I am using a BAFX OBDII scanner with the Torque app to try and diagnose some hesitation / idle problems with my '12 Civic.

I'm seeing a short-term fuel trim reading of -3.61% and a long-term fuel trim reading of -7.81% (-11.42% total). When I increase to 2,000 RPMs the fuel trim numbers increase to about +5-10%. The numbers drop again to ~-3.5% and ~-7.8% when I let off the pedal.

Is this a sign of a possible dirty MAF?

 

Run the car without the air filter, your numbers will improve. This small change will help you determine if the MAF can respond to small changes in airflow. This would be the easiest for a DIY person. If you have a idle stumble with those readings, the PCM will see it, and reduce fuel, which is what it is doing. This is normal. If this causes the misfire, you will get a DTC.

Typically when I see a MAF failure, there is a 20-30% or more ST or LT correction. This will set the MIL on most cars.

Mileage? Warranty? Fuel quality? When does the problem occur? Engine hot? Cold? Humid? Need more information. A long term reading of 7% is acceptable to me given environmental and production variables.

 

^^ agreed, remove the filter restriction and then run the diagnostic again and look for changes. Or you could just go right ahead and use some MAF/electronics cleaner and clean the sensor and see if that resolves the problem. Are you currently storing any codes at all, or just experience the little hiccups?

 

Only Ford's are that picky about STLT fuel trims, and will set around the +/- 12% mark. I've seen GM's go to 18% without a DTC. Fuel trims are by far a Ford thing for some reason.

I've only seen a few Honda's throw a legit lean code.

 

Yea new Ford/Lincoln vehicles are definately very sensitive. My parents have a 2013 Lincoln MKX 3.7L V6 and I have a 2014 F150 FX4 5.0L V8 now and previously a 2011 F150 XLT 4.6L V8 and they are all very MAF sensitive. I literally clean the slot style sensor and K&N panel filters in both of those vehicles every time I do an oil change.
(Every ~5,000 miles) The PCMs are very picky and fuel mileage and throttle response etc will noticeably change if I allow it to become dirty. The computer is very in depth and intricate, and with the SCT software I can edit and log just about everything straight thru the OBD port.

 

I ended up removing and cleaning the MAF after posting the original post so I never got a chance to test the numbers with no air filter in. I pulled the ECU fuse to clear out the fuel trim numbers, and afterwards the fuel trim definitely improved, showing -2.0-3.0% STFT and ~-1.0% LTFT. However I still have a very rough idle and acceleration hesitation. So it looks like the MAF wasn't the original issue.

I'm at 150k miles now and it's a 2012. I use regular/87 gas usually from Hess or BP.

The hesitation occurs whenever I'm accelerating, either from a stop or, for example, while taking over another car on the highway. The problem happens when the engine first starts in the morning and when it's warm. We've had weather ranging from 55 degrees to 95 degrees this month (NJ) with varying humidity and the problem has been constant.

@B20VtecVillain I haven't ever had any codes, even before resetting the ECU (I'm the original owner, no possibility of previous clearing, etc.). I scanned anyway for good measure and still got nothing.

Funny thing is when this whole hesitation/idle problem all started, I noticed I had a small 3" tear in the air intake boot.. however it never set a Bank 1 Lean code. I'm wondering if the ECU is not working properly.. when I turn the ignition to ON, the CEL illuminates for a few seconds (expected) to show it's working, but it has never set a legit code.

So far I've replaced the air intake boot, changed all four plugs and all coils, cleaned the MAF and changed the air filter. No luck yet...

Thanks all

 

Fuel filter every been changed? Fuel line, injector cleaning ever done?

 

Fuel filter wasn't changed, I looked into it but on my car it's built into the fuel pump and the entire fuel pump needs to be replaced to change the filter, unfortunately. I checked with a few Honda dealerships to make sure and they all said the same thing. Never had a professional injector cleaning done. I did use a few bottles of STP Fuel Injector Cleaner at the recommendation of a tech at my local Honda (one bottle every third tank). Didn't really do anything to help.

Today while driving home I had Torque open monitoring the temperature on "Catalyst Bank 1 Sensor 1" and while cruising at 70mph the temperature read 1,515 degrees F. I'm not a car expert whatsoever but that seems incredibly high to me? The temperature would drop when I laid off the pedal. Below is immediately after I parked at home, sitting idle for 30 seconds:



Is 500-700 degrees F normal operating temperature while idle or all around? If it's all around, mine is probably burning up. I'll drive and check it to see if it's red once it gets a little darker out.

 

Could be a bad/clogged cat if the temps are exceeding the acceptable range. That could definately cause performance issues and also affect the a/f ratio. Forgot about the lifelong fuel filter deal in the new vehicles. As far as the injector cleaning, I've always liked seafoam and Lucas products, but I have no idea if any one brand truly works better or more effective than another. I would definately check into the cat and pre cat though.

 

I went out for a drive tonight and the highest temp I could see on the Catalyst B1S1 monitor was 1,607 degrees F. This was while I was accelerating to 70mph and at 3,250rpm. I read a few different sites that say 1,600-1,700 degrees F is acceptable but pretty much on the higher-end of what's safe for the cat.. but then another site will say that's pretty much a meltdown point..?

Not sure what you mean by check the cat / precat? Sorry, not too familiar myself with cars or terminology, just started learning since having this problem. I'm just a computer guy

Only way to check if it's clogged is to take it out right?

Thanks again

 

No you don't have to remove the cat, they make exhaust back pressure gauges. You can either buy or most likely also rent/borrow this and what you will do is look up the acceptable numbers online. (Google/Bing is your friend) and then depending on the type you will jack up the car, and either drill a very small hole, usually 1/4" drill bit, in the pipe directly behind the cat and insert a small needle into the hole to get a reading and compare the results to what is acceptable. (Don't worry, there are little expanding metal pin plugs for under $5 that slide in to seal such a hole at the parts store) I have also seen other pressure test setups where drilling a hole is not necessary and there is an adapter that will allow you to get a reading using an existing threaded 02 bung, so it really depends on what tools your using.

 

Lets start out fresh. First, don't change 20 things all at the same time. If you do manage to fix it, great, and you'll also have no clue as to what was causing the problem, or how to prevent it. As I said before, Fords are very sensitive to fuel trim changes, and will create a DTC if long term fuel trims near 8-10%. Most other manufacturers (including Honda) will not set a DTC until much higher trim percentages. The fact that Fords are more sensitive has a lot to do with the stated emissions for Ford vehicles. It has nothing to do with sensitivity, as these MAF's are also used on Mazda's without the DTC "problem" that Ford has. Looking to fuel trims to solve this problem is practically useless.

Things like cam/crank correlation and position are more important. Commanded and actual throttle position, are also important, since your car has an electronic throttle. I'd also start some reading into VTEC and VTC.

I also hope the parts you used are correct for your application, and that your replacement coils actually fire to specification.

The converter temperature is modeled, that is not an actual reading. It is derived from other inputs to the PCM.

Your fuel filter is just fine, as is the pump output, as evidenced by the -7% LTFT. This means fuel is being removed from the system, not added. -7% means a shortage of air, which you clearly do not have.

If your vehicle has a noticeable drop in acceleration and lack of power overall, THEN I would start with the converter. This is not your problem, because P0420 is not set. This code will set well before a cat melts or becomes damaged.

Again, you need to provide us with more information. Is the problem repeatable, meaning can you invoke it at will. When did the problem start? What was the last thing done to the car prior to the problem becoming apparent. Have you contacted the dealership about this problem. You seem intent on throwing money at this, why not start with a call to the dealer to look for software updates at the least?

 

No. And dont remove the air filter,per anyones instructions. That is ridiculous advice. Fuel trims are not affected at all by a restricted/plugged air filter and many(most) can be adversely affected with out the presence of the air filter because of increased turbulence.

Your trim readings mean nothing as you display them. They need to be graphed out and the trend needs to be analyzed in order to determine the issue at hand. Trims alone are also not enough. You need to graph the O2s, MAF ,Calculated load ,and throttle positon, under varying speeds(loads) along with the trims in order to paint the picture of the vehicles problem.




Trims are extremely useful and can indicate anything from a plugged cat to timing that is off. One simply needs to know how to analyze and interpret the data. Not every mechanic knows how and are quick to dismiss them. (BTW your cat can be completely melted and NOT set a P0420 code. Do not let the lack of a code lead you into a false sense of confidence regarding your cats health)

 

Up to 1800F degrees is normal operating temp.....

 

Please then, tell the OP how to fix the problem, Mr. Know it all.

The advice I provide is of my own determination and experience, and not just with Honda vehicles. Some of us don't have the luxury like Mr. Know it all, of working at a dealership environment. As I do not, I expect diagnostic information regarding this situation from you, since you've probably seen this many times before. You can bash on me all you want man, I don't mind. If you have some insight on the problem, provide it.

 

Ive been called worse.

So you've seen plugged air filters skew fuel trim readings? On what vehicle? This flies in the face of every modern feed back system that I am aware of.

Next thing you know,you'll start saying dirty air filters will reduce MPG,LoL!!


I work in an independent repair shop. On everything from Chevys to Toyotas. Have done so for the last 13 years.My first 7 years as a tech were spent in a dealership.I didnt bash you,or adress you at all. I merely provided my insight. I don't know whats wrong with his car,I asked for data to try to help me help him.....

 

Thanks all for the advice. I'm still new to auto repair in general so this is all pretty fresh info for me.

B20VtecVillain, thanks, I will definitely get the exhaust back pressure checked. Seems pretty simple and as long as I can plug the hole back up I can't forsee it being an issue to test. Definitely a good tip

slowcivic2k, yeah I was trying not to take the "fix a bunch of random crap" approach. I really want to understand all of the possible root causes that could be creating my problem and work my way up starting with the basics. Lots of what I did needed to be done anyway (new air filter, clean MAF, new plugs/coils). I've noticed the performance get better with each thing I do so I can tell now that my problem is a combination of multiple 'smaller' issues.

At 100k miles I put in new plugs but they were Autolite, not OEM Denso or NGK. Stupid me.. I swapped all four plugs for Denso OEM plugs and new OEM coils (all ordered directly from Honda). What a difference.. acceleration is MUCH better, still not great, but definitely smoother. When accelerating I feel the shifting (A/T) is a lot less rough.

Right now the only issues are a slight (much less than prior to fixing anything) rough idle and also slight hesitation while accelerating. Once I get going, all is good. I noticed this morning there was a squeal when turning the ignition on. It looks like my serpentine belt needs replacing-- there is a very tiny crack forming in it and it looks worn. Could this at all cause rough idle / hesitation accelerating? Or is this mainly just to control power steering, A/C, etc. (i.e. non-performance)?

I will check the TPS next to make sure it's good. Also I did take apart the intake boot / airbox while cleaning the MAF to take a look around and noticed the throttle body needs cleaning. I got some CRC TB cleaner from Autozone so I'll get on that.

As for being repeatable, the problem occurs all the time. I will occasionally notice a hard start where the engine takes an extra 1-2 seconds to start, which might just be my aging battery. Prior to any of these problems starting I had no issues between 100k miles and 135k. At 100k I replaced the plugs/coils but they were fine until 135k, then everything started.

I've started hearing about software updates. Do you know roughly what is involved in updating the software? I'm assuming this would be software on my ECU? Haven't ever thought of getting it updated but hell, if it could help I will definitely pursue it. Thanks a ton for your advice.

DCFIVER, the air filter was old anyway so I figured replacing it was painless, took only about 30 seconds and $12 for the filter. Even if this wasn't my main issue, I thought any restriction in the airflow (i.e. clogged filter) could create a richer fuel trim? I'll definitely get everything graphed out and analyzed together.. O2, MAF, fuel trims, etc.. I'll report back once I can get this all done. And yeah I'm definitely not counting on a CEL. I wish I'd get one for obvious reasons but I'm still getting as much checked as possible even if there is no CEL. At 150k my car could use a nice refresh anyway. P.S. thanks, had no clue 1,800'F was normal for the CAT. At least that's a bit of good news.

I think at this point my next step is having the vehicle professionally analyzed by a mechanic. The throttle body needs cleaning so I'll probably do this myself, but beyond that I can only get so far with my OBDII scanner and Torque app.. beyond basic fixes and with my lack of deep knowledge I don't want to cause more problems. If any of you are in NJ, do you have any suggestions for a good shop? I would rather pay an experienced individual mechanic rather than the dealership if possible.

Thanks again for all of the help. I'll report back with any updates and definitely if/when I find a resolution.

 

On an old carburated vehicle,yes, on modern feedback controlled vehicles,not at all.
Im from CA, so no help from me there Im afraid. However I strongly suggest you avoid dealerships,as diagnostics are not their forte anymore. They will simply recommend a bunch of parts. Best thing to do is use Google or Yelp to find a Honda/Acura or Import specialist in your area.