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FD3S light throttle 3000rpm buckling (Link G4+)

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Hi guys, whenever I feather the throttle to 3000rpm the car would buckle hard and my AFR would shoot up to 15.5 from 12-13ish, once it got past 3200rpm everything went back to normal again. I replaced the stock ground wire running from upper intake manifold to the firewall and the symptom was much improved, however, it was still there. I tried to enrich the fuel maps in areas where buckling occurs, I made the AFR down to 11ish around 3000rpm, but buckling still there. I am clueless now.

Thanks guys

I had a similar problem that turned out to be a broken wire at my TPS sensor. Look at all your inputs sensors data when the bucking occurs and see if any are changing unexpectedly -- I would particularly look at TPS, MAP, Air Temp. Also, make sure your crank trigger isn't the problem.

If you can log injector pulse width and ignition advance that will usually give you a clue if the ECU is trying to operate in some vastly different area of the fuel map.

Thank you David,

I did not see anything noticeable for my previous logs, I went through those parameters you mentioned but nothing seems abnormal, I will try to log a file specifically for the buckling next time.

If you can capture the issue and upload a log file I'll be happy to have a look at it. Is the engine ported? What size injectors are you running for primary and secondary?

Hi Andre, thank you for replying

I am currently out from the town and will upload a log file once I'm back, it is full bridge port, running ID 850 primary and ID2000 secondary

Interested to hear how to fix this as I'm having the same issue with a similar set up (Bridgeport, stock primaries, Bosch 2200s). However I am using a Power FC. The engine builder says that this is right on port overlap and I couldn't get rid of it no matter how much I changed the fueling. In the end I skipped that section and then interpolated between the cells.

Any update on this one??

I will be able to log some file next weekend :)

Will post update soon


Problem solved, adjusted fuel injection timing and replaced underdrive alternator pulley with stock pulley.

Injection timing I can understand, but how does the underdrive pulley cause this? Not enough voltage to fuel pump?

Im still using stock alternator with twin parallel fuel pumps, could have been not getting enough voltage, im seeing 13.5V idle previously, now 14-14.2V.