Slight but SERIOUSLY annoying bucking on decel
 

All,

My frustration grows with this simple problem: when I get off the throttle, no matter how gently, the car bucks slightly--once. It's not the dash pot; the problem exists no matter how slowly I close the throttle.

I've done some datalogging, and the problem appears to be related to the ECU suddenly dropping the injector duty cycle to 0%.

I thought that this problem might be linked to the removal of the factory O2 sensor, but after replacing it (and enabling it in the ECU) the problem persists.

Rather than focus on my particular mod configuration, I'd just like to hear from anyone who has experienced a similar problem. It's not a huge buck, but one that is unnerving while cornering hard. It unsettles the car, and it's also just plain annoying.

If ANYONE knows about this issue, please respond or PM me! I'll forever be in your debt. Thanks,

-ch

Quick mod list: stock motor and tubos, upgraded intake/IC/exhaust and ECU.

For reference, here is my original post on the PFC forum.
https://www.rx7club.com/forum/showth...hreadid=236464

Here's the screenshot of my datalogging. The cursor is right at the part when the bucking occurs. You can see the little dip in the RPM just when the injectors drop to 0% duty.

https://www.rx7club.com/forum/attach...postid=2276809

Check your ignition system.Change the plugs ,wires and also check the harness that goes to your 3 coil packs.Had and still do have the same problem.I have to change that little piece of the harness to fix it for good.
What helped out was to strip the coil harness,clean the wires and put fresh electrical tape on them.It alleviated my engine flooding problem and hard bucking but i still get light bucking.

Have you checked your TPS adjustment? Some people have had this cause bucking on deceleration.

I doubt it's your ignition system.

I started playing with my TPS to try to fix the bucking. I ended up making it a lot worse by screwing up the TPS position. When I reset it properly the bucking got better, but is still there.

Read this thread. Buck on Deccel Starts out about fuel in oil and rambles to deccel fuel cut.

It may take you some fiddling to get it to stop.

I'll look into the TPS thing, but TYSON's lead is very interesting. If I understand the thread correctly, I am going to have to tune the vacuum cells to take out fuel until the transition from vac to decel fuel cut is more graceful?

It's a good theory, but it doesn't explain why this started all of a sudden when I changed to the PFC. There are lots of guys who have the same ECU and base fuel map that don't have my problem.

Any more ideas?

-ch

Mine always has a slight kick when I let off the throttle. It is a Microtech setting: "Flames or No Flames." It really should be "Lots of Flames or Not so Many Flames." I'm told it just totally shuts off the injectors after a second of no throttle. It's not really noticable unless right around 2k RPMs.

piano,

Yeah, it's much more noticable in the cruising RPMs. Around 5k RPM, I don't see it. So you're saying that it was related to your ECU change?

I'm going to try some different maps today to see if anything changes. The bucking is killing me!

-ch

Okay, so, some updates but no progress:

I tried resetting the map back to the stock PFC 5.08--no good. I then checked the TPS voltages:

Idle: 0.44V
WOT: 4.34V

These are perfectly in spec according to the factory manual. I even did some dynamic tests where I let the throttles snap closed, but the lowest the voltage goes is 0.4V. (Spec is 0.1-0.7V.)

I think the next plan is for me to either swap ECUs with another PFC owner or (horrors) put the factory ECU back in and see what happens.

Gah!

-ch

Update: I put the factory ECU in and drove the car around the block. The bucking is gone, so now I am wondering if there is something messed up with my PFC. I'm hoping to hook up with some PFC owners in the bay area to swap and see if the problem goes away. Sigh.

-ch

There's nothing wrong with your PFC.

You have to tune it.

Do you have an airpump hooked up? Whenever my airpump isn't working (electrical short somewhere I would like to find) that is when my car does the exact same thing. Don't know exactly why but maybe that could lead you in another direction to check. Hope you get it figured out.

Spoke with Steve while we were doing some fine tuning the other day about this.

He said he's seen this on just about every PFC he's tuned, and it has something to do with the fuel cutting on decel. Also said he's never been able to get rid of it completely, and doesn't know anybody that can.

:( ah well, something to live with.