. Even my 66 year old, retired carpenter’s brain was able to figure it out. It will eliminate lot of guesswork.
 

Dallas281

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I always look at my maintence when/if/before I have issues. Filters, oils, bushings ect. When was the last time you replaced your fuel filter? I replace mine every year.
 

ghunt81

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Have you scanned the ECU? You may have fault codes even without a CEL.
It'll be a lot easier to troubleshoot the problem if you can log live data using something like an ELM 327 Bluetooth OBD 2 dongle paired to a car scanning software app (e.g. Car Scanner, Forscan) downloaded onto your smartphone or laptop. It's a very useful device, and it could save you a lot of money by not randomly buying parts that don't fix the problem.

I have done live datalogging for Lito before through my SCT with whatever the datalogging software is that he uses, but that's it...and I don't really know how to read the datalogs. I may have to look into that.

In the meantime, I was thinking I should run the codes, just haven't had a chance to do it yet.
 

ghunt81

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I ran the codes today after work and stored on it was P0316- Random misfire detected at startup.

Is this generally a spark issue or fuel injector issue?
 

ghunt81

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Well I guess I'm gonna see if Lito can take a look at a datalog for me and maybe see what's going on. It's weird, the car runs fine on initial startup and after a minute or so, starts stumbling/missing/whatever it's doing.
 

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Four things arise in the tech manual for 0316. It also indicates that there would be additional codes pointing to a specific cylinder (s) in freeze frame data if cylinder specific related. Of course this is with respect to a high end diagnostics service center unit so I do not know if Forscan could see this or not. Assuming (and that is a very dangerous word to use when troubleshooting) Forscan can see freeze frame data and none is there accommodating the primary 0316 code, one would then be inclined to then look at fueling issues or crank trigger related issues logically.

Here is the link. Hope it works.


https://iihs.net/fsm/?d=10&f=Diagnostic Trouble Code (DTC) Charts and Descriptions.pdf&p=76
 

Juice

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You want to look at Mode 6 data in forscan. Look at the individual cylinder misfire counts. See if it is a specific cylinder or all have similar misfire counts. I would also look at live data, while running, and see what the fuel trims are. Less than 10% correction Im ok with. My cars run @5% or less fuel trims.
 

ghunt81

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Well Lito says he can't see much on the datalog so I will try forscan. Not really sure what else to do right now. Also am going to replace the fuel filter.
 

ghunt81

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Ok so about a week ago I pulled all the plugs, and a couple of them looked weird (gap looked too big and they had brownish discoloration on the boot end ceramic) so I swapped those out with a couple new plugs and put it all back together.

Drove it to work today, ran pretty good in the morning and afternoon but when I went home it literally sounded like I was running on 7 cylinders. I scanned the codes when I got home and got P0300 and P0308...so apparently my problem exists on cylinder 8. First time seeing the P0308 so I'm wondering if I have a bad injector there or something?
 

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Ok so about a week ago I pulled all the plugs, and a couple of them looked weird (gap looked too big and they had brownish discoloration on the boot end ceramic) so I swapped those out with a couple new plugs and put it all back together.

Drove it to work today, ran pretty good in the morning and afternoon but when I went home it literally sounded like I was running on 7 cylinders. I scanned the codes when I got home and got P0300 and P0308...so apparently my problem exists on cylinder 8. First time seeing the P0308 so I'm wondering if I have a bad injector there or something?
Plug, Coil or injector
 

DieHarder

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^^^
This.

Try moving COP for 7 to 8 to see if problem moves. If so you know what the likely problem is though you could still have a bad plug on 8 as well. One thing I did do last year on my list of long-term maintenance items was install new OEM COPs. Made a significant difference. Car runs great.
 
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ghunt81

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These ARE new OEM COP's. I replaced the coils and plugs in 2021 and I don't even think they have 3000 miles on the whole set.

How do you test plugs outside the engine?
 

DieHarder

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Besides COPs/Plugs did you touch anything else? Any other work? For spark plugs I use Brisk (I know expensive but worth it; at least to me). Never any problems with them or had one fail.

Quick test is disconnect the wiring on a COP while running. If idle changes COP/plug/injector are working. (Don't reconnect; just turn it off).

Did you keep the old COPs? If so, I'd swap out the COP on 8 and note any changes (or not). Then the plug. Something else I'm religious about is adding dielectric grease to the top of the plugs/boots when I change plugs. Maybe not necessary but works for me. Other than inspecting/ensuring electrical wiring to the COP is good if no change I'd consider a new injector.

Not that I rely on these sources for advice but a few items that may be of interest here including basic troubleshooting coil packs/plugs and other possibilities:

https://themustangsource.com/forums/f637/rough-idle-after-changing-spark-plugs-547263/

https://www.americanmuscle.com/best-mustang-spark-plugs.html
 
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Just my 2 cents, I was dealing with the similar issue, coil and plug are the main suspects, and yes coil can fail even if it has 3000 miles on them, had that with oem coil, defects happen. As for plugs make sure the gap is right, as die harder mentioned - brisk is the way to go , I’m running one step colder - single piece design plug alone is worth it for our cars, I’m tuned by Lito as well and he had no issues tuning with those plugs or any nonsense that people tell about colder pugs online. My issue ended up being wiring to the coil pack, age of our cars and constant heat isn’t good for insulating material and stuff is getting exposed which ended up being my issue with poor connection, I redid insulation for every wire in the bay after that. Bad or clogged injector is also an option, there are shops that do injector cleaning. Worst case scenario check compression in that cylinder
 
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ghunt81

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I only did plugs and coils. Formerly had E3 one piece plugs, I know they are a gimmick but they had a really good deal on them when I was doing plugs...anyway, they misfired at high RPM's, so I swapped to Autolite HT1's and installed new Motorcraft coils since the car had 105K on it.

I see now Autolite's have the strap welded into the end of the plug rather than a 1 piece design (Lito told me about it before I saw it myself) so if I do replace the plugs, it won't be another set of Autolite's anyway.

Well some good info here...will have to take a look at cylinder 8 and see what is going on there. I do still have the old coil packs.

Also is there any way to check if a coil pack is defective?
 

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