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Old 01-18-2013, 02:01 PM   #1 (permalink)
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Help me kill my fickle woman...

Car model: Honda Fit Sport; 2007

Attempting to make: Engine kill switch

Background information:

I have had this Honda fit for about 6 months. She's been relatively good to me. Occasionally, in the right circumstances she would jerk for no reason. I finally decided to take her to the dealership because there were some "pending codes" on my scangauge.

They scanned it with a computer and found nothing wrong, but told me I needed to "let it out" on the interstate every once in a while. So I did it as soon as I left the dealership...

The jerking was immediately being duplicated, and the car threw an error code. I immediately took it back to the dealership. The technician (who was pissed to see the car again 45 minutes later) told me that some carbon may have gotten into the engine that built up from me "puttering around town," causing a misfire I RARELY go above 2k RPMS, and the jerking normally happened above that point.

Things to keep in mind: Every time I would do an engine off coast (EOC) via turning the key, the check engine light would start blinking. I posted that problem here, and many suggested it might be a cylinder misfire. The Honda manager stated that this was the problem. When my mechanic took the spark plug out, he showed me where there was UNBURNT FUEL on the spark plug. This was @ 80K miles and the sparkplugs that he took out were aftermarket NGK iridiums, implying that they had been replaced before, and therefore there should be nothing wrong with them this early.

The mechanic said that it was quite possibly caused by be doing EOC. I have seen explanations on kill switches this forum that would lead me to believe he was right. I have read that using the key to engine off coast can keep spraying fuel into the engine.

Which method should I use to build a kill-switch for my honda?

I am attaching pictures of all the fuses in my car.

Lastly, but most importantly, THANK YOU! I haven't been EOC'ing and my gas mileage is plummeting by about 10mpg.

Honda Fit Cabin Fuses

Honda Fit Engine Fuses

Files are too big to attach to post...

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Old 01-18-2013, 03:09 PM   #2 (permalink)
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I'm not familiar with Honda but I would reasonably suspect that the flashing MIL after EOC is caused by an ECM conflict of seeing vehicle speed sensor input and no input from the cam sensor or crankshaft sensor.

If the jerking is caused by misfire, two things can happen. The camshaft position sensor will command retarded ignition timing, and the 02 sensors will command lean as they are in a HC rich atmosphere.

When it is jerking, look at the short term fuel trim (stft). A negative number indicates a rich fuel mixture and a positive number in excess of 10 indicates a lean condition. These numbers would be very useful to know to make an accurate diagnosis
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Old 01-18-2013, 07:47 PM   #3 (permalink)
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all of the symptoms you've described can be caused by your EOC method. Cycling the key on many (though not all) vehicles will cause the fuel pump to automatically prime the system by turning on full blast for 2-3 seconds. if your system is already pressurized, this can cause an overly rich mixture at restart.

excess fuel can cause stumbling in many forms:
carbon rich egr (ie: blockages, unburnt fuel into intake, etc)
fuel on the spark plugs (misfire, incomplete burn, etc)
AFR's richer then even the "optimal power" band of 12.5:1 (fuel pooling, incomplete burn, ignition retardation, etc)

Best bet for EOC kill switch is dependent upon the make, model, and year of the vehicle... options include but are not limited to:
-Fuel injector cut-off
-Crank/cam angle sensor
-distributor/coil
-EFI fuse circuit
-fuel pump (mainly mechanical injection diesels, not gasoline engines, for the very reasons stated above)
-intake block off (again, generally a diesel application, and usually only in the case of emergency!)

as far as your particular application, it may be tough, as these newer engines have a LOT more monitoring perimeters, and can throw codes under many more conditions then older generation vehicles, and depending on whether the code is active/passive, may end up throwing your car into limp mode, and then the FE really sucks! (not to mention, if you know you're running on a passive code, a more detrimental active code may rear its head just by coincidence, and you'd have no idea that's happening, and then you're left walking!)

As far as the tech saying to open it up every now and then, I couldn't agree more! on-ramps to interstates are the perfect opportunity, as entering in the flow of traffic at speed is generally much safer (and more convenient) then entering in at a lower speed.
Benefits:
-Detergents in fuel will help clean intake valves/runners
-higher piston speeds help blow out built up carbon on piston surfaces
-prevents cylinder walls from forming ridges near the head
-helps keep EGR system clean by allowing additional purging
-helps clear blockages from Catalytic Converter, muffler, etc.

I'm not advising that you red-line it at every intersection, but that little fit engine was designed to be let loose every once and a while!
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Old 01-18-2013, 11:53 PM   #4 (permalink)
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Quote:
Originally Posted by MTXA View Post
If the jerking is caused by misfire
It was most likely caused by a misfire. That's the code I managed to get it to throw after "letting it out"

Quote:
Originally Posted by MTXA View Post
flashing MIL after EOC is caused by an ECM conflict of seeing vehicle speed sensor input and no input from the cam sensor or crankshaft sensor.
The crankshaft position sensor has been replaced in the last 3 months. Is there a way to stop this from happening?

Quote:
Originally Posted by MTXA View Post
When it is jerking, look at the short term fuel trim (stft). A negative number indicates a rich fuel mixture and a positive number in excess of 10 indicates a lean condition.
It is no longer jerking. I have stopped using EOC because I'm too scared to have this happen again

Also, I'm losing power steering for about 3 seconds (I believe it's electric, because in my other cars it was gone completely until the engine was restarted)

Last edited by HilseeJ; 02-01-2013 at 09:15 PM..
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Old 01-19-2013, 12:04 AM   #5 (permalink)
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Quote:
Originally Posted by nbleak21 View Post
Best bet for EOC kill switch is dependent upon the make, model, and year of the vehicle... options include but are not limited to:
-Fuel injector cut-off
-Crank/cam angle sensor
-distributor/coil
-EFI fuse circuit
-fuel pump (mainly mechanical injection diesels, not gasoline engines, for the very reasons stated above)
-intake block off (again, generally a diesel application, and usually only in the case of emergency!)
AND WE HAVE OPTIONS! THANK YOU SIR.

Still lost, however

Going to repost the links to my fuses in case anyone has some ideas.

Honda Fit Cabin Fuses

Honda Fit Engine Fuses

And here's what I'm seeing from the pictures:

IG (Ignition?) fuse under the hood.

IG COIL fuse in the cabin

Other possibilities:

IGP

IG FUEL PUMP

IG HAC

IG METER

After searching:

The user WeatherSpotter has suggested to try using the Ignition Coil Fuse to perform EOC. Does anyone have any experiences, or even vague thoughts on why this will or will not work?

Here is the link I found...

Tried EOC for the first time

EDIT:

I'm beginning to believe that this topic might have been better placed in the modding section. I'll let it sit for a few more days and then delete/repost if need be.

Last edited by HilseeJ; 01-22-2013 at 12:44 AM..
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Old 01-22-2013, 04:03 PM   #6 (permalink)
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Have you read the wiki page on kill switches? Engine kill switch - EcoModder

the idea is to kill power to the injectors while leaving everything else on. the engine and ECU will think you stalled it with the clutch. the engine keeps turning till the gas is burnt up (spark is still on) but no additional fuel is added to the cylinders. re supply power to the injectors and the car stays off as the ECU sees 0 rpm. bump to restart.
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Old 01-22-2013, 04:15 PM   #7 (permalink)
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this thread may also help:
Engine off coasting on my matrix

you need to find the wire from the ECU to the injectors then you can duplicate my switch. check Honda forums for a master wire diagram set (my matrix forums had one for me) and start looking for the wire you need.

try this diagram:
Wiring Diagram
you want to add your relay in line with the yellow/black wire after it combines the injectors but before it merges with anything else.
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Old 01-22-2013, 04:40 PM   #8 (permalink)
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I edited the picture of the ECM wiring you posted with a marked place of where I think your talking about....

http://img201.imageshack.us/img201/1498/ecumap.jpg

Is that correct?

Also, after reading the wiki, I'm not sure where the camshaft position sensor would be... (But I know I have one)
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Old 01-22-2013, 05:15 PM   #9 (permalink)
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that is the exact right spot. now you have to find it on the car
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Old 01-23-2013, 12:31 PM   #10 (permalink)
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Opening it up once in a while is a good idea - as long as you don't do it so often you kill your FE or do damage to the engine.

For me, coming home from my parents, there's a very hilly stretch where I can climb to heat the engine up AND rev it out a bit on the hills. Of course, I can let it DFCO down the other side of the hill so my FE doesn't suffer a bit! (Mileage is usually exactly the same if I go this way or the flat way ... plus the flat way is more miles).

The other thing is the engine will "wear" in and be more used to the lower RPM. Then if you end up selling it to someone who drives it much more spirited, they're going to notice that it may be carboned up and the "wearing in" causes it to burn oil , etc if revved out.

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