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Hi everybody, i usually find what i need without posting but this time I’m hitting a wall. Nothing matches my problem and i can’t figure it out. For the last coupe of days my ‘08 DX coupe M/T has been doing some strange things. Started out of the blue really. Starts, stops and runs perfect, well as perfectly as a 12 yo car with 250 000km’s will. Anyway, taking off from a stop, if i give it little gas it goes fine, but when i want to take off normally or anything faster it will buck and jerk and the speedometer will basically show any speed it feels like... 73...267...123...yeah so i might be doing say 40 with little throttle input, everything is fine when suddenly the speedo goes crazy but still runs fine. If i push down harder at that moment it will immediately start bucking.

has anybody seen this before? Nobody I’ve spoken to yet can give an explanation. Next step is to talk to honda i guess?!

Thanks ?
241986
 

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Any codes come up?

My best guess is that either a wheel speed sensor is bad or the computer is reading the speed incorrectly. The computer limits the top speed to 137mph so I think the bucking is it cutting fuel when the speedo reads above that.

I dont usually recommend going to dealers but with such a strange issue I think it would be best to go to them.
 

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Any codes come up?

My best guess is that either a wheel speed sensor is bad or the computer is reading the speed incorrectly. The computer limits the top speed to 137mph so I think the bucking is it cutting fuel when the speedo reads above that.

I dont usually recommend going to dealers but with such a strange issue I think it would be best to go to them.
CEL isn’t on and both wss on the front were changed last summer... could they be faulty?
 

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Not 100% sure, but I believe the vehicle speed (i.e. the speed shown on the speedo) is from a sensor on the transmission, not the wheel speed sensor. I believe the wheel speed sensors are just for ABS. Does ABS function normally after the sensors were replaced? -Sam
 

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Alright, finally getting around to updating. The CEL lit up and i borrowed a code reader and this is what came up(Output shaft speed. Sensor circuit). I then picked up a VSS and changed it. FYI it’s on the back of the transmission, kind of a pain to reach but took about 10min to do. Removed the air box and reach behind the trans. Anyway, after changing the vss, my speedometer was normal again. Although the bucking is still there, drivability is greatly improved as the bucking is no longer random. It bucks at 3500rpm on the dot every time. then again it doesn’t so much as buck feel like i let off the gas.
I’ve been reading around and i think the next step will be the crank position sensor.
thoughts?
242101
 

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Not 100% sure, but I believe the vehicle speed (i.e. the speed shown on the speedo) is from a sensor on the transmission, not the wheel speed sensor. I believe the wheel speed sensors are just for ABS. Does ABS function normally after the sensors were replaced? -Sam
I confirm that. I drove around without wss for a few days and the speedometer wasn’t affected, and now that I’ve changed the vss on the trans the speedometer is back to normal
 

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Once you replaced the VSS, do you still have any codes? Also, does the bucking stop once you get past 3500 RPM? (i.e. can you push past it and it is smooth again?

I would think that a faulty crank sensor would not fail at a single RPM point, and I would expect it to set a code.

My experience in the past has been that rapid jerking is usually spark related. Have old are your spark plugs? At higher RPMS, they might not be sparking properly. Weak spark doesn't always set a code for a misfire.
 

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Discussion Starter #9
Actually i do still have a cel. But no it doesn’t go past 3500rpm, it just won’t go any higher at all. Maybe i have to get a shop to clear the vss code i don’t know. The spark plugs are...embarassingly old, like maybe 7 years and well over 130 000 km’s on them but i checked them and they aren’t fowled or oily or anything. Just well worn. I will be changing them soon as they are well past their lifespan.
 

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Update:
Just remembered i started working at a dealership on monday haha they have a bunch of scanners! Yeah i borrowed one over the break and cleared the vss codes but this big mofo is reading 2 more codes that the itty bitty code reader wasn’t seeing. Or they popped up since. I was able de to erase the vss code and that was that but these two just aren’t ready to give up. And my rev limiter is still at 3500rpm.
242118
431D8C8A-B64A-4544-9925-CBB393092422.jpeg
 

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The mass air flow sensor and the intake air temperature sensor tell the engine how dense and how much air is bring sucked into the engine and it will then calculate how much fuel to add. Bad data in would mean the fueling calcuation would be off.

I believe the MAF sensor and IAT sensor are a combo sensor on the top of the air filter box. It usually is unhooked when the air filter is serviced. Any chance it was not re-connected? Or not completely snapped back together? Usually (not always) a code describing something as "high" or as "low" means the signal is outside the normal range that the computer expects. That could mean the sensor has drifted (i.e. over time it is reading higher and higher (or lower and lower) until the computer says "somethings not right" Or, it could mean that it is not getting any signal at all or to high a signal. That could mean an break in the wire, a short to ground, or just a disconnected sensor.

I don't have my manual with me at work, but I'm pretty sure you can diagnose both sensors with just an ohmmeter. Just Google I suppose.

MAF sensors can be cleaned - there is a special spray cleaner from CRC you can buy at Walmart or an Autozone type place. IAT sensors are just replaced if they don't ohm out right. In this case, I think it is one unit.

I'd first make sure that the sensor is plugged in and nothing is obviously wrong with the wiring that goes to it.

Good luck.
 

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Discussion Starter #13
Ive been shopping for sensors and could never find and iat so i guess it being combined with the maf wouldf explain that.
I will check that it is properly plugged in and everything else is tip top. Thanks for the insight!
 

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Discussion Starter #14
Well it turns out i had only forgotten to plug the MAF back in :LOL: run great now lol
 
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