Is the fuel pressure really increasing or is it the EM2/3 reading?  Steve B. has posted good advice for tuning around the staging point with different size injectors.

 

Bobby

 

 

I noticed that my indicated fuel consumption appeared to be about 50% higher than actual.

So I decided to start calibrating engine monitor fuel flow.

The first step is to check/adjust fuel flow around the staging point (20"Hg) where the secondary injectors open (secondary injectors are larger than primary injectors on the 4-port Renesis).

I thought I had previously tuned the engine for a smooth transition around the staging point, at least to the point when I didn't notice anything when dvancing throttle through the staging point.

However, now doing stationary run ups around the staging point (especially when engine is getting hot) I get the weird phenomenon of it going very lean when secondary injectors (supposedly) open. Another odd thing is that fuel pressure increases markedly.

On the HomebuiltAirplanes.com forum a guy that raced RV-8s for a couple of seasons mentioned troubles with the stock Renesis injectors.

Now I'm wondering if I have (intermittently) bad secondary injectors -- not opening when they should.

However, I'm confused by the rise in fuel pressure. Is there a injector failure mode where pressure in intake runners could push back through the injector into the fuel line?

Note that these are factory-new, maybe 10 to 20 hours of total engine run (or attempted run) time.

Another possibility is heated secondary fuel rail. But if there were boiling fuel there the fuel pressure should still drop when secondary injectors open...

I tried to look but didn't find a chart of 87 octane 10% ethanol boiling point vs temperature.

Anybody here had any trouble with stock Renesis injectors? Symptoms? Other ideas?

Finn

RX-8 4-port:
Primary: Denso 195500-4430    33.3 lb/hr @ 43.5 psi (350cc/min)    13.8 ohm
Secondary: Denso 195500-4460    51.4 lb/hr @ 43.5 psi (540cc/min)    13.8 ohm