hyperion

iTrader: (2)

All,

(This is continued from an original thread: https://www.rx7club.com/showthread.p...hreadid=236464 )

I've been doing some more investigating in trying to eliminate a very annoying bucking when the car decelrates. When I let off the gas at low-to-mid RPMs, the car hesitates--just a single jolt--that bucks the chassis noticably. It doesn't matter how slowly I get off the throttle. As soon as the plates close completely, the car bucks.

I use the Apex'i PFC, but this problem didn't start when I installed the ECU, only after some other modifications. I have done the following to try to determine the cause of this problem:

* I verified the proper operation of the TPS and O2 sensor.

* I tried about a dozen PFC maps: the problem is constant. (I have a wideband and have done tuning myself. This is not a tuning issue.)

* I tried to tune the high vacuum cells where this problem exists. However, either leaning out or richening the cells had no effect. It appears that the PFC goes into some kind of routine just before the fuel cut decel happens. Nothing I do to the fuel map makes any difference...

* I replaced the PFC with the factory ECU: the problem went away.

* I put the PFC back in: the problem came back.

* I put in a different PFC in: the problem did not go away. (The owner of this PFC did not have this problem with his car.)

* I disconnected the idle speed contol solenoid: the problem went away.

My next step is to try replacing the ISC with another to see if the problem persists. I also checked the throttle plates to make sure that they're completely closed when the cable runs slack. I'm also going to disconnect the double throttle, although I don't think the double throttle even opens when crusing around town.

Anyway, if there are any other ideas I'd greatly appreciate them. Thanks,

-ch

RX7SpiritR

iTrader: (1)

I guess that would have to be it if your ISC made the problem go away. But it still doesn't make a lot of sense to me that the problem wasn't there with the stock ecu though. Maybe someone here knows why??

clayne

This may sound obvious, but full PFC reset and 20-minute idle learn?

clayne

For the record, I have a PFC w/ O2 disabled and I have never noticed this before.

hyperion

iTrader: (2)

RX7spiritR: Yeah, it's wierd, isn't it? The only think I can think of is that the PFC uses the ISC a little differently than the stock ECU does.

clayne: When you say full reset, you mean reset with the commander, and then turn the ignition off and on, right?

I've been looking a little closer at the logs and I've found a few things that worry me. Just around the time the buck occurs, the timing drops about 20 degrees. This always happens in the P3 row. I've checked my IGL and IGT maps and they do not have any retard in them at all. The ECU seems to pull out a huge amount of timing for just a second. Originally I thought that the fuel cut was causing the buck, and earlier today I was convinced it was the ISC. But after looking at the logs, now it may be that removing the ISC simply caused the ECU to no longer pull out the timing. (When the ISC is disconnected, the vacuum goes lower because there is no bypass of the throttle plates.)

I've looked all over the PFC configurations for something that correlates ignition retard with either decel or high vacuum, but I can't find anything. The timing goes from 30deg to 5deg instantly, and then back to 30deg. Very, very odd.

I'm going to datalog another FD and see if this behavior is the same. If not, it may point to some kind of problem with the ignition system.

-ch