Interesting Crank Profile failure mode
So this was another learning experience. I will admit that I did not do my research first and instead, jumped right into testing. If I had researched first I would have found the Honda bulletin that addressed this problem and fixed it with a crank relearn. But then I wouldn't have recorded some interesting data. If you want the short story, read the bulletin attached. If you want some more detail, read on.
The car came from a used car lot I deal with. They said they had replaced the crank sensor because of a code but it was running very poorly and they couldn't do the crank relearn. It started and idled normally but when trying to accelerate it had no power and would start to misfire heavily. I immediately started to think that they had a bad coil and killed the Cat. I threw the escan on it to see what the VE and fuel trim looked like. The trim chart wouldn't fill normally but what did populate was good. The VE chart however made no sense. The measured airflow read far higher than the predicted airflow. I wasn't sure what to make of this but since the thing misfired so bad I decided to go right to ignition testing. Sorry for the poor pic. I was using a tablet and the touch screen was buggy. VE
I did a current ramp of all the coils and they looked good even when the misfire was present so I decided to look at the injectors. This is when I saw the cylinder 2 injector stop firing every time the rpm was raised. (Yel-cyl1 ignition), (Red-injector current), (Grn-Cam), (Blu-Cam), (White-Crank) (Purple-cyl2 injector).
After looking at the cam and crank signals, injector current and control, I could not see any reason for the injector to stop firing. This is when I stepped back and did some research. I found the bulletin so I checked for a software update. It already had the latest software so I performed the crank profile relearn and to my surprise the thing ran smooth as silk at all speeds and loads after that. The extreme lack of power and misfiring was due to nothing more than an incorrect learned crank profile. I have seen crank learn faults on other vehicles cause "phantom" misfires but on this vehicle it causes REAL misfires.
On this model you have to first do a profile "Clear" then you can successfully do the re-learn.
Be aware that the bulletin says this condition can be caused by cranking the engine with a weak battery. With the driveability symptoms this thing had I don't think most techs would suspect a crank profile issue first.
I had similar instance—didnt do research jumped right to testing 2 dead misfire cylinders- common sence right. Engine runs smooth but throws code right away cylinder 2 & 3 misfire. Misfire data shows Constant Misfire on 2 & 3 cylinders... and all it was is—-> Cam and Crank Relearn. Tricky for common sense logic diagnosi.
Bob good information...I guess you forgot one of my case studies in my seminar that you attend a few years back. I have a example of a Honda misfiring that came from another shop that could not fix it. I showed the Honda HDS scan tool screen shots step by step. Honda states that Clear and Relearn need to be performed if the engine has a misfire, cam or crank is replaced, timing belt or chain…
Thanks G. Sadly I think I have reached the age where I am forgetting more than I remember. Part of my issue is that I have been a one man show for the last 10 years, so I do everything. I work on a wide range of cars and problems both mechanical and technical. In my younger days it was definitely easier to process and remember everything. Nowadays, by the end of the week I can't remember what…
Bob I understand...I enjoy reading your case studies keep up the good work...be safe
That's basic learning skills right there, Bob. Read it, talk about it, write about.....and then you remember it. That's actually why those evil school teachers assigned us homework and asked us questions in class. :-) This is a really good example of how something so "easy" can, instead, be so counter-intuitive in today's world. Thanks!
I sometimes wish I took school more seriously. It appears that nothing can be taken for granted anymore. The computer networks and software have become extremely complex and sophisticated and have many different strategies and failure modes. I remember some training classes where it was said that for a cylinder to fire correctly you need SPARK, FUEL, COMPRESSION and correct TIMING. We can now…
Hi Bob! Good captures! I too fell victim in the same way and like you, when I saw the PCM was causing the misfires on the vehicle I was working on, I then looked at TSBs (& found the same one you did). The more people who post this (illogical) phenomenon the better off the "next guy/gal" will be.
Bob, don't feel bad it happens to all of us at some time. This serves as a good reminder to everyone to have a good, repeatable diagnostic process and use it every time and not to skip a step.Thanks for the post.
Thats why I Identifix everything first, now. Way too many makes and models for a generalist to try and remember it all. I know how to use a scope, a scanner,voltage-drop,load-test, read a wiring diagram and every other diagnostic technique necessary to fix a vehicle. However, in my diag process, those tools come after an information search. With all of this information at our fingertips, it…
Rudy, I saw that Hotline Article, that's where I found the TSB. The one thing I like about the Identifix "Silver Bullets" is that they usually included specific testing you can do to verify the problem. I'm not normally going to toss a part based on the SB alone, I want to know what I should test, how to test it and how to confirm the repair. The tips usually contain that along with supporting…