I just converted my 95 over to WVO and am amazed at how smoothly it runs. One thing that I have noticed that when I am on veg oil, the truck idles around 8-850 rpm, when I switch back to diesel (#2) and let it 'purge' through the idle will drop back to about 650. I am not sure that it is bad that it idles a bit higher on veg, I am just wondering why. What role does the optical fuel sensor play in engine management? Is it sensing a different fuel and adjusting the idle accordingly? Thanks for any input.

That's really interesting. Do you heat your oil? Could it be cold advance from the fuel?

History did not repeat itself today!!! It idled today on oil just as it did on diesel, I saw no variation. I'm heating it with an ATF cooler in the tank and have HOH run up to the engine compartment. For right now I'll just enjoy the WVO and see what happens. Thank for your response.

The optic sensor does not have the ability to 'sense' different fuel, just reads the data tracks inside the pump. The optic sensor does however have a fuel temperature sensor incorporated and this is probably what caused the higher idle speed. Very interested to hear your results, fuel economy and performance particularly and details on just how you did the conversion.

Hey tex,


I get a high idle like veggie suburban describes after restarts when the engine is still hot. It idles at 850 and goes away after a hard acceleration or two. What could cause this?

completely normal, every 6.5 I've ever seen does that.


The PCM keeps idle high until it senses APP, for what reason, i really can't tell you, GM engineers designed it that way.