Troubleshooting a stock V6

[allexanderlee]

Hello all,

Just got my first Mustang this summer, 2011 Kona Blue with V6/MT82. It was a bit neglected and had 215k km (or 135k miles) on it. Since I'm in Eastern Europe, finding a good manual Mustang was quite a hard task, even more so finding a mechanic proficient with US-spec cars.

I've been a car enthusiast for the most part of my life and finally it paid off - I was able to fix a lot of things myself.
The engine was running okay-ish, a bit hot, idling a bit rough, but no codes and no power loss.

Done brakes, leaking valve covers, new plugs, leaking pinion seal, burned fan resistor - everything was fixed, along with significant cosmetic improvements and of course fresh fluids for everything.

Idle is almost smoothed out now, but a mysterious low RPM misfire appeared (no codes, just appearing in FORScan, please see images attached) and evap/purge valve is cycling constantly, once every 15 seconds. I swapped out EVAP and PCV valves for the new Motorcraft ones, but the behavior persists.

That begs the question, how normal is that for our V6?

I assume misfires are not acceptable at all. First plugs I threw in were Champion Iridium plugs, they worked with no issues, but I got low load/low RPM misfires in all 6 cylinders without affecting the power. I ordered Motorcraft SP520s and replaced Champions, now the engine runs a tad smoother, but misfires are still there.
They usually appear when I apply really light pressure on the gas pedal to keep the speed. They do not appear when accelerating. Crank relearn and adaptation reset was done of course. No vacuum leaks were found with the water spray method.
As per purge valve, I've been told by the local mechanics it is normal, but I want to check with you guys.

Any feedback or ideas are much appreciated.

 

[Juice]

I would only be concerned with misfires if it trips the check engine light.

 

[allexanderlee]

Thanks Juice! Can't help but overthink it, since previously I had German cars.
With the Mustang, I didn't have a single code related to the engine in my time of ownership. Just the mechanic told me it sounded like it was misfiring, then I got curious and wanted to check it with FORScan.
Before maintenance, there was some exhaust popping present, now I think it's gone.

 

[Juice]

A true misfire will log thousands of misfires in a short time. If the counter stays near ~10 or less, you are fine.

 

[Eman]

135k mi I'd start with a compression test. How are the plug wires? Did you ohm test the coil? Vacum leak best test is using a smoke machine, easily made from PVC pipe parts. Have you cleaned the throttle body? Do you feel the misfire at all?

 

[allexanderlee]

135k mi I'd start with a compression test. How are the plug wires? Did you ohm test the coil? Vacum leak best test is using a smoke machine, easily made from PVC pipe parts. Have you cleaned the throttle body? Do you feel the misfire at all?

Thanks a lot for the suggestions!
Compression seems to be ok, although I'd better test it. Plug wires are visually intact, I did not test the coils. However I ruled out the coils because the misfire happens in all 6 cylinders as per attached picture. I figured if they were failing, I'd have at least one or two coils still functioning properly.

Really good idea about smoke machine, I never had problems with vacuum leaks before, so it didn't cross my mind.

Throttle body has been cleaned, yes. The car pulls really well, no misfire is felt - that is what I'm confused about.

 

[86GT351]

Have you looked into possibly having the injectors flow tested? Data does not show specific flow of the injectors. If they are gummed up at all, it can will change the way the vehicle performs. What happens when you are washing the car and you piull the hose and it gets caught under a tire? Water flow gets restricted. Same concept with an injector. I have included a picture showing dirty vs clean. Not supporting Rislone products.

 

[allexanderlee]

Have you looked into possibly having the injectors flow tested? Data does not show specific flow of the injectors. If they are gummed up at all, it can will change the way the vehicle performs. What happens when you are washing the car and you piull the hose and it gets caught under a tire? Water flow gets restricted. Same concept with an injector. I have included a picture showing dirty vs clean. Not supporting Rislone products.

Thanks for your input!

Injectors and their proper functioning were a big deal with my previous diesel cars, so yes, I did think about it, but never connected it to the misfires. Since they happen in low load situations with lower fuel pressure, it actually could be the reason.

I'm using 98 octane fuel (which I believe is equivalent to 93 octane in the US), so the system itself should be pretty clean.
Anyway it would be nice to have clean (or even better, new) injectors. So I'll look into it anyway.

I really appreciate all the ideas you guys are giving me here. Firing the parts cannon is a bit expensive on this side of the pond due to taxes and import fees. Now I got a lot of things to check and hopefully this will bring me closer to a perfectly running Cyclone V6.

 

[86GT351]

Thanks for your input!

Injectors and their proper functioning were a big deal with my previous diesel cars, so yes, I did think about it, but never connected it to the misfires. Since they happen in low load situations with lower fuel pressure, it actually could be the reason.

I'm using 98 octane fuel (which I believe is equivalent to 93 octane in the US), so the system itself should be pretty clean.
Anyway it would be nice to have clean (or even better, new) injectors. So I'll look into it anyway.

I really appreciate all the ideas you guys are giving me here. Firing the parts cannon is a bit expensive on this side of the pond due to taxes and import fees. Now I got a lot of things to check and hopefully this will bring me closer to a perfectly running Cyclone V6.

I have been in the industry for many years. Please don't think because you are using a higher Octane that it is "cleaner". That is what they want you to believe.

 

[allexanderlee]

I have been in the industry for many years. Please don't think because you are using a higher Octane that it is "cleaner". That is what they want you to believe.

Honestly I never expected any miracles from higher octane fuel, but I perceive that this engine does run a tiny bit better with 98.
I was flying piston engine aircraft in the past and circumstances forced us to use automotive fuels, 95 and 98. The difference between them was much more pronounced in that application.
That being said, it has to do with the efficiency, not with the cleaning qualities of a certain type of fuel. So I am completely with you on this.

 

[Eman]

Don't know anything about fuels where you are, know little enough about what we have. I do know that here if a pump has a sticker that states Top Tier Fuel it does have certain cleaning additives. Usually found at name brand gas pumps.

 

[86GT351]

Don't know anything about fuels where you are, know little enough about what we have. I do know that here if a pump has a sticker that states Top Tier Fuel it does have certain cleaning additives. Usually found at name brand gas pumps.

Not sure if you know ths or not. Buying at a GENERIC ctation does NOT mean generic fuels. What the generic stations do is buy at auction. WHen fuels are made, there is always an over abbundance available to the actual stations. Left over gets sold at auction to the generic stations so you could very possibly be getting the BETTER fuels when going generic.