burtcheca
farmer/cabinetmaker
What could be the cause for the idle speed to get below the factory setting? I have not touched anything in my van's engine and now is a little under and with some hesitation.
Thanks,
Burt.
Thanks,
Burt.
Idle speed question.
- Thread starter burtcheca
- Start date
SparkandFire
We're drinking beer
Burt, I believe there is actually a "bi-metallic idle/advance compensator" inside the pump that is supposed to compensate for variations in fuel temperature and viscosity. That's the reason why all the trucks I've owned with a DB2 pump seem to idle higher when warm than when cold (once the high idle has kicked off, of course.) My guess as to why it forces a higher idle when the fuel is warm is because warm fuel is less viscous than cold fuel, since there is no real physical seal on the distributor section of the pump (just a very precise machined fit) the pump causes slightly higher idle to compensate for more fuel leakage past the machined parts in the pump...
There's alot at play inside these pumps that can affect idle speed, really. As different parts wear differently the idle changes mostly because it is a static point of reference (since it is set by the idle set screw) whereas all other engine speeds are relative to the throttle cable position.
My guess as to why it forces a higher idle when the fuel is warm is because warm fuel is less viscous than cold fuel, since there is no real physical seal on the distributor section of the pump (just a very precise machined fit) the pump causes slightly higher idle to compensate for more fuel leakage past the machined parts in the pump...There's alot at play inside these pumps that can affect idle speed, really. As different parts wear differently the idle changes mostly because it is a static point of reference (since it is set by the idle set screw) whereas all other engine speeds are relative to the throttle cable position.
One possible reason would be if your high idle solenoid was disconnected, but your cold idle advance was not, and your cold temperature switch has been shorted all along but now for some reason is not.
That's a real stretch.
That's a real stretch.
Diesel JD
Full Access Member
Burt, there is a procedure here to adjust the idle on these engines. I don't recall exatly how to do it. How low is your idle, if it isn't much below 650rpm it's probably nothing to be concerned about, f it's below 500 something definitely isn't right. It could be a sticky metering valve in the injection pump. If that's the case, shock treating the fuel with PowerService or Howe's or Stanadyne lubricity formula at about double the recommended dose particularly on one of your trips to Miami or something might clean out any gumming of that valve.
burtcheca
farmer/cabinetmaker
Thanks guys for the info. I wrote the thread early before going out to work and I came back just now to read the advices. I'm going to check carefully everything early next Sunday morning and do the shock treatment Diesel JD recommended. I'll post what are the results. I'm changing the fuel filter too, it has been there for more than 20,000 miles.
Thanks
Thanks
