2013 Mustang GT/5.0 V8. I am experiencing rough idle and what feels like a misfire at idle. (Although I guess it’s not bad enough to trigger misfire code.) Accelerating under load and driving seems OK.
Even though I have headers and high flow cats I’ve been running them for 6 months with perfect drivability and no o2 codes until now. When I installed the headers 6 months ago I replaced all 4 brand new o2 sensors with OEM Motorcraft ones from dealership.
I am getting one trouble code which is P0141 on my scanner which is for o2 sensor bank 1 sensor 2 (downstream/after cat).
Yes I’ve driven several drive cycles and probably at least 50 miles since it first threw the code, then I scanned it again and the P0141 is still the only code.
The strange part is when I look at the live data on my scanner it shows bank 1 short term fuel trims are stable/constant but bank 2 short term fuel trims are fluctuating up and down like crazy. Also bank 1 AFR are stable but bank 2 AFR is fluctuating like crazy.
Normally my short term fuel trims fluctuate gradually between 0.8 - 1.05 or so and readings are more or less the same on both banks. With the problem I have now bank 2 is going between 0.7 and 1.3 rapidly up down up down while bank 1 fluctuates slightly and gradually. AFR on bank 1 stays around 13-14 and AFR on bank 2 fluctuates rapidly between 10-20.
What gives? If my only code is P0141 which points to bank 1/downstream, why are my bank 1 fuel trims and AFR normal but the bank 2 is acting up?
I believe a bad downstream/after cat o2 sensor would not cause drivability issues or misfire/misfire like symptoms because downstream o2s don’t effect AFR - only a bad pre-cat o2 sensor would. So if this is factual then would the rough idle/misfire point to another problem then?
I haven’t done any recent work or mods the only thing I’ve done recently was changed my oil with full synthetic a couple weeks before the drivability issues started…and my spark plugs were changed 8000 miles ago with Motorcraft.
Any suggestions of where I start? Normally whenever I have engine problems I’d always start by addressing whatever the codes are saying but in this case they appear to be contradictory to the live data on the scanner and I don’t want to just throw parts at it.
I agree with this assesment. I think bank 2 has an issue not related to the P0141. Ignore it for now. It should not affect how it runs.
I think you may have a sticking injector causing your STFT fluctuations. You might try swapping injectors bank to bank to see if the problem moves with the injectors. Be sure to use new O rings. Check the bank 2 plugs at the same time to see if one looks different. A sooty plug might show a rich condition from a sticking injector or failing coil not throwing a code yet.
A sticking injector wouldn’t always throw a code correct? Is it correct to say it would only throw a code if there was an electrical issue in the injector with either the harness/wiring or one or both of the fuel injector connectors and it wouldn’t throw a code if it was sticking due to just being gummed up? In that case maybe I should try some bg44k?
Correct. No open circuit or short, the ECU figures all is OK.
As long as the upstream O2 sensor can keep the mixture correct for that bank of cylinders, the ECU thinks all is OK. So stick open or stick closed for just a moment doesn’t set a code until it is out of range and you have a long way to go with STFT.
A little BG44K could not hurt and it may clear up the problem. I owned a Taurus SHO with the hot V6 that needed fuel cleaner every so often when the idle got lumpy. Give it a try.
What are you using to look at live data? Something better than a typical DIY code reader (Autel, Snap On) should give you a live Cylinder Contribution Test that will pick up misfires way before the car sets a code for one.
Also agreed. The only purpose of the downstream O2 is to monitor the cat. And the P0141 is just about the heater circuit which is only relevant briefly when starting up, in any case.
As I was reading along, I was thinking a leaky bank 2 intake manifold. But @Mustangman 's suspicion of a sticky injector also isn’t out of the question. And, as he explains, you can have either that or a leaky intake without getting codes. Eventually…if things get bad enough and go on long enough you’d get a rich or lean code (which comes from the upstream O2 sensor).
I’m used to seeing fuel trim numbers as percentages that will bounce negative to positive, and pretty regularly if all is well. Positive numbers are lean (adding fuel), negative numbers are rich (cutting back on it). It’s just the computer adjusting constantly to hit a perfect 14.7:1 air/fuel ratio.
I did replace the intake manifold about 3 months ago with a manifold from a 2018 car for better top end performance. It was brand new and came with brand new gaskets. I did it myself. Not drivability problems until yesterday. I did have to remove the new manifold shortly after installing it because one of the fuel injector connectors had curled up and gotten caught underneath when I installed the new manifold facepalm so I’m not sure if removing it and then reinstalling it damaged or weakened the new gaskets because maybe they had already been compressed? Although again, it drove fine for 3 months.
Maybe I’ll try to spray some starter fluid around the drivers side of the manifold with car running and see if it bogs down. If it does then that means there’s a leak.
That should tell you something. Did you torque with a known-good torque wrench to spec? If all of the fasteners are accessible, I’d also be inclined to go ahead and check them with the torque wrench.
A quick test just to rule out a bad O2 would be to just swap banks to see if the code follows… Also make sure no exhaust leaks and the connection is secure as well as the sensor is tight…
Better top end power for sure. Since the stock manifold falls off at like 6700-6800 rpm. The 2018 can rev into the low to mid 7000s and not drop off in power. Low end torque with the 2018 shouldn’t really be any different from the stock 11-14 manifold. I would definitely recommend. If you can swing it a cobra jet is king but it’s pretty expensive for just like 5 more whp than the 2018 and not worth it imo.
I bought a kit for a 2018+ manifold from VMP with IMRC lockouts. I would definitely recommend this over the boss 302 intake since you lose quite a bit of low end torque with that one. However this doesn’t matter for people that only want to race (especially from a roll) because the boss 302 has a substantial top end increase in horsepower (maybe slightly more than the 2018) and you’re near or at redline anyway when you’re racing the car so the low end loss doesn’t matter (for some people). I just wanted to keep as much around town drivability so I went with the 2018.
By the way does anyone know a reputable source for seeing torque specs? I can’t find reliable torque specs for a 2013 5.0 manifold bolts. Most sources say 89 inch pounds and some say 22-25 foot pounds which obviously is a big difference. First time around I just did hand tight but I want to be sure I get it right this time.
Hey guys, I ended up replacing the intake manifold gasket torquing to spec in correct tightening sequence. Manifold ports on engine block and manifold itself looked fine. Not warped or gouged. I also swapped all coil packs across banks. Erratic AFR did not switch banks so I know coil packs are fine as well.
Neither of these things fixed the issue. Car still has a rough idle and erratic AFR (fluctuating from 9-23 at idle) on bank 2 only. Bank 1 stays stable fluctuating from 14-15 at idle)
Would the best next step be to swap all fuel injectors across banks? And see if the erratic AFR switches banks?
And what would be the next step after that if injectors appear to not be the cause? Still no engine codes besides P0141. Car seems to drive OK otherwise, mainly idle is problematic.
Do you mean swapping bank 1 and bank 2 downstream o2s? I thought the consensus earlier was the bad bank 1 downstream o2 from p0141 had nothing to do with the out of range fluctuating AFR on bank 2
Do you happened to know if the header bolts are able to get a wrench on them from the engine bay and/or from under the car without taking a lot apart?
Compression check seems logical if injectors are fine and header bolts are tight, although I haven’t recently overheated the car and I don’t see smoke from the exhaust. No knocking noises and no metal shavings in oil either when I did oil change 2 weeks ago
No, just take a look and see what access you have.
Doesn’t matter. A compression check determines the health of the engine. Leaking valves or worn rings from one cylinder would be signs of worn engine (this car is near 100K, right?). A 15 to 20% low compression in one cylinder may not misfire enough to cause a code but might create the “feel” of a misfire you now perceive. Basically the reason a misfire code will eventually be set.
If the easy stuff (manifold gaskets, coil swap, injector swap, header check) don’t show results, the mechanicals inside the engine are the logical next step. Compression test, pull the valve cover and check rocker arms, cams, and looseness at the timing chain between the cams is the next most accessible area to check.
While my Mustang doesn’t have a lumpy idle, my 154K truck does. It doesn’t set any codes but I can feel it just the same. Still runs good though.