4000 rpm buck and stutter

K-Series Programmable ECU installation questions / support issues
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K-raig24
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4000 rpm buck and stutter

Post by K-raig24 »

So here recently my car has started to buck at around 4000rpm. When it does it its not like a limp mode rev limiter, its more like a tps failure that you can power through and it doesnt always do it but its very frequent. The MIL will flash when it does it but won't hold a code and after it does it VTEC wont engage but i can shift and vtec will engage again. Also the tps and vss drop to zero when it does it. Please someone give me some insight. I know its not a tps issue
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Spunkster
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Re: 4000 rpm buck and stutter

Post by Spunkster »

Post the calibration and a datalog showing the issue.
K-raig24
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Re: 4000 rpm buck and stutter

Post by K-raig24 »

0711buckingissue.kdl
datalog
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K-raig24
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Re: 4000 rpm buck and stutter

Post by K-raig24 »

This is in a 99 civic with a 2007 K24a2, Ep3 engine harness, Ktuned swap harness and a V1 PRB Kpro
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Hondata
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Re: 4000 rpm buck and stutter

Post by Hondata »

The lambda shows very lean in places and then very rich in other places. eg 16.5:1 AFR at 0.8s and then 11.4:1 at 2s. I'd say it was tuning but it is not consistent, and the MAP is reading low in places (15s), so I'd check the sensor VCC wires are all 5V. Also the ignition looks very advanced in places under light load (50+ degrees).
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timot_one
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Re: 4000 rpm buck and stutter

Post by timot_one »

Do you recommend checking only VCC for 5V on the TPS and MAP, or should we be checking the SG for them too? Should we also check the IG/IGP for 12V on the CKP, CMP A and CMP B sensors?
Timothy CM55 K24A2 TVS2300
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Hondata
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Re: 4000 rpm buck and stutter

Post by Hondata »

No, just check the VCC and SG for the MAP and TPS.

Oh, just checked your datalog for battery voltage and that probably is one of the problems. If you look at at 4s mark it drops to 9.9V and then 12.2V at 17s. Fix this first.
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timot_one
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Re: 4000 rpm buck and stutter

Post by timot_one »

Thank you. We will focus on the VCC and SG for the MAP and TPS.

The voltage drop is an odd anomaly. The battery and charge harness have been replaced with new units. The alternator has been replaced as well, but not with a new or remanufactured part. Is there anywhere else we should be looking to remedy the problem, or would it be best to replace the alternator with a new/reman unit?
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Hondata
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Re: 4000 rpm buck and stutter

Post by Hondata »

It is unlikely to be the alternator. Something has a connection which is going high resistance intermittently.

In the datalog there is more fluctuation on the ECU voltage than normal so I would start by measuring the alternator output voltage to the battery negative. If it is steady at ~14.2V then it is not the alternator. Even if the voltage fluctuates at the alternator, what you need to do next is to measure the voltage between the battery negative and body of the alternator. If there is resistance in the ground path then it will show up as a voltage difference. eg I anodized the bracket holding an alternator and had to run a separate ground to the alternator, as anodizing insulates.

You can also check the voltage difference from the battery negative to just about any other ground (engine, harness, ECU pin) to try and isolate the problem.
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timot_one
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Re: 4000 rpm buck and stutter

Post by timot_one »

Perfect. Thank you for the advice.

I will test the alternator output voltage, then test to see if there is a voltage differential between the alternator and battery negative. I can confirm that the alternator and water pump housing are unmodified OEM pieces with no anodizing. I will test to see if there is a voltage differential between the battery negative and different ground points on the engine, chassis, harness and ECU.
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m5james
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Re: 4000 rpm buck and stutter

Post by m5james »

Anything ever come of this?

K24A2 swapped into a 91 MR2, Krpo V4. Car's been a summer time DD for two years now, same tune, nothing's been changed on the car.

Regapped the plugs to .25 since some were around .20. Voltages are fine. I can slowly accelerate in 1st or 2nd and around 4k it starts bucking but it'll stop if I just press the gas harder. It's fine WOT as well. Decelerating on the highway can sometimes cause fuel fumes, so I had the injectors cleaned but still no luck.

I can also idle and slowly rev up to 4k and it does the same thing and it gets worse the higher I go up, but more gas and it's fine.
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Re: 4000 rpm buck and stutter

Post by rkhan »

Did you guys found out the cause of the problem?
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