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Check Engine Light ON Right After Mods & Flex-Fuel Tune

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Really could use some help. Here’s the gist of work that was completed Friday before I noticed the CEL came on Saturday...

Stainless Works long tube headers
Ford intake manifold (ported) for 2018+ GT
JLT Performance CAI
Ford Racing EV6 fuel injectors
MMR lightweight billet aluminum 3-bolt water pump pulley
Reische Perfromance 170° thermostat
JLT Perfprmance air-oil separator
HP Tuners inferred flex-fuel tune

Got codes P0305 & P0300, so #5 Cylinder Misfire.

I’m not sure how long the CEL was on before I noticed it, but I probably worked the engine pretty hard after it came on because hey, more power! I hope I’ve done no harm. The car also exhibited a weird occasional “thump” under light steady throttle in high gear, almost like it went over a small bump but there weren’t any. Makes a faint sound and I could feel it too.

Bad plug? Ignition coil? Any idea of what might’ve caused this vis a vis the tune and mods? I doubt it’s a coincidence. I’m at 15K miles. 2017 GT.

I’m going to call the speed shop first thing tomorrow, but wanted to tap into the knowledge here before I speak with them. Thanks!
 
Really could use some help. Here’s the gist of work that was completed Friday before I noticed the CEL came on Saturday...

Stainless Works long tube headers
Ford intake manifold (ported) for 2018+ GT
JLT Performance CAI
Ford Racing EV6 fuel injectors
MMR lightweight billet aluminum 3-bolt water pump pulley
Reische Perfromance 170° thermostat
JLT Perfprmance air-oil separator
HP Tuners inferred flex-fuel tune

Got codes P0305 & P0300, so #5 Cylinder Misfire.

I’m not sure how long the CEL was on before I noticed it, but I probably worked the engine pretty hard after it came on because hey, more power! I hope I’ve done no harm. The car also exhibited a weird occasional “thump” under light steady throttle in high gear, almost like it went over a small bump but there weren’t any. Makes a faint sound and I could feel it too.

Bad plug? Ignition coil? Any idea of what might’ve caused this vis a vis the tune and mods? I doubt it’s a coincidence. I’m at 15K miles. 2017 GT.

I’m going to call the speed shop first thing tomorrow, but wanted to tap into the knowledge here before I speak with them. Thanks!
The P030X codes are specific to the cylinder that the PCM detects a misfire. P0305 = cylinder 5.

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I'm late on the reply so assuming you already called the shop but will still give my 2 cents. I have headers, xpipe, cat delete , 18 manifold and the 47lb injectors and wouldn't call it a coincidence either. You could check that coil and plug but it's probably related to the headers, ported manifold and the tune or the O2 sensor is not happy or went bad on that bank. FYI headers and E85 are not O2 sensor friendly. I still throw codes even on a 92 tune occasionally if I'm not up to operating temp. I was on E85 but had "detuned" due to no ETOH near my home track. My original E85 tune and 6th gear below 2000 rpm did not mix when I I tried to accelerate - weird engine response and cel within a short distance. Sometimes now even with the 92. I try not to lug the car and gradually throttle when at low RPM. It seems to help. When I got my car dynoed my shop recommended a dedicated E85 and 92 tune with a fuel dump program and speifically tuned my car safe towards the rich side. 5-10 more HP was not worth a blown motor for me. They use the SCT tuning though. I'm not sure if HP has the same type of programing or if your shop can adjust. See if your shop can have you datalog with your hand held or HP gauge (whatever you have) and see what is really going on.

Nice stang and setup!
 
The P030X codes are specific to the cylinder that the PCM detects a misfire. P0305 = cylinder 5.

View attachment 68935
I'm late on the reply so assuming you already called the shop but will still give my 2 cents. I have headers, xpipe, cat delete , 18 manifold and the 47lb injectors and wouldn't call it a coincidence either. You could check that coil and plug but it's probably related to the headers, ported manifold and the tune or the O2 sensor is not happy or went bad on that bank. FYI headers and E85 are not O2 sensor friendly. I still throw codes even on a 92 tune occasionally if I'm not up to operating temp. I was on E85 but had "detuned" due to no ETOH near my home track. My original E85 tune and 6th gear below 2000 rpm did not mix when I I tried to accelerate - weird engine response and cel within a short distance. Sometimes now even with the 92. I try not to lug the car and gradually throttle when at low RPM. It seems to help. When I got my car dynoed my shop recommended a dedicated E85 and 92 tune with a fuel dump program and speifically tuned my car safe towards the rich side. 5-10 more HP was not worth a blown motor for me. They use the SCT tuning though. I'm not sure if HP has the same type of programing or if your shop can adjust. See if your shop can have you datalog with your hand held or HP gauge (whatever you have) and see what is really going on.

Nice stang and setup!
Thanks! Really appreciate that. The shop sent a tow truck yesterday (as I’m an hour away) and they‘ve started to check it out. Said there is something wonky with the tune right at start-up with e85 and something else I can’t recall. Making some adjustments this AM and will contact me later today. This has been damn disappointing - missed an Autocross Sunday - and I hope they get it straight soon.
 
Thanks! Really appreciate that. The shop sent a tow truck yesterday (as I’m an hour away) and they‘ve started to check it out. Said there is something wonky with the tune right at start-up with e85 and something else I can’t recall. Making some adjustments this AM and will contact me later today. This has been damn disappointing - missed an Autocross Sunday - and I hope they get it straight soon.
Keep a pair of O2 sensors for backup box. You'll know when one really acts up... It just plain runs like crap. You don't want to get stuck at an event and waist part of it. Auto Zone honors Bosch's 12 month warranty. My last couple were free. Take the day old one in and they give you a new one. There are a few vids an posts around the interwebs that say if the O2 header bung is relocated from horizontal to something like a 45 that helps with water destroying sensors. IDK personally though.
 
Keep a pair of O2 sensors for backup box. You'll know when one really acts up... It just plain runs like crap. You don't want to get stuck at an event and waist part of it. Auto Zone honors Bosch's 12 month warranty. My last couple were free. Take the day old one in and they give you a new one. There are a few vids an posts around the interwebs that say if the O2 header bung is relocated from horizontal to something like a 45 that helps with water destroying sensors. IDK personally though.
Thanks again. I got the car back again. Seems they’ve remedied the CEL coming on - They say it was a cold start issue and they adjusted the tune. No CEL so far, but the faint “thump” can still be felt through the car in higher gear under light throttle. I’m having some buyer’s remorse right now - Maybe I should’ve simply got the more straightforward 93 octane tune. If it has to go back in a third time, I might ask them to do that.

Appreciate the tip on spare sensors. Will keep that in mind.
 
Thanks again. I got the car back again. Seems they’ve remedied the CEL coming on - They say it was a cold start issue and they adjusted the tune. No CEL so far, but the faint “thump” can still be felt through the car in higher gear under light throttle. I’m having some buyer’s remorse right now - Maybe I should’ve simply got the more straightforward 93 octane tune. If it has to go back in a third time, I might ask them to do that.

Appreciate the tip on spare sensors. Will keep that in mind.
Did your shop get it all sorted?
 
Did your shop get it all sorted?
I’ve still got the car. I reported to them and we’ve agreed I’ll keep it and drive it for a while. No clue what the faint “thump” could be. The car feels very different, and some or all of that might be normal. I think when I can run it hard in an autocross or track sprint I’ll know a lot more - Weather hasn’t been cooperating.
 
I’ve still got the car. I reported to them and we’ve agreed I’ll keep it and drive it for a while. No clue what the faint “thump” could be. The car feels very different, and some or all of that might be normal. I think when I can run it hard in an autocross or track sprint I’ll know a lot more - Weather hasn’t been cooperating.
I just reread your 1st post. That thump that you actually feel would make me nervous. Just a shot in the dark. I play with and soup up chainsaws as a hobby. If the timing is advanced to much a saw runs like crap. Is it possible the tune has too much advance at low rpms under light load and causing pre-ignition ( not piston friendly). If not the advance is the A/F ratio jacked up at low rpms. Is the flex tune adjusting properly for the E85 and going rich enough? Lean will cause pre-ignition also.
 
I just reread your 1st post. That thump that you actually feel would make me nervous. Just a shot in the dark. I play with and soup up chainsaws as a hobby. If the timing is advanced to much a saw runs like crap. Is it possible the tune has too much advance at low rpms under light load and causing pre-ignition ( not piston friendly). If not the advance is the A/F ratio jacked up at low rpms. Is the flex tune adjusting properly for the E85 and going rich enough? Lean will cause pre-ignition also.
Well, I‘m nervous now. LOL. Seriously though, I appreciate your take. This is all way over my head, and I’m just going on what the shop says. No clue if they are right or wrong, but the project manager heard the thump after I brought the car back - They don’t seem to think it’s a concern, but what is it though? It sounds like it’s under the car (exhaust, transmission?) and it’s faint, pretty hard to pick up. And the car seems to run well otherwise. If your theory is correct, I’m probably destined to several rounds of gremlin-chasing with this shop which is an hour away. Just not sure what to do right now - Take it back or continue to drive and assess for a while.
 
Well, I‘m nervous now. LOL. Seriously though, I appreciate your take. This is all way over my head, and I’m just going on what the shop says. No clue if they are right or wrong, but the project manager heard the thump after I brought the car back - They don’t seem to think it’s a concern, but what is it though? It sounds like it’s under the car (exhaust, transmission?) and it’s faint, pretty hard to pick up. And the car seems to run well otherwise. If your theory is correct, I’m probably destined to several rounds of gremlin-chasing with this shop which is an hour away. Just not sure what to do right now - Take it back or continue to drive and assess for a while.
I'm not advanced on engine stuff by far. Sometimes I just look at things from a different way. I like figuring things out. if the guys heard it and they were not worried. This one's real and can happen with headers I don't know which brands happen more. If you hear a weird sound and can even feel at times when turning only right it's probably the header rubbing on the steering shaft. Mine does occasionally even with new motor mounts. All the stuff we have to figure out and go through in the name of pony power.... 🤣
 
I'm not advanced on engine stuff by far. Sometimes I just look at things from a different way. I like figuring things out. if the guys heard it and they were not worried. This one's real and can happen with headers I don't know which brands happen more. If you hear a weird sound and can even feel at times when turning only right it's probably the header rubbing on the steering shaft. Mine does occasionally even with new motor mounts. All the stuff we have to figure out and go through in the name of pony power.... 🤣
Yeah, I don’t have much time for figuring things out. Maybe not the brain either. LOL. But I hope this all was worth it.

They think the tune just doesn’t like those low rpms and pulls timing occasionally between 1200-1500 in 5th and 6th gear. They‘re not sure if they can tune it away, but they are pretty sure the car is otherwise fine to drive (and to race). It’s pretty easy to avoid that rpm range without losing much fuel economy. Trying to decide now whether to give them a THIRD crack at it or continue to drive & assess.

The added 65 whp isn’t a dramatic difference with a Coyote, but it’s very noticeable. Quite strong in the 4000-7000 rpm range. With Brembos installed too now, I’m anxious to see what it translates to on the track and in autocross.
 

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