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.

[DRPHIL914]

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.

Jeff, i suppose this is a possibility, so i can recheck these areas, motor has been together for a couple years and about 5,000 miles. Tuning as you know, on a 2056 using d-jet can be a challenge but it has been running really well, It was on a dyno a few months back and at that time the AF used by them showed it pretty much where we want it for mixture until about 4800rpm then from there to 5500 it gets lean but at a cruzing rpm and part load it was perfect. hwoever certainly i can make sure i dont have a leak.

but since the beginning with this motor with all new seals etc its always required a bit more air at idle with the idle air screw partly open , it is timed correctly , no vac canister on the 123 distributor is hooked up no not having the vac retard on, but even with out this the idle would be very low. I am also going to recheck timing again but with the 123 the last 3 times i checked, it was spot on.
If i had an air leak wouldnt you suspect that the idlw would be too high not low at temp?

[iankarr]

Forgive me if thesse suggestions sound basic...they're more for anyone less experienced who comes across this thread later (IMG:style_emoticons/default/wink.gif)

Have you tried turning the adjustment screw on the CPU? Do just a notch or two at a time and wait a minute to see the effects.

Does the RPM value of your timing light agree with the RPMs shown in the 123 app? The 123 is more of a "virtual" unit, so if the dizzy isn't "synched" to the real world, there will be an offset in your timing curve. Easiest way to synch (for anyone who hasn't done it)...

– Clear out all points and set one point at 10 degrees @ 1000 rpm and one at 27 degrees @ 3500.

– Set your timing light for 27 degrees

– Rev the engine up to 3,500 as shown on the timing light and turn the dizzy until you see whatever mark you're using line up to the correct spot.

– Lock down the dizzy. It's now synched to reality. Load (or re-load) your timing curve.

[emerygt350]

You may want to try a cheapo Amazon o2. Air cooled engines from 50 years ago are hard on them. I suspect you are rich but that may not be the problem here.

[MDTerp]

My vote is for CHT sensor. I had a similar running issue on my 75. Replaced the CHT sensor and found the old one like this. New one fixed the problem. I carry several with me now.