D-jet masters question/help needed, very low idle/stall when motor is hot Options

[DRPHIL914]

I think this has been getting slowly worse but I dont really run the car for a long drives around here and its been cold too, but yesterday during a longer drive to a PCA event, on my way back having a lot of stop and go traffic after the motor had warmed up and reached full operational temperatures, my idle was dropping below normal , about 500-600, and after stopping for gas and sitting for about 10 minutes idle was normal (1000rpm)

Motor is 2056 with d-jet, with ignition 123 distributor.
fuel pressure is perfect, timing etc all good. all sensors were put in new when this motor was built 3-4 years ago. and i have always left the idle about 1100-1200 due to the fact that when it was fully hot it would come tdownt o 850-900 but never wanted to stall.

My thought is that the CHT is acting up and the resistance must be too high hot and now is sending a signal making it just like normal d-jet would get heat sink if a hot motor sat for a short time then wouldnt start. - is that a lean or rich condition that happens i cant remember but looking for your ideas thoughts here.

Phil

[914Sixer]

I would check fuel pump first. Heat is a killer for pump.. Are fuel lines wrapped to prevent boiling off(vapor lock)? Where is fuel pump?

[DRPHIL914]

it’s a 75, fuel pump up front, it’s maybe only 2-3yeara old

and fuel pressure was good(i have an inline fuel gauge)

will check this when it gets hot and see , supposed to be doing AX this coming weekend,

[DRPHIL914]

my other thought on the cht would be to pull it and put it in some oil, check resistance when oil temp is around 300 degrees or so to see where its at.

i hate just swapping parts but i do have several other cht's but this one is not that old it was i believe one of the ones made by 914rubber.

Phil . - also could add a pot. in line, a variable resistance that could be dialed in, i ahve 2 of those in the box from 15 years ago when i was dealing with cht issues and the hot start issue on the original motor way back when i first bought the car and was sorting thru the many issues at that time.

[emerygt350]

Another possibility is that it is not running correctly when cold and the compensation for the high cold idle is causing it to run at low rpms when hot.

[emerygt350]

do you have an AFR gauge in it?

[JeffBowlsby]

Here is another thought.

Maybe the 'below normal 500-600' is actually normal - what the air bleed screw is actually calibrated to. When idle later increased to 1000, it was really reacting to a free air leak. If this is true, then you might look for a small air leak allowing free air in, somewhere in the intake system. Suggest using a smoke pencil to explore.

[DRPHIL914]

Another possibility is that it is not running correctly when cold and the compensation for the high cold idle is causing it to run at low rpms when hot.

do you have an AFR gauge in it?

Yes i have an A/F , but the O2 sensor is sometimes throwing a error code sometimes and either may need to be cleaner or replaced i believe its no longer working correctly,
-
I do need to order a new one from Summit or Dakota Digital.