Hello all. Running great on VO for a while now, and (hopefully) I have only one last tweak/addition to the truck, but not sure how. What I'd like to do is to add a switch in the cab that will change my idle speed. I find that when running on VO and when my engine is really warmed up (hot), my truck idles really low. I thought about increasing the idle, but then the truck would race on diesel (don't want that). Is it possible to have a switch control for this?

On a related note, could someone explain this low idle phenomenon? I would think that it would idle low when colder (thicker oil) not hotter.

thanks

low idle governor on youre rotary pump is not really much of a governor, it is not the greatest at precice amounts of fuel, it pretty much keeps it the same, so the slightly thicker and less btu value of the oil will make it idle slower as it is still injecting same volume of fuel. so a solenoid or a cable to set the low idle will fix yah right up. if you turn up youre pump you would be changing youre idle too to prevent it from running away at an idle. as long as you know its not a big deal, the p7100 pumps are way better at it, but cost more generally. i like the rotary one's myself

Interesting -I drive a 92 Dodge, same truck exactly, all miles on original injection pump (have had to slowly turned the IP idle screw out over time to keep the idle up to speed), my original low idle problem WAS with cold thicker oil, eliminated this by increasing the size of the fuel line to 3/8 inch ID all the way from the bottom of the fuel tank up to the lift pump. I run cold blends of anywhere from 30% to 80% veg/umo/dsl/rug.

What RPM do you have the idle speed set for when running diesel, factory book says 700 rpm with all accessories on including the air conditioner, this gives you around 800 rpm when the air is off.

How does the engine start on diesel, if the IP is in good condition it should start on the first or second compression stroke (almost instantly), if it takes more than that your IP is worn enough that it's internal clerances cause low injector pressure on startup, once the engine fires the pumps plunger pump moves fast enough that the leakage is minimal so it runs ok. My IP is well worn, it takes about a second of cranking for the engine to start on diesel, a cold blend of 30% veg (or used motor oil)/dsl starts on the first or second compression stroke in warm temps.

This worn IP causes the idle speed to be dependant on the thickness of the fuel, thicker fuel still idles slower. On a cool morning with the 30% blend the engine idles slow for about 30 seconds then speeds up to normal.

Are you adding heat to your veg, if so, how much and by what method. The only thing I can think of to cause low idle on veg is that your IP is worn and the fuel is being thinned to a point that the increased clearances inside the IP are causing a lot of internal fuel leakage at low speed?

I made a trip to Arizona a couple weeks ago, the weather temps were above 100 deg f and I had been running hard on the freeway, pulled off the freeway and the engine stalled at the first stop sign, the IP was so hot that it would not pump enough 30% cold blend to even run, dumped a big 40 oz cup of soft drink and ice over the pump and got it started so I could at least get it out of the rush hour intersection - Bummer - also turned out that the fuel filter was almost fully plugged, may not have had the stall problem if I wasn't starving the pump for fuel?

Adding a idle speed solenoid could be done I suppose but it would take making up some sort of bracket and using a solenoid, or possibly a manual push/pull choke cable (solid wire inside a spiral sheath), to place a spacer between the idle adjust screw and the pump tab, you would likely have to depress the accelerator a bit to move the pump tab away from the idle adjust screw so the spacer could move into place.

This links to a running blog about the mods to my truck and the experiance with verious blends. I also have pics of the tools I modified to allow adjustment of the idle speed set screw, as well as info about the fuel line and internal fuel tank updates. I will add the AZ trip pics and info shortly.

Tim - If I respond to your questions out of order, sorry. I think the IP is fine, the only time the truck hasn't started imeediately on the first stroke is when I don't purge and it gets cold over night.
If I remember correctly, I, also, have 3/8" hose.
I don't know the RPMs.
I've got a 2-tank system with about a 12" loop in the VO tank, HOH fuel lines with foam insulation wrapped around (would like to do a better job, but no problems after about 2 years) to a 16 plate heat exchanger, to a coolant wrapped filter (there are some bare fuel lines/fittings here, so I'm planning on cleaning this up soon too, but again, no major problems after aobut 2 years).
I like the cable idea, that makes sense to me....I'll keep you posted. (hopefully I'll get too it soon....)
The IP may be starting to go. This may be an early warning sign. We'll see.