Thread: Bucking under cruise conditions, misfire?

With how those plugs look. It is certainly a problem with the ignition system. Mine looked very similar when I was having horrible misfire problems and "bucking" under load. This poor condition was intensified when the atmosphere contained a lot of humidity.

Log&config were attached in a few posts up. All signals look smooth, nothing out of the ordinary. Map signal is as flat as it can be.


Should have clarified, VE+T, 10.3:1 compression, sorry

Thanks for the input guys, I'll order some new ignition parts and swap out some stuff with my mates car. Will keep you updated!

Sorry, I can't get at nor view the logs from here. Got a screen shot of a log showing the bucking?

I just tried a known good set of sparkplug wires. No difference 

I will screenshot the log when I get home

EDIT:



Freeze frame data. This is right at 2900rpm where it bucks hard. Don't mind the AFR, it's not connected to NEMU.

You could try checking TPS voltage and see if it's within spec. Maybe look at the TPS voltage on the Nemu with the engine off and see if the voltage range makes sense when you open/close it. .47 -> ~4.10

I still can't get over how retarded that timing is. 22 degrees just cruising along? Jesus... That should be closer to 35 or so...

I wish I could see graphs of all the data, but the snapshot of data looks great otherwise. One or more injectors may be failing, but that is so rare. I would try ruling out other things first.
The other things not logged that might contribute would be the fuel pump (who knows what the pressure is doing), the fuel pressure regulator as well...

One time I had an electrical gremlin miss at 100km/hr which ended up being the tps overloading. It was getting too hot, shtting the bed till it cooled and started the cycle over. Resistance was fine just testing, but at long idle and high temps it failed. Right at the base of the plug there were only two strands of the wire still attached!

Thing is, you only see bucking with timing if it's too advanced, right? It may be severely retarded but the car should just feel slower, not buck. I'd also think fuel pump being the culprit isn't probable because at more than 3k rpm or higher load, it doesn't sound like there are any issues (correct me if I'm wrong Dala).

One step ahead of you. Regrounded it to the manifold and calibrated it a few months ago when I did the waxstat delete. Nemu sees 0% TPS when closed, and 98% when fully open. I keep the TunerView android app on while driving, and TPS is rock solid. I even did a full sweep (1% at a time) while warm, versus cold, and the two graphs were identical. TPS is the thing working best on my car now



I promise, I will fix the timing map once I get this solved

I also think your guess is the closest one now. Injectors are very high on my suspicion list, since I recently changed them. The pump is a Walbro 255, 2½ years old. I try to keep as much fuel in the tank as possible, to avoid overheating it. I think it is still good, mechanically it gives the same whine as always, but only a fuel pressure test can verify this. However, since I can do WOT pulls just fine, and the AFR never strays, I don't think the pump is the culprit.

I also tested the FPR the last time I had the rail off the car. I connected it to an air compressor, and it opened perfectly at 3bar pressure.

I will update this thread when I swap over old injectors.

If the injectors are to blame, it would show up in a detailed, high sample rate log. You'd see the bucking, and corresponding lean or rich conditions. The problem with that, is the lean conditions could be a symptom of bad ignition as well. So it's sort of a crap shoot.