I was thinking about this yesterday. I don't think it's possible by making the car think it's rolling. It would disable the cooling fans also. I've noticed that at any rolling speed the fans won't work, but if you come to a complete stop, they'll turn on. I guess if you could control those seperately also, then it would be fine, but I don't know if you would have to rewire anything.

 

In theory, this solution would work. Unfortunately, we have two issues here :
- the PCM is not connected to any sensor feeding vehicle speed. It gets the info through the CAN line from one of the ABS/TC/DSC modules.
- as there are 4 wheel speed sensor, you'd probably have to fool all 4 signals with a very neat signal generator pulsing as you were driving at 1MPH for example. Expensive. And it could disable/trigger a CEL on the ABS, as wheel locking would not be recognised anymore.
Unless you're some king of CAN expert... Then I have other ideas...

Fabrice

 

well if it could increase fuel economy as well as sorting out the judder that would certainly be interesting

 

All I can say is it won't affect real life FE.

F

 

There's a thread somewhere that says something was disabled during idle to save gas.

 

The solution I'm investigating increases idle speed, and it does not force the PCM to go outside idle mode. So the idle strategy is untouched (closed loop regulation as a function of idle speed, close loop lambda control...).

Fabrice

 

bump

 

Fabrice -
If the idle strategy is intact, would the reverse firing split still be in effect?

S

 

Difficult to say, as this reverse split might depend upon idle speed too.

F

 

I believe a pair of ignition coils is disabled during idle in order to save gas. Leading coils, methinks.

 

....and what leads you to "believe" this?

S

 

I believe because RotaryGod said so.

There was mention of it among the various piggyback / standalone / ignition control threads.

 

bump

 

bump

 

Did your engine mounts help your idle problem? I've had mine replaced twice, with no improvement. When the A/C clutch kicks on, the RPMs drop a bit and the car shakes so much the steering column vibrates. I have been told by the service department that "all the RX-8s do that". Somehow I don't think that Mazda engineers would have designed the RX-8 to vibrate the steering column, but maybe I give them too much credit. Moot point now, since I'm out of warranty and have given up the battle to make my $33K car feel like one.

 

whtas this reverse idling split? I'm just framiliar with the rx7 and it's simple firing order

 

The engine mounts and spark plugs were replaced 3 days ago. It seems there is a marked improvement in idle stability and vibration containment. I think the spark plugs helped a lot.
My car has 40000 km on the clock. Plugs replacement is not scheduled until 60000 km normally.

In term of root cause, I would say, for a car with engine mounts that haven't failed, the influence on the issue goes in the following order (decreasing) :
1) idle speed too low : rise it to 1000 RPM and you would have no issues whatever the other factors
2) new spark plugs : they improved the stability in all conditions, including in tip-in and tip-out, or going out of DFCO (decel fuel cut-off)
3) engine mounts : mine were the old type but did not fail. I don't think it has a major influence on the issue, maybe a slightly better containment of the vibrations

Fabrice

 

so do you think your idea will still work? I'm going to fix the problem with the interceptor by richening the idle mixture, but another solution would be good also.

 

This project is a low priority now. And I don't intend to market anything anymore. I would share the idea as a DIY.

Richening up should reduce COVimep and increase idle speed stability. A wee tad more spark advance could also help.

Fabrice

 

Fabrice,

could you elaborate on "COVimep" ? not sure what you mean by that. I'm going to play with both fuel and spark on the interceptor to see what I can do as far as idle roughness, but it would sure be nice to be able to just kick it up to 950 or so.

 

guess I posted this in the wrong thread:

https://www.rx8club.com/showpost.php...0&postcount=22