[DeTomaso] Improving gas mileage with the Cleveland

[Thomas Tornblom]

Daniel C Jones wrote:
>> I also have some slight leaks between the collectors and exhaust, and
>> that may apparently cause negative exhaust pulses to suck air into the
>> exhaust, and the oxygen sensors may then sense a lean condition. We
>> noticed this last night while filling the A/C, we noticed that the
>> exhaust was really rich, yet the wide band indicated a normal 14.7 AFR
> 
> Was that at idle or under load while moving?  Does the mixture get less
> lean quickly off-idle?  An unstable idle can fool the O2 sensor.  I tuned

That was at idle, or slightly off-idle. The EFI raises the idle when the 
A/C compressor is active.

It appears to lean out quickly if I increase the rpms slightly, so the 
cam may definitely have an influence.

I'm using a Crane 529801, 290/294 adv.

> a carb over the weekend using a wideband and the wideband was reading 18:1
> at idle but the cam was a lumpy 294S Comp.  I got it down to 17:1 at
> lean-best idle mixture.  Richening it past that point would not pick up
> RPM so that leads me to believe the idle mixture was fine and the O2 sensor
> was being fooled.  As soon as the RPM picked up enough to smooth out the
> idle, the mixture was right around stoich (14.7:1).
> 
> Did you smell it really rich or were you judging by exhaust soot?

The eyes were watering, no soot.

The problem with the EFI is that it runs in closed loop also at idle, so 
as long as it hasn't reached the adaptation limit, it will add fuel 
until it gets to stoich.

> Was this during start-up or once warm?  The O2 sensors are only in
> the loop during cruise.  At cold start, enrichment is used to keep
> the engine running and tables are used at WOT to provide a rich
> mixture for best power.  I'd be surprised is a slight exhaust leak
> would cause it to run rich during cruise.

You are most likely correct.

I will replace the gaskets and then go about tuning the idle. I have a 
good write-up on how to tune the idle properly with the EFI. The idle is 
a bit unstable at the moment.


> 
> Dan Jones


Thomas